Abstrict A method for conditioning air for an enclosure in which a supply
air stream is cooled with a refrigerant system containing a variable
compressor by passing the air over a cooling coil to reduce the
temperature thereof; the thus cooled supply air stream is then passed
through a segment of a rotating desiccant wheel under conditions
which increase its temperature and reduce its moisture content,
and then delivered to the enclosure. The desiccant wheel is regenerated
by heating a regeneration air stream with the condensing coil of
the refrigerant system, and then passing the heated regeneration
air stream through another segment of the rotating desiccant wheel.
At least one condition of the supply air stream, the regeneration
air stream, and/or the refrigerant system is sensed or monitored
and the output of the compressor is controlled in response to the
sensed condition.
Claims What is claimed is:
1. A method for conditioning air for an enclosure comprising the
steps of cooling a supply air stream with a refrigerant system containing
a variable compressor by passing the air over a cooling coil to
reduce the temperature thereof, passing the thus cooled supply air
stream through a segment of a rotating desiccant wheel under conditions
which increase its temperature and reduce its moisture content,
and then delivering the thus treated air to said enclosure; regenerating
the desiccant wheel by heating a regeneration air stream with the
condensing coil of the refrigerant system, and then passing the
heated regeneration air stream through another segment of the rotating
desiccant wheel to regenerate the desiccant in the wheel; sensing
at least one condition of the supply air stream, the regeneration
air stream, and/or the refrigerant system; and controlling the output
of the compressor in response to the sensed condition.
2. The method as defined in claim 1 including the steps of supplying
make-up air to said supply air, sensing at least one condition of
the air in the enclosure and controlling the supply of make-up air
in response to such sensed condition.
3. The method as defined in claim 1 including the step of sensing
the regeneration air temperature entering the regeneration segment
of the desiccant wheel and controlling the volume of regeneration
air passing the condenser coil and entering the regeneration segment
of the condenser coil to control the air temperature entering that
segment to a predetermined value.
4. The method as defined in claim 2 including the step of sensing
the regeneration air temperature entering the regeneration segment
of the desiccant wheel and controlling the volume of regeneration
air passing the condenser coil and entering the regeneration segment
of the condenser coil to control the air temperature entering that
segment to a predetermined value.
5. The method as defined in clam 1 including the step of sensing
the condensing coil pressure and maintaining it at a predetermined
pressure condition, and controlling the volume of regeneration air
passing the condenser coil and entering the regeneration segment
of the condenser coil thereby to maintain a relatively uniform regeneration
air temperature.
6. The method as defined in clam 2 including the step of sensing
the condensing coil pressure and maintaining it at a predetermined
pressure condition, and controlling the volume of regeneration air
passing the condenser coil and entering the regeneration segment
of the condenser coil thereby to maintain a relatively uniform regeneration
air temperature.
7. The method as defined in claim 1 including the step of sensing
the temperature of the cooled supply air leaving the desiccant wheel
and controlling compressor capacity in response to that sensed temperature
to maintain the cool air temperature leaving the wheel at a predetermined
value.
8. The method as defined in claim 5 including the step of sensing
the temperature of the cooled supply air leaving the desiccant wheel
and controlling compressor capacity in response to that sensed temperature
to maintain the cool air temperature leaving the wheel at a predetermined
value.
9. The method as defined in claim 6 including the step of sensing
the temperature of the cooled supply air leaving the desiccant wheel
and controlling compressor capacity in response to that sensed temperature
to maintain the cool air temperature leaving the wheel at a predetermined
value.
10. A method for condition air for supply to an enclosure comprising
the steps of cooling a supply air stream having a temperature range
of between 65.degree. F.-95.degree. and above and a moisture content
of between 90-180 gr/lb. with a refrigerant system cooling coil
to reduce the moisture content and temperature thereof to a first
predetermined moisture content saturation level and saturation temperature
range, passing the thus cooled and dried ambient supply air stream
through a segment of a rotating desiccant wheel under conditions
which increase its temperature to a second predetermined temperature
range of about 68-81.degree. F. and reduce its moisture content
further to a predetermined humidity level of between 30-80 gr/lb.;
and then delivering the thus treated air to said enclosure; regenerating
the desiccant wheel by heating a regeneration air stream with the
condensing coil of the refrigerant system to increase its temperature
to a predetermined temperature range of 105.degree. F.-135.degree.
F. and then passing the heated regeneration air stream through another
segment of the rotating desiccant wheel to regenerate the desiccant
in the wheel; sensing at least one condition of the supply air stream,
the regeneration air stream and/or the refrigeration system; and
controlling the output of the compressor in response to the sensed
condition.
11. The method as defined in claim 10 including the steps of supplying
make-up air to said supply air, sensing at least one condition of
the air in the enclosure and controlling the supply of make-up air
in response to such sensed condition.
12. The method as defined in claim 11 including the step of sensing
the regeneration air temperature entering the regeneration segment
of the desiccant wheel and controlling the volume of regeneration
air passing the condenser coil and entering the regeneration segment
of the condenser coil to control the air temperature entering that
segment to a predetermined value.
13. The method as defined in claim 12 including the step of sensing
the temperature of the cooled supply air leaving the desiccant wheel
and controlling compressor capacity in response to that sensed temperature
to maintain the cool air temperature leaving the wheel at a predetermined
value.
14. The method as defined in clam 12 including the step of sensing
the condensing coil pressure and maintaining it at a predetermined
pressure condition, and controlling the volume of regeneration air
passing the condenser coil and entering the regeneration segment
of the condenser coil thereby to maintain a relatively uniform regeneration
air temperature.
15. The method as defined in claim 14 including the step of sensing
the temperature of the cooled supply air leaving the desiccant wheel
and controlling compressor capacity in response to that sensed temperature
to maintain the cool air temperature leaving the wheel at a predetermined
value.
16. An air conditioning and dehumidification system comprising
an enclosed housing having a wall dividing the housing into first
and second separate air plenums; a refrigeration circuit in the
housing including an evaporator coil in the first plenum and a condenser
coil, at least one refrigerant compressor, and condenser fan located
in series in the second chamber such that the condenser fan draws
supply air over the condenser coil from outside the housing through
the second plenum and discharges it outside the housing; and a dehumidification
system in the housing including a desiccant wheel rotatably mounted
in the housing to rotate in a plane traversing perpendicular to
said central wall whereby one segment of the wheel functioning as
the process segment is located in the first plenum and a second
segment of the wheel functioning as the process segment is located
in the first plenum and a second segment of the wheel functioning
as the regeneration segment is located in the second plenum; a supply/process
air fan in the first plenum located adjacent one side of the wheel
and a sub-divider wall in said first plenum extending from near
said one side of the wheel to divide a sub-plenum in said first
plenum whereby the process air fan draws a supply/process air stream
into the first plenum, through the process section of the wheel
into the sub plenum and then discharges the thus cooled and dried
supply/process air to an enclosure; said desiccant wheel segment
in the second plenum being located downstream of the air flowing
over the condenser coils, a regeneration fan in said second plenum
adjacent the downstream side of the desiccant wheel and baffle means
in the second chamber extending from the desiccant wheel, downstream
thereof towards a side wall of the housing for preventing back flow
of air leaving the wheel toward the condenser coil or the inlet
side of the wheel when the regeneration fan draws air leaving the
condenser coil through the wheel to regenerate it.
17. A device for selecting heating, cooling and dehumidifying air
enclosed space comprising a desiccant wheel based dehumidification
system and at least one refrigeration circuit, said desiccant wheel
dehumidification system including a desiccant wheel having a process
section and a regeneration section, a blower for drawing air from
said space through the regeneration section of the wheel; said refrigeration
circuit including a first circuit including a condenser coil positioned
between the enclosure and the regeneration section of the wheel
in the path of regeneration air from the enclosure flowing to said
regeneration section, an evaporator coil, blower means for drawing
supply air over the evaporator coil, through the process section
of the desiccant wheel to the enclosure, and a compressor for moving
refrigerant in a circuit between the condenser and evaporation coils;
and a second refrigeration circuit including a condenser coil, blower
means for drawing ambient air over that condenser coil and exhausting
the same to the atmosphere, an evaporator coil located in the supply
air stream in the first regeneration system upstream of the desiccant
wheel and a compressor for moving refrigerant between its associated
coils, whereby operation of only said first refrigeration system
produces cooling only; operation of only the desiccant wheel based
system and the first refrigeration circuit produces dehumidification
only; operation of the desiccant wheel based system and the first
and second refrigeration system results in both cooling and dehumidification;
operation of the desiccant wheel based system only produces enthalpy
exchange between the regeneration air stream and the supply air
stream; operation of neither the desiccant wheel systems, nor the
refrigerant circuits, and only operation of said blowers, produces
only fresh air circulation.
18. A device for selecting heating, cooling and dehumidifying air
enclosed space comprising a desiccant wheel based dehumidification
system and at least two refrigeration circuits, said desiccant wheel
dehumidification system including a desiccant wheel having a process
section and a regeneration section, a blower for drawing air from
said space through the regeneration section of the wheel; said refrigeration
circuits including a first circuit including a condenser coil positioned
between the enclosure and the regeneration section of the wheel
in the path of regeneration air from the enclosure flowing to said
regeneration section, an evaporator coil, blower means for drawing
supply air over the evaporator coil, through the process section
of the desiccant wheel to the enclosure, and a compressor for moving
refrigerant in a circuit between the condenser and evaporation coils;
and at least a second refrigeration circuit including a condenser
coil, blower means for drawing ambient air over that condenser coil
and exhausting the same to the atmosphere, an evaporator coil located
in the supply air stream in the first regeneration system upstream
of the desiccant wheel and a compressor for moving refrigerant between
its associated coils, whereby operation of only said first refrigeration
system produces cooling only; operation of only the desiccant wheel
based system and the first refrigeration circuit produces dehumidification
only; operation of the desiccant wheel based system and the first
and second refrigeration system results in both cooling and dehumidification;
operation of the desiccant wheel based system only produces enthalpy
exchange between the regeneration air stream and the supply air
stream; operation of neither the desiccant wheel systems, nor the
refrigerant circuits, and only operation of said blowers, produces
only fresh air circulation.
19. A method as defined in claim 1 including the step of using
at least two compressors in the refrigerant system and selectively
operating one or both of the compressors in response to the differences
in actual humidity in the enclosure and a predetermined humidity
set point.
Description [0001] This application is a continuation in part of U.S. patent
application Ser. No. 09/795818 filed Feb. 28 2001 the disclosure
of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present invention relates to air conditioning and dehumidification
equipment, and more particularly to an air conditioning method and
apparatus using desiccant wheel technology.
[0003] It is well known that traditional air conditioning designs
are not well adapted to handle both the moisture load and the temperature
loads of a building space. Typically, the major source of moisture
load in a building space comes from the need to supply external
make-up air to the space since that air usually has a higher moisture
content than required in the building. In conventional air conditioning
systems, the cooling capacity of the air conditioning unit therefore
is sized to accommodate the latent (humidity) and sensible (temperature)
conditions at peak temperature design conditions. When adequate
cooling demand exists, appropriate dehumidification capacity is
achieved. However, the humidity load on an enclosed space does not
vary directly with the temperature load. That is, during morning
and night times, the absolute humidity outdoors is nearly the same
as during higher temperature midday periods. Thus, at those times
there often is no need for cooling in the space and therefore no
dehumidification takes place. Accordingly, preexisting air conditioning
systems are poorly designed for those conditions. Those conditions,
at times, lead to uncomfortable conditions within the building and
can result in the formation of mold or the generation of other microbes
within the building and its duct work, leading to what is known
as Sick Building Syndrome. To overcome these problems, ASHRAE Draft
Standard 62-1989 recommends the increased use of make-up air quantities
and recommends limits to the relative humidity in the duct work.
If that standard is properly followed, it actually leads to a need
for even increased dehumidification capacity independent of cooling
demands.
[0004] A number of solutions have been suggested to overcome this
problem. One solution, known as an "Energy Recovery Ventilator
(ERV)," utilizes a conventional desiccant coated enthalpy wheel
to transfer heat and moisture from the make-up air stream to an
exhaust air stream. These devices are effective in reducing moisture
load, but require the presence of an exhaust air stream nearly equal
in volume to the make-up air stream in order to function efficiently.
ERVs are also only capable of reducing the load since the delivered
air will always be at a higher absolute humidity in the summer months
than the return air. Without active dehumidification in the building,
the humidity in the space will rise as the moisture entering the
system exceeds the moisture leaving in the exhaust stream. However,
ERVs are relatively inexpensive to install and operate.
[0005] Other prior art systems use so-called cool/reheat devices
in which the outside air is first cooled to a temperature corresponding
to the desired building internal dew point. The air is then reheated
to the desired temperature, most often using a natural gas heater.
Occasionally, heat from a refrigerant condenser system is also used
to reheat the cooled and dehumidified air stream. Such cool/reheat
devices are relatively expensive and inefficient, because excess
cooling of the air must be done, followed by wasteful heating of
air in the summer months.
[0006] A third category of prior art device has also been suggested
using desiccant cooling systems in which supply air from the atmosphere
is first dehumidified using a desiccant wheel or the like and the
air is then cooled using a heat exchanger. The heat from this air
is typically transferred to a regeneration air stream and is used
to provide a portion of the desiccant regeneration power requirements.
The make-up air is delivered to the space directly, or alternatively
is cooled either by direct or indirect evaporative means or through
more traditional refrigerant-type air conditioning equipment. The
desiccant wheel is regenerated with a second air stream which originates
either from the enclosure being air conditioned or from the outside
air. Typically, this second air stream is used to collect heat from
the process air before its temperature is raised to high levels
of between 150.degree. F. to 350.degree. F. as required to achieve
the appropriate amount of dehumidification of the supply air stream.
Desiccant cooling systems of this type can be designed to provide
very close and independent control of humidity and temperature,
but they are typically more expensive to install than traditional
systems. Their advantage is that they rely on low cost sources of
heat for the regeneration of the desiccant material.
[0007] U.S. Pat. Nos. 3401530 to Meckler, 5551245 to Carlton,
and 5761923 to Maeda disclose other hybrid devices wherein air
is first cooled via a refrigerant system and dried with a desiccant.
However, in all of these disclosures high regeneration temperatures
are required to adequately regenerate the desiccant. In order to
achieve these high temperatures, dual refrigerant circuits are needed
to increase or pump up the regeneration temperature to above 140.degree.
F. In the case of the Meckler patent, waste heat from an engine
is used rather than condenser heat.
[0008] U.S. Pat. No. 4180985 to Northrup discloses a device wherein
refrigerant condensing heat is used to regenerate a desiccant wheel
or belt. In the Northrup system, the refrigerant circuit cools the
air after it has been dried.
[0009] The invention as described in our parent application Ser.
No. 08/795818 is particularly suited to take outside air of humid
conditions, such as are typical in the South and Southeastern portions
of the United States and in Asian countries and render it to a space
neutral condition. This condition is defined as ASHRAE comfort zone
conditions and typically consists of conditions in the range of
73-78.degree. F. and a moisture content of between 55-71 gr/lb.
or about 50% relative humidity. In particular, the system is capable
of taking air of between 85-95.degree. F. and 130-145 gr/lb. of
moisture and reducing it to the ASHRAE comfort zone conditions.
However, that system also works above and below these conditions,
e.g., at temperatures of 65-85.degree. F. or 95.degree. F. and above
and moisture contents of 90-130 gr/lb. or 145-180 gr/lb.
[0010] As compared to conventional techniques the invention of
the parent application has significant advantages over alternative
techniques for producing air at indoor air comfort zone conditions
from outside air. The most significant advantage being low energy
consumption. That is, the energy required to treat the air with
a desiccant assist is 25-45% less than that used in previously disclosed
cooling technologies. That system uses a conventional refrigerant
cooling system combined with a rotatable desiccant wheel. The refrigerant
cooling system includes a conventional cooling coil, condensing
coil and compressor. Means are provided for drawing a supply air
stream, preferably an outdoor air stream over the cooling coil of
the refrigerant system to reduce its humidity and temperature to
a first predetermined temperature range. The thus cooled supply
air stream is then passed through a segment of the rotary desiccant
wheel to reduce its moisture content to a predetermined humidity
level and increase its temperature to a second predetermined temperature
range. Both the temperature and humidity ranges are within the comfort
zone. This air is then delivered to the enclosure. The system also
includes means for regenerating the desiccant wheel by passing a
regeneration air stream, typically also from an outside air supply,
over the condensing coil of the refrigerant system, thereby to increase
its temperature to a third predetermined temperature range. The
thus heated regeneration air is passed through another segment of
the rotatable desiccant wheel to regenerate the wheel.
[0011] It is an object of the present invention to treat outside
supply air at any ambient condition and render it to practically
any drier and cooler psychrometric condition with lower enthalpy.
[0012] Yet another object of the present invention is to provide
a desiccant based dehumidification and air conditioning system which
is relatively inexpensive to manufacture and to operate.
[0013] Another object of the present invention is to heat make-up
air while recovering enthalpy from a return air stream.
[0014] Yet another object of the present invention is to provide
a desiccant based air conditioning and dehumidifying system using
single, multiple and or variable compressors operating at the highest
suction pressures possible to produce stable operating conditions
and enhanced energy savings.
[0015] A further object of the present invention is to utilize
the exhaust air from the building as a regeneration air source.
This air will be at an absolute moisture condition substantially
lower than ambient air for a portion of the year. Using this air
and adding heat from the condenser coil will produce a better sink
for process air moisture removal.
[0016] In accordance with an aspect of the present invention the
system of the present invention includes an air conditioning or
refrigeration circuit containing a condensing coil, a cooling or
evaporation coil and a compressor and a desiccant wheel having a
first segment receiving supply air from the cooling coil of the
refrigeration circuit to selectively dry the supply air. A regeneration
air path supplies regeneration air to a second segment of the desiccant
wheel as it rotates through the regeneration air path. According
to the invention this system is modulated to provide a constant
outlet air condition from the process portion of the desiccant wheel
over a wide range of inlet conditions and volumes. Preferably the
system uses variable compressors whose output can be varied in response
to air or refrigerant conditions at predetermined points in the
system. In one embodiment the system may be operated in numerous
different modes from fresh air supply only to supply of simultaneous
cooled and dehumidified air. In addition a particularly simple and
inexpensive housing structure for the system of the invention is
provided.
[0017] The above, and other objects, features and advantages of
the present invention will be apparent in the following detailed
description of illustrative embodiments thereof, which is to be
read in connection with the accompanying drawings, wherein:
[0018] FIGS. 1 1A and 1B are schematic diagrams of a first embodiment
of the basic system of the present invention;
[0019] FIG. 2 is a psychrometric chart describing the cycle achieved
by the embodiment of FIG. 1;
[0020] FIG. 3 is a psychrometric chart describing the cycle achieved
by the embodiment of FIG. 1 using a different control system.
[0021] FIG. 4 is a schematic view of another embodiment of the
present invention which is adapted to treat make-up air and recover
enthalpy from the return air stream.
[0022] FIG. 5 is a psychrometric chart showing the cycle achieved
with the system of FIG. 4 in the cooling only mode;
[0023] FIG. 6 is a psychrometric chart showing the cycle achieved
with the system of FIG. 4 in the dehumidification only mode;
[0024] FIG. 7 is a psychrometric chart showing the cycle achieved
with the system of FIG. 4 in the dehumidification and cooling mode;
[0025] FIG. 8 is a psychrometric chart showing the cycle achieved
with the system of FIG. 4 in an enthalpy exchange mode;
[0026] FIG. 9 is a psychrometric chart showing the cycle achieved
with the system of FIG. 4 in a fresh air exchange mode;
[0027] FIG. 10 is a schematic diagram of an embodiment similar
to that of FIG. 1 but utilizing two compressors;
[0028] FIG. 11 is an evaporator cross plot for the system of FIG.
10;
[0029] FIG. 12 is a schematic diagram similar to FIG. 1 showing
yet another embodiment of the invention using a reactivation temperature
control scheme; and
[0030] FIG. 13 is a schematic plan view of a housing structure
for use with the system of FIG. 1.
[0031] Referring now to the drawings in detail, and initially to
FIG. 1 thereof, a simplified air conditioning and dehumidification
system 10 according to the present invention is illustrated which
utilizes a refrigerant cooling system and a rotating desiccant wheel
dehumidification system. This system is a refinement of the system
disclosed in our parent application. In this case the system takes
air at any ambient condition and renders it to practically any drier
and cooler psychrometric condition with a lower enthalpy.
[0032] In system 10 the refrigerant cooling system includes a
refrigerant cooling circuit containing at least one cooling or evaporator
coil 52 at least one condenser coil 58 and a compressor 28 for
the liquid/gas refrigerant which is carried in connecting refrigerant
lines 29. In use, supply air from the atmosphere is drawn by a blower
50 through duct work 51 or the like, over the cooling coil 52 of
the refrigerant system where its temperature is lowered and it is
slightly dehumidified. From there, the air passes through the process
sector 54 of a rotating desiccant wheel 55 where its temperature
is increased and it is further dehumidified. That air is then provided
to the enclosure or space 57.
[0033] Desiccant wheel 55 of the dehumidification system is of
known construction and receives regeneration air in a regeneration
segment 60 from ducts 61 and discharges the same through duct 62.
The wheel 55 is regenerated by utilizing outside air drawn by a
blower 56 over the condenser coil 58 of the air conditioning system.
This outside air stream is heated as it passes over the condenser
coil and is then supplied to regeneration segment 60 to regenerate
the desiccant. The regeneration air is drawn into the system and
exhausted to the atmosphere by the blower 56.
[0034] In this embodiment, compressor 38 is a variable capacity
compressor and preferably an infinitely adjustable screw type compressor
with a slide valve. As is understood in the art the volume through
the screws in such a compressor is varied by adjusting the slide
valve and thus the volume of gas entering the screw is varied. This
varies the compressor's output capacity. Alternatively a time proportioned
scroll compressor, a variable speed scroll or piston type compressor
may be used to circulate the refrigerant in line 29 through a closed
system including an expansion device 31 between the condenser coil
58 and the evaporator or cooling coil 52.
[0035] It has been found that by using a single non variable compressor
in refrigeration systems, the compressor does more work than needs
to be done with the results that the desired set point of the system
may be over shot. By using variable compressors as described the
system can modulate to provide a constant outlet condition over
a range of inlet air conditions and volumes. That is, the operation
of the compressor is controlled in response to one or more conditions.
As a result, for example, one can maintain a desired usable and
selectable humidity condition leaving the desiccant wheel by modulating
the compressor capacity.
[0036] Such modulation can be achieved by using more than one compressor
or variable compressors, such as the time proportional compressor
offered by Copeland, or variable frequency compressors which use
synchronous motors whose speed may be varied by varying the hertz
input to the motor, which causes variation in work output.
[0037] The refrigeration system described above can be modulated
or controlled to provide a constant outlet condition over a range
of inlet conditions and volumes. It allows the system to be used
in make-up air applications to meet requirements for ventilation,
pressurization or air quality (e.g., in restaurants where make-up
air is required to replace kitchen exhaust air). Thus control of
the delivered make-up air volume can be made dependent on pressure
(through use of pressure sensors for clean rooms and the like),
CO.sub.2 content (through use CO.sub.2 sensors) to control quality,
or based on occupancy (using room temperature sensors). Such sensors
would control make-up air volume using known techniques to control,
for example, the speed of blower 50 or air diverter valves (not
shown) in duct 51. The system, using the variable compressor, can
still be modulated to accommodate the variation of temperature or
humidity caused by the addition of make-up air in order to maintain
the desired environmental conditions.
[0038] According to this invention a desired delivered air temperature
and humidity level for the supply air to the enclosure or space
57 can be maintained within the ASHRAE comfort zone discussed above.
From those temperatures and humidity conditions the corresponding
wet bulb temperature can be determined, establishing the desired
conditions represented at Point 3 on the psychrometric chart of
FIG. 2. This wet bulb temperature is used as the target set point
for the cooling and drying of the supply air (whether it is return
air alone or mixed with make-up air as described above). Utilizing
the variable capacity of the compressor 28 the capacity of the
cooling coil 52 is controlled to maintain the supply air temperature
leaving the coiling coil at a temperature which will allow the conditioning
of Point 3 to be attained after the air passes through the process
segment 54 of the desiccant wheel. This temperature will be slightly
lower than the calculated wet bulb temperature of the desired delivered
air. Thus, as shown in FIG. 2 supply air (in this case ambient
air as shown in FIG. 1) which will typically have a temperature
range of between 65.degree. and 95.degree. F. DBT and above and
a moisture content of between 90-180 grains/lb. enters the cooling
coil 52 at 95.degree. F. Dry Bulb Temperature ("DBT"),
78.5.degree. F. Web Bulb Temperature ("WBT") and a moisture
content of 120 grains/lb. (Point 1 on FIG. 2). As the air passes
through coil 52 its conditions move along the dotted line in FIG.
2 from Point 1 at relatively constant humidity until it reaches
saturation and its humidity is then reduced with temperature along
the saturation line to Point 2 where it leaves the coil in a saturated
condition of between 50.degree.-68.degree. DBT and 30-88 grains/lb.
moisture content, in this case at 61.degree. DBT and 80.4 grains/lb.
The air then enters the process segment 54 of the desiccant wheel.
As it passes through the wheel the air is dried and heated adiabatically,
following the approximate path of the wet bulb line. It is further
dried to its leaving condition of between 68-81.degree. F. DBT,
50-65.degree. F. WBT, and 30-88 grains/lb. moisture content, in
this case at Point 3 of 77.degree. F. DBT, 61.5.degree. WBT and
57 grains/lb. Of course it is understood that the compressor is
operated in response to the temperature of the air leaving the cooling
coil at Point C in FIG. 1 to achieve the desired final air temperature.
[0039] The length of travel down the line from Point 2 to Point
3 depends on the regeneration conditions of wheel 55. In accordance
with this invention the regeneration air temperature is increased
to provide a longer path down the wet bulb line, i.e., more drying,
and reduced to provide less movement, i.e., less drying. In this
manner the appropriate drying of the wheel also can be achieved
so that the supply air leaving condition (Point 3) will equal the
intended design condition.
[0040] As will be understood, given the capacity demanded from
the cooling side set point, the condensing coil 58 will need to
eject varying amounts of heat to the ambient air stream entering
that coil depending on conditions at Point E (FIG. 1). The variable
heat flux entering at Point E would, under normal conditions, result
in an uncontrolled regeneration temperature F. entering the wheel
55. According to the present invention the volume of air flow through
coil 58 is varied by the use of a bypass or exhaust fan 70 in order
to achieve the appropriate regeneration temperature entering wheel
55. This is done by sensing the temperature of air entering the
wheel and controlling the fan 70 to selectively increase or decrease
the volume of air drawn through coil 58 with blower 56 in order
to control the temperature of air entering the wheel. Any unnecessary
volume of air is then dumped to the atmosphere by fan 70. Airflow
is increased to reduce the temperature and reduced to increase the
temperature. The remaining air is then drawn through the desiccant
wheel to provide the appropriate desiccant dryness required to achieve
the desired drying results, i.e., the movement from Point 2 to Point
3 in FIG. 7. By dumping excess air passing coil 58 when the air
quantity required to maintain the desired regeneration temperature
exceeds the air flow needed to regenerate the desiccant total, energy
is conserved by not exposing the incremental air flow to the pressure
drop associated with the desiccant wheel. It also means a smaller
blower 56 may be used.
[0041] This system allows compressor 28 to operate at the highest
suction pressure necessary to obtain the leaving air condition,
i.e., the temperature of air leaving the wheel 55. When this is
done the compressor operates against the minimum pressure ratio
possible to produce the intended result. Thus the performance of
the cycle is maximized, reducing energy consumption.
[0042] When it is required to obtain additional sensible cooling
a secondary cooling coil 52' may be used to further cool air leaving
the desiccant wheel. This coil may be supplied with refrigerant
from the same compressor 28. As shown in FIGS. 1A and 1B this additional
coil 52' can be placed on either side of blower 50. In the position
shown in FIG. 1A, coil 52' allows for reduction in the supply air
temperatures after a slight rise in the air temperature occurring
from its passage through blower 50. In the position shown in FIG.
1B, coil 52' is upstream of blower 50 in the case where the temperature
increase from the blower is immaterial. Since the cooling coil performs
more efficiently on the suction side of a fan this is the preferred
embodiment where added blower heat is not a factor.
[0043] As an alternative to the control system described above,
control also can be achieved without the calculation of wet bulb
temperature by controlling the capacity of the cooling side of the
device to provide the desired cooling capacity for the space, i.e.,
controlling the compressor using the desired space temperature and
allowing the condensing side of the system to modulate accordingly.
In this case the volume of air drawn through the condenser 58 is
controlled to achieve the required regeneration temperature, within
limits of acceptable condensing pressure, and thus also achieve
the required regeneration capacity. The regeneration temperature
is increased to reduce outlet humidity ratio, and decreased to reduce
drying capacity, within acceptable pressure limits. This system
is shown in FIG. 3 wherein ambient air at Point 1 95.degree. F.
DBT 78.5.degree. F. WBT, 120 grains/lb. enters the cooling coil.
It follows the dotted line to the saturated curve as it passes the
cooling coil to Point 2 at 50.degree. F. saturated and 64.6.degree.
grains/lb. This air then enters the process segment 54 of the desiccant
wheel. As the air passes through the wheel it dries and is heated
adiabatically following the approximate path of the wet bulb line
to Point 3 which is its leaving condition at 69.degree. F. DBT;
52.degree. F. WBT, 30 grams/lb. The combined effect of minimizing
and controlling the precooled temperature and regeneration temperatures
as described above achieves the target leaving conditions within
the ASHRAE comfort zone.
[0044] The length of travel down the wet bulb line depends on the
regeneration condition. As noted above the regeneration temperature
is increased to provide a longer path down the line, or more drying,
and is reduced in order to produce less drying. In the alterative
control system first described the sensible cooling capacity is
increased allowing the equipment to provide cooling of the space.
[0045] FIG. 13 shows a schematic plan view of an air conditioning/dehumidifying
unit 10 according to FIG. 1 wherein the components bear the same
reference numerals. As seen therein the unit 10 is contained in
a housing 100 in an arrangement which eliminates the need for the
duct work 51 61 described above. Housing 10 is a rectangular box
like structure which defines an internal plenum 100 that is divided
by an internal wall 102 into plenum sections 104 106. The desiccant
wheel is rotatably mounted in wall 102 so that its process segment
or sector 54 is located in plenum 104 and its regeneration segment
60 is in plenum 106. Blower 70 is located at one side 108 of plenum
106 to draw supply air through apertures (not shown) in the opposite
side 110 over and through coil 58. That air flows over the compressor
28 to cool that as well and is discharged through apertures in wall
108 to the atmosphere.
[0046] Blower 50 is located in plenum 104 near the process segment
of wheel 55 in a sub plenum 112 defined by a wall 114 in plenum
104. Blower 50 draws supply air through openings (not shown) in
end wall 116 over and through evaporator coil 52 and then through
the process segment 54 into plenum 112. From there the supply air
is discharged through openings (not shown) in wall 110 at sub plenum
112 to the enclosure of separate duct work leading to the enclosure
57.
[0047] Blower 56 is mounted in plenum 106 adjacent the downstream
side of the regeneration segment 54 of the desiccant wheel. A baffle
or other separating or channel means 118 is positioned in plenum
106 adjacent wheel 55 and extends part way towards wall 108. As
described above, blower 56 draws some of the air leaving coil 58
through the regeneration segment 60 of the desiccant wheel to regenerate
the wheel. The baffle 118 prevents recirculation of air leaving
the wheel from recirculating back around the wheel. That air then
either mixes with air being expelled from the plenum by fan 70 to
the atmosphere or it may be separately ducted, in whole or in part,
to the supply air line.
[0048] This structure has numerous advantages including its compact
size, elimination of duct work, and reduction in condenser and regeneration
fan/blower horsepower. It also eliminates the use for any anti-back
draft louvers on the condenser circuit.
[0049] Another embodiment of the invention is illustrated in FIG.
4. In this embodiment the system is adapted to treat make-up air
and recover enthalpy from a return air stream. Return air is often
available in applications where fresh air is provided due to high
space make-up air requirements resulting from occupant capacity,
and where a large amount of air is not required for space pressurization
for infiltration load minimization. This type of design is typically
used for schools, theaters, arenas and other commercial spaces where
humidity need not be controlled to below normal level (such as is
required in supermarkets and ice rinks, which see energy and quality
benefits from lower humidity conditions.) Moreover such large spaces
use large volumes of air which have substantial heat value in them.
[0050] The system 80 of this embodiment comprises a cooling coil
52 for treatment of an outdoor ambient supply air stream A followed
by a desiccant wheel 55 and blower 50 for conveying the supply air
stream to the space or enclosures. This air stream constitutes the
make-up air. The evaporator or cooling coil 52 is connected to a
plurality of DX refrigerant compressor circuits. This is illustrated
in FIG. 4 as two coils 52 52' and their associated compressors
28 and 28'. However it is to be understood that the cooling circuit
containing coil 52 and compressor 28 may consist of more than two
separately operable circuits containing separate coils and compressors.
[0051] A second or regeneration air stream E is drawn from the
space 82 and is of a quantity approximately equal to 50 to 100%
of the make-up air in the first air stream A. This air first flows
through the condensing coil 58 then through the regeneration segment
of desiccant wheel 55 and is ejected from the enclosure to ambient.
The refrigeration circuit for this system is designed such that
the required heat rejected (i.e., given up) in the condenser to
the air stream does not exceed the heat carrying capacity of the
second air stream between its return air temperature and the maximum
refrigeration circuit condensing temperature of approximately 130.degree.
F. The refrigerant from this coil 58 is then used to cool the first
(supply) air stream.
[0052] As also seen in FIG. 4 one or more additional compressors
are connected to the cooling coil of the supply air stream. These
are sized to provide the additional cooling capacity to take the
ambient make-up air stream from ambient conditions down to 57.degree.-63.degree.
F. These additional cooling circuits possess their own condensing
circuits that eject their heat directly to ambient. This is shown
in FIG. 4 at condenser 58' which treats ambient air drawn through
it by fan 70.
[0053] In this embodiment, desiccant wheel 55 is equipped with
a drive motor arrangement that enables the desiccant wheel to rotate
selectively at high revolutions, namely 10-30 rpm, and at low revolutions,
namely 4-30 rph. In the high speed mode the desiccant rotor will
act as an enthalpy exchanger and will transfer latent and sensible
heat between the regeneration and make-up air stream. In the winter
an enthalpy wheel heats and humidifies the make-up air, and in the
summer it will cool and dehumidify.
[0054] The system of this embodiment can operate in five different
modes. As described hereinafter, the compressors and wheel speed
states are changed to adapt the performance of the system to the
space requirements. The system can run in any or a combination of
the five modes. The main five modes are: Cooling only mode; Dehumidification
only mode; Cooling and dehumidification mode; Enthalpy exchange
mode; and Fresh air mode.
[0055] Operation of this system in the cooling only mode is illustrated
on the psychrometric chart of FIG. 5. In this mode desiccant wheel
55 is not operated and only the number of compressors necessary
to provide sufficient cooling to the space are operating. However
the compressor 28' whose condenser coil 58 is in the return air
line is not operating since the wheel is not operating. Operating
in this manner, as seen in FIG. 5 ambient air in air stream A enters
the bank of cooling coils at the conditions of Point 1 at 95.degree.
F. DBT, 78.5.degree. F. WBT, and 120 grains/lb. moisture content.
As it passes through the cooling/evaporator coils it moves along
the dotted line to and then down the saturation curve to Point 2
at 65.degree. F. saturated, 92.8 grains/lb. The air has been cooled
and dehumidified at this point, but not necessarily to the ASHRAE
comfort zone since no dehumidification from the wheel occurs. Heat
absorbed in the condensing coil 58' is simply rejected to the ambient
air stream via the condenser and fan 70.
[0056] Operation of the system of FIG. 4 in the dehumidification
only mode is shown in the psychrometric chart of FIG. 6. In this
mode the desiccant motor is operated at low speed mode (i.e., 4-30
rph) and the compressor 28' which serves the condensing coil 58
in the return air stream E is operating to heat the regeneration
air. The other refrigeration circuits, including compressors 28
and coils 58', 52 are not operating. Thus, as seen in FIG. 6 ambient
air A enters the bank of evaporation coils at the conditions of
Point 1 at 95.degree. F. DBT, 78.5.degree. F. WBT, and 120 grain/lb.
As this air passes coil 52 52' it is cooled in coil 52' along the
dotted line on the chart to and down the saturation line to Point
2 at 65.degree. F. saturated, 92.8 grains/lb. Because the desiccant
wheel is operating, air stream A is processed in the wheel where
it is dried and heated adiabatically following the approximate path
of the wet bulb line. It leaves the desiccant wheel and is supplied
to enclosure 82 at the conditions of Point 3 at 79.degree. F. DBT,
66.degree. F. WBT and 75 grains/lb.
[0057] In this example and in typical operation the regeneration
air taken from the space 82 by blower 56 will be at conditions of
about 80.degree. F. DBT an 67.degree. F. WBT, approximately the
same condition as the supply air stream of ambient air. This regeneration
air (i.e., the exhaust air from the space) is passed through condenser
coil 58 receives heat rejected from that coil and then flows through
wheel 55 to regenerate it. This is a substantial advantage, in this
condition of operation, over the use of ambient air alone to regenerate
the wheel since the exhaust air leaving the condenser coil will
have lower relative humidity than if ambient air was used. Thus
it will absorb more moisture from the wheel and improve desiccant
performance over what is achievable with outside air alone. After
passing the wheel it is vented to the atmosphere.
[0058] Operation of the system of FIG. 4 in the cooling and dehumidification
mode is illustrated on the psychrometric chart of FIG. 7. In this
mode, as in the dehumidification only mode, desiccant wheel 55 is
rotated slowly (4-30 rph) but additional cooling is provided by
the additional cooling circuit or circuits containing coils 58',
52 and compressor 28 which are operated, as they do in the cooling
only mode. In this case the cooling and dehumidification modes work
together. The first stage of refrigeration circuit containing coil
58 52' and compressor 28' also operate and provide the reactivation
energy source.
[0059] Operating in this manner, supply air A (either all ambient
or a mixture of ambient and some return air) enters the bank of
cooling coils at Point 1 (FIG. 7) at 95.degree. F. DBT, 78.5.degree.
F. WBT, 120 grains/lb. It again follows the dotted line and down
the saturation line to Point 2 exiting coil 52'. Because the second
or additional stages of cooling circuits are operating the condition
of that air continues further down the saturation line arriving
at Point 3 after exiting the secondary cooling stage 52. At that
point the supply air stream conditions are 57.degree. F. saturated,
69.5 grains/lb.rh. This air then enters the process segment 54 of
the desiccant wheel 55 where it is dried and adiabatically heated.
It follows generally the path of the wet bulb line and leaves the
wheel at Point 4 at 74.degree. F. DBT, 58.degree. F. WBT, and 48
grains/lb.
[0060] Operation of the system of FIG. 4 in the enthalpy exchange
mode is illustrated in the psychrometric chart of FIG. 8. This mode
is typically used in summer when the outside air is at a higher
enthalpy than the indoor air, or in winter when indoor enthalpy
exceeds outdoor enthalpy.
[0061] In this case the desiccant wheel 55 is driven at high speed
(10-30 rpm) and all the refrigeration circuits are off. As shown
in FIG. 8 in winter, when 100% outside air is used having the conditions
at Point 1 of 40.degree. F. DBT, 32.degree. F. WBT and 12.6 grains/lb.
passage of the air through the process section 54 of the wheel will
cause the conditions of the air exiting the wheel to move along
the dotted line from Point 1 to Point 2 at 52.5.degree. F. DBT,
44.5.degree. F. WBT, and 30.5 grains/lb. From that point a conventional
heater 80 can heat the air to the desired room temperature. The
exhaust air drawn from the heater is supplied to section 60 to transfer
heat and moisture thereto.
[0062] In the summer condition using 100% outside air at Point
5 82.5.degree. F. DBT, 56.degree. F. WBT and 42 grains/lb. the
system will operate in a reverse manner by causing the air to move
along the dotted line from Point 5 to Point 6 i.e., to 80.degree.
F. DBT,61.5.degree. F. WBT, 42 grains/lb., just at the ASHRAE comfort
zone.
[0063] Using the system of FIG. 4 in its enthalpy exchange mode
with 50% ambient air and 50% return air will cause the air conditioning
entering the desiccant wheel process section 54 to move from Point
3 to Point 4 on FIG. 8.
[0064] The final, fresh air exchange mode of operation of the embodiment
of FIG. 4 is shown on the psychrometric chart of FIG. 9. In this
case all cooling circuits and the desiccant wheel are off, and only
the blowers are on to constantly replenish fresh air. As a result
the system delivers fresh ambient air without heat recovery, cooling
or dehumidification.
[0065] Preferably the compressors used in this embodiment are also
of the variable type to provide more efficient operations.
[0066] Yet another embodiment of the present invention is illustrated
in FIG. 10. The system of this embodiment is similar to that of
FIG. 1 except that two compressors 28 are used in the refrigeration
circuit. As seen in the evaporator cross plot of FIG. 11 for a representative
two compressor cooling circuit two operating conditions for the
system are possible depending upon whether one or both compressors
are operating. To minimize energy use, by increasing the coefficient
of performance (COP) of the system it is desirable to operate the
system at the highest suction pressures possible which permits the
desired space humidity and temperature conditions to be achieved.
Operating one compressor instead of two wherever possible also conserves
energy.
[0067] FIG. 8 shows two sloping lines rising to the right showing
the capacity in BTUH of one and two compressors versus saturated
suction temperature with the compressors operating at 100% capacity
for that temperature. The term saturated suction temperature means
the temperature of the coolant gas leaving the evaporator cooling
coil 52 and entering the compressors.
[0068] The three lines which slope upwardly and to the left in
FIG. 11 represent the suction temperature of the refrigerant gas
when the supply air stream is at one of three conditions noted on
the graph and shows the corresponding capacity of the compressors
at each temperature. Where the two sets of sloping lines cross,
the evaporator and compressor are operating at the same conditions
and therefore the most efficiency.
[0069] Typically multiple compressors (as well as variable compressors)
have been operated to cut in and out of operation based on either
fixed pressure points detected in the refrigerant line or based
on the temperature of the supply air leaving the evaporator/cooling
coil. In the present invention, using a humidity control unit (i.e.,
desiccant wheel), the space humidity error can be used to control
compressor operation. Thus "error" is the difference between
the actual humidity sensed in the room or space and the humidity
set point (i.e., the desired humidity level). This signal is then
used to reset the suction pressure cut in point for the second compressor.
If the error is large, which means humidity is not being reduced,
the reset action will move the suction cut in pressure to a lower
setting. On the other hand if the error is small, or the unit cycles
on or off rapidity, reset will increase the suction pressure cut
in. In this way the unit operates at the highest suction pressure
possible producing the most stable conditions and increased energy
savings.
[0070] A still further embodiment of the present invention is illustrated
in FIG. 12 which also allows operation of the unit in cooling or
dehumidification, or in both modes simultaneously.
[0071] Existing technology has traditionally controlled the discharge
pressure of refrigeration systems (i.e., the pressure of gas leaving
the evaporator or cooling coil) to prevent excessively low discharge
pressure during winter. One common technique of head pressure regulation
is to reduce condenser fan speed, which produces the beneficial
side effect of reducing the power needed to operate the fan.
[0072] For humidity control units reducing fan speed has the same
effect and benefit at low temperatures. However, because cooling
applications and the humidity control units as used in the present
invention have the ability to operate in cooling, dehumidification,
or both modes simultaneously, a variation on the industry-accepted
practice of pressure head regulation is needed.
[0073] When not limited by high outside ambient temperatures or
a condenser's particular design criteria it is desirable to maintain
the discharge pressure of the compressor at the equivalent of between
80.degree. F. and 100.degree. F. saturated discharge temperature.
The control system of this embodiment will, in the cooling mode,
optimize cooling performance by setting the head pressure set point
within this range. Maximum efficiency is achieved at lower pressure
ratios, which are characterized by higher suction pressures and
lower discharge pressures.
[0074] On the other hand a desiccant wheel humidity control unit
relies on creating a sufficient difference between the supply air's
entering relative humidity and the regeneration air's relative humidity.
This is the force driving moisture transfer in the desiccant wheel.
It also is beneficial to operate the refrigeration system across
the lowest pressure ratio possible. This means that higher suction
pressures and lower condensing pressures should be used. The system
of the present invention balances the performance of the entire
unit without giving preference to either the refrigeration system
or the desiccant system.
[0075] To accomplish this a humidity sensor 90 is placed in the
regeneration air stream, after the heating condenser coil 58. An
exemplary target RH value would be in the range of 10 to 30 percent
RH. Assuming that saturation of the cooled air leaving the cooling
coil 52 is achieved (Point 2 on the psychrometric charts) the space
humidity sensor in space 57 would reset the head pressure to attain
a specific RH sensed entering the wheel. The reset would be limited
to keep the head pressure within a predefined range of conditions.
For example, with R-22 refrigerant the range of head pressure limits
would be from 168 psig (90.degree. F.) to 360 psig (145.degree.
F.). These are generally accepted conditions of operation for known
scroll compressors. This achieves a range of leaving air temperatures
from the condenser coil or inlet to the wheel of 80.degree. F. to
140.degree. F. and avoids drawing up condenser head pressures with
attendant loss of performance in the refrigeration system. Thus
the compressor would run at the lowest head pressure while still
producing the target relative humidity. The savings would be that
the 45.degree. F. leaving air temperature obtained with a head pressure
of 260 psig reaches the target RH% at a lower pressure thereby reducing
compressor power input while increasing refrigeration capacity.
[0076] Another way of accomplishing the same result would be by
utilizing the differential or elasticity of reactivation outlet
or differential temperature to reactive inlet temperature. For example,
the desiccant wheel will presumably have a lower outlet air temperature
when the wheel is still wet. Conversely the outlet air temperature
will begin to climb when the wheel is fully reactivated, i.e., dry.
The temperature of the air on either side of the wheel could be
detected by conventional temperature sensors 92 and continuously
monitored. When air increase in reactivation inlet air temperature
yields a nearly similar increase in outlet air temperature it indicates
that the energy is not being used to displace moisture from the
wheel and therefore that head pressure should be reduced by appropriate
control of the compression.
[0077] Alternatively the control could be set to maintain a target
20.degree. F. differential in temperature across the wheel.
[0078] This system reduces lost energy by matching reactivation
energy to load to reduce reactivation temperatures which in turn
reduces head pressure that results in improved refrigeration performance.
[0079] Although illustrative embodiments of the present invention
have been described herein with reference to the accompanying drawings,
it is to be understood that the invention is not limited to those
precise embodiments, but that various changes and modifications
can be effected therein by those skilled in the art without departing
from the scope or spirit of this invention. |