U.S. patent application number 13/333727 was filed with the patent office on 2013-06-27 for hvac system, a controller therefor and a method of measuring and managing ventilation airflow of an hvac system.
This patent application is currently assigned to Lennox Industries Inc.. The applicant listed for this patent is Jonathan Douglas, Erroll Eaton. Invention is credited to Jonathan Douglas, Erroll Eaton.
Application Number | 20130161403 13/333727 |
Document ID | / |
Family ID | 48653013 |
Filed Date | 2013-06-27 |
United States Patent
Application |
20130161403 |
Kind Code |
A1 |
Douglas; Jonathan ; et
al. |
June 27, 2013 |
HVAC SYSTEM, A CONTROLLER THEREFOR AND A METHOD OF MEASURING AND
MANAGING VENTILATION AIRFLOW OF AN HVAC SYSTEM
Abstract
A controller, an HVAC system employing the controller and a
computer programmable product to implement a method of measuring
and managing ventilation airflow of an HVAC system is disclosed. In
one embodiment, the controller includes: (1) an interface
configured to receive feedback data from the HVAC system, the
feedback data corresponding to a pressure difference across the
outdoor damper and an economizer damper position and (2) a
ventilation director configured to determine a ventilation airflow
rate of the HVAC system based on the pressure difference, the
economizer damper position and economizer ventilation data of said
HVAC system.
Inventors: |
Douglas; Jonathan;
(Lewisville, TX) ; Eaton; Erroll; (McKinney,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Douglas; Jonathan
Eaton; Erroll |
Lewisville
McKinney |
TX
TX |
US
US |
|
|
Assignee: |
Lennox Industries Inc.
Richardson
TX
|
Family ID: |
48653013 |
Appl. No.: |
13/333727 |
Filed: |
December 21, 2011 |
Current U.S.
Class: |
236/49.3 |
Current CPC
Class: |
F24F 11/30 20180101;
F24F 2110/00 20180101; F24F 2110/30 20180101; F24F 2110/40
20180101 |
Class at
Publication: |
236/49.3 |
International
Class: |
F24F 11/00 20060101
F24F011/00 |
Claims
1. A controller for a heating, ventilating and cooling (HVAC)
system having an economizer with an outdoor damper, comprising: an
interface configured to receive feedback data from said HVAC
system, said feedback data corresponding to a pressure difference
across said outdoor damper and an economizer damper position; and a
ventilation director configured to determine a ventilation airflow
rate of said HVAC system based on said pressure difference said
economizer damper position and economizer ventilation data of said
HVAC system.
2. The controller as recited in claim 1 wherein said ventilation
director is further configured to adjust a position of said
economizer based on said economizer damper position and a desired
ventilation airflow rate.
3. The controller as recited as recited in claim 1 wherein said
ventilation director is configured to determine said ventilation
airflow rate based on said economizer ventilation data, said
pressure difference, said economizer damper position and a supply
airflow rate of said HVAC system.
4. The controller as recited in claim 3 wherein said economizer
ventilation data is developed based on measured data obtained while
operating said HVAC system over multiple operating conditions
during manufacturing or engineering thereof.
5. The controller as recited in claim 1 wherein said economizer has
a single damper assembly.
6. The controller as recited in claim 1 wherein said economizer
damper position indicates a blade angle of said outdoor damper and
is based on a feedback signal from an actuator of said
economizer.
7. The controller as recited in claim 6 wherein said ventilation
director is further configured to compensate for hysteresis between
said feedback signal and an actual position of blades of said
outdoor damper.
8. The controller as recited in claim 1 wherein said ventilation
director is further configured to employ an outside air temperature
and an elevation associated with said HVAC system to determine said
ventilation airflow rate.
9. The controller as recited in claim 1 wherein said ventilation
director is configured to select data from said economizer
ventilation data to calculate said ventilation airflow rate based
on said economizer damper position.
10. The controller as recited in claim 1 wherein said ventilation
director is further configured to determine a prorated ventilation
rate based on said ventilation airflow rate.
11. The controller as recited in claim 1 wherein said ventilation
director is further configured to generate an alarm or a status of
said economizer based on said feedback.
12. A computer program product, comprising a non-transitory
computer usable medium having a computer readable program code
embodied therein, said computer readable program code adapted to be
executed to implement a method of measuring and managing
ventilation airflow of a heating, ventilating and air conditioning
(HVAC) system having an economizer with an outdoor damper, said
method comprising: receiving feedback data from said HVAC system,
said feedback data corresponding to a pressure difference across
said outdoor damper and an economizer damper position of said HVAC
system; applying said pressure difference and said economizer
damper position to economizer ventilation data representing
ventilation airflow rates of said HVAC system; and determining a
ventilation airflow rate based on said applying, wherein said
ventilation airflow rate corresponds to one of said ventilation
airflow rates of said economizer ventilation data according to said
pressure difference and said economizer damper position.
13. The computer program product as recited in claim 12 wherein
said method further comprises receiving a desired ventilation
airflow rate and adjusting a position of said economizer based on
said economizer damper position and said desired ventilation
airflow rate.
14. The computer program product as recited in claim 12 wherein
said economizer ventilation data is developed based on measured
data obtained while operating said HVAC system over multiple
operating conditions during manufacturing or engineering
thereof.
15. The computer program product as recited in claim 12 wherein
said economizer damper position indicates a blade angle of said
outdoor damper and is based on a feedback signal from an actuator
of said economizer.
16. The computer program product as recited in claim 15 wherein
said method further comprises compensating for hysteresis between
said feedback signal and an actual position of blades of said
outdoor damper.
17. The computer program product as recited in claim 12 wherein
said determining further includes employing a supply airflow rate
of said HVAC system.
18. The computer program product as recited in claim 12 wherein
said method further includes determining a prorated ventilation
rate based on said ventilation airflow rate.
19. A heating, ventilating and cooling (HVAC) system, comprising:
an economizer having an outdoor damper and an actuator to move
blades thereof; a pressure sensor configured to determine a
pressure difference across said outdoor damper; and a controller,
comprising: an interface configured to receive feedback data from
said HVAC system, said feedback data corresponding to said pressure
difference and an economizer damper position; and a ventilation
director configured to determine a ventilation airflow rate of said
HVAC system based on said pressure difference, said economizer
damper position and economizer ventilation data of said HVAC
system.
20. The HVAC system as recited in claim 19 wherein said ventilation
director is further configured to adjust a position of said
economizer based on said economizer damper position and a desired
ventilation airflow rate.
Description
TECHNICAL FIELD
[0001] This application is directed, in general, to heating,
ventilating and air conditioning (HVAC) systems, and more
specifically, to determining and employing a ventilation airflow
rate in HVAC systems.
BACKGROUND
[0002] (HVAC) systems can be used to regulate the environment
within an enclosed space. Typically, an air blower is used to pull
air (i.e., return air) from the enclosed space into the HVAC system
through ducts and push the air (i.e., return air) back into the
enclosed space through additional ducts after conditioning the air
(e.g., heating, cooling or dehumidifying the air). Various types of
HVAC systems may be used to provide conditioned air for enclosed
spaces. For example, some HVAC units are located on the rooftop of
a commercial building. These so-called rooftop units, or RTUs,
typically include one or more blowers and heat exchangers to heat
and/or cool the building, and baffles to control the flow of air
within the RTU. Some RTUs also include an air-side economizer that
allows selectively providing fresh outside air (i.e., ventilation
or ventilating air) to the RTU or to recirculate exhaust air from
the building back through the RTU to be cooled or heated again.
[0003] At least one type of an economizer includes two damper
assemblies driven by a common actuator. The damper blades are
linked such that when the outdoor damper is open, the return air
damper is closed. When a building is occupied, the outdoor damper
of the economizer is typically opened a small amount (e.g., ten to
twenty five percent) to allow fresh air into the building to meet
ventilation requirements. When the outdoor air is colder than the
return air and cooling is needed, the outdoor damper is typically
opened to a hundred percent to allow the cooler outdoor air to
enter the building. These two functions of an economizer are often
referred to as a ventilation mode and a free cooling mode,
respectively.
[0004] Some HVAC systems use a powered ventilation damper that has
a single damper assembly intended to bring only enough outdoor air
to meet ventilation needs. Thus, for these economizers, the single
damper assembly is an outdoor damper that is used to control the
amount of fresh air that is allowed to enter a building through the
HVAC system.
SUMMARY
[0005] In one aspect, a controller for an HVAC system is disclosed.
In one embodiment, the controller includes: (1) an interface
configured to receive feedback data from the HVAC system, the
feedback data corresponding to a pressure difference across the
outdoor damper and an economizer damper position and (2) a
ventilation director configured to determine a ventilation airflow
rate of the HVAC system based on the pressure difference, the
economizer damper position and economizer ventilation data of said
HVAC system.
[0006] In another aspect, a computer program product, including a
non-transitory computer usable medium having a computer readable
program code embodied therein, the computer readable program code
adapted to be executed to implement a method of measuring and
managing ventilation airflow of an HVAC system having an economizer
with an outdoor damper. In one embodiment the method includes: (1)
receiving feedback data from the HVAC system, the feedback data
corresponding to a pressure difference across the outdoor damper
and an economizer damper position of the HVAC system, (2) applying
the pressure difference and the economizer damper position to
economizer ventilation data representing ventilation airflow rates
of the HVAC system and (3) determining a ventilation airflow rate
based on the applying, wherein the ventilation airflow rate
corresponds to one of the ventilation airflow rates of the
economizer ventilation data according to the pressure difference
and the economizer damper position.
[0007] In yet another aspect, an HVAC system is disclosed. In one
embodiment, the HVAC system includes: (1) an economizer having an
outdoor damper and an actuator to move blades thereof, (2) a
pressure sensor configured to determine a pressure difference
across the outdoor damper and (3) a controller. The controller
includes: (3A) an interface configured to receive feedback data
from the HVAC system, the feedback data corresponding to the
pressure difference and an economizer damper position; and (3B) a
ventilation director configured to determine a ventilation airflow
rate of the HVAC system based on the pressure difference, the
economizer damper position and economizer ventilation data of said
HVAC system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Reference is now made to the following descriptions taken in
conjunction with the accompanying drawings, in which:
[0009] FIG. 1 illustrates a block diagram of an embodiment of an
HVAC system constructed according to the principles of the
disclosure;
[0010] FIG. 2 illustrates a block diagram of an embodiment of a
controller constructed according to the principles of the
disclosure;
[0011] FIG. 3 illustrates a block diagram of an embodiment of
ventilation director constructed according to the principles of the
disclosure;
[0012] FIG. 4 illustrates a flow diagram of an embodiment of a
method of repositioning the dampers of an economizer according to
the principles of the disclosure; and
[0013] FIG. 5 illustrates a flow diagram of an embodiment of a
method of measuring and managing ventilation airflow of a HVAC
system carried out according to the principles of the
disclosure.
DETAILED DESCRIPTION
[0014] Knowing the ventilation airflow rate (i.e., airflow rate
through the outdoor damper of the economizer) during the various
operating modes of an economizer, such as the ventilation mode and
the free cooling mode, is advantageous. When in the ventilation
mode, the ventilation airflow rate provides verification that
ventilation as required is being provided. If the ventilation
airflow rate is too high, then energy may be wasted due to over
ventilation. In a free cooling mode, knowing the ventilation
airflow rate provides an indication of the energy savings provided
by the economizer. Thus, determining the ventilation airflow of an
HVAC system is often needed to verify that the system is providing
the desired ventilation.
[0015] This disclosure provides a scheme for determining the
ventilation airflow rate of an HVAC system employing feedback data
of the operating HVAC system and the relationship of that feedback
data to economizer ventilation data for the HVAC system. In one
embodiment, a controller is disclosed that calculates the
ventilation airflow rate employing the feedback data and the
economizer ventilation data. The economizer ventilation data is
developed from measured data obtained during manufacturing or
engineering of the HVAC system. In one embodiment, the type of
economizer ventilation data that is employed to calculate the
ventilation airflow rate varies based on economizer damper
position.
[0016] As disclosed in an embodiment herein, the feedback data
employed to determine the ventilation airflow rate includes the
economizer damper position and the pressure drop across the outdoor
dampers of the economizer. In some embodiments, a supply airflow
rate is also employed. Employing the supply airflow rate provide an
enhancement that can increase the accuracy when the outdoor damper
is 50% open or greater. Additionally, employing the supply airflow
rate can increase the response time of control. Additionally, an
outside air temperature and an elevation of the installed HVAC
system can be employed. The economizer damper position can be
determined from an actuator of the economizer. In one embodiment,
position information from an actuator of the economizer is employed
to determine and control the position of the damper blades of the
economizer. Employing the position information from the actuator
that moves the damper blades provides real-time data for accurately
calculating outside airflow into the HVAC system.
[0017] In addition to determining the real-time ventilation airflow
rate, a controller is disclosed that monitors and directs the
economizer's dampers to achieve a user specified ventilation rate.
The controller can also be configured to perform diagnostics and
generate alarms to warn a user when the actual ventilation rate is
above or below a desired value. In some embodiments, a controller
and/or operating schemes are disclosed that compensate for
hysteresis in the operation of an economizer actuator,
automatically calibrate an actuator offset in the field, select
economizer ventilation data based on the opening percentage of an
economizer's outdoor dampers and compensate for temperature and
elevation.
[0018] In one embodiment, a controller and operating schemes are
also disclosed that employ the ventilation airflow rate that has
been calculated to determine a prorated ventilation rate. The
prorated ventilation rate can then be used to obtain a ventilation
rate over a desired amount of time while reducing the run-time on
the indoor fan or blower of the HVAC system. In one embodiment
described herein, the HVAC controller monitors the fraction of time
the compressor ran during the previous hour. Based on that runtime,
the controller calculates a new higher ventilation rate which, when
ventilating during only the compressor on time, provides the same
amount of ventilation over an hour period as the original
ventilation rate would provide with continuous operation. This
enables the indoor fan to be turned off when the compressor is not
running while still providing the required amount of ventilation.
Turning the fan off when the compressor is not running will
dramatically improve the ability to dehumidify. When the fan is
running without the compressor on, water collected on the cooling
coil evaporates, negating the dehumidification done when the
compressor was running. Thus, disclosed herein are embodiments of
dynamically adjusting a ventilation rate to allow fan off time.
[0019] FIG. 1 illustrates a block diagram of an embodiment of an
HVAC system 100 constructed according to the principles of the
disclosure. The system 100 includes an enclosure 101 (e.g., a
cabinet) with openings for exhaust air, ventilation air, return air
and supply air. The enclosure 101 includes exhaust vents 102 and
ventilation vents 103 at the corresponding exhaust air and
ventilation air openings. Within the enclosure 101, the system 100
includes an exhaust fan 105, economizer 110, a cooling element 120,
an indoor fan or blower 130 and a heating element 140.
Additionally, the system 100 includes a fan controller 150 and a
HVAC controller 160. The fan controller 150 is coupled to the
blower 130 via a cable 155. The cable 155 is a conventional cable
used with HVAC systems. The HVAC controller 160 can be connected
(not illustrated) to various components of the system 100,
including a thermostat 119 for determining outside air temperature,
via wireless or hardwired connections for communicating data.
Conventional cabling or wireless communications systems may be
employed. Also included within the enclosure 101 is a partition 104
that supports the blower 130 and provides a separate heating
section.
[0020] The system 100 is an RTU. One skilled in the art will
understand that the system 100 can include other partitions or
components that are typically included within an HVAC system such
as an RTU. While the embodiment of the system 100 is discussed in
the context of a RTU, the scope of the disclosure includes other
HVAC applications that are not roof-top mounted.
[0021] The blower 130 operates to force an air stream 170 into a
structure, such as a building, being conditioned via an
unreferenced supply duct. A return airstream 180 from the building
enters the system 100 at an unreferenced return duct.
[0022] A first portion 181 of the air stream 180 re-circulates
through the economizer 110 and joins the air stream 170 to provide
supply air to the building. A second portion of the air stream 180
is air stream 182 that is removed from the system 100 via the
exhaust fan 105.
[0023] The economizer 110 operates to vent a portion of the return
air 180 and replace the vented portion with the air stream 175.
Thus air quality characteristics such as CO.sub.2 concentration and
humidity may be maintained within defined limits within the
building being conditioned. The economizer 110 includes an indoor
damper 111, an outdoor damper 113 and an actuator 115 that drives
(opens and closes) the indoor and outdoor dampers 111, 113 (i.e.,
the blades of the indoor and outdoor dampers 111, 113). Though the
economizer 110 includes two damper assemblies, one skilled in the
art will understand that the concepts of the disclosure also apply
to those economizers or devices having just a single damper
assembly, an outdoor damper assembly.
[0024] The controller 160 includes an interface 162 and a
ventilation director 166. The ventilation director 166 may be
implemented on a processor and/or a memory of the controller 160.
The interface 162 receives feedback data from sensors and
components of the system 100 and transmits control signals thereto.
As such, the controller 160 may receive feedback data from, for
example, the exhaust fan 105, the blower 130 and/or the fan
controller 150, the economizer 110 and the thermostat 119, and
transmit control signals thereto if applicable. One skilled in the
art will understand that the location of the controller 160 can
vary with respect to the HVAC system 100.
[0025] The interface 162 may be a conventional interface that
employs a known protocol for communicating (i.e., transmitting and
receiving) data. The interface 162 may be configured to receive
both analog and digital data. The data may be received over wired,
wireless or both types of communication mediums. In some
embodiments, a communications bus may be employed to couple at
least some of the various operating units to the interface 162.
Though not illustrated, the interface 162 includes input terminals
for receiving feedback data.
[0026] The feedback data received by the interface 162 includes
data that corresponds to a pressure drop across the outdoor damper
113 and damper position of the economizer 110. In some embodiments,
the feedback data also includes the supply airflow rate. Various
sensors of the system 100 are used to provide this feedback data to
the HVAC controller 160 via the interface 162. In some embodiments,
a return pressure sensor 190 is positioned in the return air
opening to provide a return static pressure. The return pressure
sensor 190 measures the static pressure difference between the
return duct and air outside of the HVAC system 100. In one
embodiment, a supply pressure sensor 192 is also provided in the
supply air opening to indicate a supply pressure to the HVAC
controller 160. The supply pressure sensor 192 measures the static
pressure difference between the return duct and the supply duct.
Pressure sensor 193 is used to provide the pressure drop across
outdoor damper 113 of the economizer 110. The pressure sensor 193
is a conventional pressure transducer that determines the static
pressure difference across the outdoor damper 113. The pressure
sensor 193 includes a first input 194 and a second input 195 for
receiving the pressure on each side of the outdoor damper 113. The
pressure sensors discussed herein can be conventional pressure
sensors typically used in HVAC systems.
[0027] The HVAC controller 160 is configured to determine supply
airflow according to conventional means. For example, in one
embodiment, the HVAC controller 160 is configured to calculate the
supply airflow rate based on a set of blower curves, fan power and
fan speed.
[0028] Economizer damper position is provided to the HVAC
controller 160 via the actuator 115. The actuator 115 is configured
to rotate or move the indoor and outdoor dampers 111, 113, of the
economizer 110 in response to a received signal, such as control
signals from the HVAC controller 160 (i.e., the ventilation
director 166). The actuator 115 is a conventional actuator, such as
an electrical-mechanical device, that provides a signal that
corresponds to the economizer damper position (i.e., blade angle of
the outdoor damper 113 of the economizer 110). The signal is an
electrical signal that is received by the ventilation director 166
which is configured to determine the relative angle of the outdoor
damper 113 based on the signal from the actuator 115. A lookup
table or chart may be used by the processor 117 to determine a
relative blade angle with respect to an electrical signal received
from the actuator 115. The angle can be based on (i.e., relative
to) the ventilation opening of the HVAC system 100. In some
embodiments, the economizer damper position can be determined via
other means. For example, an accelerometer coupled to a blade (or
multiple accelerometers to multiple blades) of the outdoor damper
113 may be used to determine the economizer damper position. The
outdoor damper 113 is opened at 100 percent when the blades thereof
are positioned to provide maximum airflow of ventilation air 175
into the system 100 through the ventilation opening. In FIG. 1, the
blades of the outdoor damper 113 would be perpendicular to the
ventilation opening or the frame surrounding the ventilation
opening when opened at 100 percent. In the illustrated embodiment,
the blades of the outdoor damper 113 would be parallel to the
ventilation opening when opened at zero percent.
[0029] The ventilation director 166 is configured to determine an
operating ventilation airflow rate of the HVAC system based on the
static pressure difference across the outdoor dampers 113, the
economizer damper position and economizer ventilation data. In some
embodiments, the ventilation director 166 also employs the supply
airflow rate to calculate the operating ventilation airflow rate.
In one embodiment, using the supply airflow rate for the
calculation is based on the economizer damper position being above
50 percent. In one embodiment, the economizer ventilation data is
developed during manufacturing or engineering of the system 100 or
similar type of HVAC systems. During development, a ventilation
airflow rate is measured in, for example, a laboratory, at a
variety of operating conditions. Various sensors and/or other type
of measuring devices are employed during the development to obtain
the measured data for the various operating conditions. Economizer
ventilation data is developed from the measured data and loaded
into the HVAC controller 160, such as a memory thereof. During
operation in the field, the HVAC controller 160 (i.e., the
ventilation director 166) receives the feedback data and calculates
the ventilation airflow rate employing the feedback data and the
economizer ventilation data. FIG. 3 provides a more detailed
embodiment of a ventilation director 166.
[0030] The ventilation director 166 is further configured to adjust
a position of the economizer 110 based on the economizer damper
position and a desired ventilation airflow rate. The desired
ventilation airflow rate can be preprogrammed into a memory of the
HVAC controller 160 during manufacturing. In some embodiments, the
desired ventilation airflow rate is entered into the HVAC
controller 160 in the field during, for example, installation, a
maintenance visit or a service visit. The ventilation director 166
generates a signal that directs the actuator 115 to adjust a
position of the blades of the economizer 110 based on the desired
ventilation airflow rate. In some embodiments, this signal
represents a difference between the operating ventilation airflow
rate and the desired ventilation airflow rate.
[0031] FIG. 2 illustrates a block diagram of an embodiment of a
controller 200 constructed according to the principles of the
disclosure. The controller 200 is configured to direct the
operation of or at least part of the operation of an HVAC system,
such as HVAC system 100. As such, the controller 200 is configured
to generate control signals that are transmitted to the various
components to direct the operation thereof. The controller 200 may
generate the control signals in response to feedback data that is
received from the various sensors and/or components of the HVAC
system. The controller 200 includes an interface 210 that is
configured to receive and transmit the feedback data and control
signals. The interface 210 may be a conventional interface that is
used to communicate (i.e., receive and transmit) data for a
controller, such as a microcontroller.
[0032] The interface 210 may include a designated input terminal or
input terminals that are configured to receive feedback data from a
particular component. The controller 200 also includes a processor
220 and a memory 230. The memory 230 may be a conventional memory
typically located within a controller, such as a microcontroller,
that is constructed to store data and computer programs. The memory
230 may store operating instructions to direct the operation of the
processor 220 when initiated thereby. The operating instructions
may correspond to algorithms that provide the functionality of the
operating schemes disclosed herein. For example, the operating
instructions may correspond to the algorithm or algorithms that
implement the method illustrated in FIG. 5. The processor 220 may
be a conventional processor such as a microprocessor. The
controller 200 also includes a display 240 for visually providing
information to a user. The interface 210, processor 220 memory 230
and display 240 may be coupled together via conventional means to
communicate information. The controller 200 may also include
additional components typically included within a controller for a
HVAC unit, such as a power supply or power port.
[0033] The controller 200 is configured to receive feedback data
from the HVAC system including feedback data that corresponds to,
for example, a pressure difference across an outdoor damper of an
economizer, supply airflow rate and economizer damper position of
the HVAC system. Additionally, the controller 200 is configured to
determine an operating ventilation airflow rate of the HVAC system
based on operating data, such as, the outdoor damper pressure
difference, the supply airflow rate and the economizer damper
position during operation. In some embodiments, the controller 200
also receives and employs condition data, such as, the outside
ambient temperature and the elevation at the HVAC system, when
calculating the ventilation airflow rate. The controller 200
calculates the ventilation airflow rate employing the feedback
data, that includes the operating and condition data of the HVAC
system, with the appropriate corresponding economizer data. In one
embodiment, the economizer data is predetermined economizer
ventilation data that is specific for particular HVAC systems or
types of HVAC systems.
[0034] The controller 200 is further configured to adjust a
position of an economizer of the HVAC system based on the
economizer damper position and a desired ventilation airflow rate.
In one embodiment, the controller 200 generates and transmits
control signals to an actuator of the economizer to adjust the
economizer damper position. In addition to the operation schemes
disclosed herein, the controller 200 can be configured to provide
control functionality beyond the scope of the present
disclosure.
[0035] The controller 200 is also configured to generate alarms and
status based on the ventilation airflow rate. In some embodiments,
the controller 200 is configured to employ the ventilation airflow
rate to determine a prorated ventilation airflow rate and direct
the operation of an HVAC system based thereon.
[0036] FIG. 3 illustrates a block diagram of an embodiment of
ventilation director 300 constructed according to the principles of
the disclosure. The ventilation director 300 may be embodied as a
series of operation instructions that direct the operation of a
processor when initiated thereby. In one embodiment, the
ventilation director 300 is implemented in at least a portion of a
memory of an HVAC controller, such as a non-transistory computer
readable medium of the HVAC controller. The ventilation director
300 includes a ventilation airflow determiner 310 and a ventilation
changer 320.
[0037] The ventilation airflow determiner 310 is configured to
calculate the operating ventilation airflow rate based on feedback
data and economizer ventilation data. The economizer ventilation
data is measured data that was obtained under various operating
conditions in a laboratory environment. In one embodiment, the
economizer ventilation data is specific for a particular type of
HVAC system.
[0038] The ventilation airflow determiner 310 receives feedback
data, such as operating data and condition data, from the HVAC
system. The feedback data includes the outdoor damper pressure
difference, the supply airflow rate and the economizer damper
position. In one embodiment, the outdoor damper pressure difference
is received from a pressure transducer, such as pressure sensor
193, that determines the pressure difference. In some embodiments
the return duct pressure drop is employed for the outdoor damper
pressure difference. The return duct pressure drop may be
determined via conventional means and provided to the ventilation
airflow determiner 310 for the outdoor damper pressure
difference.
[0039] In typical applications, the return static pressure is
within a range of a tenth of an inch to a half of an inch (0.1 inch
to 0.5 inch) of water column. In some embodiments, the ventilation
airflow rate ranges from 10 percent to 30 percent of the design
airflow rate for the HVAC system. This 30 percent ventilation
airflow rate of the designed system airflow rate can usually be
obtained with a damper opening of 35 percent.
[0040] The elevation of the HVAC system can be stored in a memory
of an HVAC controller. In one embodiment, the elevation is stored
in the ventilation airflow determiner 310. The elevation is a
parameter that is typically entered by a user during initial setup.
The elevation may be entered, for example, during installation or a
service visit. The outdoor temperature can be provided by a
thermometer associated with the HVAC system. As discussed with
respect to FIG. 1, the supply airflow rate can be provided by
conventional means the economizer damper position can be provided
from feedback data of an economizer actuator.
[0041] The ventilation airflow determiner 310 is configured to
calculate the ventilation airflow rate employing a combination of
equations, feedback data and the economizer ventilation data. In
some embodiments, the economizer ventilation data is stored in
look-up tables.
[0042] The ventilation airflow determiner 310 calculates the
ventilation airflow rate differently according to the current
economizer damper position. When the current economizer damper
position is 50 percent or less, the ventilation airflow determiner
310 employs Equation 1 to calculate the ventilation airflow
rate.
Ventilation Airflow Rate=1096*CA(.DELTA.P/.rho.).sup.1/2 (Equation
1)
[0043] In Equation 1, .DELTA.P is the outdoor damper pressure
difference and CA is the damper effective open area expressed in
squared feet (i.e., ft.sup.2). The value 1096 is a conversion
constant that is used to make the measurement units more useable.
The effective open area CA is calculated employing a flow
coefficient table of the economizer ventilation data established
for the HVAC system. Flow coefficient data is a parameter developed
from testing of HVAC systems that is a function of damper position
and relates outdoor damper position to the effective open area CA.
The ventilation airflow determiner 310 is configured to select the
appropriate flow coefficient data from the economizer ventilation
data based on the economizer damper position. For a current
economizer damper position that is 50 percent or less, a first
table of flow coefficient data is selected and employed. Table 1 is
an example of a flow coefficient table that is selected for an
economizer damper position less than or equal to 50 percent. The
values in Table 1 are unique for a particular economizer damper
assembly and are provided as an example. The flow coefficients for
two HVAC models, Model A and Model B, are provided in Table 1. One
skilled in the art will understand that flow coefficient tables for
other particular HVAC systems can be developed and stored with a
controller of the particular HVAC systems. In some embodiments, the
ventilation airflow determiner 310 is configured to determine the
effective air opening CA by interpolation of the data in a flow
coefficient table such as Table 1.
TABLE-US-00001 TABLE 1 Flow Coefficients for Economizer Damper
Position Equal To or Less Than Fifty Percent CA CA % OPEN MODEL A
MODEL B 0 0.0 0.0 5 0.055736 0.04812 10 0.083934 0.095381 15
0.113264 0.125026 20 0.151411 0.166996 25 0.208313 0.219794 30
0.278474 0.289318 35 0.354823 0.390838 40 0.460648 0.538106 45
0.588303 0.718347 50 0.722145 0.942691
[0044] In Table 1, % Open represents the outdoor damper blade
position relative to the frame of the HVAC system at the
ventilation opening. In one embodiment, the % Open is calculated
using an actuator feedback signal. The relationship between the %
Open and the actuator feedback signal is typically dependent on the
characteristics of the actuator and the design of the economizer.
In one embodiment, the relationship between % Open and the actuator
feedback signal is represented with Equation 2.
% Open=100.times.(V.sub.feedback-V.sub.offset)/8 (Equation 2)
[0045] V.sub.feedback and V.sub.offset correspond to the type of
actuator that is used. V.sub.feedback is the feedback voltage
output by the actuator. V.sub.offset is a voltage value that
corresponds to a fully closed economizer. In one embodiment,
V.sub.offset is nominally two volts, V.sub.feedback is two volts
when the damper is 0% open and V.sub.feedback is ten volts when
100% open. The number 8 in Equation 2 is a conversion constant that
is specific to the type of actuator employed.
[0046] V.sub.offset may vary from part to part. For example, in one
embodiment V.sub.offset can vary between 2.1 volts to 2.75 volts
with a closed damper. As such, instead of using a fixed offset
based on the actuator specification, in some embodiments a measured
offset is used. To determine the measured offset, the actuator is
commanded to go to its minimum position during calibration. After
waiting the amount of time required to move to its minimum
position, the ventilation airflow determiner 310 measures the
feedback voltage. If the feedback voltage is within the normal
variation of offset voltage, the current feedback is recorded as
the offset voltage. If the feedback voltage is not within the
normal variation of offset voltage, an error code is generated and
the default offset is used.
[0047] During operation, hysteresis in the relationship between the
actuator feedback signal and the actual position of the economizer
damper blades can occur. As such, the ventilation director 300
(i.e., the ventilation airflow determiner 310 or the ventilation
changer 320) can reposition the damper blades. The flow diagram of
FIG. 4 illustrates an embodiment of such a method.
[0048] Returning to Equation 1, p is the density of air entering
the outdoor damper. In one embodiment, the ventilation airflow
determiner 310 calculates the air density p employing Equation
3.
P=0.075((460+64)/(460+T.sub.OD))(P.sub.atm/14.696) (Equation 3)
[0049] In Equation 3, T.sub.OD is the outdoor temperature in
Fahrenheit and P.sub.atm is the atmospheric pressure calculated by
Equation 4.
P.sub.atm=14.696*(1-6.876E-6*ALT).sup.5.25588 (Equation 4)
[0050] In Equation 3, ideal gas relationships are being used to
correct air density for temperature and pressure variations. 0.075
is a reference density of air at 64F and 14.696 psia (sea level).
The first term 460+64/46+T corrects the reference density for
temperature (460 is used to convert the temperature to the absolute
ranking scale). The term P.sub.amt/14.696 corrects for atmospheric
pressure. Thus, the density is calculated using T.sub.OD and
P.sub.atm and ideal gas relationships. Equation 4 is a standard
equation used by the national weather service to calculate
atmospheric pressure as a function of elevation wherein the terms
have been converted for US units.
[0051] In Equation 4 ALT is the elevation of the HVAC system in
feet and is a user entered parameter. An elevation of 650 feet,
which is approximately the median elevation, is entered as a
default elevation. This can be entered during manufacturing of an
HVAC system or when programming a controller of the HVAC system.
Additionally, a default outdoor temperature of 70 degrees
Fahrenheit may also be used. Calculating the air density based on
elevation and temperature increase the accuracy of the ventilation
measurement across wide temperatures and at high altitudes.
[0052] When the current economizer damper position is greater than
50 percent, the ventilation airflow determiner 310 employs a
different flow coefficient table to calculate the ventilation
airflow rate. For example, Table 2 represents a flow coefficient
table for a particular type of HVAC system when the current
economizer damper position is greater than 50 percent. In some
embodiments, the ventilation airflow determiner 310 is configured
to determine the percentage of outdoor air by interpolation of the
data in a flow coefficient table such as Table 2. Once the
percentage of outdoor air is known, the ventilation airflow
determiner 310 multiplies the percentage of outdoor air by the
total supply airflow to determine the ventilation airflow rate. As
with Table 1, the flow coefficients for two different models of
HVAC systems are provided as an example.
TABLE-US-00002 TABLE 2 Flow Coefficients for Economizer Damper
Positions Greater Than Fifty Percent % OD AIR % OD AIR % OPEN MODEL
A MODEL B 50 65.3 65.3 60 79 79 70 88.2 88.2 80 95.1 95.1 90 97 97
100 97 97
[0053] Thus, the ventilation airflow determiner 310 selects the
appropriate flow coefficient table to employ based on the current
economizer damper position and determines the operating ventilation
airflow rate that is provided to the ventilation changer 320. The
ventilation changer 320 receives the operating ventilation airflow
rate and a desired ventilation airflow rate. Based on these
received airflow rates, the ventilation changer 320 adjusts the
economizer damper position to obtain the desired ventilation
airflow rate. The desired ventilation airflow rate may be received
via a user interface, such as a touch screen or keypad, associated
with an HVAC controller or the ventilation director 300. In one
embodiment, the desired ventilation airflow rate is stored and
received from a memory, such as the memory of an HVAC controller.
The various ventilation airflow rates may be provided to a user via
a display of an HVAC controller.
[0054] The ventilation changer 320, therefore, uses the ventilation
airflow rate determined above to automatically adjust the damper
actuator position command delivered to the actuator to achieve a
user specified ventilation rate. In some embodiments, the
ventilation changer 320 is configured to minimize movement of the
actuator. As such, concerns about reliability limitations of an
economizer actuator are minimized. Accordingly, in some
embodiments, a ventilation changer 320 is configured to change the
damper position once per a designated time. In some embodiments,
the ventilation changer 320 is configured to change the damper
position only once in every 10 minutes. In other embodiments, the
ventilation changer 320 is configured to change the damper position
when the operating state of the fan system has changed. The basis
for determining when to change the damper position and the
designated time for changing the damper position are
adjustable.
[0055] In some embodiments, designated events may be predetermined
to use as a basis for determining when to change the damper
position. For example, a change in supply air fan speed and a
change in ventilation setpoint can be used to trigger a change in
damper position. In one embodiment, the ventilation changer 320 is
configured to continuously integrate the error between the actual
ventilation rate and the desired rate when waiting to make a
control move. In one embodiment, the ventilation changer 320, when
determining it is time to make a control move, determines the next
position of the damper blades of the outdoor damper with following
procedure:
[0056] 1) Calculate an integral offset of the actuator where the
integral offset=-1*Integrated Error/Integral Gain. If the absolute
value of the integral offset is greater than the desired
ventilation rate, then the integral offset is set equal to the
integral offset multiplied by the desired ventilation rate divided
by the absolute value of the integral offset. To prevent over
opening or over closing the damper, a ventilation rate more than
twice the normal ventilation rate may not be employed.
[0057] 2) Calculate the new ventilation target airflow using the
following by adding the desired ventilation rate and the integral
offset together.
[0058] 3) Calculate the current ventilation airflow rate using a
procedure defined above with respect to the ventilation airflow
determiner 310.
[0059] 4) Acquire the current outdoor damper pressure
difference.
[0060] 5) Acquire the current supply airflow.
[0061] 6) Acquire the current economizer damper position.
[0062] 7) Calculate the new predicted damper pressure difference
employing the following equation, Equation 5, wherein CurrentDP is
the current economizer damper position, CurrentCFM is the current
supply airflow and VentTarget is the ventilation target. For
Equation 5, the ventilation changer 320 can employ the return duct
static pressure difference as the pressure difference across the
outdoor damper. Typically, the return duct pressure drop is
proportional to the square of the airflow rate through the return
duct. In this embodiment, the ventilation changer 320 assumes that
the airflow through the return duct is equal to the supply airflow
rate minus the ventilation airflow rate.
newDP=CurrentDP*((CurrentCFM-VentTarget)/(CurrentCFM-CurrentVent))
2 (Equation 5)
[0063] 8) Calculate the new CA employing Equation 6.
newCA=VentTarget/(newDP) 0.5 (Equation 6)
[0064] 9) Use the economizer ventilation data (such as Table 1) to
determine the economizer damper position, i.e., the new damper
position associated with the new CA, and determine the position
difference between the new damper position and the current damper
position. If the absolute value of the position difference is less
than Deadband (i.e., less than the steps at which the actuator can
move, such as 1.5% step), then set the new damper position as the
new damper position. Otherwise, set the new damper position equal
to the current position.
[0065] The ventilation director 300 (i.e, either the ventilation
airflow determiner 310 or the ventilation changer 320 or a
combination thereof) can also perform diagnostics, detect faults
with the economizer and generate alarms. The alarms could be
visually presented on a display of a controller and/or communicated
to a monitor or monitoring service. An audible alarm may also be
generated. The diagnostics can be used to warn a user of a fault
which could cause an inaccurate measurement of ventilation airflow.
An example of an alarm resulting from receiving feedback data from
the economizer actuator includes Damper Stuck. Damper Stuck can be
determined by comparing actuator feedback position to command
position. During operation of the damper actuator, the feedback
position of the damper is compared with the desired position. Once
the actuator has stopped moving, if the feedback position in not
within a prescribed tolerance of the desire position, the algorithm
indicates a fault. The ventilation director 300, will continue to
monitor the feedback position and automatically clear the fault
should the feedback start to match the command.
[0066] In one embodiment, the ventilation director 300 is also
configured to perform damper pressure sensor diagnostics. Based on
normal operating data that can be stored in an HVAC controller, the
ventilation director 300 can compare the outdoor damper pressure
difference with the percent of damper opening and generate an alarm
if the measured pressure is out of range compared to the stored
operating data. An error can be recorded and an alarm generated
based on the comparison.
[0067] The ventilation director 300 can also be configured to
employ the ventilation airflow rate to determine the damper
position necessary to deliver required ventilation only when the
compressor is running. As such, humidity problems associated with a
continuous fan can be reduced or eliminated and operation of the
HVAC system can still comply with Indoor Air Quality standards
established by governing bodies, such as the ASHRAE 62.1 standard.
In one embodiment, the ventilation director 300 is configured to
determine a prorated ventilation airflow rate and deliver the
required ventilation as described below. An hour is used in the
embodiment discussed below but other amounts of time may also be
used in different embodiments.
[0068] 1) At the beginning of each hour: [0069] a. determine the
fraction of compressor on time during the past hour (i.e.,
runfrac); [0070] b. calculate the required ventilation rate (when
compressor is on using Equation 7 employing runfrac and the
ventilation rate when the compressor is on continually
(Qvent.sub.CONT). The constant 1.2 in Equation 7 is a margin of
safety which ensures the correct amount of ventilation is delivered
even if the compressor runs 20% less than the previous hour.
[0070] Qvent.sub.compOn=1.2(Qvent.sub.CONT/runfrac) (Equation
7)
[0071] 2) When the compressor is on, set the ventilation controller
setpoint to Qvent comp ON.
[0072] 3) When the compressor is off, set the ventilation setpoint
to 0.
[0073] 4) Integrate the amount of ventilation airflow delivered
over an hour. If the integrated amount exceeds Qvent cont*60 then
set the ventilation setpoint=0.
[0074] Turning now to FIG. 4, illustrated is a flow diagram of an
embodiment of a method 400 of repositioning the dampers of an
economizer according to the principles of the disclosure. In some
embodiments, hysteresis results in the relationship between the
actuator feedback signal and the actual position of the economizer
damper blades. In some embodiments, the hysteresis can be
significant enough to cause a ten percent error in the relationship
between the actuator feedback and the damper blade position. The
method 400 can be employed to correct this problem. In one
embodiment, a ventilation airflow determiner is configured to
perform the method 400. The method 400 represents an algorithm that
can be implemented as a series of operating instructions.
[0075] The method 400 begins in a step 405 with a change in the
position of the dampers being desired. In a decisional step 410, a
determination is made if the new desired damper position is less
than the current damper position. Thus, step 410 includes comparing
the current damper position (e.g., the current percentage of
opening) to the desired damper position (e.g., the desired
percentage of opening). If the desired position is less than the
current position, then the method continues to step 420 where the
actuator is closed directly to the desired position. If the desired
position is not less than the current position, then the method
continues to step 430 where the actuator is opened to the desired
position plus an actuator specific buffer. In one embodiment, the
actuator specific buffer is based on the amount of slack of the
drive train of the actuator. In some embodiments, the actuator
specific buffer is 1.5 volts. The method 400 then ends in a step
440 where the actuator is closed to the new desired position.
[0076] One skilled in the art will understand that the buffer
employed can vary based on the type of actuator and the actual
installation. The value (e.g., voltage) of the buffer can be
determined during calibration. The method 400 represents
compensating for hysteresis employing a final close operation (step
440). A similar compensation can be performed by ending in an open
operation. For example, in step 430, the actuator could be opened
to the new position with the addition of a negative buffer (e.g.,
-1.5 volts). As such, in step 440, the actuator would be opened to
the new position.
[0077] FIG. 5 illustrates a flow diagram of an embodiment of a
method 500 of measuring and managing ventilation airflow of a HVAC
system carried out according to the principles of the disclosure.
The method 500 may be carried out under the direction of a computer
program product. In one embodiment, a controller of an HVAC system
is employed to carry out the method 500. The method 500 begins in a
step 505.
[0078] In a step 510, feedback data is received from an HVAC
system. In one embodiment, the feedback data corresponds to the
pressure difference across an outdoor economizer damper and
economizer damper position of the HVAC system. Additionally, the
feedback data may include the supply airflow rate. The feedback
data is real time data obtained during operation of the HVAC
system.
[0079] The feedback data is applied to economizer ventilation data
in a step 520. The feedback data applied may include the outdoor
economizer damper pressure difference, the supply airflow rate and
the economizer damper position. The economizer ventilation data
represents ventilation airflow rates of the HVAC system and is
based on measured data obtained before installation of the HVAC
system.
[0080] In a step 530, an operating ventilation airflow rate is
calculated based on the feedback data and the corresponding
economizer ventilation data.
[0081] A desired ventilation airflow rate is received in a step
540. In a step 550, a position of the economizer is adjusted based
on the economizer damper position and the desired ventilation
airflow rate. In some embodiments, the adjustment is zero when the
operating ventilation airflow rate is at or within a designated
percentage of the desired ventilation airflow rate. In some
embodiments, the desired airflow rate is entered by a user in the
field. In other embodiments, the desired airflow rate is
predetermined and established before or during installation. In
these embodiments, the desired airflow rate can be changed after
installation. The method 500 ends in a step 560.
[0082] The above-described methods may be embodied in or performed
by various conventional digital data processors, microprocessors or
computing devices, wherein these devices are programmed or store
executable programs of sequences of software instructions to
perform one or more of the steps of the methods, e.g., steps of the
method of FIG. 5. The software instructions of such programs may be
encoded in machine-executable form on conventional digital data
storage media that is non-transitory, e.g., magnetic or optical
disks, random-access memory (RAM), magnetic hard disks, flash
memories, and/or read-only memory (ROM), to enable various types of
digital data processors or computing devices to perform one,
multiple or all of the steps of one or more of the above-described
methods, e.g., one or more of the steps of the method of FIG. 5.
Additionally, an apparatus, such as dedicated HVAC controller, may
be designed to include the necessary circuitry to perform each step
of the methods disclosed herein.
[0083] Those skilled in the art to which this application relates
will appreciate that other and further additions, deletions,
substitutions and modifications may be made to the described
embodiments.
* * * * *