Note: Descriptions are shown in the official language in which they were submitted.
CA 02511732 2005-07-07
Docket No.: 20714-0056
HVAC&R HUMIDITY CONTROL SYSTEM AND METHOD
BACKGROUND OF THE INVENTION
(0001] The present invention relates generally to a control application for a
HVAC&R system. More specifically, the present invention relates to a system
and
method for humidity control in a HVAC&R system.
[0002] To achieve climate control for a structure or enclosed space, a
heating,
ventilation, air conditioning and refi-igeration (HVAC&R) or air treatment
system is
commonly used. The HVAC&R system is typically thermostat controlled to provide
temperature control for the interior space of the structure. However, in
addition to
temperature, other parameters are significant for providing comfort to the
occupants
within the structure. For example, relative humidity, or the ratio of the
amount of
water vapor actually present in the air to the greatest amount possible at the
same
temperature, is one such parameter. At increased levels of relative humidity,
the
temperature must be lowered to provide an equivalent level of comfort for an
individual. Complicating matters, individual sensitivity to changes in
humidity and
temperature differ, so that it is not possible to provide a definitive
temperature
correction when humidity levels are elevated.
[0003] Several techniques have been used to control humidity within a
structure.
These techniques typically include a combination of reheating and/or cooling
the air.
Cooling the air, such as by passing the air through evaporator coils, removes
moisture
from the air since an amount of the air moisture collects and condenses on the
evaporator coils. Heating may then need to be performed to raise the air
temperature
to a level that is comfortable to the occupant. Having both heating and
cooling adds
HVAC&R components, complexity and cost.
[0004] What is needed is a control for use with HVAC&R systems that is simple
to operate, and which can provide an individualized temperature/humidity
correction
inside a structure in response to elevated humidity levels.
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Docket No.: 20714-0056
SUMMARY OF THE INVENTION
[0005] The present invention is directed to a method for controlling humidity
in a
structure with a HVAC&R system. The method steps include: sensing a
temperature
and a humidity level inside a structure; calculating a temperature correction
value in
response to a predetermined humidity level, the sensed humidity level and a
predetermined humidity sensitivity factor; comparing a predetermined
temperature
setting for a HVAC&R device with the sum of the sensed temperature and the
temperature correction value; and initiating operation of the HVAC&R device to
reduce the humidity level inside the structure when the sum of the sensed
temperature
and the temperature correction value is greater than the predetermined
temperature
setting.
[0006] The present invention further includes a controller for controlling
humidity
in a structure with a HVAC&R system. The controller includes a first sensor
for
sensing a temperature inside a structure and a second sensor for sensing a
humidity
level inside the structure. A controller is responsive to the first and second
sensors for
a HVAC&R device, the controller calculating a temperature correction value in
response to a predetermined humidity level, the sensed humidity level and a
predetermined humidity sensitivity factor. The controller initiates operation
of the
HVAC&R device to reduce the humidity level inside the structure when the sum
of
the sensed temperature and the temperature correction value is greater than
the
predetermined temperature setting.
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levels within a structure.
[0008] Another advantage of the present invention is that it can provide a
selectable relationship between temperature and elevated humidity levels
within a
structure.
(0009] A further advantage of the present invention is that it requires a
minimum
amount of memory to operate.
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Docket No.: 20714-0056
(0010] A yet further advantage of the present invention is that it is
extremely
simple to operate.
(0011] Other features and advantages of the present invention will be apparent
from the following more detailed description of the preferred embodiment,
taken in
conjunction with the accompanying drawings which illustrate, by way of
example, the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Figure 1 illustrates schematically an embodiment of a heating,
ventilation
and air conditioning or refrigeration system for use with the present
invention.
[0013] Figure 2 illustrates a flow chart detailing the humidity control method
of
the present invention.
[0014] Wherever possible, the same reference numbers will be used throughout
the drawings to refer to the same or like parts.
DETAILED DESCRIPTION OF THE INVENTION
[0015] One embodiment of the heating, ventilation and air conditioning or
refrigeration (HVAC&R) system 10 of the present invention is depicted in Fig.
1.
Compressor 12 is connected to a motor 14 and inverter or variable speed drive
(VSD)
16, for selectively controlling operational parameters, such as rotational
speed, of the
compressor 12. Compressor 12 is typically a positive displacement compressor,
such
as screw, reciprocating or scroll, having a wide range of cooling capacity,
although
any type of compressor can also be used. The controller 20 includes logic
devices,
such as a microprocessor or other electronic components, for controlling the
operating
parameters of compressor 12 by controlling VSD 16 and motor 14. AC electrical
power received from an electrical power source 18 is rectified from AC to DC,
and
then inverted from DC back to variable frequency AC by VSD 16 for driving
compressor motor 14. The compressor motor 14 is typically an AC induction
motor,
but might also be brushless permanent magnet motor or switched reluctance
motor.
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Docket No.: 20714-0056
[0016] Refrigerant gas that is compressed by compressor 12 is directed to the
condenser 22, which enters into a heat exchange relationship with a fluid,
preferably
water, flowing through a heat-exchanger coil 24 connected to a cooling tower
26. The
refrigerant vapor in the condenser 22 undergoes a phase change to a
refrigerant liquid
as a result of the heat exchange relationship with the liquid in the heat-
exchanger coil
24. The condensed liquid refrigerant from condenser 22 flows to an expansion
device
28, which lowers the pressure of the refrigerant before entering the
evaporator 30.
Alternately, the condenser 22 can reject the heat directly into the atmosphere
through
the use of air movement across a series of finned surfaces (direct expansion
condenser).
[0017] The evaporator 30 can include a heat-exchanger coil 34 having a supply
line 34S and a return line 34R connected to a cooling load 36. The heat-
exchanger
coil 34 can include a plurality of tube bundles within the evaporator 30.
Water or any
other suitable secondary refrigerant, e.g., ethylene, calcium chloride brine
or sodium
chloride brine, travels into the evaporator 30 via return line 34R and exits
the
evaporator 30 via supply line 345. The liquid refrigerant in the evaporator 30
enters
into a heat exchange relationship with the water in the heat-exchanger coil 34
to chill
the temperature of the water in the heat-exchanger coil 34. The refi-igerant
liquid in
the evaporator 30 undergoes a phase change to a refrigerant gas as a result of
the heat
exchange relationship with the liquid in the heat-exchanger coil 34. The gas
refi-igerant in the evaporator 30 then returns to the compressor 12.
[0018] Controller 20, which controls the operations of HVAC&R system 10,
employs continuous feedback from indoor temperature sensor 38 and humidity
sensor
40 to continuously determine whether to incorporate a temperature correction
to
achieve a reduction in the humidity level within the structure being cooled by
the
system 10. In other words, the humidity reduction control of the present
invention is
preferably used when the HVAC&R system 10 is in a cooling mode.
[0019] The HVAC&R system 10 is first discussed without considering the
humidity sensor 40. An operator initially inputs a desired temperature setting
"TD", or
settings if multiple temperatures are to be achieved at different times of the
day or
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Docket No.;'20714-0056
different days, which are typically referred to as programmed settings. Once
the
desired temperature settings) TD have been input, the sensed temperature
inside a
structure "Ts" as sensed by the indoor temperature sensor 38 is compared to
the
desired temperature setting TD which was previously input into the controller
20 by
the operator. When the inside temperature Ts of the structure as sensed by the
indoor
temperature sensor 38 is greater than the desired temperature setting TD, the
controller
20 activates the HVAC&R system 10 to operate in cooling mode. The HVAC&R
system 10 continues to operate in cooling mode until the desired temperature
setting
is achieved, wherein upon achieving the desired setting, the HVAC&R system 10
is
deactivated. This process is then repeated to provide temperature control
inside of the
structure.
[0020] While providing temperature control of the temperature inside of the
structure, other parameters important to the comfort of the occupants of the
structure,
such as humidity control, are not taken into account in the above-referenced
process.
The HVAC&R system 10 is again discussed, with the addition of the humidity
sensor
40, which senses a relative humidity percentage inside the structure "Hs", and
a
corresponding control algorithm that is programmed into the controller 20. In
addition to initially inputting a desired temperature settings) TD, an
operator
additionally inputs a desired relative humidity percentage "HD" and a humidity
sensitivity factor "HS",". A humidity sensitivity factor "HS"," is a
correction factor that
correlates an excess in percentage of the relative humidity inside the
structure to a
reduction of the temperature inside the structure, which reduction in
temperature
being referred to as a temperature correction "TC". More specifically, the
temperature
correction T~ can be calculated by subtracting the desired relative humidity
percentage HD from the sensed relative humidity Hs, and dividing that result
by the
humidity sensitivity factor Hst,, as shown in equation 1.
Tc = (Hs - HD)~Hsc~~ C 1 l
[0021] Stated another way, a humidity sensitivity factor of 5, for example,
means
that for every 5 percent the sensed humidity percentage Hs, as sensed by the
humidity
sensor 40, exceeds the desired relative humidity percentage Hs, the
temperature
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Docket No.: 20714-0056
correction T~ inside the structure must be lowered by one °F to achieve
a similar level
of comfort due to the humidity. The humidity sensitivity factor Hsc~ is
subjective,
possibly differing for each individual, and can range from about 1 up to about
10,
although typically it is about 5 or less.
[0022] In operational example, assume the following input values: desired
relative
humidity percentage HD is 50 percent, the humidity sensitivity factor HS,,, is
S, the
desired temperature setting TD is 70°F and a maximum correction
temperature
"ToM,~" is 5. The maximum correction temperature ToM,~ is an operator-input
maximum deviation temperature from the desired temperature TD. Further assume
a
sensed relative humidity Hs of 80 percent and a sensed inside structure
temperature Ts
of 70°F. In a conventional HVAC&R system, since the sensed inside
structure
temperature Ts and the desired temperature setting TD are equal, the HVAC&R
system would remain deactivated. However, since the sensed relative humidity
Hs is
greater than the desired relative humidity HD, occupants within the structure
can be
made more comfortable by cooling the temperature within the structure as
provided
by the control algorithm. The temperature correction T~ as provided by
equation [ 1 ]
is calculated as follows: (80 - 50)/5, which simplifies to 6°F.
However, in this
example, the maximum correction temperature ToM~ is 5, or S°F, so the
maximum
correction temperature value is applied in place of the calculated correction
temperature. By application of the control algorithm in this example, the
equivalent
temperature inside the structure is reduced by the maximum correction
temperature
Tc~x, so that the HVAC&R system is activated to operate until the temperature
inside the structure is lowered to 65°F, at which point the HVAC&R
system is
deactivated.
[0023] In summary, for the above example, occupants inside the structure are
made more comfortable by operation of the control algorithm, since the
elevated level
of relative humidity is reduced as the air inside the structure is passed
through the
evaporator coils for the additional time required to cool the structure by the
amount of
temperature correction T~. This process is then repeated to provide
temperature and
humidity control inside of the structure.
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CA 02511732 2005-07-07
Docket No.: 20714-0056
[0024] After the control algorithm completes a cycle, especially when the
sensed
relative humidity Hs is significantly greater than the desired relative
humidity HD, the
reduction of the sensed relative humidity Hs is typically sufficient to
likewise reduce
the amount of temperature correction T~. In the above example, after the
temperature
inside the structure is lowered to 65°F, if the relative humidity
inside the structure is
reduced to 70 percent, the temperature correction of equation [1] is
calculated as
follows: (70 - 50)/5, which simplifies to 4°F. By application of the
algorithm, the
equivalent temperature inside the structure is reduced by less than the
maximum
correction temperature TcM,~, or 4°F. Thus, upon the temperature inside
the structure
being sufficiently raised to activate the HVAC&R system, the HVAC&R system
operates until the temperature inside the structure is lowered to 66°F,
at which point
the HVAC&R system is deactivated. In other words, so long as the control
algorithm
removes more moisture from the air inside the structure than is added, such as
by
activities of the occupants or by moisture producing processes occurring
within the
structure, the temperature correction should continue to decrease. As the
relative
humidity inside the structure is reduced to the desired humidity level, the
temperature
correction approaches zero.
[0025] Although the desired relative humidity level could be set to an
extremely
low level, such as thirty percent or less, there is typically little benefit,
from a comfort
standpoint, to reduce the humidity below a level of about 45 percent.
[0026] The controller 20 can include an analog to digital (A/D) converter, a
microprocessor, a non-volatile memory, and an interface board to control
operation of
the HVAC&R system 10. The controller 20 can also be used to control the
operation
of the VSD 16, the motor 14 and the compressor 12. The controller 20 executes
a
control algorithms) or software to control operation of the system 10. In one
embodiment, the control algorithms) can be computer programs or software
stored in
the non-volatile memory of the controller 20 and can include a series of
instructions
executable by the microprocessor of the controller 20. While it is preferred
that the
control algorithm be embodied in a computer programs) and executed by the
microprocessor, it is to be understood that the control algorithm may be
implemented
and executed using digital and/or analog hardware by those skilled in the art.
If
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CA 02511732 2005-07-07
Docket No.: 20714-0056
hardware is used to execute the control algorithm, the corresponding
configuration of
the controller 20 can be changed to incorporate the necessary components and
to
remove any components that may no longer be required.
[0027] Figure 2 illustrates a flow chart detailing the control process of the
present
invention relating to cooling control in an HVAC&R system 10, as shown in
Figure 1,
wherein control is maintained by the thermostat (not shown). The cooling
control
process of Figure 2 can also be implemented as a separate control program
executed
by a microprocessor, or control panel, or controller 20 or the control process
can be
implemented as a sub-program in the control program for the HVAC&R system 10.
Once the process is started in step 105 of Figure 2, values are selected and
set for the
desired humidity percentage HD, the humidity sensitivity factor Hst,,, desired
temperature TD and the maximum temperature correction Tc~ in step 110.
Controller keypads on existing controllers 20 or other suitable entry devices
can be
used with the control algorithm and can be used to enter all required
parameters.
After the desired humidity percentage HD, humidity sensitivity factor HS,,,,
desired
temperature TD and maximum temperature correction Tc~ are set, the temperature
inside the structure Ts as sensed by the indoor temperature sensor 38 and the
relative
humidity Hs as sensed by the humidity sensor 40 are sensed in step 115. Once
the
temperature inside the structure Ts and the relative humidity Hs are sensed,
the sensed
relative humidity Hs is compared to the desired humidity percentage HD in step
120.
[0028] In step 120, if the sensed relative humidity Hs is greater than the
desired
humidity percentage HD, then a calculation is performed to determine the
humidity
correction temperature T~ in step 125. However, if in step 120, the sensed
relative
humidity Hs is not greater than the desired humidity percentage HD, a humidity
temperature correction is not greater than zero, the humidity temperature
correction
T~ is set to zero in step 140 and control of the process is returned to step
145.
[0029] Once the humidity temperature correction T~ in step 125 has been
calculated, the humidity temperature correction T~ is compared to the maximum
temperature correction Tc~ in step 130. If the humidity correction temperature
T~
is greater than the maximum temperature correction T~~ in step 130, the
humidity
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CA 02511732 2005-07-07
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temperature correction Tc is set equal to the maximum temperature correction
TcM,~
in step 135 and control of the process is returned to step 145. However, if
the
humidity temperature correction T~ is not greater than the maximum temperature
correction ToM,~ in step 130, the value of the humidity temperature correction
To is
retained, and control of the process is returned to step 145.
[0030] In step 145, the desired temperature TD is compared to the resulting
value
obtained by adding the humidity temperature correction TC and the sensed
temperature inside the structure Ts. If the desired temperature TD is less
than the
resulting value obtained by adding the humidity correction temperature T~ and
the
sensed temperature inside the structure Ts, the HVAC&R system 10 is activated
in
step 150 and control of the process is returned to step 145. However, if in
step 145
the desired temperature TD is greater than the resulting value obtained by
adding the
humidity correction temperature T~ and the sensed temperature inside the
structure
Ts, a query is performed as to whether the HVAC&R system 10 is activated in
step
155. If the HVAC&R system 10 is activated, the HVAC&R system 10 is deactivated
in step 160 and control of the process is returned to step 115, wherein the
process
between steps 115-160 are repeated. However, if the HVAC&R system 10 is not
activated in step 155, control of the process is returned to step 115, wherein
the
process between steps I 15-160 are repeated.
[0031] In another embodiment, after activating the HVAC&R system 10 in step
150, the control can return to step 115 and steps 115-160 can be repeated.
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mounted configurations, the control process of the present invention can also
be used
with residential structures. The residential structures include split systems
where the
condenser is located outside the structure.
[0033] While the invention has been described with reference to a preferred
embodiment, it will be understood by those skilled in the art that various
changes may
be made and equivalents may be substituted for elements thereof without
departing
from the scope of the invention. In addition, many modifications may be made
to
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CA 02511732 2005-07-07
Docket No.: 20714-0056
adapt a particular situation or material to the teachings of the invention
without
departing from the essential scope thereof. Therefore, it is intended that the
invention
not be limited to the particular embodiment disclosed as the best mode
contemplated
for carrying out this invention, but that the invention will include all
embodiments
falling within the scope of the appended claims.
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