U.S. patent application number 10/967634 was filed with the patent office on 2005-04-28 for thermal balance temperature control system.
Invention is credited to Attridge, Russell G..
Application Number | 20050087616 10/967634 |
Document ID | / |
Family ID | 34435169 |
Filed Date | 2005-04-28 |
United States Patent
Application |
20050087616 |
Kind Code |
A1 |
Attridge, Russell G. |
April 28, 2005 |
Thermal balance temperature control system
Abstract
A method and apparatus for controlling a temperature-regulated
zone utilizing a thermal balance temperature control system. The
thermal balance control system is a dynamic real time control
system that measures the sensible thermal load in the zone, and
directly regulates the BTU output of the HVAC package to balance
such output with the measured sensible thermal load.
Inventors: |
Attridge, Russell G.;
(US) |
Correspondence
Address: |
HOFFMANN & BARON, LLP
6900 JERICHO TURNPIKE
SYOSSET
NY
11791
US
|
Family ID: |
34435169 |
Appl. No.: |
10/967634 |
Filed: |
October 18, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60512410 |
Oct 17, 2003 |
|
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Current U.S.
Class: |
236/91D ;
165/254; 165/255 |
Current CPC
Class: |
F24F 11/30 20180101;
F24F 2110/10 20180101; F24F 11/62 20180101; F24F 2140/50 20180101;
F24F 3/044 20130101 |
Class at
Publication: |
236/091.00D ;
165/254; 165/255 |
International
Class: |
F25D 023/12; F25B
029/00 |
Claims
What is claimed is:
1. A method of controlling room temperature within a zone of a
temperature control system utilizing supply air having a
temperature T, comprising the steps of: defining a thermal demand
set point temperature curve for said temperature control system;
measuring a sensible thermal load within said zone; calculating a
thermal demand set point temperature based upon said sensible
thermal load; defining at least one load band for said temperature
control system corresponding to an equilibrium condition; and
operating said temperature control system to maintain individual
components of said system in a constant operating condition for as
long as said system operates within said load band.
2. The method according to claim 1, wherein said first defining
step includes the steps of establishing a heating curve extending
between a minimum heating thermal demand set point corresponding to
a condition of minimum heating output and a maximum heating thermal
demand set point corresponding to a condition of maximum heating
output and establishing a cooling curve extending between a minimum
cooling thermal demand set point corresponding to a condition of
minimum cooling output and a maximum cooling thermal demand set
point corresponding to a condition of maximum cooling output.
3. The method according to claim 2, wherein said sensible thermal
load is equal to the amount of deviation between a set point
temperature for said zone and an actual room temperature for said
zone, and wherein said measuring step includes the step of
calculating the difference between said set point temperature and
said actual room temperature.
4. The method according to claim 3, wherein said calculating step
includes the further steps of: establishing a point on said thermal
demand set point temperature curve corresponding to said sensible
thermal load; determining a delta temperature T from said set point
temperature; and calculating said thermal demand set point
temperature based upon said room set point temperature and said
delta temperature T.
5. The method according to claim 4, wherein said second defining
step includes the steps of establishing an operating load band
having a preselected width corresponding generally to the operating
characteristics of a unit temperature control stage.
6. The method according to claim 5, further comprising the step of
defining an upper integrating region located above said operating
load band and a lower integrating region located below said
operating load band; and providing integrating action for
increasing the responsiveness of said system when a signal enters
one of said upper and lower integrating regions.
7. The method according to claim 6, wherein said operating step
includes the step of energizing a temperature control unit stage to
move said temperature T of said supply air into said load band, and
maintaining said unit in an energized state as long as said
temperature T remains within said load band.
8. A thermal balance temperature control system for controlling
room temperature within a predefined zone, comprising: at least one
air handling unit for providing supply air at a preselected
temperature, said air handling unit including at least one unit
stage; a supply duct for transporting said supply air from said air
handling unit to said predefined zone; at least one controller for
controlling room temperature within said predefined zone, said
controller comprising at least one processor circuit for measuring
a sensible thermal load within said zone and for calculating a
thermal demand set point temperature based upon said sensible
thermal load in accordance with a predefined thermal demand set
point temperature curve, and wherein said processor circuit
operates said temperature control system to maintain said unit
stage in an energized condition for as long as said system operates
within a predefined load band corresponding to an equilibrium
condition.
9. The system according to claim 8, wherein said sensible thermal
load is equal to the deviation between a set point temperature for
said zone and an actual room temperature for said zone.
10. The system according to claim 9, wherein said predefined
thermal demand set point temperature curve includes a heating curve
extending between a minimum thermal demand set point corresponding
to minimum heating output and a maximum thermal demand set point
corresponding to maximum heating output and also includes a cooling
curve extending between a minimum thermal demand set point
corresponding to minimum cooling output and a maximum thermal
demand set point corresponding to maximum cooling output.
11. The system according to claim 11, wherein said predefined load
band includes an upper integrating region located above said
operating load band and a lower integrating region located below
said operating load band, and wherein said integrating regions
provide integrating action for increased responsiveness to signals
entering one of said upper and lower integrating regions.
12. A controller for controlling room temperature within a zone of
a temperature control system utilizing supply air A, said supply
air having a temperature T, comprising: at least one processor
circuit for measuring a sensible thermal load within said zone and
for calculating a thermal demand set point temperature based upon
said sensible thermal load in accordance with a predefined thermal
demand set point temperature curve, and wherein said processor
circuit operates said temperature control system to maintain
individual components in a constant operating condition for as long
as said system operates within a predefined load band corresponding
to an equilibrium condition.
Description
[0001] This application claims the benefit of U.S. Provision
Application Ser. No. 60/512,410 filed on Oct. 17, 2003.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a temperature control
system and, more particularly, to a system which directly regulates
the system output to balance such output with the sensible thermal
load.
[0003] Heating, ventilating and air-conditioning (HVAC) systems are
used to both heat and cool the air within an enclosure, e.g., a
building or zone within such building. An HVAC system typically
includes a heating unit, a cooling unit, a supply air fan, a supply
duct for directing air into the enclosure, and a return duct for
removing air from the enclosure. It will be appreciated by those
skilled in the art that HVAC systems are generally designed to
operate in one of three modes: a heating mode to heat the
enclosure, a cooling mode to cool the enclosure and a economizer
mode to ventilate the enclosure. The economizer mode typically
utilizes both an outdoor air damper and a return air damper,
commonly referred to as an economizer, that can be selectively
modulated opened to allow the return air to mix with fresh outside
air.
[0004] There is typically a control system associated with an HVAC
system, such control system including a thermostat (typically
located within the enclosure) and associated hardware/software for
controlling the components of the particular HVAC system in
response to pre-programmed instructions. Typically, the control
system allows a user to pre-select one of the three operating
modes, as well as selecting a desired temperature for the
enclosure. Thereafter, the control system activates either the
heating or cooling portion of the HVAC system to maintain the
pre-selected temperature within the enclosure. Under certain
conditions the economizer mode may be able to maintain the
enclosure at the pre-selected temperature.
[0005] When set in the cooling mode, the control system will
provide cold air to the enclosure when the temperature of the
enclosure exceeds the pre-selected temperature. The control system
accomplishes this task by activating the cooling unit (or stage of
a multi-stage cooling unit) and the supply air fan. The supply air
fan blows the air through the cooling unit and into the enclosure.
As a result of the cold air entering the enclosure, the temperature
in the enclosure is lowered. Once the temperature in the enclosure
falls below the pre-selected temperature, the thermostat in the
enclosure provides a signal to the control system which either
turns off the cooling unit, or turns off a stage of cooling (if
part of a multi-stage unit).
[0006] Similarly, when set in the heating mode, the control system
will provide hot air to the enclosure when the temperature of the
enclosure falls below the pre-selected temperature. The control
system accomplishes this task by activating the heating unit (or
stage of a multi-stage heating unit) and the supply air fan. The
supply air fan blows the air through the heating unit into the
enclosure. As a result of the hot air entering the enclosure, the
temperature in the enclosure is raised. Once the temperature in the
enclosure rises above the pre-selected temperature, the thermostat
in the enclosure provides a signal to the control unit which either
turns off the heating unit, or turns off a stage of heating (as
part of the multi-stage unit).
[0007] As mentioned, the economizer mode may be able to maintain
the enclosure at the pre-selected temperature under certain
conditions. Particularly, during times when the outside air
temperature is low (e.g., 50.degree. F.), and the control system
needs to provide cold air to the enclosure to cool such enclosure,
the system can utilize the economizer mode to provide the desired
cold air to the enclosure. In the economizer mode, the control
system will selectively modulate open and close both an outside air
damper and a return air damper to mix the cool outside air with the
warmer return air. In this manner, the air being supplied to the
enclosure is cooled to the desired temperature without the need for
activating the cooling unit. Of course, if the outside air
temperature is too high and/or too humid, the cooling unit will
need to be activated.
[0008] The above-described temperature control systems are
typically designed to allow "time cycling" of the heating/cooling
components, which of course limit/preclude these known systems from
regulating the BTU output of the HVAC to balance such output with
the measured sensible thermal load.
[0009] More to the point, those skilled in the art will appreciate
that "time cycling" prevents a system from operating in a "real
time" mode, and often allows undesirable temperature swings, as
well as inefficient operation of the individual components. This
inefficient operation can include the operation of excess
cooling/heating capacity (resulting in unneeded energy costs) and
excess cycling of the systems components (resulting in the
shortening of the life of the unit and/or an increase in
maintenance of such unit). In fact, the prior art has generally
believed that real time temperature control systems which attempt
to directly regulate BTU output to balance such output with the
system load are inherently unstable, and will produce excessive and
potentially damaging "short cycling" of the heating/cooling
components.
[0010] Moreover, the prior art systems are generally inefficient
because the supply air is often colder/hotter than necessary to
satisfy the measured sensible thermal load. Finally, such systems
are generally incapable of satisfying an unmet cooling/heating
load.
[0011] There is therefore a need in the art for a dynamic real time
temperature control system which directly regulates the BTU output
of an HVAC package to balance such output with the sensible thermal
load being measured in the temperature-regulated enclosure, thereby
eliminating/reducing undesirable temperature swings in the
regulated environment, reducing excess cycling of components and
eliminating/reducing utilization of unneeded excess capacity.
SUMMARY OF THE INVENTION
[0012] The present invention, which addresses the needs of the
prior art, relates to a method of controlling room temperature
within a zone of a temperature control system. The method generally
includes the steps of defining a thermal demand set point
temperature curve for the temperature control system, measuring a
sensible thermal load within the zone, calculating a thermal demand
set point temperature based upon the sensible thermal load,
defining at least one load band for the temperature control system
corresponding to an equilibrium condition, and operating the
temperature control system to maintain individual components of the
system in a constant operating condition for as long as the system
operates within the load band.
[0013] The present invention further relates to a thermal balance
temperature control system for controlling room temperature within
a predefined zone. The system includes at least one air handling
unit for providing supply air at a preselected temperature, the air
handling unit includes at least one unit stage. The system further
includes a supply duct for transporting supply air from the air
handling unit to the predefined zone. Finally, the system includes
at least one controller for controlling room temperature within the
predefined zone. The controller comprises at least one processor
circuit for measuring a sensible thermal load within the zone and
for calculating a thermal demand set point temperature based upon
the sensible thermal load in accordance with a predefined thermal
demand set point temperature curve. The processor circuit operates
the temperature control system to maintain the unit stage in an
energized condition for as long as the system operates within a
predefined load band corresponding to an equilibrium condition.
[0014] Finally, the present invention relates to a controller for
controlling room temperature within a zone of a temperature control
system. The controller includes at least one processor circuit for
measuring a sensible thermal load within the zone and for
calculating a thermal demand set point temperature based upon the
sensible thermal load in accordance with a predefined thermal
demand set point temperature curve. The processor circuit operates
the temperature control system to maintain individual system
components in a constant operating condition for as long as the
system operates within a predefined load band corresponding to an
equilibrium condition.
[0015] As a result, the present invention provides a dynamic real
time temperature control system which directly regulates the BTU
output of an HVAC package to balance such output with the sensible
thermal load being measured in a temperature-regulated enclosure,
thereby eliminating/reducing undesirable temperature swings in the
regulated environment, reducing excess cycling of components and
eliminating/reducing utilization of unneeded excess capacity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematical representation of a heating,
ventilating and air conditioning system including the thermal
balance temperature control system of the present invention;
[0017] FIG. 2 is a schematical representation of the components of
an HVAC package used in accordance with the present invention;
[0018] FIG. 3 is a graphical representation of the thermal demand
set point temperature curve for the thermal balance temperature
control system of the present invention;
[0019] FIG. 4 is a graphical representation of a cooling load band
curve for the thermal balance temperature control system of the
present invention;
[0020] FIG. 5 is a graphical representation of an economizer load
band curve superimposed on the curve of FIG. 4; and
[0021] FIG. 6 is a schematical representation of the controller
used in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] As discussed more fully hereinbelow, the present invention
is directed to a method and apparatus for controlling a
temperature-regulated zone utilizing a thermal balance temperature
control system. The thermal balance control system is a dynamic
real time control system that constantly measures the sensible
thermal load in the mentioned zone, and directly regulates the BTU
output of the HVAC package to balance such output with the measured
sensible thermal load, thus providing a state of system
equilibrium. The system will continue to operate in this
equilibrium state (without time cycling of any heating/cooling
components) until the system measures a change in the sensible
thermal load within the mentioned zone.
[0023] The sensible thermal load is the amount of deviation
(measured in degrees) between the set point temperature for the
zone and the actual zone temperature. When the actual room
temperature is above the set point temperature, the sensible
thermal load is a cooling load, and the system must therefore
reduce the supply air temperature to balance the BTU output of the
HVAC package with such load. If the actual room temperature is
below the set point temperature, then the sensible thermal load is
a heating load, and it is necessary for the system to increase the
supply air temperature to balance the BTU output with such
load.
[0024] The thermal balance control system of the present invention
utilizes the formula: Thermal Transfer Rate (BTU/HR)=Supply Air
Volume (cubic feet per minute).times.1.08.times.(Room
Temperature-Supply Air Temperature). As will be appreciated from
the foregoing formula, the thermal transfer rate is equal to 0 when
the room temperature is equal to the supply air temperature.
[0025] As discussed herein, the thermal balance control system of
the present invention operates in a "load cycling" manner, in
contrast to the "time cycling" manner of conventional units. It
will be appreciated that available HVAC units which operate in an
on/off function (e.g., direct expansion (DX) cooling, electric
heat, etc.) are typically utilized in a time-cycled manner.
Particularly, if the prior art system requires supply air at
55.degree. and stage 1 of a DX cooling system only reduces the
temperature to 60.degree., the second stage of such system will be
cycled on and off to reduce the temperature of the supply air to
below 55.degree.. Every time a unit cycles on and off the system
can experience wide and comfortable temperature swings. With
respect to the cycling on and off of a DX cooling unit,
condensation caught in a coil will evaporate back into the supply
air when such unit is cycled off. This increase in humidity of the
supply air can cause discomfort to the occupants in the building,
and also decreases the overall efficiency of the unit (in that the
unit must again remove the vapor from the air when cycled back on).
For example, the cycling of a stage of DX cooling on a rainy summer
day may cause such an undesirable condition.
[0026] Referring to FIG. 1, a thermal balance temperature control
system 10 in accordance with the present invention includes a
heating, ventilating and air conditioning (HVAC) package 12 for
supplying cold or heated supply air 14 (as well as fresh outside
air) into a supply air duct 16, which communicates with an interior
enclosure, i.e., zone 18. Return air 20 is thereafter removed from
zone 18 via return air duct 22. Temperature control system 10 also
includes a thermal balance controller 24, which is a dynamic real
time controller that measures the sensible thermal load in zone 18,
and regulates the output capacity of HVAC package 12 to balance
such output with this measured load.
[0027] As shown in FIG. 2, HVAC package 12 includes a supply air
fan 26 for moving supply air into zone 18 and a return air fan 28
for removing return air from zone 18. HVAC package 12 further
includes an economizer section 30, a heating unit 32, a cooling
unit 34 and a supply air temperature sensor 36. Package 12 may also
include a filter 38, a low temperature alarm 40 and low limit
temperature sensor 42.
[0028] Economizer section 30 preferably includes an exhaust damper
44, an outside air damper 46 and a return air damper 48. Return air
damper 48, together with outside air damper 46, control the percent
mixture of return air/fresh air being fed into supply air duct 16.
Those skilled in the art will understand that exhaust damper 44,
outside air damper 46 and return air damper 48 are preferably
operated to meet at least some of the following goals: 1) to
operate in economizer mode when conditions permit; 2) to take
maximum advantage of the temperature of the return air; and 3) to
mix sufficient fresh air into the supply air.
[0029] In one preferred embodiment, HVAC package 12 includes an
economizer section, a two-stage gas heating section, a three-stage
direct expansion (DX) cooling unit, a constant volume supply fan
and a constant volume return air fan. One preferred package is
rated at 25 tons at 10,000 cubic feet per minute. This design
capacity is based on approximately 400 cubic feet per minute per
ton, and 5-6 air changes per hour. The operation sequence of HVAC
package 12 preferably follows an ASHRAE Cycle II.
[0030] Thermal balance temperature control system 10 can be used in
a constant volume system or in a variable air volume (VAV) system.
It will be recognized by those skilled in the art that a VAV system
would utilize variable speed supply and return fans (in contrast to
the constant speed fans used in a constant volume system). Unlike
the constant volume system, the VAV system will typically include a
differential pressure gauge located in the supply air duct
downstream from the supply air fan.
[0031] Thermal balance temperature control system 10 may operate in
either the heating, economizer or cooling mode, depending on the
sensible thermal load measured within zone 18. More particularly,
the heating mode is preferably controlled by cycling (in sequence)
the two gas valves to maintain a desired supply air temperature.
The heating mode is generally not initiated until outside air
damper 46 is at its minimum open setting. Preferably, morning
warm-up will be accomplished with both outside air damper 46 and
exhaust damper 44 fully closed, and return damper 48 fully opened.
The economizer cooling mode is preferably controlled by modulating
exhaust damper 44, outside air damper 46 and return air damper 48
to maintain the desired supply air temperature. The economizer
cooling mode is preferably limited by an outside air temperature
sensor set at 60.degree. that reduces the intake of fresh outside
air (for ventilation) to a minimum value at temperatures exceeding
60.degree.. Of course, this 60.degree. setting is adjustable,
depending on system criteria. Finally, the cooling mode is
preferably controlled by cycling the stages of cooling in direct
relation to the sensible thermal load measured within zone 18.
Because temperature control system 10 seeks to balance the BTU
output of HVAC package 12 with the sensible thermal load measured
within zone 18, the stages of heating and cooling do not experience
short cycling (i.e., excessive cycling on and cycling off of the
individual stages). Rather, such stages remain activated until such
time as the system measures a change in the sensible thermal
load.
[0032] It will be appreciated by those skilled in the art that a
multi-stage heating/cooling unit generally provides better overall
efficiency. For example, in a multi-stage cooling unit having three
stages, each stage providing approximately 33% of the total cooling
capacity of the unit. When maximum cooling is required, all three
stages can be activated. However, when maximum system output is not
needed, one or more stages can be deactivated, thus allowing the
system to operate in a more energy-efficient mode. Similarly, each
stage in a two-stage unit provides 50% of the total capacity of the
unit, while each stage of a four-stage unit provides 25% of the
total capacity. In one embodiment, the relay differential of a
stage of cooling is made greater then the temperature change which
results from that stage being energized or deenergized. This
prevents the cooling stage from short cycling due to the action of
the discharge sensor. Preferably, the relays should be set up to
provide Vernier controls.
[0033] It will be understood by those skilled in the art that
resetting the temperature of the supply air in response to certain
system measurements can improve the performance and operation of
the overall system. Although prior art systems utilize reset
schedules, such schedules generally consist of a standard fixed
ratio which does not directly correlate to the operating
characteristics of the system and does not allow the system to
reach a state of equilibrium. In contrast, the thermal demand set
point temperature curve for the system of the present invention (as
shown in FIG. 3) is established to directly correlate with the
operating characteristics of HVAC package 12 and to allow the
system to reach a state of equilibrium (i.e., the BTU output is
balanced with the measured sensible thermal load).
[0034] Referring now to FIG. 3, the illustrated thermal demand set
point temperature curve for HVAC package 12 includes a heating
portion and a cooling portion. For example, if the particular
heating unit is capable of providing a maximum temperature rise of
50.degree., then the heating portion of the curve is drawn to
extend between a minimum thermal demand set point P.sub.0 (wherein
0 heat is required) and a maximum thermal demand set point P.sub.1
(wherein maximum heat, i.e., plus 50.degree. F.) is required. This
maximum heat condition corresponds to a measured sensible thermal
load of -2.degree. F. The cooling portion of the curve is drawn in
accordance with the particular cooling unit installed in the
system. For example, if the system is capable of reducing the
supply air temperature by a maximum of 25.degree., then the curve
is drawn between a minimum thermal demand set point P.sub.0
(wherein 0 cooling is required) and a maximum thermal demand set
point P.sub.2 (wherein maximum cooling, i.e., minus 25.degree. F.,)
is required. This maximum cooling condition corresponds to a
measured sensible thermal load of +2.degree. F.
[0035] The thermal demand set point temperature curve of FIG. 3 is
based upon a temperature band of plus and minus 2.degree. F. On a
drop in space temperature of 2.degree. F., the supply air
temperature will be reset from set point temperature P.sub.0 to
P.sub.0 plus 50.degree. F. On a rise in space temperature of
2.degree. F., the supply air temperature will be reset from set
point temperature P.sub.0 to P.sub.0 minus 25.degree. F. This band
can, of course, be widened (although widening the band may cause
the temperature in zone 18 to move into an uncomfortable region),
may be narrowed (which may increase the cost of operating such
system) or may include integral control action for improved
responsiveness.
[0036] The method of the current system will now be described with
respect to FIGS. 3 and 4. As described, FIG. 3 is used to calculate
the thermal demand set point temperature of the supply air during
operation of the system. To begin, the sensible thermal load in
zone 18 is measured. If, for example, the room set point is
73.degree. F. and the actual measured room temperature is
74.degree. F., the deviation from set point (i.e., the sensible
thermal load) is +1.degree.. Referring to the thermal demand set
point temperature curve of FIG. 3, a +1 temperature deviation is
within the cooling portion of the curve and corresponds to
approximately -12.5.degree. on the Y axis. The set point P.sub.0 of
FIG. 3 corresponds to the set point temperature of zone 18. Thus,
the thermal demand set point temperature for the supply air would
be calculated to be 73.degree.-12.5.degree.=60.5.degree.. This is
the temperature at which the system is balanced, i.e., providing
supply air at 60.5.degree. F. to zone 18 will maintain zone 18 in a
state of equilibrium at 74.degree. F.
[0037] In certain applications, as described in commonly-owned
co-pending U.S. application Ser. No. 10/704,251 filed Nov. 7, 2003,
the disclosure of which is incorporated herein by reference, the
system can be designed to recognize this unmet cooling load (i.e.,
the +1.degree. F. in zone 18). Thereafter, the system would
calculate and supply the additional cooling necessary to move the
actual room temperature towards the room set point.
[0038] FIG. 4 illustrates the novel load band curve of the present
invention, which is preferably a proportional curve having
preselected parameters which correspond to the components of the
system. The particular graph shown in FIG. 4 represents a plot for
a multi-stage DX cooling system having three stages wherein the
maximum cooling is approximately 20.degree.. A 40% allowance (i.e.,
8.degree.) may be designed into the system such that the X axis
extends from 0.degree. to 28.degree. (20.degree.+(40% of
20.degree.)). The X axis of the load band is 10.degree. wide (i.e.,
it extends from 9.degree. to 19.degree.). It will be appreciated
that each stage of the three stage DX cooling system is capable of
approximately a 7.degree. temperature drop. Again, a 40% allowance
may be designed into the system to provide a total of approximately
10.degree. (7.degree.+(40% of 7)=9.8, which is approximately
10.degree.).
[0039] If the desired supply air temperature is calculated to be
60.5.degree. (as discussed hereinabove), the set point S of the
graph of FIG. 4 will be set to 60.5.degree.. The value of this
point will remain fixed until the system measures a change in the
sensible thermal load in zone 18 and recalculates the thermal
demand set point temperature from FIG. 3. The actual supply air
temperature (as measured by sensor 36) is then plotted along the
curve. With set point S set at 60.50.degree. F., point S.sub.1 will
correspond to 55.5.degree. F. and point S.sub.2 will correspond to
65.5.degree. F.
[0040] The first stage of cooling will be turned on, resulting in a
7.degree. drop of temperature. If this is sufficient to bring the
supply air temperature within the load band which, in this example,
will extend from 55.5.degree. to 65.5.degree. (5.degree. on either
side of the set point), then no additional stages will be turned
on. As long as the supply air temperature remains within this load
band, the first stage of the compressor will remain on. Unlike
conventional systems which would automatically begin time cycling
this stage of the compressor, the system of the present invention
will allow this stage of the compressor to stay on as long as the
supply air temperature remains within in such load band. In other
words, the thermal balance control of the present invention has
reached a state of system equilibrium, and may remain in this state
until a change in the sensible thermal load is measured.
[0041] The portion of the curve of FIG. 4 extending from point
S.sub.1 to S.sub.2 is referred to herein as the load band. Once the
supply air temperature moves outside of the load band, it moves
into one of two integrating regions. For example, if two stages of
the three stage compressor are on and the supply air temperature
continues to decrease such that it moves down the curve into the
lower integral region, an integral factor will increase the speed
at which the supply air temperature moves towards the stage-off
point. Once, the supply air temperature hits this point, the
particular stage is turned off, thereby raising the supply air
temperature and pushing such supply air temperature back towards
the load band. Likewise, if the supply air temperature increases
such that it moves up the curve into the upper integral region,
eventually additional stages of cooling will be turned on. Again,
integral action decreases the time necessary to reach the point
where an additional stage of cooling is turned on. Thus, the system
anticipates overcooling and undercooling through the integral
action portions of the control system.
[0042] More particularly, the system anticipates a change in the
sensible thermal load. If the load is increasing (thus indicating
the need for an extra stage of cooling), the thermal demand set
point temperature will decrease (thus providing a lower set point
to the cooling control module). The supply air temperature will now
be higher than the thermal demand set point temperature, and will
begin to move up the curve into the upper integral region. An
integral factor will increase the speed at which the supply air
temperature moves towards the stage-on point. If the sensible
thermal load is decreasing, the reverse action will occur. As a
result, the system provides load change anticipation.
[0043] Stated differently, the present invention anticipates gain
in the wrong direction, and corrects this unwanted gain prior to
the regulated enclosure experiencing an uncomfortable temperature
swing. It will be appreciated by those skilled in the art that
although a conventional system would eventually compensate for the
change in the temperature of the supply air, because of the
inherent time delays and time constants associated with HVAC
systems, the conventional system cannot respond until "after the
fact". In other words, the regulated enclosure has already
undergone the unwanted temperature swing before it begins to react
to the temperature swing due the change in the temperature of the
supply air.
[0044] FIG. 5 illustrates an economizer load band curve
superimposed on the cooling load band curve of FIG. 4. In this
particular example the economizer load band will extend plus and
minus 1.5.degree. from set point S. Once the supply air temperature
has increased 1.5.degree. above set point S, the system will begin
to modulate open the outside air damper. Similarly, once the supply
air temperature decreases 1.5.degree. below set point S, the system
will begin to modulate closed the outside air damper. While the
supply air temperature is within the economizer load band, the
outside air damper will be maintained in a constant position.
[0045] Referring to FIG. 6, the control system of the present
invention, i.e., controller 24, uses three individual control
modules, namely a first control module 50 for the heating unit, a
second control module 52 for the economizer unit and a third
control module 54 for the cooling unit. The control system is
designed so that each one of the individual control modules
operates its respective unit depending on whether the supply air
temperature is above or below the thermal demand set point
temperature calculated from FIG. 3.
[0046] The system calculations and operations described hereinabove
are preferably performed by controller 24, and particularly by the
individual control modules. More particularly, the controller
and/or control modules preferably include hardware/software which
is capable of performing the mentioned calculations, and of
utilizing predefined thermal demand set point temperature and load
band curves to control the operations of system 10 in accordance
with the parameters described herein.
[0047] It should be noted that each control module receives two
sets of numbers. Specifically, each module receives the thermal
demand set point temperature T.sub.P for the supply air (from FIG.
3), and the actual temperature of the supply air T.sub.SA (as
measured by sensor 36). Moreover, each control module has a
specific temperature set point that is used to determine which of
three individual modules is activated. The specific temperature set
point for each module is based on the thermal demand set point
temperature, as well as a predefined bias setting.
[0048] In a preferred embodiment, the modules are all biased to
control at a different temperature based on the thermal demand set
point temperature for the supply air so that only a single module
will activate at any one time. Depending on whether the supply air
is above or below each one of the module's specific temperature set
points determines which unit will be activated, and thus
controlling the system. For example, should the actual supply air
temperature (as measured by sensor 36) be below the thermal demand
set point temperature, the heating control module would be
activated to raise the temperature of the supply air. During this
time, the cooling control module and economizer control module are
not activated since the supply air temperature is below their
specific temperature set points. As mentioned, the heating,
economizer and cooling control modules are set up with a predefined
bias setting. The heating control module has a bias setting of
-3.degree. F., the economizer control module has a bias setting of
0.degree. F., and the cooling control module has a bias setting of
+2.degree. F. These bias set point are of course adjustable.
[0049] Referring back to the example set forth above wherein the
thermal demand set point temperature for the supply air was
calculated to be 60.5.degree. F., the local set point of the
heating control module would be calculated to be
60.5.degree.-3.degree.=57.5.degree. F. The local set point for the
economizer control module would be calculated to be 60.5.degree.
F.+0.degree.=60.5.degree. F., while the local set point for the
cooling control module would be calculated to be 60.5.degree.
F.+2.5.degree. F.=63.degree. F.
[0050] The local set point separates the control action of the
individual control modules. If the supply air temperature (as
measured by sensor 36) is below 57.5.degree. F. (the local set
point of the heating control module) the system will add heat to
satisfy the demand. If the supply air temperature (as measured by
sensor 36) is above 60.5.degree. F. (the local set point of the
economizer control module) and cool outside air is available the
economizer control module will modulate damper 46 satisfy the
demand. If the outside air temperature is above a predefined
temperature limit, the cooling control module will cycle the
cooling to satisfy the demand. Finally, if the supply air
temperature (as measured by sensor 36) is above 63.degree. F. (the
local set point of the cooling control module), the system will
cool the supply air to satisfy the demand.
[0051] The set point of each control module is 50. Each control
module defines a load band and upper and lower integrating regions
(for load anticipation). The heating control module is reverse
acting, and the economizer and cooling control modules are direct
acting.
[0052] The control modules are set up to stabilize whenever the
supply air temperature is within the load band. The system then
stabilizes at that level of BTU output, i.e., it will stay there
until there is a change in the sensible thermal load in the zone.
The load band is set up to match the BTU output to the measured
sensible thermal load. The load anticipation feature operates when
the sensible thermal load changes, indicating a required increase
or decrease in the BTU output of the HVAC package.
[0053] For heating control applications, the heating control module
can be set up for single control, multiple-stage control, or
modulating control. For economizer control applications, the
economizer control module can be set up for mixing damper control
with minimum damper position or modulating a free cooling valve
with a high temperature limit. For DX cooling control applications,
the cooling control module can be set up to utilize the load band
and load anticipation adjustments to provide load cycling. When a
stage of DX cooling is energized the stage will stay ON until there
is a decrease in the measure sensible thermal load. The system
provides load cycling of the DX stages, not time cycling. The
control module will lengthen the ON time of a stage of cooling if
there is an increase in the latent load on the unit, internal or
external.
[0054] In accordance with the present invention, control system 10
can eliminate droop, overshoot and mechanical lag by providing the
optimum cycle rate of any stage for efficient operation under all
load conditions. Control system 10 can respond immediately to a
change in the measured sensible thermal load by optimizing the
cycle rate of the heating or DX cooling stages or repositioning the
mixed air dampers. Control system 10 can also respond immediately
to the measured change in the BTU output of the HVAC package (due
to changes in the outdoor air temperatures) by optimizing the cycle
rate of the heating or DX cooling stages or repositioning the mixed
air dampers.
[0055] Control system 10 can dynamically optimizes the cycling rate
of the heating or cooling stages based on the BTU output of the
HVAC package by measuring the supply air temperature and adjusting
the cycle rate to match the BTU output to the measured sensible
thermal load. The cycle rate can be adjusted real time to match the
BTU output to the load; the system does not compute the cycle rate
based on a developed software program. The load response of control
system 10 can be characterized by automatic initialization of the
stages for an optimum cycle rate.
[0056] Control system 10 can adapt to the operating characteristics
of the various modes, heating, economizer and cooling, whether
staging or proportional. The control system can match the BTU
output of the unit to the load in the space without cycling from
one mode to the other or short cycle between stages. The control
system does not require time delays between stages. Control system
10 can adapt automatically to a change in the latent load in the
space of a change in the temperature of the outside ventilation
air, and vary the cycle rate of DX cooling for optimum latent heat
removal and improved IAQ.
[0057] Control system 10 will not heat and cool simultaneously, nor
will it cycle between heating and cooling. Control system 10 does
not require a heating or cooling mode switch. Rather, the system
can measure the load and responds accordingly.
[0058] Control system 10 can recognize changes in the load, either
internal (space) or external (entering the unit) that will affect
the relationship of matching the BTU output to the measured
sensible thermal load, and can respond immediately.
[0059] Control system 10 can identify a stage failure, heating or
cooling, and can activate the next stage if available and activate
an alarm. Control system 10 can monitor the HVAC package
performance continuously. Any malfunction can be alarmed, if
desired.
[0060] It will be appreciated that the present invention has been
described herein with reference to certain preferred or exemplary
embodiments. The preferred or exemplary embodiments described
herein may be modified, changed, added to or deviated from without
departing from the intent, spirit and scope of the present
invention, and it is intended that all such additions,
modifications, amendment and/or deviations be included within the
scope of the following claims.
* * * * *