U.S. patent application number 11/538454 was filed with the patent office on 2008-05-01 for system and method for estimating temperature drift and drive curves.
Invention is credited to Steve Krebs, Ronald L. Pitt, Robert Zirpoli.
Application Number | 20080099570 11/538454 |
Document ID | / |
Family ID | 39328936 |
Filed Date | 2008-05-01 |
United States Patent
Application |
20080099570 |
Kind Code |
A1 |
Krebs; Steve ; et
al. |
May 1, 2008 |
SYSTEM AND METHOD FOR ESTIMATING TEMPERATURE DRIFT AND DRIVE
CURVES
Abstract
A method for estimating temperature drift and drive curves
comprises the steps of: (1) obtaining a plurality of temperature
data samples over a period of time, the period of time
corresponding to one of a drive operation or a drift period of an
environmental control unit; (2) if the period of time corresponds
to a drive operation, calculating a plurality of drive curves, each
curve calculated using a different data sample subset; (3) else if
the period of time corresponds to a drift period, calculating a
plurality of drift curves, each curve calculated using a different
data sample subset; (4) determining which curve best fits the data
samples; and (5) using the best fit curve to predict one of a
future temperature at a known time or a future time at which a
known temperature will be reached.
Inventors: |
Krebs; Steve; (Las Vegas,
NV) ; Pitt; Ronald L.; (Cardiff by the Sea, CA)
; Zirpoli; Robert; (Henderson, NV) |
Correspondence
Address: |
Thomas & Raring, P.C.
536 GRANITE AVENUE
RICHMOND
VA
23226
US
|
Family ID: |
39328936 |
Appl. No.: |
11/538454 |
Filed: |
October 4, 2006 |
Current U.S.
Class: |
236/46R |
Current CPC
Class: |
F23N 5/203 20130101;
F24F 2120/10 20180101; F24F 2110/10 20180101; F24F 11/30 20180101;
F24F 2110/50 20180101; F24F 2130/30 20180101; Y02B 30/70
20130101 |
Class at
Publication: |
236/46.R |
International
Class: |
F23N 5/20 20060101
F23N005/20 |
Claims
1. A method for estimating temperature drift and drive curves, the
method comprising: obtaining a plurality of temperature data
samples over a period of time, the period of time corresponding to
one of a drive operation or a drift period of an environmental
control unit; if the period of time corresponds to a drive
operation, calculating a plurality of drive curves, each curve
calculated using a different data sample subset; else if the period
of time corresponds to a drift period, calculating a plurality of
drift curves, each curve calculated using a different data sample
subset; determining which curve best fits the data samples; and
using the best fit curve to predict one of a future temperature at
a known time or a future time at which a known temperature will be
reached.
2. The method of claim 1, wherein the curves are described by
equation T=C+Ae.sup.-t/B, in which T is temperature, t is time, and
A, B, and C are constants.
3. The method of claim 2, wherein constants A, B, and C are
calculated using equations: B = ( t mid - t start ) ln { ( T mid -
T start ) / ( T end - T mid ) } ; ##EQU00009## A = n = start end (
T n - T avg ) 2 n = start end ( - ln / B - t avg ) 2 ; and C = T
avg - A t avg ; ##EQU00009.2## in which T.sub.start is a first
temperature sample at time t.sub.start; T.sub.end is a last
temperature sample at time t.sub.end; T.sub.mid is a midpoint
temperature sample at time t.sub.mid; T.sub.avg is an average
temperature sample across all the samples; t.sub.avg is an average
of times at which all the samples were taken; and T.sub.n is a
temperature at time t.sub.n.
4. The method of claim 3, wherein determining which curve best fits
the data samples comprises: calculating, for each curve,
theoretical temperature values for each sample time in the data set
using equation T=C+Ae.sup.-t/B; calculating a fit value for each
curve using equation Fit = A 2 { n = start end ( - ln / B - t avg )
2 n = start end ( T n - T avg ) 2 } ; ##EQU00010## and determining
which curve has the highest calculated fit value.
5. The method of claim 4, wherein using the best fit curve to
predict a future temperature or a future time comprises using the
curve having the highest calculated fit value.
6. An apparatus for governing levels of an environmental attribute
of a room by controlling operation of an environmental control unit
for affecting the levels of the attribute of the room, the
apparatus including an interface coupled to the environmental
control unit to control the operation thereof by control signals,
the apparatus comprising: a controller including a processor
coupled to a memory, the memory storing an environmental control
program including program instructions for controlling the
operation of the environmental control unit by generating the
control signals and further storing data; and an environmental
attribute sensor coupled to the controller for providing, at any
given time, a signal representing the level of the attribute within
the room; wherein the controller is configured to obtain a
plurality of attribute data samples from the environmental
attribute sensor over a period of time and to store the data
samples, the period of time corresponding to one of a drive
operation or a drift period of the environmental control unit;
wherein, if the period of time corresponds to a drive operation,
the controller is further configured to calculate a plurality of
drive curves, each curve calculated using a different data sample
subset; else wherein, if the period of time corresponds to a drift
period, the controller is further configured to calculate a
plurality of drift curves, each curve calculated using a different
data sample subset; wherein the controller is further configured to
determine which curve best fits the data samples; wherein the
controller is further configured to use the best fit curve to
predict one of a future attribute level at a known time or a future
time at which a known attribute level will be reached; and wherein
the controller is further configured to use the predicted future
attribute level or the predicted future time to control the
operation of the environmental control unit.
7. The apparatus of claim 6, wherein the attribute of the room is
temperature; wherein the environmental attribute sensor comprises a
temperature sensor; and wherein the environmental control unit
includes at least one of a heating unit, an air conditioning unit
and a ventilating unit.
8. The apparatus of claim 7, wherein the curves are described by
equation T=C+Ae.sup.-t/B, in which T is temperature, t is time, and
A, B, and C are constants.
9. The apparatus of claim 8, wherein the controller calculates
constants A, B, and C using equations: B = ( t mid - t start ) ln {
( T mid - T start ) / ( T end - T mid ) } ; ##EQU00011## A = n =
start end ( T n - T avg ) 2 n = start end ( - ln / B - t avg ) 2 ;
and C = T avg - A t avg ; ##EQU00011.2## in which T.sub.start is a
first temperature sample at time t.sub.start; T.sub.end is a last
temperature sample at time t.sub.end; T.sub.mid is a midpoint
temperature sample at time t.sub.mid; T.sub.avg is an average
temperature sample across all the samples; t.sub.avg is an average
of times at which all the samples were taken; and T.sub.n is a
temperature at time t.sub.n.
10. The apparatus of claim 9, wherein the controller determines
which curve best fits the data samples by: calculating, for each
curve, theoretical temperature values for each sample time in the
data set using equation T=C+Ae.sup.-t/B; calculating a fit value
for each curve using equation Fit = A 2 { n = start end ( - ln / B
- t avg ) 2 n = start end ( T n - T avg ) 2 } ; ##EQU00012## and
determining which curve has the highest calculated fit value.
11. The apparatus of claim 10, wherein the controller uses the best
fit curve to predict a future temperature or a future time by using
the curve having the highest calculated fit value.
12. An apparatus for governing levels of an environmental attribute
of a room by controlling operation of an environmental control unit
for affecting the levels of the attribute of the room, the
apparatus including an interface coupled to the environmental
control unit to controlling the operation thereof by control
signals, the apparatus comprising: a controller including a
processor coupled to a memory, the memory storing an environmental
control program including program instructions for controlling the
operation of the environmental control unit by generating the
control signals and further storing data including a drift
relationship, a drive relationship, a predetermined set point
representing a predetermined level of the attribute, a
predetermined maximum range relative to the set point, a
predetermined minimum range relative to the set point and a
predetermined maximum recovery time, the controller further
including a timer coupled to the processor for timing events
related to the environmental control, the events including
generation of the control signals and reception of signals
representing the levels within the room; an input device coupled to
the controller for inputting at least one of the predetermined set
point, maximum range, minimum range and recovery time; an
environmental attribute sensor coupled to the controller for
providing, at any given time, one the signal representing the level
of the attribute within the room; and an occupancy sensor coupled
to the controller for determining whether the room is occupied, and
for sending a the control signal to the controller to take one of a
first action and a second action, the first action being taken if
the room is unoccupied to allow the level in the room to drift
towards an ambient level of the attribute in a region adjacent the
room and the second action being taken if the room is occupied to
operate the environmental control unit to drive the attribute level
in the room away from the ambient level; wherein the environmental
control program includes instructions to allow the drift only to
the maximum range when the space is unoccupied, and then, when
reoccupied, to activate the environmental control unit for driving
the attribute level in the room towards a target level of the
attribute within the minimum range of the set point; wherein the
maximum range is limited such that an amount of drive time for the
environmental control unit to drive the attribute level in the room
from the maximum range to the target level of the attribute is no
greater than the predetermined maximum recovery time; wherein the
controller is configured to obtain a plurality of attribute data
samples from the environmental attribute sensor over at least a
first period of time and a second period of time, the first period
of time corresponding to a drive operation of the environmental
control unit, the second period of time corresponding to a drift
period of the environmental control unit; wherein the controller is
further configured to determine the drive relationship by
calculating a plurality of drive curves, each drive curve
calculated using a different data sample subset and determining
which drive curve best fits the data samples; and wherein the
controller is further configured to determine the drift
relationship by calculating a plurality of drift curves, each drift
curve calculated using a different data sample subset and
determining which drift curve best fits the data samples.
13. The apparatus of claim 12, wherein: the attribute of the room
is temperature; the environmental attribute sensor comprises a
temperature sensor; and the environmental control unit includes at
least one of a heating unit, an air conditioning unit and a
ventilating unit.
14. The apparatus of claim 13, wherein the drive and drift curves
are described by equation T=C+Ae.sup.-t/B, in which T is
temperature, t is time, and A, B, and C are constants.
15. The apparatus of claim 14, wherein the controller calculates
constants A, B, and C using equations: B = ( t mid - t start ) ln {
( T mid - T start ) / ( T end - T mid ) } ; ##EQU00013## A = n =
start end ( T n - T avg ) 2 n = start end ( - ln / B - t avg ) 2 ;
and C = T avg - A t avg ; ##EQU00013.2## in which T.sub.start is a
first temperature sample at time t.sub.start; T.sub.end is a last
temperature sample at time t.sub.end; T.sub.mid is a midpoint
temperature sample at time t.sub.mid; T.sub.avg is an average
temperature sample across all the samples; t.sub.avg is an average
of times at which all the samples were taken; and T.sub.n is a
temperature at time t.sub.n.
16. The apparatus of claim 15, wherein the controller determines
which drive curve and which drift curve best fits the data samples
by: calculating, for each drive curve and each drift curve,
theoretical temperature values for each sample time in the data set
using equation T=C+Ae.sup.-t/B; calculating a fit value for each
drive curve and each drift curve using equation Fit = A 2 { n =
start end ( - ln / B - t avg ) 2 n = start end ( T n - T avg ) 2 }
; ##EQU00014## and determining which drive curve and which drift
curve has the highest calculated fit value.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the temperature and other climate
control of interiors of buildings, and in particular to a system
for controlling the temperature of an environment according to
predetermined criteria including the presence or absence of people,
programmable comfort ranges, and programmable time tolerances to
reach those comfort ranges.
BACKGROUND OF THE INVENTION
[0002] In conventional temperature or climate control systems (e.g.
heating, ventilating and air conditioning systems, referred to
herein generally as "HVAC"), thermostats are used to control when
the HVAC system turns on and off. The user presets a desired
temperature (or "user set point"), and when the temperature of the
controlled space is different from the preset temperature, the HVAC
system heats or cools the air until the preset temperature is
reached.
[0003] Thus, conventional enclosed space thermostats are merely
on/off switches with a sensor to measure the enclosed space
temperature and means for users to set their preferred
temperatures. A problem with such thermostats is that the
temperature is maintained at the user set point whether people are
present or not, using costly natural resources. Heating or cooling
when people are not present wastes a great deal of these
resources.
[0004] Some enclosed space thermostats come with a built-in clock
and have a method for people to program different user set points
for different times and days. Such clock-thermostats provide
different HVAC service when people are expected to be present than
when they are expected to be absent. Problems with this approach
are that the programming of the clock-thermostats is troublesome,
and moreover that, even when the programming is done correctly,
people's schedules change and thus often do not match the
preprogrammed times.
[0005] Some enclosed space thermostats come with sensors to detect
people. They switch from one conventional thermostat when people
are present to a second conventional thermostat when people are
absent. The second thermostat may have a second fixed temperature,
in order that it may shift ("setback" or "setup") a fixed number of
degrees from the first temperature when people are absent. The
problem with these thermostats is the second temperature is often
either too far away from the first temperature to provide
satisfactory comfort when someone returns to the room, or too close
to the first temperature to achieve adequate energy savings.
Further, enclosed space and ambient conditions change constantly,
so these thermostats are very difficult to regulate for optimal
energy savings versus comfort trade-offs. Even if a user could
figure out the optimum second thermostat setting for comfort and
maximum energy savings at a given time, conditions constantly
change and that setting may quickly become non-optimal. (In
general, the term "ambient"--as in "ambient temperature"--will be
used to refer to the temperature or other conditions of the region
surrounding the controlled, usually enclosed, room or other space.
"Space temperatures" will be used to refer to temperatures within
the controlled space.)
[0006] There is thus a need for a climate control system that takes
into account the occupancy status of a controlled space and
automatically responds to variations in space and ambient
conditions so as to minimize energy usage while meeting
predetermined comfort, health and other criteria that may be preset
by the user. Such a system should preferably take into account
variable comfort settings for different people, both as to
temperature and as to the time allowed for the temperature to
recover to the preferred setting when people return from an absence
(referred to herein as "recovery time"). The system should also
automatically accommodate variable enclosed space conditions,
including variable thermal energy leakage to and from the enclosed
space, and variable thermal energy sinks (furniture, equipment,
wall and floor coverings, etc.) in the enclosed space. Moreover,
variable ambient conditions should be accommodated (such as day or
night, summer or winter, clear or rainy, calm or windy), and
additionally the system should compensate for variations in HVAC
equipment operating capabilities. All of these goals are met
automatically by the system of the present invention.
[0007] Conventional systems do not take into account the nonlinear
relationships between HVAC equipment operation and the responses
(temperature, humidity, etc.) of the controlled space with time.
There is a need for a system that recognizes and utilizes such
nonlinear relationships to effect climate control, such as by using
exponential curve fitting.
BRIEF SUMMARY OF THE INVENTION
[0008] The object of the present invention is to overcome the
aforementioned drawbacks and to provide a method and apparatus for
estimating temperature drift and drive curves. The estimated curves
of the present invention provide a more accurate representation of
actual temperature data than the curves determined using prior
methods. Therefore, the present invention provides a more accurate
way of predicting a future temperature value at particular time or
of predicting at which time a particular temperature value will be
reached.
[0009] In one embodiment of the invention, a method for estimating
temperature drift and drive curves comprises the steps of: (1)
obtaining a plurality of temperature data samples over a period of
time, the period of time corresponding to one of a drive operation
or a drift period of an environmental control unit; (2) if the
period of time corresponds to a drive operation, calculating a
plurality of drive curves, each curve calculated using a different
data sample subset; (3) else if the period of time corresponds to a
drift period, calculating a plurality of drift curves, each curve
calculated using a different data sample subset; (4) determining
which curve best fits the data samples; and (5) using the best fit
curve to predict one of a future temperature at a known time or a
future time at which a known temperature will be reached.
[0010] The curves are described by equation T=C+Ae.sup.-t/B, in
which T is temperature, t is time, and A, B, and C are constants.
Constants A, B, and C are calculated using equations
B = ( t mid - t start ) ln { ( T mid - T start ) / ( T end - T mid
) } ; ##EQU00001## A = n = start end ( T n - T avg ) 2 n = start
end ( - ln / B - t avg ) 2 ; ##EQU00001.2##
and C=T.sub.avg-At.sub.avg; in which T.sub.start is a first
temperature sample at time t.sub.start; T.sub.end is a last
temperature sample at time t.sub.end; T.sub.mid is a midpoint
temperature sample at time t.sub.mid; T.sub.avg is an average
temperature sample across all the samples; t.sub.avg is an average
of times at which all the samples were taken; and T.sub.n is a
temperature at time t.sub.n.
[0011] Determining which curve best fits the data samples comprises
the steps of: (1) calculating, for each curve, theoretical
temperature values for each sample time in the data set using
equation T=C+Ae.sup.-t/B; (2) calculating a fit value for each
curve using equation
Fit = A 2 { n = start end ( - ln / B - t avg ) 2 n = start end ( T
n - T avg ) 2 } ; ##EQU00002##
and (3) determining which curve has the highest calculated fit
value. Using the best fit curve to predict a future temperature or
a future time comprises using the curve having the highest
calculated fit value.
[0012] In another embodiment of the invention, an apparatus governs
levels of an environmental attribute of a room by controlling
operation of an environmental control unit for affecting the levels
of the attribute of the room, the apparatus including an interface
coupled to the environmental control unit to control the operation
thereof by control signals. The apparatus comprises a controller
and an environmental attribute sensor. The controller includes a
processor coupled to a memory, the memory storing an environmental
control program including program instructions for controlling the
operation of the environmental control unit by generating the
control signals and further storing data. The environmental
attribute sensor is coupled to the controller for providing, at any
given time, a signal representing the level of the attribute within
the room. The controller is configured to obtain a plurality of
attribute data samples from the environmental attribute sensor over
a period of time and to store the data samples, the period of time
corresponding to one of a drive operation or a drift period of the
environmental control unit. If the period of time corresponds to a
drive operation, the controller is further configured to calculate
a plurality of drive curves, each curve calculated using a
different data sample subset. Else, if the period of time
corresponds to a drift period, the controller is further configured
to calculate a plurality of drift curves, each curve calculated
using a different data sample subset. The controller is further
configured to determine which curve best fits the data samples. The
controller is further configured to use the best fit curve to
predict one of a future attribute level at a known time or a future
time at which a known attribute level will be reached. The
controller is further configured to use the predicted future
attribute level or the predicted future time to control the
operation of the environmental control unit.
[0013] The attribute of the room may be temperature. The
environmental attribute sensor may comprise a temperature sensor,
and the environmental control unit may include at least one of a
heating unit, an air conditioning unit and a ventilating unit.
[0014] The curves may be described by equation T=C+Ae.sup.-t/B, in
which T is temperature, t is time, and A, B, and C are constants.
The controller may calculate constants A, B, and C using
equations:
B = ( t mid - t start ) ln { ( T mid - T start ) / ( T end - T mid
) } ; ##EQU00003## A = n = start end ( T n - T avg ) 2 n = start
end ( - ln / B - t avg ) 2 ; ##EQU00003.2##
and C=T.sub.avg-At.sub.avg; in which T.sub.start is a first
temperature sample at time t.sub.start; T.sub.end is a last
temperature sample at time t.sub.end; T.sub.mid is a midpoint
temperature sample at time t.sub.mid; T.sub.avg is an average
temperature sample across all the samples; t.sub.avg is an average
of times at which all the samples were taken; and T.sub.n is a
temperature at time t.sub.n
[0015] The controller may determine which curve best fits the data
samples by: (1) calculating, for each curve, theoretical
temperature values for each sample time in the data set using
equation T=C+Ae.sup.-t/B; (2) calculating a fit value for each
curve using equation
Fit = A 2 { n = start end ( - ln / B - t avg ) 2 n = start end ( T
n - T avg ) 2 } ; ##EQU00004##
and (3) determining which curve has the highest calculated fit
value. The controller may use the best fit curve to predict a
future temperature or a future time by using the curve having the
highest calculated fit value.
[0016] In another embodiment of the invention, an apparatus governs
levels of an environmental attribute of a room by controlling
operation of an environmental control unit for affecting the levels
of the attribute of the room, the apparatus including an interface
coupled to the environmental control unit to controlling the
operation thereof by control signals. The apparatus comprises a
controller, and input device, an environmental attribute sensor,
and an occupancy sensor. The controller includes a processor
coupled to a memory, the memory storing an environmental control
program including program instructions for controlling the
operation of the environmental control unit by generating the
control signals and further storing data including a drift
relationship, a drive relationship, a predetermined set point
representing a predetermined level of the attribute, a
predetermined maximum range relative to the set point, a
predetermined minimum range relative to the set point and a
predetermined maximum recovery time. The controller further
includes a timer coupled to the processor for timing events related
to the environmental control, the events including generation of
the control signals and reception of signals representing the
levels within the room. The input device is coupled to the
controller for inputting at least one of the predetermined set
point, maximum range, minimum range and recovery time. The
environmental attribute sensor is coupled to the controller for
providing, at any given time, one the signal representing the level
of the attribute within the room. The occupancy sensor is coupled
to the controller for determining whether the room is occupied, and
for sending a the control signal to the controller to take one of a
first action and a second action, the first action being taken if
the room is unoccupied to allow the level in the room to drift
towards an ambient level of the attribute in a region adjacent the
room and the second action being taken if the room is occupied to
operate the environmental control unit to drive the attribute level
in the room away from the ambient level. The environmental control
program includes instructions to allow the drift only to the
maximum range when the space is unoccupied, and then, when
reoccupied, to activate the environmental control unit for driving
the attribute level in the room towards a target level of the
attribute within the minimum range of the set point. The maximum
range is limited such that an amount of drive time for the
environmental control unit to drive the attribute level in the room
from the maximum range to the target level of the attribute is no
greater than the predetermined maximum recovery time. The
controller is configured to obtain a plurality of attribute data
samples from the environmental attribute sensor over at least a
first period of time and a second period of time, the first period
of time corresponding to a drive operation of the environmental
control unit, the second period of time corresponding to a drift
period of the environmental control unit. The controller is further
configured to determine the drive relationship by calculating a
plurality of drive curves, each drive curve calculated using a
different data sample subset and determining which drive curve best
fits the data samples. The controller is further configured to
determine the drift relationship by calculating a plurality of
drift curves, each drift curve calculated using a different data
sample subset and determining which drift curve best fits the data
samples.
[0017] The attribute of the room may be temperature. The
environmental attribute sensor may comprise a temperature sensor,
and the environmental control unit may includes at least one of a
heating unit, an air conditioning unit and a ventilating unit.
[0018] The drive and drift curves may be described by equation
T=C+Ae.sup.-t/B, in which T is temperature, t is time, and A, B,
and C are constants. The controller may calculate constants A, B,
and C using equations:
B = ( t mid - t start ) ln { ( T mid - T start ) / ( T end - T mid
) } ; ##EQU00005## A = n = start end ( T n - T avg ) 2 n = start
end ( - ln / B - t avg ) 2 ; ##EQU00005.2##
and C=T.sub.avg-At.sub.avg; in which T.sub.start is a first
temperature sample at time t.sub.start; T.sub.end is a last
temperature sample at time t.sub.end; T.sub.mid is a midpoint
temperature sample at time t.sub.mid; T.sub.avg is an average
temperature sample across all the samples; t.sub.avg is an average
of times at which all the samples were taken; and T.sub.n is a
temperature at time t.sub.n
[0019] The controller may determine which drive curve and which
drift curve best fits the data samples by: (1) calculating, for
each drive curve and each drift curve, theoretical temperature
values for each sample time in the data set using equation
T=C+Ae.sup.-t/B; (2) calculating a fit value for each drive curve
and each drift curve using equation
Fit = A 2 { n = start end ( - ln / B - t avg ) 2 n = start end ( T
n - T avg ) 2 } ; ##EQU00006##
and (3) determining which drive curve and which drift curve has the
highest calculated fit value.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0020] Having thus described the invention in general terms,
reference will now be made to the accompanying drawings, which are
not necessarily drawn to scale, and wherein:
[0021] FIG. 1 is a block diagram of a system implementing the
present invention;
[0022] FIG. 1A shows a user interface control for use with the
system of FIG. 1;
[0023] FIG. 2 is a flow chart illustrating a preferred embodiment
of the method of the invention;
[0024] FIG. 3 is a graph depicting the drift and drive temperature
responses of a space;
[0025] FIG. 4 is a graph depicting the drift temperature response
of a space, identifying parameters to an exponential equation
representing the response;
[0026] FIG. 5 is a graph depicting the drive temperature response
of a space, identifying parameters to an exponential equation
representing the response;
[0027] FIG. 6 is a block diagram showing a base station of the
invention in use with multiple remote sensors;
[0028] FIG. 7 is a block diagram of a remote sensor for use with
the invention;
[0029] FIGS. 8-10 are block diagrams of various embodiments of the
base station;
[0030] FIG. 11 is a block diagram of a programmable presets adapter
for use with the invention; and
[0031] FIG. 12 shows a zero-crossing circuit for use with an
embodiment of the invention
DETAILED DESCRIPTION OF THE INVENTION
[0032] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. This invention
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein; rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. Like numbers refer to like
elements throughout.
[0033] Embodiments of the invention are described herein in
conjunction with thermostatic climate control systems capable of
estimating recovery times in order to drive the temperature back
to, or within range or, the user setpoint within a specified
recovery time. However, it should be appreciated that systems and
methods of embodiments of the invention may be used in conjunction
with any temperature management or climate control system in which
it is desirable to estimate a future temperature at a particular
time or to estimate at which time a particular temperature will be
reached.
[0034] The present invention is directed to a system for
controlling levels of a predetermined environmental attribute of a
room or enclosed space by operating an environmental control unit
or equipment in response to changes in such attribute levels, so as
to keep the current level of the attribute in the room within a
certain range of a user set point, i.e. a user-determined desired
level for the attribute. A preferred embodiment of the invention
involves the controlled operation of heating, ventilating and air
conditioning (HVAC) equipment. The use of the present invention
leads to considerable energy savings over existing systems.
[0035] The invention is preferably implemented in a computer system
10 for controlling the equipment, as in FIG. 1, which shows a
conventional multipurpose or dedicated computer base station 20
including a microprocessor 30 coupled to a memory 40. Input is
provided via a user input device 50 coupled to the computer 20; the
device 50 may include a keyboard, microphone for voice control,
infrared or radio remote devices, touch screens, or any one of many
other conventional input devices for computers, including input
ports for communications from other computers or electronic
devices. Output is provided through output device(s) 60, which may
include any one or more standard output devices such as a monitor,
a printer, audio devices, communications ports for other computers,
or other devices that can receive and utilize computer outputs.
[0036] One or more environmental attribute sensors such as
temperature sensors 70 are provided, and are directly coupled to an
input to the computer 20 or communicate with the computer via a
conventional remote means, such as infrared, radio or building
wiring. Other sensors 90 are similarly coupled to or otherwise
communicate with the computer 20, as well as one or more occupancy
sensors 100 for detecting the presence of people in a given space
whose climate is to be controlled.
[0037] The occupancy sensor(s) 100 may be a conventional personnel
detector (such as a commercially available infrared detector) and
preferably communicates with the computer 20 via a remote link,
such as by infrared or radio transmission or transmission over
building wiring.
[0038] The system described below and each of its variations are
controlled by the computer 10 in response to instructions in an
environmental control program stored in the memory 40. Wherever a
controller or processor is mentioned, it should be taken as meaning
a conventional or dedicated processor such as processor 30, which
in each case will have an associated memory for storing both the
control program and the data that are generated and sensed or
otherwise input during the course of operating the system.
[0039] FIG. 1A shows an appropriate control unit 110 to act as a
user interface for the system, to be used as described after the
discussion of FIG. 2.
[0040] Specific embodiments of sensors and base stations which may
be used to implement features of the invention are discussed below
in connection with FIGS. 6-11.
[0041] FIG. 2 is a flow chart illustrating the operation of the
system of the invention, which will first be described in its basic
form, followed by a description of numerous variations on the
fundamental embodiment. The method is based upon the fact that the
temperature response of a given space to climate control equipment,
and to ambient temperatures different from the space temperature,
is very difficult to predict. Thus, the present invention uses an
empirical approach to climate control, which will first be
described in general terms, followed by a detailed description of
the method as illustrated in the flow chart of FIG. 2.
[0042] --Drift and Drive Temperature Response of a Space--
[0043] FIG. 3 shows the nature of the response of a room or other
space to temperature control and to ambient temperatures different
from the temperature within the space. The graph of FIG. 3
illustrates the temperature response of such a room where the
ambient temperature is in general higher than the temperature
within the room, such as would be the case for an airconditioned
room on a hot day. For a heated room on a cold day, the principles
are the same, but the direction of increasing temperature on the
y-axis would be inverted.
[0044] Curve 400 in FIG. 3 shows the exponential temperature
response of the space over time, beginning at a low temperature
TEMPSET (which would be a temperature at which an air conditioner
thermostat is set, for instance) and approaching the ambient
temperature (e.g. the outside temperature on a hot day) as time
passes. Curve 410 is a similarly exponential curve showing the
response of the space to the air conditioner being driven from
ambient down toward TEMPSET.
[0045] The ambient temperature is generally the temperature that
the unoccupied, enclosed space will drift to when the HVAC
equipment is off; i.e., if the temperature is higher outside than
inside, the temperature of a room will tend to drift towards the
hotter outside temperature. (In some cases, the temperature inside
may get hotter than the temperature outside, in which case it will
not always be true that the space temperature approaches the
outside ambient temperature; this does not affect the present
system, which in either case will work to cool the space down
towards TEMPSET. What is true in both cases is that the enclosed
space drifts towards some equilibrium temperature, which usually
will be substantially the same as the ambient temperature of the
region surrounding the enclosed space. For the examples in the
present application, "ambient" temperature may be taken to mean
equilibrium temperature for the space.)
[0046] The unoccupied, enclosed space temperature thus generally
drifts toward the ambient at a decreasing rate and may be driven
from the ambient at a decreasing rate. These variable rates
"deceleration curves") are very closely described by exponential
equations of the form T=C+Ae.sup.-t/B, where T=temperature, t=time,
and A, B, and C are known or learned parameters, discussed below.
The drift and drive equations have the same form, with different
values for the parameters. By measuring changes in temperature and
time, these equations can be solved (i.e., all six parameters are
"learned").
[0047] Once solved, the time to drive the temperature from one
point to another, or the time it takes for the temperature to drift
from one point to another, can be computed. As the ambient
temperature changes, the A and C parameters of the drift and drive
equations are recalculated. Recovery times under continuously
varying conditions can then be computed, which enables the system
to continuously adjust and maximize the drift boundary temperature,
thus minimizing HVAC equipment use while always being ready and
able to drive the temperature back to, or within a range of, the
user set point in the specified recovery time. Specific
implementations of these functions are discussed below.
[0048] The above equations give accurate, empirically determined
predictions for drift and drive with only temperature and time
measurements. Additional variables, such as humidity, may be added
to the system, for which more complex nonlinear equations would be
used to accurately characterize the "comfort" relationships that
must be learned for accurate control.
[0049] FIG. 4 shows a curve 420 similar to curve 400 of FIG. 3, and
graphically illustrates the parameters A, B and C mentioned above.
These parameters are defined as follows (for the drift
situation):
[0050] A: the temperature deviation of the controlled space at time
t=0;
[0051] B: the exponential time constant (or "Tau constant") of the
equation; and
[0052] C: the temperature to which the controlled space will drift
over time (i.e. the equilibrium temperature of the space with the
HVAC equipment shut off).
[0053] FIG. 5 shows a curve 430 similar to the curve 410 of FIG. 3,
and is the drive counterpart to the drift curve of FIG. 4. The
parameters in FIG. 5 are defined in a similar manner to the
parameters of FIG. 4, with C being the temperature that the space
would asymptotically approach if the HVAC equipment were driven for
a very long time under the same conditions (ambient temperature,
HVAC power setting, etc.).
[0054] The A parameter may be regarded as the distance the
temperature would have to travel to reach C from where it is at
time zero.
[0055] The B parameter (the Tau or time constant) is the time it
would take the temperature to travel 63% (1-1/e) of the distance
toward C from where it starts at time zero. The proportion of the
distance traveled toward C can be calculated as "n" Tau's
(-1-(1/e).sup.n).
[0056] The C parameter is, as noted above, the temperature (in both
the drift and drive equations) to which the space is headed. In the
drift equation, it is the extreme (maximum or minimum, depending
upon whether ambient is hotter or colder) temperature the enclosed
space will reach if left alone long enough with a constant ambient
temperature (i.e., the enclosed space equilibrium temperature
without HVAC equipment running). In the drive equation, it is the
extreme (again, minimum or maximum, counterposed to the extreme in
the drift situation) temperature that the HVAC equipment can drive
to with a constant ambient temperature (i.e., the enclosed space
equilibrium temperature with the HVAC equipment running).
[0057] The rate at which an enclosed space temperature changes with
time decreases as it drifts closer to the ambient. The rate at
which an enclosed space temperature changes with time decreases as
it is driven farther away from the ambient. These phenomena are
shown by the curves plotted in FIG. 3. Curve 400 illustrates that
more time is needed to drive a specified distance (.DELTA.T) away
from the ambient temperature at a lower temperature (see segment
410L) than at a higher temperature (see segment 410H), i.e.,
t2>t4.
[0058] Curve 400 for its part illustrates that it takes less time
for the temperature to drift toward the ambient temperature a
specified distance (.DELTA.T) when it is farther away from the
ambient temperature (see segment 400L) than when it is closer (see
segment 400H), i.e., t1<t3.
[0059] Curves 400 and 410 further demonstrate, by a comparison of
the segments 400H, 400L, 410H and 410L (see the segments (410H) and
(410L), repositioned for comparison with 400H and 400L,
respectively) that the proportion of time spent driving when
holding (i.e., cycling repeatedly through both drift and drive to
maintain) an enclosed space temperature within a specified range
(.DELTA.T) is greater when the temperature is farther from the
ambient temperature than when it is nearer. Mathematically, this is
expressed as: (t2/(t1+t2))>(t4/(t3+t4)).
[0060] The current system records in the computer memory a series
of measurements of temperature vs. time when (1) the enclosed space
is drifting, and (2) when it is being driven by HVAC equipment.
These measurements are used to solve the drift and drive equations,
where Temperature T=C+Ae.sup.-t/B. Each equation can be solved
precisely, with three pairs of measurements, provided the time
intervals between measurements are equal; this is discussed in
detail below.
[0061] As the ambient temperature changes, the A and C parameters
of the drift and drive equations must be adjusted. Once the B
parameters are learned for an unoccupied space, they remain
constant until the space is reoccupied and vacated. In the drift
equation, the initial temperature T.sub.0=C+A, so changes in C are
linearly coupled to changes in A; i.e., A=T.sub.0-C.
[0062] --Deriving the Drift and Drive Parameters--
[0063] The curves and parameters shown in FIGS. 3-5 provide
description of the behavior of a space in response to temperature
control. The equation is of the form T=C+Ae.sup.-t/B. It will be
assumed for this example that it is a hot day and the HVAC
equipment is being used to drive the temperature downward, though
because of the symmetry of the mathematics the example will work
equally well for a cold ambient temperature where the space is
instead being heated.
[0064] The sensors measure temperature, the system of the invention
measures the temperature and elapsed time as pairs of data points
(in a manner to be described below in connection with FIG. 2). In
this example, time periods of measurement are selected that are
equal, i.e. three points are selected that are evenly spaced in
time, as follows:
TABLE-US-00001 time (seconds) Temperature (.degree. F.) t.sub.0 (or
t0) = 0 t.sub.0 = 80.00 t.sub.1 (or t1) = 180 t.sub.1 = 74.59
t.sub.2 (or t2) = 360 t.sub.2 = 71.61
[0065] The A, B, and C parameters have closed form solutions,
assuming (t.sub.1-t.sub.0)=(t.sub.2-t.sub.1), as follows:
B=(t.sub.1-t.sub.0)/ln{(T.sub.2-T.sub.1)/(T.sub.1-T.sub.0)}
A=(T.sub.1-T.sub.2)(e.sup.-t.sup.1.sup./B-e.sup.-t.sup.2.sup./B)
C=T.sub.1-A*e.sup.-t.sup.1.sup./B
Computing the parameters, the drive equation becomes:
T=68+12*e.sup.-t/300
which means that the drive Tau is 300 seconds; i.e., about
1-(1/e).sup.300/300=63% of the temperature differential that can
ultimately be driven is reached 300 seconds after driving (here,
cooling) is begun, and the total drive distance will ultimately be
12.degree. downward from 80 degrees (=68+12).
[0066] In this example, the lowest temperature to which the system
can practically be driven is 68.degree. F., this being the value
that T asymptotically approaches as t (time) goes to very large
numbers (i.e. e.sup.-t/300 approaches zero, and thus t approaches
"infinity"). This will be the case where, for instance, the HVAC
equipment is not very powerful, or there is a leak in the space so
that cool air is being lost, or where the temperature of the air
blown by an air conditioner is, in fact, 68.degree.. In other
words, the system of the invention automatically determines the
practical limitations of the physical space and the climate control
equipment in an empirical manner.
[0067] These drift and drive parameters will be used in the method
of the invention as shown in the flow chart of FIG. 2.
[0068] --The Method of FIG. 2--
[0069] A conventional approach to climate control is to take the
user set point as a target temperature, and whenever the
temperature in the controlled space drifts away from this set
point, to drive HVAC equipment until the temperature within the
space returns to the set point, or within a practical margin
(.DELTA.TEMP) from the set point. A variation on this is to include
an occupancy detector such as sensor 100, and when no one is
present to allow for a greater deviation from the set point, but to
drive the temperature back to the set point .+-..DELTA.TEMP when
someone returns.
[0070] The first of these approaches is accommodated by the method
illustrated in flow chart of FIG. 2 by the loop labeled as loop A
through boxes 200-250 (and back through box 210). The user inputs
the set point TEMPSET, and the margin .DELTA.TEMP may be input at
this time or may be preprogrammed. Indeed, any of the input
variables discussed below (such as those listed in box 200) may be
preprogrammed, and specified by the manager/owner of the system to
be changeable by the user or not, as desired. The variables input
at box 200 have the following dimensions and definitions: [0071]
TEMPSET: (temperature): the user-defined set point; [0072]
.DELTA.TEMP: (temperature): the margin around TEMPSET (or
TEMPLIMIT) within which the temperature is actually held; [0073]
TEMPMIN: (temperature): an optionally set margin around TEMPSET,
used in conjunction with RECOVMAX to determine TEMPLIMIT, as
discussed below; [0074] TEMPMAX: (temperature): a user-specified
margin around TEMPSET at which the space temperature is preferably
maintained when the space is unoccupied; [0075] RECOVMAX: (time): a
user-specified time representing the maximum time period that the
system should take to return the space to TEMPSET (.+-..DELTA.TEMP
or TEMPMIN) when a person first occupies the space after it has
been unoccupied; [0076] drift/drive initial variables: A, B and C
in the drift/drive equations; A and C are temperatures, and B is in
units of time; and [0077] DD RATIO: (dimensionless): This variable
represents an energy-saving ratio, specified by the user or the
system manager, of drift time to drive time outside the range of
TEMPMAX in the "genius" mode, discussed below.
[0078] The initial values of the drift and drive parameters may be
input by the system manager or user if enough is known about the
system to make a good guess at the values. They will in any case be
automatically adjusted as the system collects empirical information
as the space is heated and/or cooled, and it is preferable to
generate accurate drift and drive data as described in the above
section entitled "Deriving the drift and drive parameters" The
system would in this case by cycled through at startup time to
gather the necessary data, and then it would be ready to accurately
execute the required control of the HVAC equipment pursuant to the
method of FIG. 2.
[0079] Once all input data is collected and stored by the system,
the occupancy status (i.e. the presence or absence of someone in
the controlled room or space) is detected at box 210, and the
temperature TEMP of the space is detected at box 220. These are
stored in the memory, as are all of the variables and input data
during the execution of the method. At box 230, the current TEMP
and the time are stored together, i.e. correlated, which will be
used later in calculating drift and drive curves for the room or
other space being controlled.
[0080] At box 240, it is determined whether the current space
temperature TEMP is within the predetermined margin .DELTA.TEMP
from the set point TEMPSET. For example, the user may have input
72.degree. as a comfortable temperature, and .DELTA.TEMP may be
0.5.degree.. If the temperature in the space is within the range
71.5.degree. to 72.5.degree., then the determination at box 240 is
positive, so the method branches to box 250. If the system has been
driving the HVAC equipment, this ceases at this point; if the
system was not already driving the HVAC equipment, then it remains
off at box 250. Then the method branches to box 210 and loop A
begins anew. Note that in loop A (boxes 210-250 of FIG. 2), the
occupancy status is not relevant, since the temperature is
substantially at the set point, and the HVAC equipment will not be
driven in any case.
[0081] Loop B represents the situation where the space is occupied
and the space temperature drifts outside the desired range
(TEMP.+-..DELTA.TEMP); namely, at box 260 it is determined that
someone is present, and thus the step at box 270 causes the
computer to turn on the HVAC equipment, for which the program is
provided with commands for controlling the equipment in a
conventional manner. Thus, whenever TEMP drifts up (on a hot day)
above can calculate what this figure would be if it were holding
the temperature at the user set point, and compare the two
percentages. For example, at the drift boundary the equipment might
be on for 4 minutes and drift for 16 minutes in a cycle, for a
proportion of 20% [4/(4+16)]. At the same time, it might be
determined that if the system tried to hold the temperature at the
user set point, it would be on for 12 minutes and off for 6
minutes, for a proportion of 66.67% [12/(12+6)].
[0082] The amount of energy savings is the user set point
temperature proportion (the 66.67% figure above) minus the drift
temperature proportion, or 66.67%-20% [2/3-1/5= 7/15], or 47%. In
this example, in one cycle at the drift boundary, the savings
amount to 47% times 20 [4+16] minutes, or 91/3 minutes of run time,
where the HVAC system is off when it would have had to run to hold
at the user set point.
[0083] The energy savings additionally includes an amount
represented by the following.
TABLE-US-00002 (TEMPSET duty cycle) * (drift time to TEMPLIMIT)
minus (1 - TEMPSET duty cycle) * (drive time from TEMPLIMIT to
TEMPSET),
where the TEMPSET duty cycle is defined as the (on-time) divided by
(on+off time) in maintaining the temperature at TEMPSET. It is a
straightforward matter to calculate and include this savings amount
in the output from the system to the user.
[0084] The system of the invention can be programmed to store these
figures at regular intervals, such as every hour, and to generate a
report to be output for the system operator, reflecting the
aggregate savings in total time of equipment operation, and in
addition the proportion of the total time the equipment would have
had to run if the temperature were always held at the user set
point. Finally, it is an uncomplicated matter to configure the
program to determine the wattage output that would have been
required in the latter case, since the equipment's power use rate
generally is known, or may be determined empirically by a power
meter, and the power consumption figures may be digitized and input
as data to the computer 20 to arrive at actual power savings
figures. These may easily be translated into figures as to money
saved, for output in a report to the system operator.
[0085] Following is an application of the savings calculation to
the example used earlier, wherein the drift and drive equations
were determined to be: [0086] Drive equation:
[0086] T=68+12*e.sup.-t/300 .fwdarw.t=-300*ln[(T-68)/12]
72.5.degree., in this example, or (on a cold day) below
71.5.degree., the HVAC equipment will be activated to drive the
temperature back to within 0.5.degree. of the set point, 72.degree.
(e.g. down to 71.5.degree. or up to 72.5.degree., respectively).
Alternatively, the system may be configured such that whenever on a
hot day the temperature drifts above 73.degree., when the set point
is 72.degree. and .DELTA.TEMP is 1.degree., the HVAC equipment
drives the temperature down to 72.degree.. Similar variations are
used without substantive departure from the principle of keeping
the temperature within some margin .DELTA.TEMP of a set point.
[0087] Loop B returns to box 210, and the method begins anew at
that point. If the temperature has returned to
(TEMP.+-..DELTA.TEMP), then loop A is executed, and the HVAC
equipment is turned off; otherwise, loop B is executed again, and
at box 270 the (already operating) HVAC equipment continues to
run.
[0088] It may be, however, that before the preset range around the
set point is reached (i.e. before the range of temperatures
TEMP.+-..DELTA.TEMP is reached), everyone who has been in the
controlled space leaves. Alternatively, it may be that the
temperature of an unoccupied space drifts outside the preset range.
In either case, the decision at box 260 branches to box 280, where
variables in the drift and drive equations (as in FIGS. 3-5) are
updated.
[0089] --Steps 280-290: Calculations of Drift and Drive Variables
and TEMPLIMIT--
[0090] At step 290, the variable TEMPLIMIT is set to the smaller of
(1) TEMPMAX and (2) the temperature deviation from TEMPSET for
which the time to recover to TEMPSET (or optionally, TEMPMIN) is no
greater than RECOVMAX.
[0091] The value for TEMPMIN is selected as some temperature range
around TEMPSET such that a person in the controlled space will be
comfortable even though the temperature may be outside the range
TEMP.+-..DELTA.TEMP. For example, if TEMP is 70' and .DELTA.TEMP is
0.5.degree., normally the system would maintain the temperature at
69.5.degree. to 70.5.degree.. However, with the use of the variable
TEMPMIN the operator has the option of specifying a temperature
range near 70.degree., such as .+-.2.degree., such that it will be
acceptable if the system reaches this slightly broadened range
within a given period of time RECOVMAX, e.g. six minutes. It may
then take additional minutes to reach the ideal of
70.5.degree..+-.0.5.degree., but the persons in the loom will
probably not notice the difference, once the 2.degree. TEMPMIN
margin is reached. Note that TEMPMIN may be set to be zero or the
same as .DELTA.TEMP, if desired, thus bypassing the "comfort range"
option. In this case, the calculation under step 290, item (2) is
carried out with TEMPSET as the target temperature.
[0092] The temperature deviation under step 290, item (2) is
derived from the value of RECOVMAX in the following manner: if the
HVAC system drives the temperature down to, for example, 70 degrees
and shuts off (i.e. the user set point is 70 degrees, ignoring
.DELTA.TEMP for the moment), then--using the exemplary drive
equation discussed above--one can see that 70 degrees is reached
after 537.53 seconds (almost nine minutes). If RECOVMAX is set, for
instance, to six minutes, or 420 seconds, the system must determine
how far the system can allow the temperature to drift and still be
able to drive back to 70 degrees in 420 seconds. Using the
foregoing exemplary equation, T.sub.max would be calculated as
follows:
T.sub.max=68+12*e.sup.-(537 53-420)/300=76.11
Thus, the temperature can be allowed to drift to 76.11 degrees and
the system can still drive back to 70 degrees in 420 seconds.
[0093] The foregoing calculation is performed in the same manner
when .DELTA.TEMP or TEMPMIN is taken into account; the only
difference is that the latter variables are taken into account when
calculating the time it will take to drive to the target
temperature. Thus, if TEMPMIN=2.degree., then the time it would
take to drive to 72.degree. would be compared with RECOVMAX to
generate the value for T.sub.max, and this value would be larger
than 76.11.degree. since the system would not need to drive all the
way back to TEMPSET.
[0094] Essentially the same procedure as for the drive equation
parameters is used to find the drift equation A, B, and C
parameters, which are different from the drive equation parameters
and yield a different equation of the same form. For instance, for
a user set point of 70.degree. and a maximum drift to 90.degree.,
the drift equation describing the behavior of the temperature when
the equipment is turned off may be:
T=90-20*e.sup.-t/720
which means the drift Tau is 720 seconds, and that when the HVAC
equipment is turned off, the farthest the temperature will drift is
up to 90.degree.. (Note that at t=0, the temperature is
70.degree..) The slope of the drift equation at T=76.11.degree. is
given by:
dT/dt=-A/B*e.sup.-t/B,
so, observing that T=76.11.fwdarw.t=262.49:
dT/dt=-(-20)/720*e.sup.-262 49/720=0.01929 degrees/sec.
[0095] In the drift mode, B varies so little it may be taken as
constant. At the drift temperature boundary in this example, with
B=720 and t=262.49, only A will vary significantly as the ambient
temperature forces the enclosed space leakage rate (i.e., the
slope) to change. As it gets hotter outside, dT/dt will increase at
the drift temperature boundary. To hold the temperature at 76.11,
the system repeatedly allows the temperature to drift a little
(such as 0.5.degree.) above 76.11, and then drives it back a little
(again, such as 0.5.degree.) below 76.11. (Alternatively, the
temperature could be allowed to drift to 76.11, and then be driven,
for instance, one degree below that.)
[0096] If the temperature is allowed to drift 0.5.degree. above
76.11 and is then driven 0.5.degree. below 76.11, for a 1 degree
total drift, then initially the time for this 1 degree drift is
(dT/dt).sub.0=1/0.01929=52 seconds. As it gets hotter outside, the
time for the 1 degree drift is measured. If it is, for instance, 35
seconds, then (dT/dt).sub.1= 1/35=0.02894. Since
dT/dt=-A/720*e.sup.-262 49/720=-A*constant, so that:
(dT/dt).sub.1/(dT/dt).sub.0=-A.sub.1/-A.sub.0 and
A1=A0*(dT/dt).sub.1/(dT/dt).sub.0,
and therefore
A.sub.1=-20*0.02894/0.01929=-30.
[0097] Note that, from the drift equation at t=0:
T=C+A*e.sup.-0/B=C+A,
so that
T.sub.0=90+(-20)=70=C+A
and
C.sub.1=T.sub.0-A.sub.1=70-(-30)=100,
and the new drift equation is:
T=100-30*e.sup.-t/720.
[0098] This means the drift Tau is still 720 seconds, and that when
the HVAC equipment is turned off now, the farthest the temperature
may drift to is 100.degree., i.e., C.sub.drift=100.
[0099] When C.sub.drift changes, new drive equation parameters must
be calculated at step 280. In the drive equation, C.sub.drive has a
nonlinear relationship to C.sub.drift, while A and B vary so little
they can be taken as constant. C.sub.drive can be accurately
estimated using a Gaussian equation of the form
C.sub.drive=C.sub.drift+D*exp-[(C.sub.drift-E)/F].sup.2.
In this equation, D is the amplitude of
(C.sub.drive-C.sub.drift).sub.max, E is the temperature at
(C.sub.drive-C.sub.drift).sub.max, and F is one temperature Tau of
the Gaussian equation, which is the approximate .DELTA.C.sub.drift
needed to obtain a precise equation.
[0100] Three sets of D, E, F, C.sub.drive and C.sub.drift
measurements are required to solve this equation precisely. After
three drift and drive cycles of about one Tau duration at different
ambient temperatures, all nine parameters can be precisely
calculated, and the unoccupied space fully characterized by two
exponential, one Gaussian, and one linear equation. Subsequent
changes in the ambient temperature, measured on the drift side of
the holding cycle, are used to compute new parameters and their
associated drift and drive equations.
[0101] In practice, applicant has observed that
.DELTA.C.sub.drive.apprxeq.0.2*.DELTA.C.sub.drift for small changes
in C.sub.drift, and this estimate can be used until
(C.sub.newdrift-C.sub.drift)/C.sub.drift becomes greater than a
fixed ratio set by the user or preprogrammer.
[0102] In summary, first the system learns the parameters for the
following equations:
T.sub.drive=C.sub.drive+A.sub.drive*e.sup.-t/B.sup.drive
and
T.sub.drift=C.sub.drift+A.sub.drift*e.sup.-t/B.sup.drift.
[0103] As the duty cycle changes while holding the temperature at
the current T.sub.max, the system computes C.sub.newdrift. Using
C.sub.newdrift, the system then computes
A.sub.newdrift=T.sub.drift0-C.sub.newdrift
A.sub.newdrive=A.sub.drive
C.sub.newdrive=C.sub.drive+0.2*(C.sub.newdrift-C.sub.drift)
and
T.sub.newdrive=C.sub.newdrive+A.sub.drive*e.sup.-t/B.sup.drive
T.sub.newdrift=C.sub.newdrift+A.sub.newdrift*e.sup.-t/B.sup.drift.
The concept of "duty cycle" is standard, and in this case may be
defined as the percentage of the total time that the system is on
to maintain the temperature at a given setting (such as
TEMPSET.+-..DELTA.TEMP); i.e. the quantity (time on) divided by
(time on+time off) to maintain such a temperature.
[0104] When (C.sub.newdrift-C.sub.drift)/C.sub.drift is greater
than a fixed ratio (such as 0.15), the HVAC equipment is run for a
Tau duration to learn new drift and drive parameters, saving the
first set of parameters. Then the simple linear adjustments are
used until the fixed ratio is exceeded a second time, upon which
the HVAC equipment is again run to learn new drift and drive
parameters. At this stage, the system calculates the Gaussian
parameters, and makes all further adjustments to the drift and
drive equations using only duty cycle time changes relating to
C.sub.newdrift.
[0105] --Variation on the Exponential Equation--
[0106] The form of the above equation, T=C+A*e.sup.-t/B, may
equivalently be taken as T=C+A*e.sup.-Bt, with merely a change in
dimension definition for B. The former is used in the present
examples so that Tau has the dimension of time rather than inverse
time, which makes it easier to conceptualize.
[0107] Once the parameters A, B and C in the equation
T=C+A*e.sup.-t/B are determined, it is a straightforward matter to
calculate any of the necessary values in the flow chart of FIG.
2.
[0108] The value for item (2) in step 290 can be determined in the
above manner for any values of TEMPSET and RECOVMAX. Once TEMPLIMIT
is set in this step, at step 300 it is determined whether the
current temperature TEMP is within the allowed margin TEMPLIMIT
from TEMPSET. If it is, then there is nothing to be done at this
point, so the method proceeds to step 250, where the HVAC equipment
is turned off (or, if it is already off, it remains off). The
method then returns to step 210, which completes a pass of loop C.
Loop C will be repeated, and no driving of the equipment will take
place, as long as the controlled space remains unoccupied and the
temperature in the space stays within the margin TEMPLIMIT (as
determined in step 290) of the user set point.
[0109] --Step 320: Loop E and the "Genius" Mode--
[0110] If the temperature in the space drifts outside this margin,
then the method proceeds to step 310, where it is determined
whether the "genius" mode is set. This is a mode used by the
invention to lead to greater energy savings, and can be indicating
in the program in memory by a flag or other conventional means for
indicating mode switching. The user control of the "genius" mode
may be a hardware switch whose position is detected and
communicated to the control program, or it may be a software
control, which will be equivalent.
[0111] The genius mode is used to determine whether, even though
the current temperature TEMP may have reached the TEMPLIMIT
calculated in step 290, an override may take place to allow the
temperature to drift yet further before driving back to TEMPSET
following reoccupancy. This will be allowed to take place, thus
effectively stretching the TEMPLIMIT, if the recovery time from the
new "stretched" TEMPLIMIT is small enough compared to the drift
time from the calculated TEMPLIMIT to the new "stretched"
TEMPLIMIT. Equivalently, the system inspects whether the ratio of
DRIFT to RECOV as defined in step 320 is greater than some
predetermined drift-drive ratio DD RATIO. For instance, DD RATIO
may be 5, which would mean that every five minutes of temperature
drift (with the HVAC equipment off) would require only one minute
of driving the equipment to return to the TEMPLIMIT point.
[0112] In practice, the closer the temperature of the space is to
the ambient temperature, the higher the value of DD RATIO; for
instance, very close to the ambient temperature, thirty minutes of
drift time may require only thirty seconds of corrective (return)
drive time. In this case, a 60:1 DD RATIO is realized, leading to
large blocks of downtime for the HVAC equipment, and hence
considerable energy savings.
[0113] Under such conditions, the user will want to set the
"genius" mode and choose a DD RATIO value that leads to energy
savings while not unduly inconveniencing occupants of the space.
This will be empirically determined; certainly thirty extra seconds
of drive time is acceptable, while twenty minutes would probably
not be.
[0114] There are other ways of implementing the "genius" mode than
expressing a DD RATIO value. For instance, drift may be allowed to
occur past TEMPLIMIT whenever: [0115] (a) the incremental
temperature drift does not exceed a defined percentage of the
allowed temperature drift range; and/or [0116] (b) the incremental
recovery time does not exceed a defined percentage of the specified
recovery time. Example (b) is essentially the same as the previous
example, but stressing the inverse of DD RATIO--it may be more
natural for a user to set the user-programmable value as, for
instance, specifying that the incremental recovery time does not
exceed 15% of the specified recovery time. Alternatively, as in
example (a), the user may specify that the incremental temperature
drift does not exceed 10% of the allowed drift range. In any of
these cases, with the genius mode set, the system automatically
increases the allowed maximum drift range past TEMPLIMIT by an
amount that corresponds to the range of the calculated DD RATIO.
The increased amount is thus limited by DD RATIO (and/or its
equivalent under (a) or (b) above); if DD RATIO is 10:1, then the
incremental temperature past TEMPLIMIT that the system allows the
space to drift will be substantially that temperature for which the
system calculates that the drive (recover) time to TEMPLIMIT is
one-tenth or less of the drift time. (This calculation may be
carried out in the same manner as in the above example for
calculating RECOVMAX at step 290.)
[0117] If the genius mode conditions are met as in box 320, then
the system follows loop E by proceeding to step 250, and turning
off (or leaving off) the HVAC equipment. If DD RATIO is not large
enough, the loop F is followed, at which time the HVAC equipment is
turned on (or left on), and in both cases the method then proceeds
to step 210.
[0118] In this basic form of the method of the invention, loops A
and B (without the "space occupied" detection and test of steps 210
and 260) correspond to conventional approaches to HVAC control.
When occupancy status has been taken into account in previous
systems, it has been used to extend the limit of a range such as
.DELTA.TEMP, but the features of loop C (particularly step 290)
have not hitherto been realized. The genius mode of loop E is a
further improvement leading to yet greater energy savings.
[0119] It can be seen from the above that the method of the
invention does not depend upon complex and potentially inaccurate
modeling of a controlled space. Rooms and buildings to be climate
controlled are constantly changing: doors and windows may be added,
furniture, carpets and wall coverings are altered; the ambient
microclimate will change with the seasons and as surrounding
buildings, trees and the like are added or removed; and so on. Even
during the course of a day, the ambient conditions may change
drastically as, for instance, an outside wall is exposed to direct
sunlight for the afternoon but receives a chill breeze at
night.
[0120] Not only ambient surrounding conditions change, but the HVAC
equipment itself evolves: the equipment's capacity changes when
filters are cleaned or become dirty, when coolants are added or
diminish with use, when equipment is replaced or upgraded or
downgraded, and when pipes and ducts are cleaned or become clogged
or leaky. The capacity of the HVAC equipment to drive the enclosed
space temperature depends upon all these variations, as well as
variations in the enclosed space and ambient conditions discussed
above.
[0121] The current invention automatically accommodates all of
these changes by empirically determining the drift and drive
equation parameters continually and in real time, so that reactions
to changing conditions occur as fast as the changes themselves.
[0122] The user interface control 110 shown in FIG. 1A provides a
convenient manner for the user to manipulate some of the variables
used in the method of FIG. 2, by acting on user input 50 to
interact directly with the program in the memory 40. Each of the
arrows 120-140 represents a multiposition switch or continuous dial
control. The "OFF/AUTO/Heat/Cool" switch 120 lets the user place
the system in off mode, automatic mode, heating mode, or cooling
mode, respectively (Here, the "AUTO" setting would allow automatic
switching between heating and cooling.) The temperature control 130
allows the user to specify TEMPSET by reference to a graduated
scale 150, which shows an exemplary range of 65.degree. F. to
90.degree. F. (and which would preferably include finer gradations
and temperature markings).
[0123] The energy savings control 140 is preferably a continuously
variable dial. When the control 140 is set on "high", the values
for RECOVMAX and TEMPMAX should be at some maximum, which minimizes
the amount of time the HVAC equipment is running. When the control
140 is set on "low", RECOVMAX and TEMPMAX take on minimum values,
which maximizes the comfort to the user but also uses more energy.
For instance, the system manager may predefine a range of allowed
values for RECOVMAX and TEMPMAX, and the user, by dialing the
control 140, varies these smoothly and in concert with one another
from the maximum values to the minimum values. In this embodiment,
the user need not know what the absolute values for these variables
are.
[0124] The control 140 may also interact with the program in memory
40 by setting the mode to genius or not. Thus, at some point in the
scale towards "high" energy savings, the genius mode may come into
operation.
[0125] The user interface control 110 is analog, and accordingly
includes a conventional analog-to-digital converter (not separately
shown) for each of the controls 140 and 150. The use of analog
devices to control computer programs is well known, and any of a
variety of standard equipment may be used.
[0126] A conventional digital interface may alternatively be used
in any of the embodiments herein, with precise settings for
temperature, RECOVMAX, TEMPSET and the other variables that are to
be set.
[0127] --Variations on the Basic Method--
[0128] A. Detection and Control of Conditions Other than
Temperature
[0129] The use of people and temperature sensors has already been
discussed. Humidity sensors may be used in a manner equivalent to
temperature sensors: a user may wish the humidity to remain in a
particular range, and will set a "user set point" of humidity just
as is done for the temperature in the embodiments already
discussed. All of the variables appearing in box 200 of FIG. 2 are
used, and the method variations discussed above are applicable,
except that humidity is the controlled climate condition, rather
than temperature, and the climate control equipment is
humidifying/dehumidifying equipment rather than merely temperature
control equipment. Of course, temperature and humidity may both be
controlled by the system of the invention.
[0130] Thus, if the user specifies, for; instance, a humidity of
70%, then if the humidity goes below that (or above 70%-0.5%, where
.DELTA.HUMIDITY=0.5), then the humidifier is turned on until the
humidity climbs to the correct range again. If the controlled space
is unoccupied, the humidity may be allowed to drift, just as
temperature is, and the RECOVMAX and TEMPLIMIT (or here,
HUMIDLIMIT) concepts described in connection with FIG. 2 are
directly applicable. The "genius" mode also works in the same
way.
[0131] Another application of the invention is to detect and
control the concentration of gases in the atmosphere of the
controlled space. For instance, in certain environments the buildup
of carbon dioxide (CO.sub.2) is a concern; and substituting carbon
dioxide concentration for temperature in the method of FIG. 2 shows
that the method is directly applicable to such a situation. Instead
of controlling temperature, the climate control equipment in this
case controls standard ventilation equipment and/or a conventional
degasification unit to remove toxic or undesirable gases. Other
gases that may be detected and controlled include radon, carbon
monoxide, etc. Similarly, simply the rate of flow of air may be the
controlled condition.
[0132] The invention may in like fashion be applied to any climate
condition that can be influenced by equipment controlled by a
computer. While it may be applied to lighting conditions (to
control the switching on and off of lights in occupied and
unoccupied rooms, respectively), it is particularly advantageous
when applied to the control of a variable condition with some
hysteresis effect, i.e. a condition that changes over some
appreciable period of time (at least minutes rather than
seconds).
[0133] B. Preventive Maintenance Indicator
[0134] For enclosed spaces acted upon by one controlled HVAC unit
at a constant C.sub.drift, the power effectiveness EFF may be
defined in a relationship arrived at by applicant, namely:
EFF=(C.sub.drift-C.sub.drive)/B.sub.drive.
This relationship emphasizes the HVAC equipment's effect on the
enclosed space, with the B.sub.drive denominator normalizing the
measure of effectiveness EFF by compensating for the natural
frequency (".tau.") response of the space.
[0135] As a general rule, as climate control equipment efficiency
decreases, the time it takes to change a condition (temperature,
humidity, or other condition) a fixed amount increases.
[0136] The system of the invention can thus act as a preventive
maintenance indicator by maintaining in memory the EFF and/or
(C.sub.drift, C.sub.drive, and B.sub.drive) values correlated with
time. The relative efficiency of the climate control equipment from
one time to another can then be determined whenever desired as the
absolute efficiency changes.
[0137] The system can easily be programmed to record such an
efficiency ratio regularly, such as daily, and from this an
efficiency curve can be empirically determined. Such a curve can
generally be fit to an equation EFF=100 e.sup.-Kt, where EFF is the
peak (100%) efficiency, t is time, and K is an empirical parameter
learned over time (with dimensions of inverse time).
[0138] This relative efficiency equation is updated and reported to
the user via an output device as often as desired, preferably every
time the new efficiency ratio is determined. In addition, once the
efficiency equation is established, relative efficiency at a future
time can be predicted. If the system manager specifies a minimum
relative efficiency requirement, the system can thus notify with an
output message or signal not only when the equipment is, in fact,
below desired efficiency, but in advance can notify the manager
when the equipment is expected to dip below the specified
efficiency ratio. For instance, every day for two weeks in advance
of the expected date, the system can issue a warning, such as a
computer printout, email or other message; a blinking light on the
base station and/or equipment itself; an audible alarm. A user
query device may be provided, such as a button on the base station
or equipment which, when pressed, displays on an adjacent screen
the efficiency value.
[0139] Such warnings may be coupled with a probability of the
efficiency failure, which may be determined by a least-squares fit
or other curve-fitting scheme of the empirical data with the
idealized equation EFF=100 e.sup.-Kt. To predict likely efficiency
decline past a predetermined minimum allowable efficiency, the
system of the invention can be thus programmed to project the time
at which the HVAC equipment is likely to go below that
predetermined minimum, and output this time with a probability
projection, such as the conventional "r.sup.2" curve-fit value in a
least-squares fit.
[0140] The forecasts of the system may then be used to create an
equipment maintenance schedule for a multi-unit property (such as a
hotel or a chain of hotels), thus increasing the efficiency of the
property owner's maintenance schedule. It is a straightforward
matter, given the above teaching, to author a program to: (1) run
periodic efficiency tests (or regularly extract efficiency data
from normal operation of the climate control equipment); (2)
calculate the efficiency data, including relative efficiency; and
(3) issue efficiency reports and maintenance schedules as
desired.
[0141] The determination of HVAC system efficiency can lead to
energy savings by notifying the system manager when the system is
running inefficiently; when the inefficiencies are resolved, the
temperature can be allowed to drift farther, because RECOVMAX can
be met more easily, so that the equipment is overall running a
smaller percentage of the time and the duty (holding) cycles have
smaller (temporal) drive components.
[0142] C. Backward Drive Alert
[0143] When the system turns on the climate control equipment, this
is in order to alter a given condition in the controlled space,
whether temperature, humidity, gas concentration or other
condition. It is known in which direction drift of the controlled
condition has been tending, and this information can be used to
further govern the use of the equipment.
[0144] For instance, it may happen that someone has left an outside
window open to the controlled space. If this is the case, then an
attempt to cool the space (on a hot day) may well fail. This may be
discovered by the system of the invention by determining after a
fixed period of operation of the equipment whether the temperature
is changing under drive conditions in the same direction as it was
under drift condition. Thus, if after N minutes (e.g. N=15) the
temperature direction tinder drive is the same as it is under
drift, the system infers that there is a serious leak from or to
the space. Noting this "backward" drive, the system may be
programmed to automatically turn off the climate control equipment
to stop the obviously wasteful and hopeless expenditure of
energy.
[0145] This is particularly valuable to hotels that want to turn
off automatically an air conditioner or heater when a guest has
left a window or sliding glass door open and has left the room.
Some systems have hardwired sliding glass doors (onto balconies,
for example, in tall hotels) with a switch that disables the HVAC
system when the door is ajar or open. Such a system is expensive
and troublesome to install and maintain, and for completeness such
sensors must be placed at every opening to the room. The present
system, on the other hand, automatically determines for any space
whether there is likely to be a major leak somewhere on the
enclosed space boundary (walls, ceiling, etc.), and can shut down
the HVAC system immediately or after a predefined or learned period
(see delay time learning algorithm below) under such conditions,
with or without the presence of people in the enclosed space. For
example, the system might wait 15 minutes in the presence of
people, even with an apparent leak, to let the housekeeping staff
clean the room with an open door, and then shut down the wasteful
HVAC operation. Alternatively, the system might shut down the HVAC
operation only when the space has an apparent leak and is
unoccupied.
[0146] This embodiment is also applicable to humidity detection. It
may be applied to gas impurities detection as well, although rather
than shut down the ventilation equipment, an alarm could be sounded
to indicate that the ventilation effort is not succeeding in
ridding the space of the undesired gases.
[0147] Any of the above variations can be combined with an
automatic report-generating program to notify the user or system
manager of all time periods that "backward driving" took place.
[0148] D. Fixed Drive Temperature Setting Range
[0149] Given the high cost of energy used to heat and cool space,
some property owners now prefer to limit the temperature range
users (or renters) of their space can set for themselves. For
example, some hotel room managers believe a temperature range of 64
to 80 degrees F. is sufficient to provide comfort to their guests
when a room is occupied. Even if the HVAC equipment is capable of
driving the temperature lower than 64.degree. or higher than
80.degree., the present system can be configured to limit the
temperature range to a desired range such as this one. The
temperature could still drift beyond those limits, of course, as
long as the recovery time constraints and savings goals are
met.
[0150] Similar limits may be placed on any controlled condition,
such as humidity. The limits may be specified as applying only when
the space is occupied, or whether or not the space is occupied. A
program designed to carry out the method of FIG. 2 can easily be
adapted to provide such user-defined limits, such as by taking the
limits as input from a manager's station and, if a later user
specifies a range outside that allowed, overriding the later-input
range with the extreme of the limited range (such as substituting
64.degree. for a user input of 60.degree.). The manager will
effectively have the override capability, since the manager can,
from the base station, change the limiting range at any time.
[0151] E. Adaptive Unoccupied Inference Delay Time
[0152] When people leave an enclosed space, such as a hotel room,
they may be leaving to get ice down the hall, to buy a newspaper at
the front desk, to go to the bathroom in an adjoining, unmonitored
room, or they may be leaving for an extended period. Rather than
switch to "unoccupied" mode (as at step 260 of FIG. 2) immediately
upon the room being vacated, the system can be programmed to delay
for a period of time, such as N minutes (where N=15, for example),
to be certain that the comfort requirements are satisfied in case
the space's occupant returns soon. In FIG. 2, this would entail a
determination at step 260 of whether the space (a) is unoccupied,
and (b) has been unoccupied for N continuous minutes.
[0153] By storing records relating to space occupancy over many
departure/return cycles, the system can learn how long to wait to
ensure that a certain percentage P % (where P=90%, for example) of
all or recent previous occupants do not return for at least M
minutes (M=30, for example). For example, it may be determined that
after 9 minutes of an unoccupied state, only 10% of the time do
occupants return within the following 30 minutes; in this case, the
"unoccupied inference delay time" can be set to 9 minutes, meaning
that only after 9 minutes will the occupancy status of the system
change to "unoccupied" (and proceed to box 280 in FIG. 2).
[0154] Thus, although the occupancy status of the room, strictly
speaking, alters as soon as the person has left the room, the
actual, long-term nonoccupancy status is not changed until after
the expected delay time, after which the system can predict that
the nonoccupancy will continue for a long period.
[0155] The method can be further improved by establishing two delay
times, one for when the space is lit and one for when it is dark.
Dark delay times may be longer because occupants are sleeping and
the detectors notice their movement less frequently. This variation
on the method enables the system to minimize the delay time to
engage and maximize energy savings, while minimizing the likelihood
that occupants will be inconvenienced by an uncomfortable
temperature when they continue to use and occupy the space.
[0156] F. Savings/Usage Meter
[0157] When the system holds the temperature at the maximum drift
boundary TEMPLIMIT, the HVAC system runs for some percentage of the
total cycle time [on/(on+off)] The system [0158] Drift
equation:
[0158] T=90-20*e.sup.-t/720.fwdarw.t=-720*ln[(T-90)/-20]
The cycling drift and drive times are now calculated for holding
(1) at the recovery time drift temperature boundary and (2) at the
user set point, as follows: [0159] F.1. At the recovery time drift
temperature boundary (6 minutes 76.11 degrees)
[0160] For this example, it is assumed that the temperature is held
to 76.11.degree..+-.0.5 degrees.
TABLE-US-00003 Drive time T.sub.1 = 76.11 - 0.5 = 75.61 .fwdarw.
t.sub.1 = 136.63 T.sub.2 = 76.11 + 0.5 = 76.61 .fwdarw. -t.sub.2 =
99.59 37.04 seconds Drift time T.sub.1 = 76.61 .fwdarw. t.sub.1 =
288.88 T.sub.2 = 75.61 .fwdarw. -t.sub.2 = 237.02 51.86 seconds
The total (drift+drive) cycle time is thus 37.04+51.85=88.90
seconds, while the drive portion of the cycle time is
37.04/88.90=0.417 or 41.7% of the total cycle time.
[0161] F.2. At the User Set Point (70 degrees)
[0162] The same .DELTA.TEMP is used here as at the drift boundary
(in this example, .+-.0.5 degrees) to calculate the cycle that
would be required if the temperature were being held at the user
set point:
TABLE-US-00004 Drive time T.sub.1 = 70 - 0.5 = 69.5 .fwdarw.
t.sub.1 = 623.83 T.sub.2 = 70 + 0.5 = 70.5 .fwdarw. -t.sub.2 =
470.58 153.25 seconds Drift time T.sub.1 = 70.5 .fwdarw. t.sub.1 =
18.23 T.sub.2 = 69.5 .fwdarw. -t.sub.2 = -17.78 36.01 seconds
[0163] The total (drift+drive) cycle time is thus
153.25+36.01=189.26 seconds, while the drive portion of the cycle
time is 153.25/189.26=0.810 or 81.0% of the total cycle time.
[0164] F.3. Savings
[0165] At the drift temperature boundary, the equipment is driven a
smaller percentage of the total cycle time than at the user set
point. For an hour, or any given period, the (difference in drive
times) multiplied by the (cost to operate the HVAC equipment)
yields the total amount of savings. For example, if the system
saves 20 minutes per hour, and it costs $0.15 per hour to operate
the HVAC equipment, then the savings amount to 20/60*$015=$0.05 pet
hour using the present system. Ten hours of similar saving per day
for thirty days saves $0.05*10*30=$15.00 per month. This can be a
very significant amount both relative to the total cost of running
the equipment and taking into account that for large organizations,
the savings per temperature control unit is multiplied
manyfold.
[0166] In this example, with (User Set Point.sub.Drive Proportion)
minus the amount (Drift Boundary.sub.Drive
Proportion)=0.810-0.1417=0.393, the saving amounts to 0.393 times
the total elapsed time. For every 60 minutes at the drift boundary,
the equipment is driven 60*0.417=25.0 minutes. If the temperature
were held at the user set point, the system would have to drive
60*0.810=48.6 minutes. Thus, the system saves
60*0.393=(48.6-25.0)=23.6 minutes of drive time per hour when the
temperature is held at the drift boundary rather than at the user
set point.
[0167] Gathering this data over days and months, the system
accumulates: (a) actual drive time; (b) calculated drive time
without the present system (calculated as if holding at the user
set point); (c) the difference between these two drive times
(=Drive Time Savings); and (d) this difference divided by the
calculated drive time without the system (=Savings Proportion
achieved by the present system).
[0168] G. Equipment Recycle Limitation
[0169] Minimum Off Time. Compressors build up pressure in the HVAC
tubing. When the HVAC equipment is turned off, the pressure slowly
leaks out, taking 2 to 4 or more minutes. If one tries to restart
the compressor before the pressure leaks out, electric current runs
into the compressor electric coils, trying without success to
overcome the high back pressure. Frequently, the compressor's
electric coils overheat and burn out, causing complete equipment
failure and the need for repair.
[0170] The present system solves this problem by including in the
program a governor that, for compressor-based HVAC equipment,
automatically keeps the compressor off for a minimum period of time
between on cycles, thus preventing premature burn out due to
too-frequent recycling. An appropriate such minimum period of time
is 4 minutes as the minimum off-time, but this time may be
decreased for some newer HVAC equipment.
[0171] Maximum Recycle Frequency. Each time a compressor is turned
on, there is an electric current inrush, much like the acceleration
forces required to move an automobile from rest to motion. The
stress on the HVAC's electric components carrying this current is
highest when overcoming the startup inertia and lowest when
maintaining the continuing pumping action, much like the wear and
tear difference for an automobile when acceleration is compared
with cruising. The less often HVAC equipment undergoes startup, the
longer the equipment will last.
[0172] The present system in a preferred embodiment automatically
limits the recycling frequency of compressor-based equipment to R
times per hour, which means a minimum cycle lasts 60/R minutes. One
may, for instance, set R=6, so that up to 6 recycles per hour are
allowed, or a minimum of 10 minutes for one on/off cycle. This
could trigger the temperature range above and below a temperature
holding level beyond the input or preprogrammed .DELTA.TEMP to be
increased beyond, for instance, a standard .+-.0.5.degree. F.
value, so that the holding range grows from .+-.0.5.degree. to
.+-.0.75 degrees or greater to achieve 10-minute minimum
cycles.
[0173] H. Zero-Voltage Switching
[0174] The voltage at which alternating current is delivered to
equipment varies along a sine wave from amplitude peaks to
zero-voltage crossovers. The present system can be configured to
detect the zero-voltage crossover and automatically switch on the
electric current at this point, minimizing the chance of sparks and
decreasing equipment stress which can occur due to sudden changes
in electromotive force.
[0175] FIG. 12 shows a suitable circuit for zero-crossing
switching, which uses a conventional integrated circuit 950 with an
internal zero-voltage sensing switch (with the zero switching being
performed by hardware; no microcode is required). The IC 950 is
coupled to a microprocessor 960, which is connected to outputs,
inputs and peripherals as needed and may be any of the
microprocessors or microcontrollers discussed herein for
controlling HVAC or climate control equipment. The IC 950 is
coupled to ground via a conventional relay 970. Outputs from the
microprocessor 960 are thus automatically synchronized to the line
voltage.
[0176] I. Power Factor Correction
[0177] Voltage and current are seldom delivered perfectly in phase
to users. When they are not in phase, some amount of current is
lost. Power is equal to the product of voltage and current, so when
they are in phase, optimum power delivery is possible. The present
system automatically adjusts the current phase to synchronize with
the voltage phase, achieving optimum power delivery.
[0178] The phase angle between the voltage and current can be
measured in a conventional manner. One method is to sample both the
voltage and current signals to produce two inputs into a
(multiplication) product detector integrated circuit. An output of
the product detector is a signal whose amplitude varies with phase
angle. This phase-proportionate angle is used as an input to an
analog-to-digital (AD) convertor of a microprocessor, which
controls a variable capacitor to tune the phase angle and power
factor to an optimal value.
[0179] J. Multistage HVAC Optimization
[0180] On multistage HVAC equipment, second and even third levels
of equipment are turned on when required to move the temperature
back to the user set point (see FIG. 10). For example, when it is
very cold, many heat pump systems (using the heat pump as stage 1)
turn on electric coils and move air over them to add heat to that
provided by the heat pump. These electric coils are considered a
second heating stage. Additional heating stages in very frigid
climates may include fuel oil burners and other apparatuses.
Usually, the first stage is more efficient and thus less costly to
operate than the second stage, which in turn is more efficient and
less costly to operate than the third stage. In some climates,
users are urged to operate their first stage HVAC equipment all the
time to prevent the occupied space temperature from reaching a
temperature where the more expensive stages are called upon.
[0181] The present invention is in a preferred embodiment
configured to learn the drive curves for the first stage, for the
first stage plus the second stage working together, and for the
first, second, and third stages working together. Relative cost
factors for these different stages and for different multistage
configurations and geographical regions are stored at the base
station (in the computer memory), and may be periodically updated.
Given the drive curves and relative cost factors, the system can
determine an optimum (minimum cost) energy savings boundary. This
can be done, for instance, by determining what the duty cycle to
maintain the temperature (TEMPSET or TEMPLIMIT, as the case may be)
would be for each of the stages.
[0182] Thus, the system first determines what the duty cycle would
be at stage 1, then at stage 2, then at stage 3 (if there is one).
Since the stage 1 power usage is lower, the duty cycle will be
greater than at stage 2, where the power output is higher. The
total energy consumption is (duty cycle)*(power output) for any
given stage. For instance, if stage 2 uses 1.2 times the power of
stage 1, then the break-even point, i.e. the point at which the
total energy cost is the same regardless of whether stage 1 or
stage 2 is used, is the point at which:
(duty cycle at stage 2)=(duty cycle at stage 1)/1.2.
If the left side of this equation is less, then it is economical to
progress to stage 2, since the time saved in lowering the duty
cycle more than compensates for the extra energy consumed per unit
time. If the left side is greater, then the system optimally should
remain at stage 1.
[0183] This same approach is used to determine also whether it
would be economical to move to stage 3. Whichever stage leads to
the lowest energy consumption should be used, and the system can
easily be configured (by simple programming) both to make this
determination and to move to the new stage, and furthermore to
constantly monitor the situation, using the learned and updated
drift and drive curves, to determine at any given time whether a
different stage should be used.
[0184] Moreover, although the system can be programmed to hold at
the first stage drive boundary, conditions will sometimes be such
that the temperature should be allowed to drift farther out, when
the savings exceed the return drive cost of second- or third-stage
help. The learned multistage curves combined with relative
multistage cost factors provide the precise information needed to
maximize energy savings in multistage systems.
[0185] K. Remote Base Station Parameter Settings
[0186] Parameters that are used as input (such as for the method of
the invention) are preferably alterable remotely. Such parameters
may include recovery time, maximum drift range, minimum recovery
range, and operating mode (on, to operate as in conventional
systems; "smart"--for using loop C of FIG. 2; and "genius") FIG.
1A, discussed below, shows one embodiment for accomplishing this,
while FIG. 11 (discussed below) shows another.
[0187] One method of remotely setting such parameters is to
transmit these values over the house wiring to specific, regional,
and global units. Another is to transmit these values over the air
(by radio or infrared) to intermediate transceivers located in
regionally defined base stations, which in turn transmit to all the
base stations in their region. This allows the operating values to
be changed from any computer in the building or even a laptop,
without entering rooms, and with transmission security provided by
the present system's ID verification protocols.
[0188] L. Extended Periods of Nonoccupancy
[0189] The system of the invention may be modified to keep track of
the length of occupancy and lack thereof over time, and to store
this information for the system manager's review. This information
can be used to provide further savings of energy by programming the
system with a predefined schedule of TEMPSET variations when the
controlled space has been unoccupied for long periods.
[0190] For instance, if the space has been unoccupied for 24 hours
or more, the system may institute a provisional PROVTEMPSET which
is 5.degree. F. (or a certain percentage) greater than the
programmed TEMPSET (for cooling settings), or 5.degree. F. (or,
again, a predefined percentage) less than the programmed TEMPSET
(for heating settings). In the cooling situation, the system will
then allow the space to climb up to 5.degree. hotter than it would
if the space had been occupied at any time within the preceding 24
hours. After another 24 hours, an additional 5.degree. (or
percentage) can be added to PROVTEMPSET, and so on. After a week,
the system could go into a temporary suspension of operation
altogether, until operation is again triggered by someone
reentering the space. This last variation is preferably constrained
by fixed absolute boundaries, such as 40.degree. F. to 100.degree.
F., to prevent heat or cold damage to fixtures or furnishings in
the controlled space. Any of the foregoing variations in settings
and times for implementing them can, of course, be altered to apply
to a given setting.
[0191] The same principle can be applied to variations on RECOVMAX,
where the maximum allowed recovery time is allowed to expand by a
certain percentage or number of minutes each day or other block of
time, and again the system may be programmed to suspend operations
after a predetermined large period of time, until reset manually or
when someone returns into the space.
[0192] A simpler version of this variation is to allow users to
program times that they will be away for known periods, and thus
cease or limit operation of the HVAC equipment for such
periods.
[0193] --Base Stations and Sensors: FIGS. 6-10--
[0194] Following is a discussion of preferred hardware
configurations for implementing the invention, directed to the use
of temperature sensors. Other sensors as discussed above can be
substituted for or used in addition to temperature sensors, with
appropriate changes to the control program. For instance, as
mentioned, if a CO.sub.2 sensor is used in addition to the
temperature sensor, then the program is configured to drive only
the ventilator subunit of the HVAC equipment, i.e. the fans alone.
FIGS. 6-11, then, while directed to a temperature-control
embodiment, are generalizable to add as many sensors of other types
as desired.
[0195] In common to all of these embodiments is the acceptance of
simple user instructions, including the user set point or
temperature range when people are present and the recovery time
when they return from an absence. In each case, the systems
automatically achieve the climate condition (e.g. temperature) and
recovery time goals while minimizing wasteful equipment operation
when people are absent.
[0196] FIG. 6 is a block diagram of a system 500 using a base
station 510 with multiple remote sensor units 520-540. These
sensors may include the types of sensors illustrated in FIG. 1 for
sensing temperature, occupancy, and other conditions such as light
intensity and presence of CO.sub.2 or other gases. Also shown, as
in FIG. 1, are input/output device(s) 550 coupled to the computer
of the base station 510, and the climate control equipment 560.
[0197] A suitable remote sensor unit 520 is shown in the block
diagram of FIG. 7, and communicates with the base station 510 by
radio, infrared, house wiring, hardwired connections, or other
equivalent means. A microcontroller 570 is used, and may, for
instance, be a PIC16C54 microcontroller (of the PIC16C5X series,
made by Microchip Corporation), which is a commercially available
product programmable in assembly language. It is powered by a power
source 580, which for remote sensors that communicate by wireless
means or are positioned in inconvenient locations, preferably has
batteries that are recharged by solar cells as to the power source.
This allows for lower maintenance effort and saves on energy costs
for the power of running the remote sensor.
[0198] The sensor unit 520 also includes one or more sensors 590,
which may include any combination of the following: [0199] Types of
sensors: [0200] 1. people sensors: [0201] passive infrared (PIR)
[0202] acoustic [0203] microwave (preferably combined with PIR)
[0204] laser [0205] 2. temperature sensors [0206] 3. humidity
sensors [0207] 4. day/night (photocell) detectors [0208] 5.
pollutant concentration meters [0209] 6. airflow meters Some of
these have already been discussed. Airflow meters can be used to
ensure a minimum volume rate or velocity of airflow through a space
that must be well ventilated.
[0210] FIG. 8 shows a base station 620 in cooperation with which
the transmitter 600 and switches/indicators 610 shown in FIG. 7 can
be used, in an embodiment of the invention using a through-the-wall
type of air conditioner and/or heater (e.g., a typical hotel room
air conditioner). The base station includes a conventional power
unit 630 which is plugged into a wall socket and powers the HVAC
equipment 640 and the microcontroller 650, which may be any of a
number of commercially available microcontrollers, such as the
Texas Instruments TMS 370 Series microcontroller (which is
programmable in the C++ language).
[0211] The microcontroller 650 switches the HVAC equipment 640 on
and off via control line 690 connected to the power unit 630. One
or more sensors 660 may be coupled to the microcontroller 650, in
addition to or instead of the sensor(s) 590 of the remote sensor
unit 520 shown in FIG. 7.
[0212] A transceiver 670 is controlled by the microcontroller 650,
and communicates with the remote sensor unit 520.
Switches/indicators unit 680 is also coupled to the microcontroller
650. In the preferred embodiment, the microcontrollers 650 (of the
base station 620) and 570 (of the remote sensor unit 520) are
programmed to work in cooperation such that the remote sensor
identifies itself to the base station in the following manner A
user presses a programmed switch at the switches unit 680, which
causes the microcontroller 650 to ready itself to receive a remote
sensor i.d. via the transceiver 670. Any remote sensor that sends
such a user i.d. within a predetermined time is "registered" with
the base station, and will from then on will be recognized and
accepted when it communicates with that base station, which will
collect sensor readings from the remote sensor(s) in question and
respond to them. Thus, the user presses the receive-user i.d.
switch at the unit 680, and then within the predetermined time
(such as 90 seconds) presses a preprogrammed send-user i.d. switch
in the switches unit 610 (see FIG. 7). This causes the remote
sensor's microcontroller 570 to transmit the user i.d. code for
that sensor to the base station. From then on, the base station is
receptive to sensor information from that remote sensor.
[0213] This ensures that, if two remote sensors are within radio or
other transmission range of two different base stations, they may
reliably be linked to one base station each.
[0214] Other useful switches or controls in the unit 680, for
implementing the above-discussed features of the invention,
include:
TABLE-US-00005 mode (on, smart, genius) TEMPSET control (for user
set point) TEMPMIN control TEMPMAX control .DELTA.TEMP control
RECOVMAX control DD RATIO control.
Useful indicators (lights or LEDs, for instance) are:
TABLE-US-00006 on/off indicator receiving/received user i.d.
indicator remote sensor weak signal indicator remote sensor failure
indicator.
[0215] FIG. 9 shows a base station 700 which is suitable for a
central plant HVAC unit powered from standard line current, such as
is conventional in commercial buildings, typically running off
110/220 VAC. The base station 700 would replace the wall unit for
such a central plant unit, and includes a microcontroller 710,
sensors 720, transceiver 730 and switches/indicators unit 740 which
are in essential respects identical to similarly numbered features
of FIG. 8, except that the microcontroller 710 must of course be
programmed differently so that it controls central HVAC equipment
instead of a single through-the-wall unit. The base station 700
cooperates with remote sensors in the manner described above, via
the transceiver 730.
[0216] The HVAC equipment in this embodiment includes a heating
unit 750, a cooling unit 760, and a fan unit 770, all of which are
conventional HVAC equipment, and may include a system using hot and
cold water pipes and a fan, or compressor/burner equipment with a
ventilator fan, or other standard devices. The microcontroller 710
controls the HVAC equipment 750-770 individually via on-off control
lines 780 controlling heating, cooling and ventilating (fan)
relays, respectively, of power unit 790.
[0217] FIG. 10 is a block diagram of a configuration of a base
station 800 suitable for conventional multistage HVAC equipment 850
(such as a standard wall-type unit), where three stages of heating
and two stages of cooling are provided and are controlled by a
multistage power unit 860. The use of multistage HVAC equipment is
desirable to provide greater degrees of heating and cooling (with
greater power consumption) when necessary, while using the lower
stages of operation for milder conditions or where slower heating
or cooling is acceptable.
[0218] In this embodiment, a microcontroller 810 has a memory
storing the program, as with each of the other embodiments (such as
in FIGS. 8 and 9). Sensors 820, transceiver 830 and
switches/indicators unit 840 may be essentially identical to the
corresponding units 720-740 shown in FIG. 9, but they and the
microcontroller 710 and its program are adapted as necessary to the
functions of the multistage HVAC equipment 850. Each of the stages
is individually controlled by the microcontroller 810 via on/off
lines 870 operating the individual power stages shown in the power
unit 860, which may be powered by a conventional 24-volt unit
880.
[0219] It is a straightforward matter to configure a program to
implement the invention to learn the drift and drive curves (as in
FIGS. 4-5) for each of the multiple stages of operation, and to
store the operating parameters and calculate efficiency data and
for each of these stages over time.
[0220] Each of the base stations shown in FIGS. 8-10, and other
conventional base stations, implements the method of the invention
illustrated in FIG. 2 by means of a program stored in memory of the
respective microprocessor. Other types of base stations will be
needed to control different types of HVAC equipment not illustrated
here, but the principles of the present invention apply in each
case, since for any heating and cooling operation there will be
associated drift and drive curves that can be learned, and based
upon this empirical data the operation of the equipment can be
efficiently controlled.
[0221] --Programmable Presets: FIG. 11--
[0222] FIG. 11 shows a presets adapter 900 allowing programmable,
user-specific presets for the system. It includes a suitable
microcontroller 910 powered by a power unit 920 and coupled to a
transmitter 930, which may be hardwired to the base station in
connection with which the adapter is used. A switches/indicators
unit 940 is also provided, coupled to the microcontroller 910. As
with any remote sensor, the microcontroller includes a
microprocessor and a memory for storing and executing a program for
carrying out the functions of the invention.
[0223] In this case, the functions are to provide a station whereby
a user can set preferred temperatures for different times and days,
and can also override these settings. Whenever a user overrides a
given programmed schedule of temperatures, the schedule reverts to
the programmed settings at the next time indicated. Thus, if a user
sets the temperature to go to 70.degree. F. at 8:00 a.m. on
Saturday and then down to 65.degree. F. at 11:00 p.m. Saturday, the
system will automatically set TEMPSET at 70.degree. F. at 8:00 a.m.
Saturday. If the user overrides the setting on Saturday afternoon,
turning the temperature up, say, to 75.degree. F., the
predetermined schedule will come into effect at 11:00 p.m. as
programmed, and the temperature will still drop to 65.degree.
F.
[0224] The adapter 900 thus includes switches for allowing such
programs to be preset by the user, along with displays to
facilitate the programming, namely:
TABLE-US-00007 Display temperature time days of week and/or dates
Switches temperature (manual up/down) time (manual up/down) set
day/date (up/down) set [temperature/time/day-date] into program
cancel [temperature/time/day-date] from program display programmed
[temperature/time/day-date]
[0225] These switches and displays are, of course, variable
according to the user's wishes, and any standard or custom
programming interface may be provided, including, if desired,
simply a keyboard interface to the microcontroller 910. Indeed,
with any of the microcontrollers used to carry out features of the
invention, the interface may be a keyboard and/or mouse as is
conventional with personal computers. The type of interface
represented by the block diagram of FIG. 11 is, however, preferable
for a commercial HVAC control unit.
[0226] Given the foregoing teaching on the method of FIG. 2 and its
variations, and the block diagrams of the various possible
configurations for executing the functions of the invention, one
skilled in the art can readily adapt a large variety of
conventional processors, memories, user interfaces and
computer/HVAC interfaces to implement the invention. No
special-purpose hardware is required. The programming required is
routine and relatively simple, and can be accomplished in any one
of a number of languages, such as assembler, FORTRAN, BASIC, C++ or
other conventional languages.
[0227] As discussed above, the drift and drive curves may be
described by exponential equations of the form T=C+Ae.sup.-t/B,
where T is temperature, t is time and A, B and C are constants that
define the curve. Applying this equation to a drift curve (such as
curve 420 of FIG. 4) or to a drive curve (such as curve 430 of FIG.
5), it is possible to predict what the temperature will be at a
future point in time or to predict at what time a particular
temperature will be reached. The method described above uses three
points of temperature data to calculate the values for A, B and C.
Those three data points are determined by sampling the temperature
at the beginning of the curve, half way through the drive or drift,
and at the end of the drive or drift. In an ideal model, these
three temperature data points yield accurate A, B and C values and
therefore accurate temperature projections. In the real world,
however, each temperature sample is affected by noise and the
precision and accuracy of the temperature measurement device.
Variations in the sampled temperature due to noise and measurement
errors can result in erroneous temperature/time projections.
Erroneous temperature/time projections, in turn, can result in
reduced efficiency and/or reduced user comfort.
[0228] In an alternative embodiment of the invention, a different
method is used to calculate the A, B and C values. This alternative
method takes into account the entire data set of measurements and
is capable of producing more accurate results. The new algorithm
also reduces the use of random access memory and processing power,
making it suitable for implementation in an embedded processor
(e.g., in a thermostat).
[0229] In this alternative method, temperature data is sampled
repeatedly during the drift curve and also during the drive curves.
For example, the temperature may be determined every five seconds.
The A, B and C values may then be calculated using the following
equations:
B = ( t mid - t start ) ln { ( T mid - T start ) / ( T end - T mid
) } ; ##EQU00007## A = n = start end ( T n - T avg ) 2 n = start
end ( - ln / B - t avg ) 2 ; and C = T avg - A t avg .
##EQU00007.2##
[0230] In the above formulas, T represents a measured temperature
and t represents the time of the sample. Further, T.sub.start
represents the first temperature sample (taken at time
t.sub.start); T.sub.end represents the last temperature sample
(taken at time t.sub.end); T.sub.mid represents the midpoint
temperature sample (taken at time t.sub.mid); T.sub.avg represents
the average temperature sample across all the samples; t.sub.avg
represents the average time at which all the samples were taken;
and T.sub.n represents the temperature at time t.sub.n.
[0231] The above formulas yield A, B and C values calculated using
the entire set of data between the start and end samples. However,
because noise is non-linear, even this alternative method of
calculating A, B and C might not yield the curve that best fits the
data. In older to determine the curve that best fits the
temperature data and that will, therefore, most accurately predict
future temperatures, the A, B and C values may be repeatedly
calculated using different size data sets. For example, the
calculations may be repeated using successively smaller sets of the
data. The smaller data sets may be created by moving the start
point forward by ten data points each iteration. For example,
consider a data set that includes 100 data points (i.e., 100 data
samples taken at 100 points in time, termed data point 1 through
data point 100). The first A, B and C values may be calculated
using all 100 data points. The second A, B and C values may be
calculated using data point 10 through data point 100. The third A,
B and C values may be calculated using data point 20 through data
point 100. This reduction of data set size and recalculation of A,
B and C values may continue to be repeated until the data set size
is reduced to a predefined minimum data size. For example, the
predefined minimum data size may be ten samples, such that the
reduction of data set size and recalculation of A, B and C values
continues until data point 90 through data point 100 is used.
[0232] This repeated reduction of data set size and recalculation
of A, B and C values will yield a series of A, B and C values, each
calculated from a different subset of the data. In the above
example, ten different A, B and C values will be calculated. In
order to determine which values produce the most accurate
representation of the actual drift or drive, each set of A, B and C
values is used to calculate theoretical temperature values for each
time in the data set using the formula T=C+Ae.sup.-t/B. A fit value
may then be calculated for each set of A, B and C values. The fit
value represents how well the measured (i.e., actual) temperature
values fit with the calculated curve. The fit value is also termed
a coefficient of determination or an R-squared value. Generally, a
higher fit value means the calculated curve is a better predictor
of the actual temperature values. The fit value may be calculated
using the following formula:
Fit = A 2 { n = start end ( - ln / B - t avg ) 2 n = start end ( T
n - T avg ) 2 } . ##EQU00008##
The fit value for each set of A, B and C values are compared to
determine which A, B and C values yield the highest fit value. The
set of A, B and C values which yields the highest fit value are
used for drift and drive projections. The curve defined by this set
of A, B and C values provides a more accurate representation of
actual temperature data than the curves determined using only three
sets of data. Therefore, the present invention provides a more
accurate way of predicting a future temperature value at particular
time or of predicting at which time a particular temperature value
will be reached.
[0233] Many modifications and other embodiments of the invention
will come to mind to one skilled in the art to which this invention
pertains having the benefit of the teachings presented in the
foregoing descriptions and the associated drawings. Therefore, it
is to be understood that the invention is not to be limited to the
specific embodiments disclosed and that modifications and other
embodiments are intended to be included within the scope of the
appended claims. Although specific terms are employed herein, they
are used in a generic and descriptive sense only and not for
purposes of limitation.
* * * * *