Abstrict An HVAC system includes a desiccant wheel, wherein the wheel's
speed varies with airflow, the wheel is energized for at least a
set period at startup, and/or a heat recovery system (e.g., an air-to-air
heat exchanger) upstream of the wheel enhances the system's ability
to dehumidify air.
Claims 1. A refrigerant system for conditioning air for a comfort zone,
the refrigerant system comprising: an enclosure defining an upstream
air passageway, a downstream air passageway, and an intermediate
air passageway therebetween, wherein the air passes sequentially
through the upstream air passageway, the intermediate air passageway,
and the downstream air passageway; a cooling coil disposed in the
enclosure; a source associated with the cooling coil and providing
a chilled fluid thereto; a blower in a position to force the air
from the downstream air passageway into the comfort zone; a desiccant
wheel able to absorb moisture from the air passing from the intermediate
air passageway to the supply air passageway and simultaneously release
moisture to the air passing from the upstream air passageway to
the intermediate air passageway; and a controller connected to selectively
start and stop the source and selectively energize and de-energize
the desiccant wheel for rotation, wherein the controller upon starting
the source energizes the desiccant wheel for a predetermined limited
period, whereby the desiccant wheel during the predetermined limited
period helps absorb moisture that may vaporize from the cooling
coil before the cooling coil is sufficiently cool to condense moisture
from the air.
2. The refrigerant system of claim 1 further comprising a moisture
sensor in communication with the controller, wherein the controller
de-energizes the desiccant wheel in response to the moisture sensor
detecting that the air is drier than a certain limit.
3. The refrigerant system of claim 1 further comprising a temperature
sensor in communication with the controller, wherein the controller
after the predetermined limited period de-energizes the desiccant
wheel in response to the temperature sensor detecting that the air
is warmer than a certain limit.
4. The refrigerant system of claim 1 wherein the source is a compressor
and the cooling coil is disposed in the upstream air passageway.
5. A method for conditioning air for a comfort zone, the method
comprising: energizing a source of chiller fluid of a refrigerant
system; energizing a desiccant wheel for rotation for a predetermined
period; and de-energizing the desiccant wheel at the end of the
predetermined period while continuing to energize the source.
6. The method of claim 5 wherein the step of de-energizing the
desiccant wheel is performed provided the air is drier than a certain
limit.
7. The method of claim 5 wherein the step of de-energizing the
desiccant wheel is performed provided the air is warmer than a certain
limit.
8. The method of claim 5 wherein the source is a compressor.
9. A refrigerant system for conditioning air for a comfort zone,
the refrigerant system comprising: an enclosure defining an upstream
air passageway, a downstream air passageway, and an intermediate
air passageway therebetween, wherein the air passes sequentially
through the upstream air passageway, the intermediate air passageway,
and the downstream air passageway; a cooling coil disposed in the
intermediate air passageway; a desiccant wheel able to absorb moisture
from the air passing from the intermediate air passageway to the
downstream air passageway and simultaneously release moisture to
the air passing from the upstream air passageway to the intermediate
air passageway; a variable air volume blower in a position to force
the air at a variable airflow rate from the downstream air passageway
to the comfort zone; and a controller connected to the variable
air volume blower to adjust the variable airflow rate and connected
to the desiccant wheel to adjust a rotational speed thereof, wherein
the controller selectively increases the rotational speed of the
desiccant wheel upon increasing the variable airflow rate and decreases
the rotational speed of the desiccant wheel upon decreasing the
variable airflow rate.
10. The refrigerant system of claim 9 wherein the rotational speed
of the desiccant wheel is proportional to the variable airflow rate
of the blower.
11. The refrigerant system of claim 9 further comprising an airflow
sensor in fluid communication with the air, wherein the variable
airflow rate of the blower is determined based on the airflow sensor.
12. The refrigerant system of claim 9 further comprising: a heater
disposed in the upstream air passageway; and a humidistat disposed
in the upstream air passageway, wherein the heater is selectively
energized and de-energized in response to the humidistat.
13. The refrigerant system of claim 9 further comprising a temperature
sensor disposed downstream of the intermediate air passageway, wherein
activation of the cooling coil is in response to the temperature
sensor.
14. The refrigerant system of claim 9 further including a source
of chilled fluid operatively associated with and connected to the
cooling coil and the controller wherein the controller upon starting
the source energizes the desiccant wheel for a predetermined limited
period, whereby the desiccant wheel during the predetermined limited
period helps absorb moisture that may vaporize from the cooling
coil before the cooling coil is sufficiently cool to condense moisture
from the air.
15. A method of conditioning air for a comfort zone, the method
comprising: adjusting an airflow volume of a variable air volume
blower; increasing a rotational speed of a desiccant wheel upon
increasing the airflow volume; and decreasing the rotational speed
of the desiccant wheel upon decreasing the airflow volume; and cooling
a second current of air before the second current of air passes
through the desiccant wheel.
16. The method of claim 15 further comprising changing the rotational
speed of the desiccant wheel proportionally with the airflow volume.
17. The method of claim 15 further comprising, in response to
a humidistat, heating a first current of air before the first current
of air passes through the desiccant wheel.
18. The method of claim 15 further comprising: energizing a source
of chiller fluid of a refrigerant system; energizing the desiccant
wheel for rotation for a predetermined period; and de-energizing
the desiccant wheel at the end of the predetermined period while
continuing to energize the source.
19. A method of conditioning air for a comfort zone, the method
comprising: heating a first current of air at a first heat transfer
rate before the first current of air passes through a desiccant
wheel; cooling a second current of air at a second heat transfer
rate before the second current of air passes through the desiccant
wheel; decreasing the second heat transfer rate by a second delta-heat
transfer rate while still cooling the second current of air; wherein
the step of decreasing the second heat transfer rate is achieved
by increasing a surface temperature of a cooling coil that is in
heat transfer relationship with the second current of air; decreasing
the first heat transfer rate by a first delta-heat transfer rate
while still heating the first current of air, wherein the second
delta-heat transfer rate is greater than the first delta heat transfer
rate.
20. The method of claim 19 further comprising decreasing a rotational
speed of the desiccant wheel upon decreasing the second heat transfer
rate.
21. The method of claim 19 wherein the step of decreasing the
first heat transfer rate is achieved by decreasing an airflow volume
of the first airflow rate.
22. The method of claim 19 further comprising: energizing a source
of chiller fluid of a refrigerant system; energizing the desiccant
wheel for rotation for a predetermined period; and de-energizing
the desiccant wheel at the end of the predetermined period while
continuing to energize the source.
23. A refrigerant system for conditioning air for a comfort zone,
the refrigerant system comprising: an enclosure defining an outside
air inlet, an intermediate air chamber, an outside air outlet, an
upstream air passageway, an intermediate air passageway, and a downstream
air passageway, wherein the air moves downstream sequentially through
the outside air inlet, the intermediate air chamber, the outside
air outlet, the upstream air passageway, the intermediate air passageway,
and the downstream air passageway; a heat recovery system in fluid
communication with the outside air inlet, the intermediate air chamber,
and the outside air outlet, wherein the heat recovery system transfers
heat from a first current of air to a second current of air, wherein
the first current of air travels from the outside air inlet to the
intermediate air chamber, and the second current of air travels
from the intermediate air chamber to the outside air outlet; a desiccant
wheel able to absorb moisture from the air passing from the intermediate
air passageway to the downstream air passageway and simultaneously
release moisture to the air passing from the upstream air passageway
to the intermediate air passageway; a blower in a position to force
the air from the downstream air passageway to the comfort zone;
a first cooling coil disposed within the intermediate air passageway
to help cool and remove moisture from the air; and a second cooling
coil disposed in the intermediate air chamber.
24. The refrigerant system of claim 23 wherein the heat recovery
system is an air-to-air heat exchanger that places the first current
of air in proximity with the second current of air to effect heat
transfer therebetween.
25. The refrigerant system of claim 23 wherein the heat recovery
system is a refrigerant circuit that includes a condenser disposed
in heat transfer relationship with the first current of air and
an evaporator in heat transfer relationship with the second current
of air.
26. The refrigerant system of claim 23 further comprising a heater
disposed downstream of the heat recovery system and upstream of
the desiccant wheel.
27. The refrigerant system of claim 23 wherein the intermediate
air passageway conveys a greater volume of air than does the intermediate
air chamber.
28. The refrigerant system of claim 23 further including a source
of chilled fluid operatively associated with and connected to the
first cooling coil, a controller operably connected to and controlling
the source and the desiccant wheel wherein the controller upon starting
the source energizes the desiccant wheel for a predetermined limited
period, whereby the desiccant wheel during the predetermined limited
period helps absorb moisture that may vaporize from the cooling
coil before the cooling coil is sufficiently cool to condense moisture
from the air.
29. A method of conditioning air for a comfort zone, the method
comprising: conveying the air sequentially through an outside air
inlet, an intermediate air chamber, an outside air outlet, an upstream
air passageway, through a desiccant wheel, through an intermediate
air passageway, back through the desiccant wheel, and out through
a downstream air passageway; cooling the air as the air passes from
the outside air inlet to the intermediate air chamber; heating the
air as the air passes from the intermediate air chamber to the outside
air outlet; heating the air as the air passes from the outside air
outlet to the desiccant wheel; releasing moisture from the desiccant
wheel to the air as the air passes from the upstream air passageway
to the intermediate air passageway; cooling the air as the air moves
from the desiccant wheel to the downstream air passageway; and absorbing
moisture from the air as the air moves back through the desiccant
wheel upon traveling from the intermediate air passageway to the
downstream air passageway.
30. The method of claim 29 wherein the air passing from the outside
air inlet to the intermediate air chamber is what heats the air
passing from the intermediate air chamber to the outside air outlet.
31. The method of claim 29 wherein more air passes through the
intermediate air passageway than through the intermediate air chamber.
32. The method of claim 29 further including the step of de-energizing
the desiccant wheel wherein the step of de-energizing the desiccant
wheel is performed provided the air is warmer than a certain limit.
33. Apparatus for conditioning air for a comfort zone, comprising:
a refrigeration system; a source of chiller fluid for the refrigeration
system; a desiccant wheel; means for energizing the source of chiller
fluid of the refrigerant system; means for energizing the desiccant
wheel for rotation for a predetermined period; and means for de-energizing
the desiccant wheel at the end of the predetermined period while
continuing to energize the source.
Description BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The subject invention generally pertains to HVAC systems
and more specifically to an air conditioning system that includes
a dehumidifying desiccant wheel.
[0003] 2. Description of Related Art
[0004] Energy wheels and desiccant wheels are two distinct types
of wheels used in the HVAC industry. An energy wheel is a rotating,
porous mass that functions as heat exchanger by transferring sensible
heat from one air stream to another. With an energy wheel, half
the wheel absorbs heat while the other half releases it. Examples
of energy wheels are disclosed in U.S. Pat. Nos. 6141979 and 4825936.
[0005] Desiccant wheels, on the other hand, transfer moisture from
one air stream to another, usually for the purpose of reducing humidity
of a comfort zone. Examples of systems with desiccant wheels are
disclosed in U.S. Pat. Nos. 6311511; 6237354; 5887784; 5816065;
5732562; 5579647; 5551245; 5517828 and 4719761.
[0006] Although many air conditioning systems that are enhanced
with desiccant wheels have been developed, such systems often implement
the use of desiccant wheels whenever there is a dehumidification
load. However many air conditioning systems may be most efficient
if the desiccant wheel is only utilized at part load conditions
or when the load on the system shifts from a sensible cooling load
to more of a latent cooling or dehumidification load. Current systems
often fail to address these efficiency concerns. Moreover, current
systems with desiccant wheels often disregard a critical period
when the refrigerant system is first activated. At startup, it takes
a moment for the refrigerant system's evaporator to become sufficiently
cold to remove moisture from the air. So, when the refrigerant system
is first energized and before the evaporator becomes cold, condensed
water on the surface of the evaporator may actually evaporate into
the air, which can increase the humidity of the comfort zone.
[0007] Consequently, a need exists for air conditioning systems
that are enhanced with desiccant wheels that address efficiency
concerns at part load operation for variable air volume systems.
SUMMARY OF THE INVENTION
[0008] It is a primary object of the invention to improve an HVAC
system's overall effectiveness by configuring the system with a
desiccant wheel in a manner that takes full advantage of the wheel's
ability to reduce humidity over a variety of operating conditions.
[0009] Another object of some embodiments is to start a refrigerant
compressor and the rotation of a desiccant wheel regardless of the
surrounding humidity, and then discontinue the wheel's rotation
after a predetermined period, whereby the wheel, during the predetermined
period, can reabsorb moisture that may have vaporized off an evaporator
at startup.
[0010] Another object of some embodiments is to discontinue the
rotation of a desiccant wheel in response to a humidistat indicating
that the humidity is below a certain level.
[0011] Another object of some embodiments is to discontinue the
rotation of a desiccant wheel in response to a thermostat indicating
that the air temperature is above a certain level.
[0012] Another object of some embodiments is to vary the rotational
speed of a desiccant wheel in proportion to the airflow volume through
the wheel.
[0013] Another object of some embodiments is to vary the rotational
speed of a desiccant wheel in proportion to the airflow volume through
the wheel, wherein the airflow volume is determined based on a controller's
speed command signal to a variable speed blower.
[0014] Another object of some embodiments is to vary the rotational
speed of a desiccant wheel in proportion to the airflow volume through
the wheel, wherein the airflow volume is determined based on an
airflow sensor.
[0015] Another object of some embodiments is to preheat the air
entering a desiccant wheel in response to a humidistat, wherein
the preheating assists the wheel in reducing the humidity in situations
where the rotational speed of the wheel is reduced due to lower
airflow rates.
[0016] Another object of some embodiments is to heat the air entering
one portion of a desiccant wheel and cooling the air entering another
portion of the wheel, wherein the heating is in response to a humidistat,
and the cooling is in response to a temperature sensor.
[0017] Another object of some embodiments is to decrease the cooling
rate of a desiccant wheel system to meet a reduced sensible cooling
demand, while maintaining or just slightly decreasing a heating
rate to meet a latent heating demand.
[0018] Another object of some embodiments is to install a heat
recovery system upstream of a desiccant wheel to meet both a latent
and sensible cooling demand. An air-to-air heat exchanger and a
condenser/evaporator refrigerant circuit are just two examples of
such a heat recovery system.
[0019] Another object of some embodiments is to meet a latent cooling
demand without having to preheat the incoming air or otherwise increase
the sensible cooling demand.
[0020] Another object of some embodiments is to provide an HVAC
enclosure that conveys more airflow in some sections than others
to accommodate the influx of both outside air and return air.
[0021] Another object of some embodiments is to install a pre-dehumidifying
heat recovery system upstream of the desiccant wheel to meet both
a latent and sensible cooling demand.
[0022] One or more of these and/or other objects of the invention
are provided by an HVAC system that includes a desiccant wheel,
wherein the configuration and/or control of the system is such that
the system takes full advantage of the wheel's ability to cool and
dehumidify the air of a comfort zone under various conditions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a schematic diagram of one embodiment of an HVAC
system that includes a desiccant wheel.
[0024] FIG. 2 is a schematic diagram of a second embodiment of
an HVAC system that includes a desiccant wheel.
[0025] FIG. 3 is a schematic diagram of a third embodiment of an
HVAC system that includes a desiccant wheel.
[0026] FIG. 4 is a schematic diagram of a fourth embodiment of
an HVAC system that includes a desiccant wheel.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0027] A refrigerant system 10 shown in FIG. 1 is cycled on and
off to meet a latent and/or sensible cooling demand, wherein a desiccant
wheel 12 of the system operates for at least a predetermined period
at the beginning of each cycle. At the start of each cycle, it can
take a moment for a cooling coil 14 such as an evaporator of a
refrigerant circuit, to become sufficiently cool to condense moisture
from the air 16. Moisture, which may have condensed on the surface
of coil 14 during an earlier operating cycle, may later evaporate
back into the air upon starting a new cycle. So, operating wheel
12 for a predetermined period at startup can help absorb that moisture
before it raises the humidity of a comfort zone 18 such as a room
or other area of a building 20.
[0028] For the illustrated embodiment, system 10 comprises an enclosure
22 that contains cooling coil 14 desiccant wheel 12 driven by a
motor 24 a blower 26 and a controller 28.
[0029] Enclosure 22 is schematically illustrated to represent any
structure or combination of structures that can define an upstream
air passageway 30 an intermediate air passageway 32 and a downstream
air passageway 34. In this example, enclosure 22 comprises a cabinet
22A and a roof curb 22B, wherein roof curb 22B attaches cabinet
22A to a roof of building 20. Although enclosure 22 is shown having
its two components, cabinet 22A and roof curb 22B, adjacent to each
other, other embodiments may have an enclosure whose components
are separated or interconnected by ductwork.
[0030] Cooling coil 14 is schematically illustrated to represent
any structure that can cool a stream of air by means of a chilled
fluid from a chilled fluid source 33. Examples of a chilled fluid
source 33 for coil 14 include, but are not limited to, a conventional
evaporator of a conventional refrigerant circuit, and a heat exchanger
that conveys chilled water.
[0031] Blower 26 is schematically illustrated to represent any
apparatus that can move air 16 through enclosure 22. Examples of
blower 26 include, but are not limited to, a centrifugal fan, an
axial fan, etc. Although blower 26 is shown disposed within intermediate
air passageway 32 blower 26 could be installed anywhere as long
as it can move air 16 in an appropriate flow path through enclosure
22.
[0032] Desiccant wheel 12 is schematically illustrated to represent
any rotatable, air-permeable structure that can absorb and release
moisture from a stream of air 16. Wheel 12 for example, may comprise
a honeycomb structure or porous pad or cage that contains or is
coated with a desiccant, such as silica gel, montmorillonite clay,
zeolite, etc. The actual structure of various desiccant wheels are
well know to those skilled in the art. Examples of desiccant wheels
are disclosed in U.S. Pat. Nos. 6311511; 6237354; 5887784;
5816065; 5732562; 5579647; 5551245; 5517828 and 4719761
all of which are specifically incorporated by reference herein.
[0033] Controller 28 provides at least one output signal that cycles
cooling coil 14 and blower 26 on and off to meet the cooling and/or
dehumidification demand of comfort zone 18. In this example, controller
28 provides an output signal 36 for selectively energizing or energizing
the source 33 of chilled fluid and/or the cooling coil 14 (or its
associated refrigerant compressor) and an output signal 38 for energizing
blower 26. Controller 28 also provides another output signal 40
for selectively energizing and de-energizing motor 24 of desiccant
wheel 12. Controller 28 is schematically illustrated to represent
any device that can provide such output signals. Examples of controller
28 include, but are not limited to, an electromechanical relay circuit,
thermostat, PLC (programmable logic controller), computer, microprocessor,
analog/digital circuit, and various combinations thereof.
[0034] Under normal operation, blower 26 draws return air 16A and/or
outside air 16B into intermediate air passageway 32 and across coil
14 which provides latent and sensible cooling of the air. Next,
blower 26 forces the conditioned air from intermediate air passageway
32 through a portion of wheel 12 that absorbs moisture from supply
air 16C. Downstream air passageway 34 then conveys the relatively
cool, dry supply 16C to comfort zone 18. Some of the air in zone
18 may escape building 20 through a vent 42 or other outlet, and
the rest of the air becomes return air 16A that blower 26 draws
back into upstream air passageway 30. As wheel 12 rotates, wheel
12 carries the moisture it absorbed in downstream passageway 34
and releases the moisture to the return air 16A passing through
upstream air passageway 30.
[0035] Upon initially activating the source 33 and/or cooling coil
14 and blower 26 at the beginning of each on-cycle, controller 28
actuates or rotates wheel 12 for a predetermined limited period,
e.g., five or ten minutes, regardless of any current dehumidification
need. During this period, wheel 12 can absorb moisture that the
surface of coil 14 may have accumulated from a previous on-cycle
and is currently evaporating from that surface. Such evaporation
can be caused by air 16 passing across the surface of coil 14 before
the coil is sufficiently cool to hold the moisture in a condensed
state. With wheel 12 rotating at the beginning of every on-cycle,
downstream air passageway 34 can immediately convey relatively dry
supply air 16C to comfort zone 18.
[0036] Once the predetermined period expires, signal 40 can de-activate
wheel 12 while cooling coil 14 and blower 26 continue operating
to meet the sensible cooling demand of zone 18. If, however, a humidistat
44 determines that a dehumidification demand exists after the predetermined
period expires, signal 40 may command wheel 12 to continue operating.
[0037] In some cases system 10 may have difficulty meeting the
sensible cooling demand of zone 18. Such an overload can be determined
based on a thermostat 46 indicating that the zone temperature has
risen to a certain level (e.g., two degrees above a target zone
temperature) even though system 10 is still operating. In such situations,
signal 40 may de-activate wheel 12 until system 10 can satisfy the
zone's sensible cooling demand.
[0038] In another embodiment, shown in FIG. 2 a refrigerant system
48 comprises desiccant wheel 12 blower 26 cooling coil 14 an
optional heater 50 and an enclosure 52. Enclosure 52 defines an
upstream air passageway 54 an intermediate air passageway 56 and
a downstream air passageway 58. Blower 26 forces air sequentially
through upstream passageway 54 through heater 50 through a first
portion 12A of wheel 12 that releases moisture to the air, into
intermediate air passageway 56 through blower 26 through cooling
coil 14 to provide latent and sensible cooling, through another
portion 12B of wheel 12 to absorb moisture from the air, into downstream
passageway 58 and onto a comfort zone. The air in downstream air
passageway 58 is supply air, and the air in upstream air passageway
54 can be return air and/or outside air. In this case, wheel 12
transfers moisture from the supply air to the return air or outside
air.
[0039] System 48 is particularly suited for VAV systems where the
cooling demand of a building is met by a system that delivers supply
air at a variable air volume. A controller 60 similar to controller
28 provides one or more output signals to system 48. Output signal
62 for example, controls the speed or airflow volume of blower
26 an output signal 64 controls the rotational speed of wheel 12
an output signal 66 controls cooling coil 14 (e.g., by selectively
actuating its associated compressor), and an output signal 68 controls
the operation of heater 50. To meet the building's cooling needs,
controller 60 varies the air delivery of blower 26 by providing
output signal 62 in response to an input signal 70 from a temperature
sensor 72.
[0040] To help maintain the wheel's efficiency over a range of
airflow volumes, controller 60 provides output signal 64 such that
the rotational speed of wheel 12 increases with the air volume.
The wheel's speed is preferably adjusted to be proportional to the
blower's speed or airflow volume. Controller 60 can determine the
airflow volume by way of an input signal 74 from a conventional
airflow sensor 76. Alternatively, controller 60 can simply assume
the airflow volume or blower speed agrees with output signal 62
whereby flow sensor 76 can be omitted.
[0041] Heater 50 which is optional, can be used for preheating
the return air in situations where the rest of system 48 is unable
to effectively dehumidify the air without excessively cooling the
supply air to a level where the comfort zone begins feeling unpleasantly
cold. Heater 50 can be a primary or auxiliary condenser of the same
refrigerant circuit that contains cooling coil 14 or heater 50
can be a separate heater, such as an electric heater, hot water
coil, radiator, etc.
[0042] In some cases where the sensible cooling demand drops significantly
while the latent cooling demand remains high, the heat transfer
rate between heater 50 and the current of air passing therethrough
can remain constant or be reduced by a first delta-heat transfer
rate, and the heat transfer rate between cooling coil 14 and the
current of air passing therethrough can be reduced by a second delta-heat
transfer rate, wherein the second delta-heat transfer rate is greater
than the first delta-heat transfer rate. Deactivating or increasing
the surface temperature of cooling coil 14 can be the primary cause
of the second delta-heat transfer rate, while a decrease in airflow
volume can cause the first delta-heat transfer rate. If, however,
the airflow volume is not reduced, then the first delta-heat transfer
rate may be substantially zero (i.e., the heat transfer rate of
heater 68 remains substantially constant).
[0043] FIG. 3 shows a system 78 that is similar to system 48 of
FIG. 2; however, system 78 has a second cooling coil 80 and a heat
recovery system 82. With the heat recovery system and second cooling
coil, system 78 can provide greater dehumidification with little
or no auxiliary heat, i.e., heater 50 may be optional.
[0044] System 78 includes blower 26 that forces air 84 through
an enclosure 86 that defines various air passageways. In some embodiments,
blower 26 forces air 84 sequentially through an outside air inlet
88 a cooling section 82A of heat recovery system 82 an intermediate
air chamber 90 cooling coil 80 a heating section 82B of heat recovery
system 82 an outside air outlet 92 an upstream air passageway
94 where return air 84A from a comfort zone and outside air 84B
can mix, optional heater 50 a moisture-releasing section 12A of
desiccant wheel 12 an intermediate air passageway 94 that contains
blower 26 and cooling coil 14 a moisture-absorbing section 12B
of wheel 12 and a downstream air passageway 96 that discharges
supply air 85C to a comfort zone.
[0045] From upstream air passageway 94 to downstream air passageway
96 the function of system 78 is very similar to that of system
48. To enhance dehumidification, however, system 78 employs cooling
coil 80 and heat recovery system 82. Cooling coil 80 removes moisture
from the air, while heat recovery system 82 transfer heat from the
air passing from outside air inlet 88 to intermediate air chamber
90 to the air passing from intermediate air chamber 90 to outside
air outlet 92 whereby the air moving from outside air outlet 92
to upstream air passageway 94 is cooler and drier than the air entering
system 48 of FIG. 2.
[0046] The fact that the air in passageway 94 is not only drier
but is also cooler than the air in passageway 94 is an important
advantage over conventional systems that preheat or warm the air
to achieve dehumidification. With conventional systems, reheating
the air increases the sensible cooling load. With the current system,
however, dehumidification can be achieved without increasing the
sensible cooling load, thus the current system is more efficient.
[0047] Heat recovery system 82 is schematically illustrated to
represent any apparatus for transferring heat from one airstream
to another. Heat recovery system 82 for example, can be a conventional
air-to-air heat exchanger or it can be the condenser and evaporator
of a conventional refrigerant circuit.
[0048] Such a refrigerant circuit is incorporated into a system
98 that is illustrated in FIG. 4. System 98 includes a refrigerant
circuit that comprises a refrigerant compressor 100 a condenser
102 an expansion device 104 (e.g., a flow restriction, capillary,
orifice, expansion valve, etc.), and an evaporator 106. The refrigerant
circuit operates in a conventional manner in that compressor 100
discharges hot pressurized refrigerant gas into condenser 102. The
refrigerant within condenser 102 condenses as the refrigerant releases
heat to the surrounding air (the air passing from an intermediate
chamber 90' to an outside air outlet 92'). From condenser 102 the
condensed refrigerant cools by expansion by passing through expansion
device 104. The refrigerant then enters evaporator 106 where the
relatively cool refrigerant absorbs heat from the incoming outside
air. From evaporator 106 the refrigerant returns to the inlet of
compressor 100 to be compressed again. As a result, the refrigerant
circuit transfers heat from the air passing through evaporator 106
to the air passing through condenser 102.
[0049] It should be noted, that although upstream air passageway
94 conveys a mixture of outside air 84B and return air 84A, in some
embodiments there is no return air, only outside air. In such cases,
the airflow volume through intermediate air chamber 90 or 90' is
substantially equal to that of intermediate air passageway 94. If,
however, enclosure 86 or 86' receives both outside air and return
air, then intermediate air passageway 94 conveys more air than does
intermediate air chamber 90 or 90'. Any excess air can be released
from the building through some sort of exhaust or other opening
in the building. |