U.S. patent application number 11/699859 was filed with the patent office on 2008-07-31 for sensor-free optimal control of air-side economizer.
This patent application is currently assigned to Johnson Controls Technology Company. Invention is credited to John E. Seem.
Application Number | 20080179408 11/699859 |
Document ID | / |
Family ID | 39666829 |
Filed Date | 2008-07-31 |
United States Patent
Application |
20080179408 |
Kind Code |
A1 |
Seem; John E. |
July 31, 2008 |
Sensor-free optimal control of air-side economizer
Abstract
Systems and methods to regulate the amount of outdoor air that
is introduced into a building. These systems and methods use the
cooling coil control signal which is a function of the load on the
cooling coil. These systems and methods utilize extremum seeking
control logic to vary the flow of outdoor air into the building in
response to these load determinations.
Inventors: |
Seem; John E.; (Glendale,
WI) |
Correspondence
Address: |
FOLEY & LARDNER LLP
777 EAST WISCONSIN AVENUE
MILWAUKEE
WI
53202-5306
US
|
Assignee: |
Johnson Controls Technology
Company
|
Family ID: |
39666829 |
Appl. No.: |
11/699859 |
Filed: |
January 30, 2007 |
Current U.S.
Class: |
236/49.3 ;
236/13; 454/261 |
Current CPC
Class: |
G05D 23/1917 20130101;
Y02B 30/542 20130101; F24F 2011/0006 20130101; G05B 13/042
20130101; F24F 11/65 20180101; Y02B 30/54 20130101; F24F 11/0001
20130101; F24F 2011/0002 20130101 |
Class at
Publication: |
236/49.3 ;
236/13; 454/261 |
International
Class: |
F24F 13/04 20060101
F24F013/04; G05D 23/00 20060101 G05D023/00; F24F 7/00 20060101
F24F007/00 |
Claims
1. A method for operating a system which regulates an amount of
outdoor air that is introduced into a building and operates a
mechanical temperature control device that varies temperature in
the building, the method comprising: initiating a heating with
minimum outdoor air state; monitoring a heating control signal, a
cooling control signal and a damper control signal; performing a
state comparison of the heating control signal, the cooling control
signal and the damper control signal to a predetermined range of
values; and transitioning into a second state based on the
comparison.
2. The method as recited in claim 1, wherein the system includes a
single sensor.
3. The method as recited in claim 2, wherein the single sensor is a
supply air temperature sensor.
4. The method as recited in claim 1, wherein an extremum seeking
control circuit is used for varying the flow of outdoor air into
the building.
5. The method as recited in claim 1, wherein the predetermined
range of values is based on a geographic region.
6. The method as recited in claim 1, wherein the predetermined
range of values is based on a system maintenance.
7. The method as recited in claim 1, wherein the predetermined
range of values is based on a system configuration.
8. The method as recited in claim 1, wherein the predetermined
range of values is based on a system design.
9. The method as recited in claim 1, wherein performing the state
comparison of the heating control signal, the cooling control
signal and the damper control signal to a predetermined range of
values is initiated on a predetermined interval for at least the
first state.
10. The method as recited in claim 9, wherein the at least first
state comprises the heating with minimum outdoor state, a free
cooling state and a mechanical cooling with self-optimizing control
state.
11. A method for operating a system which regulates an amount of
outdoor air that is introduced into a building and operates a
mechanical temperature control device that varies temperature in
the building, the method comprising: initiating a heating with
minimum outdoor air state; monitoring a heating control signal, a
cooling control signal and a damper control signal; performing a
state comparison of the heating control signal, the cooling control
signal and the damper control signal to a predetermined range of
values; transitioning into a second state based on the comparison;
and wherein the predetermined range of values includes: (i) the
heating control signal is at a heating minimum value for five
minutes or the cooling control signal is at a cooling minimum value
for five minutes to transition to a free cooling state; (ii) the
damper control signal at a damper minimum value for five minutes to
transition to the heating with minimum outdoor air state; and (iii)
the damper control signal at a damper maximum value for five
minutes to transition to a mechanical cooling with self-optimizing
control state.
12. The method as recited in claim 11, wherein the system includes
a single sensor.
13. The method as recited in claim 11, wherein the single sensor is
a supply air temperature sensor.
14. The method as recited in claim 11, wherein an extremum seeking
control circuit is used for varying the flow of outdoor air into
the building.
15. The method as recited in claim 11, wherein performing the state
comparison of the heating control signal, the cooling control
signal and the damper control signal to a predetermined range of
values is initiated on a predetermined interval for at least the
first state.
16. The method as recited in claim 15, wherein the at least first
state comprises the heating with minimum outdoor state, a free
cooling state and a mechanical cooling with self-optimizing control
state.
17. A method for operating a system which regulates an amount of
outdoor air that is introduced into a building and operates a
mechanical temperature control device that varies temperature in
the building, the method comprising: initiating a heating with
minimum outdoor air state; monitoring a heating control signal, a
cooling control signal and a damper control signal; performing a
state comparison of the heating control signal, the cooling control
signal and the damper control signal to a predetermined range of
values; transitioning into a second state based on the comparison;
and wherein the predetermined range of values includes: (i) the
heating control signal is at a heating minimum value for a first
predetermined interval or the cooling control signal is at a
cooling minimum value for second predetermined interval to
transition to a free cooling state; (ii) the damper control signal
at a damper minimum value for a third predetermined interval to
transition to the heating with minimum outdoor air state; and (iii)
the damper control signal at a damper maximum value for a fourth
predetermined interval to transition to a mechanical cooling with
self-optimizing control state.
18. The method as recited in claim 15, wherein the first
predetermined interval, the second predetermined interval, the
third predetermined interval and the fourth predetermined interval
are configured to vary based on an user input.
19. The method as recited in claim 15, wherein the first
predetermined interval, the second predetermined interval, the
third predetermined interval and the fourth predetermined interval
are equal.
20. The method as recited in claim 15, wherein the first
predetermined interval, the second predetermined interval, the
third predetermined interval and the fourth predetermined interval
are configured to vary based on a system design.
21. A space conditioning device comprising: an air-handling unit; a
means for cooling an air coupled to the air-handling unit; a means
for heating the air coupled to the air-handling unit; a means for
controlling the space conditioning device; at least one means for
controlling a flow of the air coupled to the means for controlling
the space conditioning device and the air-handling unit; wherein
the means for controlling the space conditioning device in a start
up stage initiates a heating with minimum outdoor air state; and
wherein the means for controlling the space conditioning device is
configured to control the at least one means for controlling the
flow of the air utilizing extremum logic.
22. The space conditioning device as recited in claim 21, wherein
the system includes a single sensor.
23. The space conditioning device as recited in claim 22, wherein
the single sensor is a supply air temperature sensor.
24. The space conditioning device as recited in claim 21, wherein
an extremum seeking control circuit is used for varying a flow of
outdoor air into a building.
Description
BACKGROUND
[0001] The present application relates to the control of
air-handling units of a heating, ventilation and air conditioning
system, and more particularly to regulating the amount of outdoor
air that is introduced into the system in order to reduce the
amount of mechanical heating and cooling required.
[0002] FIG. 2 conceptually illustrates a single duct air-handling
unit (AHU) 10 of a heating, ventilation and air conditioning (HVAC)
system which controls the environment of a room 12 in a building 5.
Air from room 12 is drawn into a return duct 14 from which some of
the air flows through a return damper 16 to a supply duct 18. Some
of the return air may be exhausted outside the building through an
outlet damper 20 and replenished by fresh outdoor air entering
through an inlet damper 22. A minimum amount of fresh outdoor air
entering the system for proper ventilation within the building is
typically required by building codes. The dampers 16, 20, and 22
are opened and closed by actuators which are operated by a
controller 24 to control the ratio of return air to fresh outdoor
air. The mixture of return air and fresh outdoor air is forced by a
fan 25 through a cooling coil 26 and a heating coil 28 before being
fed into room 12.
[0003] Controller 24 also operates a pair of valves 27 and 29 that
regulate the flow of chilled fluid through cooling coil 26 and the
flow of heated fluid through heating coil 28, depending upon
whether the circulating air needs to be cooled or heated. Cooing
coil 26 and heating coil 28 provide "mechanical" heating and
cooling of the air and are referred to herein as "mechanical
temperature control elements." The amount of cooling or heating
energy that is required to be provided by mechanical temperature
control elements is referred to herein as a "mechanical load" of
the HVAC system.
[0004] Sensors 30 and 32, respectively, measure the temperature and
humidity of the outdoor air and provide signals to controller 24.
Another pair of sensors 34 and 36, respectively, measure the
temperature and humidity of the air in return duct 14. Additional
temperature sensors 38 and 39 are located in the outlet of supply
duct 18 and in room 12.
[0005] Controller 24 executes a software program that implements an
air side economizer function that uses outdoor air to reduce the
mechanical cooling requirements for air-handling unit 10. There are
three air side economizer control strategies that are in common
use: temperature, enthalpy, and temperature and enthalpy. These
strategies control transitions between two air circulation modes:
minimum outdoor air with mechanical cooling and maximum outdoor air
with mechanical cooling.
[0006] In temperature economizer control, an outdoor air
temperature is compared to the return temperature or to a
switch-over threshold temperature. If mechanical cooling is
required and the outdoor air temperature is greater than the return
air temperature or the switch-over threshold temperature, then a
minimum amount of outdoor air required for ventilation (e.g. 20% of
room supply air) enters air-handling unit 10. If mechanical cooling
is required and the outdoor air temperature is less than the return
temperature or a switch over threshold temperature, then a maximum
amount of outdoor air (e.g. 100%) enters air-handling unit 10. In
this case, outlet damper 20 and inlet damper 22 are opened fully
while return damper 16 is closed.
[0007] With enthalpy economizer control, the outdoor air enthalpy
is compared with the return air enthalpy. If mechanical cooling is
required and the outdoor air enthalpy is greater than the return
air enthalpy, then the minimum amount of outdoor air required for
ventilation enters the air-handling unit. Alternatively, when
mechanical cooling is required and the outdoor air enthalpy is less
than the return air enthalpy, then the maximum amount of outdoor
air enters air-handling unit 10.
[0008] With the combined temperature and economizer control
strategy, when mechanical cooling is required and the outdoor
temperature is greater than the return temperature or the outdoor
enthalpy is greater than the return enthalpy, the minimum amount of
outdoor air required for ventilation is used. If mechanical cooling
is required and the outdoor temperature is less than the return air
temperature and the outdoor enthalpy is less than the return
enthalpy, then the maximum amount of outdoor air enters the
air-handling unit. The parameters of either strategy that uses
enthalpy have to be adjusted to take into account geographical
environmental variations.
[0009] There are a number of different processes that can be used
to regulate dampers 16, 20, and 22 to control flow rate of outdoor
air, such as, direct airflow measurement method or energy and mass
balance method.
[0010] The direct airflow measurement method requires sensors that
measure airflow rate, which enables the fraction of outdoor air in
the supply air to be controlled with a feedback controller. Krarti,
"Experimental Analysis of Measurement and Control Techniques of
Outdoor Air Intake Rates in VAV Systems," ASHRAE Transactions,
Volume 106, Part 2, 2000, describes several well-know methods for
directly measuring the outdoor air fraction.
[0011] Alternatively, the fraction of outdoor air in the room
supply air can be determined by performing energy and mass
balances. Drees, "Ventilation Airflow Measurement for ASHRAE
Standard 62-1989," ASHRAE Journal, October, 1992; Hays et al.,
"Indoor Air Quality Solutions and Strategies," Mc-Graw Hill, Inc.,
pages 200-201, 1995; and Krarti (supra), describe methods for
determining the fraction of outdoor air in the supply air based on
a concentration balance for carbon dioxide. The fraction of outdoor
air in the supply air is determined from the expression:
f oa = C ra - C sa C ra - C oa ##EQU00001##
[0012] where C.sub.ra is the carbon dioxide concentration of the
return air, C.sub.sa is the carbon dioxide concentration of the
supply air, and C.sub.oa is the carbon dioxide concentration of the
outdoor air.
[0013] Performing mass balances on the water vapor and air entering
and leaving the room gives:
f oa = .omega. ra - .omega. ma .omega. ra - .omega. oa
##EQU00002##
[0014] where .omega..sub.ra is the humidity ratio of the return
air, .omega..sub.ma is the humidity ratio of the mixed air, and
.omega..sub.oa is the humidity ratio of the outdoor air.
[0015] Performing an energy and mass balance on the air entering
and leaving the room gives:
f oa = h ra - h ma h ra - h oa ##EQU00003##
[0016] where h.sub.ra is the enthalpy of the return air, h.sub.ma
is the enthalpy of the mixed air, and h.sub.oa is the enthalpy of
the outdoor air.
[0017] Assuming constant specific heats for the return air, mixed
air, and outdoor air yields:
f oa = T ra - T ma T ra - T oa ##EQU00004##
[0018] An estimate of the fraction of outdoor air in the supply air
can be determined from a model of the airflow in the air-handling
unit, as described by Seem et al., in "A Damper Control System for
Preventing Reverse Airflow Through The Exhaust Air Damper of
Variable-Air-Volume Air-Handling Units," International Journal of
Heating, Ventilating, Air-Conditioning and Refrigerating Research,
Volume 6, Number 2, pp. 135-148, April 2000, which reviews
equations for modeling the airflow in air-handling unit 10. See
also U.S. Pat. No. 5,791,408. The descriptions in both documents
are incorporated herein by reference. The desired damper position
can be determined based on the desired fraction of outdoor air and
the airflow model, where the desired damper position can be
determined.
[0019] One-dimensional optimization is applied to the fraction of
outdoor air in the supply air to determine the optimal fraction
which provides the minimal mechanical cooling load. Any of several
well-known optimization techniques may be employed, such as the
ones described by Richard P. Brent in "Algorithms for Minimization
without Derivatives," Prentice-Hall Inc., Englewood Cliffs, N.J.,
1973, or Forsythe, Malcolm, and Moler in "Computer Methods for
Mathematical Computations," Prentice Hall, Englewood Cliffs, N.J.,
1977. Alternatively, the "fminband" function contained in the
Matlab software package available from The Mathworks, Inc., Natick
Mass. 01760 U.S.A., may be used to find the optimal fraction of
outdoor air.
[0020] These control strategies have assumed that the reference
value or system optimal performance level was given. The reference
value is typically determined by a sensor. The reference value or
optimal operating conditions for a HVAC system is difficult to
determine under various dynamic parameters. One problem with
economizer control is the accuracy of the sensors. Humidity sensing
elements can be inaccurate and unstable, which causes the
economizer cycle to operate inefficiently. It would be advantageous
to provide an alternative control system that minimized the need
for sensors. Further, it would be advantageous to provide an
alternative control strategy were the reference value is unknown.
It would also be advantageous to provide a system that uses an
extremum seeking controller to enhance system performance.
SUMMARY
[0021] One embodiment relates to a system and/or method, which
regulates an amount of outdoor air that is introduced into a
building and operates a mechanical temperature control device that
varies temperature in the building. The system and method initiates
a heating with minimum outdoor air State. The system and method
monitors a heating control signal, a cooling control signal and a
damper control signal. The system and method performs a state
comparison of the heating control signal, the cooling control
signal and the damper control signal to a predetermined range of
values and transitions into a second state based on the
comparison.
[0022] Another embodiment relates to a system and/or method, which
regulates an amount of outdoor air that is introduced into a
building and operates a mechanical temperature control device that
varies temperature in the building. The system and method initiates
a heating with minimum outdoor air State. The system and method
monitors a heating control signal, a cooling control signal and a
damper control signal. The system and method performs a state
comparison of the heating control signal, the cooling control
signal and the damper control signal to a predetermined range of
values and transitions into a second state based on the comparison.
The predetermined range of values include the heating control
signal is at a heating minimum value for five minutes or the
cooling control signal is at a cooling minimum value for five
minutes to transition to a free cooling State; the damper control
signal at a damper minimum value for five minutes to transition to
the heating with minimum outdoor air State; and the damper control
signal at a damper maximum value for five minutes to transition to
a mechanical cooling with self-optimizing control State.
[0023] Yet another embodiment relates to a system and/or method,
which regulates an amount of outdoor air that is introduced into a
building and operates a mechanical temperature control device that
varies temperature in the building. The system and method initiates
a heating with minimum outdoor air State. The system and method
monitors a heating control signal, a cooling control signal and a
damper control signal. The system and method performs a state
comparison of the heating control signal, the cooling control
signal and the damper control signal to a predetermined range of
values and transitioning into a second state based on the
comparison. The predetermined range of values include the heating
control signal is at a heating minimum value for a first
predetermined interval or the cooling control signal is at a
cooling minimum value for second predetermined interval to
transition to a free cooling State; the damper control signal at a
damper minimum value for a third predetermined interval to
transition to the heating with minimum outdoor air State; and the
damper control signal at a damper maximum value for a fourth
predetermined interval to transition to a mechanical cooling with
self-optimizing control State.
[0024] Yet another embodiment relates to a space conditioning
device including an air-handling unit. The air-handling unit is
coupled to a means for cooling an air and a means for heating an
air. The space conditioning device includes a means for controlling
the space conditioning device and at least one means for
controlling a flow of the air coupled to the means for controlling
the space conditioning device and the air-handling unit. The means
for controlling the space conditioning device, in a start up stage,
initiates a heating with minimum outdoor air state and the means
for controlling the space conditioning device is configured to
control the at least one means for controlling the flow of the air
utilizing extremum logic.
BRIEF DESCRIPTION OF THE FIGURES
[0025] FIG. 1 is an isometric view of a building according to an
exemplary embodiment with an HVAC system including an air handling
unit.
[0026] FIG. 2 is a diagram of an air-handling unit in a HVAC
system.
[0027] FIG. 3 is a diagram of an air-handling unit in a HVAC system
without the outdoor air temperature and return air temperature and
relative humidity sensors, according to an exemplary
embodiment.
[0028] FIG. 4 is a state diagram of a finite state machine with
three operating states that are implemented in the controller of
the air-handling unit in FIG. 2, according to an exemplary
embodiment.
[0029] FIG. 5 is a diagram of an extremum seeking control system,
according to an exemplary embodiment.
[0030] FIG. 6 is another diagram of an extremum seeking control
system, according to an exemplary embodiment.
[0031] FIG. 7 is a diagram of a HVAC system in which extremum
seeking controller has been incorporated, according to an exemplary
embodiment.
[0032] FIG. 8 is an exemplary psychometric chart that shows outdoor
air conditions for the three regions of control, according to an
exemplary embodiment.
[0033] FIG. 9 is an exemplary psychometric chart that shows the
outdoor air conditions for different control states and regions of
self-optimizing damper control with an ideal coil, according to an
exemplary embodiment.
[0034] FIG. 10 is an exemplary psychometric chart that shows the
regions of optimal control and lines for transitioning between
states for a cooling coil model with a bypass factor of 0.3,
according to an exemplary embodiment.
[0035] FIG. 11 shows the extremum-controlled HVAC system tracking
the optimal solution, according to an exemplary embodiment.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0036] Before beginning the detailed description of exemplary
embodiments, several general comments are warranted about the
applicability and the scope of the present invention.
[0037] Although the description below contains many specificities,
these specificities are utilized to illustrate some of the
preferred embodiments of this invention and should not be construed
as limiting the scope of the invention. The scope of this invention
should be determined by the claims, their legal equivalents and the
fact that it fully encompasses other embodiments, which may become
apparent to those skilled in the art. A method or device does not
have to address each and every problem to be encompassed by the
present invention. All structural, chemical, and functional
equivalents to the elements of the below-described invention that
are known to those of ordinary skill in the art are expressly
incorporated herein by reference and are intended to be encompassed
by the present claims. A reference to an element in the singular is
not intended to mean one and only one, unless explicitly so stated,
but rather it should be construed to mean at least one. No claim
element herein is to be construed under the provisions of 35 U.S.C.
.sctn. 112, sixth paragraph, unless the element is expressly
recited using the phrase "means for." Furthermore, no element,
component, or method step in the present disclosure is intended to
be dedicated to the public, regardless of whether the element,
component, or method step is explicitly recited in the claims.
[0038] FIG. 1 shows a building 5 with an air-handling unit 10
according to an exemplary embodiment. Air handling unit 10 is part
of a heating, ventilation and air conditioning (HVAC) system which
controls the environment of a room 12 in a building 5.
[0039] FIG. 2 shows air-handling unit controller 24, which utilizes
software to control the air flow rate. FIG. 3 shows air-handling
unit controller 24 with only a supply air temperature sensor 38.
The underlying software configures controller 24 as a finite state
machine that has three states depicted in FIG. 4. A transition
occurs from one state to another, as indicated by the arrows, when
a specified condition or set of conditions occurs. In an exemplary
embodiment, the operational data of air-handling unit 10 is checked
when controller 24 is in a given state to determine whether a
defined transition condition exists. A number of the transition
conditions are specified in terms of the control being "saturated"
in the present state. The term saturated may be a specific time
interval, temperature condition, supply air condition and/or return
air condition.
[0040] In an exemplary embodiment, saturation occurs when
controller remains in a given operating mode for a predetermined
period of time without being able to adequately control the
environment of the building. For example, saturation occurs in a
mechanical cooling mode when the system is unable to cool room 12
to the desired temperature within a reasonable amount of time.
[0041] In State 1, valve 29 for heating coil 28 is controlled to
modulate the flow of hot water, steam, or electricity to heating
coil 28, thereby controlling the amount of energy transferred to
the air. This maintains room 12 or supply air temperature at the
setpoint. Dampers 16, 20, and 22 are positioned for a minimum flow
rate of outdoor air and there is no mechanical cooling, (i.e.
chilled water valve 27 is closed). The minimum flow rate of outdoor
air is the least amount required for satisfactory ventilation in
room 12. For example, 20% of the air supplied to room 12 is outdoor
air. The condition for a transition to State 2 is defined by the
heating control signal being saturated in the "No Heat Mode." Such
saturation occurs when valve 29 of heating coil 28 remains closed
for a defined period of time (i.e. heating of the supply air is not
required during that period). This transition condition can result
from the outdoor temperature rising to a point at which the
interior of room 12 does not need mechanical heating.
[0042] In State 2, dampers 16, 20, and 22 alone are used to control
the supply air temperature in supply duct 18 (i.e. no mechanical
heating or cooling). In this State the amount of outdoor air that
is mixed with the return air from room 12 is regulated to heat or
cool the air being supplied to room 12. Because there is no heating
or mechanical cooling, the inability to achieve the setpoint
temperature results in a transition to either State 1 or 3. A
transition occurs to State 1 for mechanical heating when either for
a defined period of time the flow of outdoor air is less than that
required for proper ventilation or outdoor air inlet damper 22
remains in the minimum open position for a given period of time.
The finite state machine makes a transition from State 2 to State 3
for mechanical cooling upon the damper control being saturated in
the maximum outdoor air position (e.g. 100% of the air supplied to
the room is outdoor air).
[0043] In State 3, chilled water valve 27 for cooling coil 26 is
controlled to modulate the flow of chilled water and control the
amount of energy removed from the air. At this time, extremum
seeking control is used to modulate dampers 16, 20, and 22 to
introduce an optimal amount of outdoor air into AHU 10. In an
exemplary embodiment, a transition occurs to State 2 when the
mechanical cooling does not occur for the given period of time
(i.e. the cooling control is saturated in the no-cooling mode).
[0044] Referring further to FIG. 4, a state diagram for controlling
an air side economizer with only supply air temperature sensor 38
is shown. Air-handling unit 10 has no sensors for controlling the
air-side economizer. In State 1, heating with minimum outdoor air
required for ventilation is initiated. In cold climates, the
initial state of control is a heating with minimum outdoor air
State 200. In this exemplary embodiment State 1 and heating with
minimum outdoor air State 200 are interchangeable terms. The system
starts up in heating with minimum outdoor air State 200 to minimize
the potential that cooling coil 26 and heating coil 28 could
freeze. State 1 controls the supply air temperature by modulating
the amount of heat supplied from heating coils 28. Dampers 16, 20,
and 22 are controlled for minimum ventilation. In an exemplary
embodiment, a transition to State 2 occurs after the heating
control signal has been at its minimum value (no-heat position) for
five minutes.
[0045] In State 2, the system is utilizing outdoor air to provide
free cooling to the system. In this exemplary embodiment State 2
and a free cooling State 202 are interchangeable terms. State 2
controls the supply air temperature by modulating dampers 16, 20,
and 22 to adjust the mixing of outdoor air with return air. In an
exemplary embodiment, a transition to State 1 occurs after dampers
16, 20, and 22 have been at a minimum ventilation requirement for
five minutes. In an exemplary embodiment, a transition to State 3
occurs after dampers 16, 20, and 22 have been controlled to supply
100% outdoor air for five minutes.
[0046] In State 3, the system utilizes mechanical cooling with
self-optimizing control to control dampers 16, 20, and 22. In this
exemplary embodiment, State 3 and a mechanical cooling with
self-optimizing control State 204 are interchangeable terms. State
3 controls mechanical cooling with self-optimizing control for the
outdoor air dampers. State 3 controls the supply air temperature by
modulating the flow rate of chilled water or refrigerant through
cooling coil 26. Self-optimizing control is used to determine
damper 16, 20, and 22 positions that minimize the amount of
mechanical cooling. Ventilation requirements are set at a lower
limit for the amount of outside air in supply duct 18. In an
exemplary embodiment, a transition to State 2 occurs after the
control signal for cooling has been in the no-cooling command mode
for five minutes.
[0047] In FIGS. 5-7, an extremum control system 62 is shown.
Extremum control is the tracking of a varying maximum and minimum
parameter. The relationship between inputs and outputs in a static
response curve is nonlinear in extremum control system 62. The
extremum controller finds the optimum operating point and tracks it
under varying conditions (e.g., changes in temperature, humidity
ratio, etc.).
[0048] In FIG. 5, a basic extremum control system 62 is shown. The
process can work in either an open loop or closed loop control
system. A search algorithm 54 continually modifies the output of
the process to approach the extremum despite a change in the
process 56 or an influence of disturbances 58. The process
communicates search algorithm 54 to plant 74. Search algorithm 54
determines a setpoint for the system. In addition to search
algorithm 54 communicating the setpoint to a plant 74, plant 74
also receives change in the process 56 signal from the process.
Plant 74 is configured to use either signal to modify the process.
In an exemplary embodiment, plant 74 may use change in the process
56 signal from the process to provide a command 60 to the process
to move the system towards the extremum. In another exemplary
embodiment, plant 74 may use search algorithm 54 signal from to
provide command 60 to the process to move the system towards the
extremum.
[0049] In FIG. 6, a basic extremum seeking static map is shown.
Where y is the output to be minimized; f* is the minimum of the
map; f'' is the second derivative (positive--f(.theta.) has a
min.); .theta.* is the unknown parameter; .theta.' is the estimate
of .theta.*; k is the adaptation gain (positive) of the integrator
1/s; a is the amplitude of the probing signal; w is the frequency
of the probing signal; h is the cut-off frequency of the washout
filter; + is "modulation" by summation and X is "demodulation" by
multiplication. Where a washout filter is given by:
h = s s + h ##EQU00005##
[0050] Extremum control system 62 starts with an estimate of the
unknown parameter .theta.*. The control system uses this parameter
to determine the optimum operating point and to track the optimum
operating point as it varies. The output to be minimized y is
transmitted to washout filter 64. Washout filter 64 screens y and
transmits the screened y to a multiplier 66. Multiplier 66
transmits .xi. to an adaptation gain filter 68. Adaptation gain
filter 68 transmits an estimate of .theta.* to an summation 70,
which transmits a control signal to plant 74. In an exemplary
embodiment, the algorithm for the extremum seeking system is a
single parameter system. It is noted that the algorithm may have
several or a plurality of parameters.
[0051] In FIG. 7, an extremum seeking control system 76 for a HVAC
system is shown. Extremum seeking control system 76 includes a heat
exchanger 80, a feedback controller 90, a high pass filter 86, a
mixer 96, an integrator 98, an amplifier 100, a damper command
control 102 and a mixing damper 88. Heat exchanger 80 lowers the
temperature of the air. Feedback controller 90 maintains a supply
air temperature 78 at a setpoint 92 by adjusting the position for
chilled water valve of cooling coil 26 (FIG. 2). Damper command
control 102 maintains the dampers between 0% and 100% outside
air.
[0052] FIG. 8 is an exemplary psychometric chart that shows outdoor
air conditions for the three regions of control. In heating with
minimum outdoor air State 200, the system heats the environment by
controlling the supply air temperature with heating coil 28.
Dampers 16, 20, and 22 are controlled to provide minimum
ventilation and there is no mechanical cooling. In free cooling
State 202, the supply air temperature is controlled by dampers 16,
20, and 22. There is no mechanical cooling and no mechanical
heating. In mechanical cooling and self-optimizing State 204, the
supply air temperature is controlled with mechanical cooling.
Dampers 16, 20, and 22 are controlled by the self-optimizing system
to minimize mechanical cooling and there is no mechanical
heating.
[0053] Referring to FIGS. 9 and 10, simulations were performed for
an ideal coil and air-handling unit 10 that had a minimum fraction
of outdoor air to supply air of 30%. FIG. 9 shows the outdoor air
conditions where the self-optimizing control will transition
between the following three fractions of outdoor air: 30% outdoor
air, between 30 and 100% outdoor air, and 100% outdoor air. FIG. 10
is a similar figure for a non-ideal coil with a bypass factor of
0.3. Cooing coil's 26 and heating coil's 28 characteristics may
change during the day as the water temperature varies. Also,
cooling coil's 26 and heating coil's 28 characteristics may change
with time as cooling coil 26 and heating coil 28 become foiled from
dirt accumulating on these coils 26, 28.
[0054] FIG. 11 shows extremum controlled system 62 varying the
percentage of outside from twenty percent 116 to one hundred
percent 118. The optimal percentage of outside air curve 114 is
tracked by the extremum controlled outside air curve 112. The
extremum controlled system tracks the optimal solution, which
causes some inefficiency 120 in the system.
[0055] In an exemplary embodiment, the cooling coil control signal
is a function of the load on cooling coil 26. The signal from
cooling coil 26 is communicated to the control circuit. The control
circuit utilizing extremum seeking logic modulates dampers 16, 20,
and 22.
[0056] While the exemplary embodiments illustrated in the figures
and described above are presently preferred, it should be
understood that these embodiments are offered by way of example
only. Accordingly, the present invention is not limited to a
particular embodiment, but extends to various modifications that
nevertheless fall within the scope of the appended claims. The
order or sequence of any processes or method steps may be varied or
re-sequenced according to alternative embodiments.
[0057] Describing the invention with figures should not be
construed as imposing on the invention any limitations that may be
present in the figures. The present invention contemplates methods,
systems and program products on any machine-readable media for
accomplishing its operations. The embodiments of the present
invention may be implemented using an existing computer processors,
or by a special purpose computer processor for an appropriate HVAC
system, incorporated for this or another purpose or by a hardwired
system.
[0058] It is important to note that the construction and
arrangement of the sensor-free control system as shown in the
various exemplary embodiments is illustrative only. Although only a
few embodiments of the present inventions have been described in
detail in this disclosure, those skilled in the art who review this
disclosure will readily appreciate that many modifications are
possible (e.g., variations in sizes, dimensions, structures, shapes
and proportions of the various elements, values of parameters,
mounting arrangements, use of materials, colors, orientations,
etc.) without materially departing from the novel teachings and
advantages of the subject matter recited in the claims. For
example, elements shown as integrally formed may be constructed of
multiple parts or elements (e.g., air-handling unit), the position
of elements may be reversed or otherwise varied (e.g., air-handling
unit), and the nature or number of discrete elements or positions
may be altered or varied (e.g., air-handling unit). Accordingly,
all such modifications are intended to be included within the scope
of the present invention as defined in the appended claims. The
order or sequence of any process or method steps may be varied or
re-sequenced according to alternative embodiments. In the claims,
any means-plus-function clause is intended to cover the structures
described herein as performing the recited function and not only
structural equivalents but also equivalent structures. Other
substitutions, modifications, changes and omissions may be made in
the design, operating conditions and arrangement of the exemplary
embodiments without departing from the scope of the present
inventions as expressed in the appended claims.
[0059] As noted above, embodiments include program products
comprising machine-readable media for carrying or having
machine-executable instructions or data structures stored thereon.
Such machine-readable media can be any available media which can be
accessed by a general purpose or special purpose computer or other
machine with a processor. By way of example, such machine-readable
media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical
disk storage, magnetic disk storage or other magnetic storage
devices, or any other medium which can be used to carry or store
desired program code in the form of machine-executable instructions
or data structures and which can be accessed by a general purpose
or special purpose computer or other machine with a processor. When
information is transferred or provided over a network or another
communications connection (either hardwired, wireless, or a
combination of hardwired or wireless) to a machine, the machine
properly views the connection as a machine-readable medium. Thus,
any such connection is properly termed a machine-readable medium.
Combinations of the above are also included within the scope of
machine-readable media. Machine-executable instructions comprise,
for example, instructions and data which cause a general purpose
computer, special purpose computer, or special purpose processing
machines to perform a certain function or group of functions.
[0060] It should be noted that although the figures herein may show
a specific order of method steps, it is understood that the order
of these steps may differ from what is depicted. Also two or more
steps may be performed concurrently or with partial concurrence.
Such variation will depend on the software and hardware systems
chosen and on designer choice. It is understood that all such
variations are within the scope of the invention. Likewise,
software implementations of the present invention could be
accomplished with standard programming techniques with rule based
logic and other logic to accomplish the various connection steps,
processing steps, comparison steps and decision steps.
* * * * *