U.S. patent application number 11/115188 was filed with the patent office on 2005-10-27 for integrated dehumidification system.
This patent application is currently assigned to DAVIS ENERGY GROUP, INC.. Invention is credited to Berman, Mark J., Hoeschele, Marc A., Phillips, James H., Springer, David A..
Application Number | 20050235666 11/115188 |
Document ID | / |
Family ID | 35135029 |
Filed Date | 2005-10-27 |
United States Patent
Application |
20050235666 |
Kind Code |
A1 |
Springer, David A. ; et
al. |
October 27, 2005 |
Integrated dehumidification system
Abstract
A dynamic system controls indoor relative humidity and
temperature to achieve specified conditions by applying multiple
stages of dehumidification. In addition to an optional stage that
increases dehumidification by reducing the speed of the indoor
blower, the system uses a reheat coil and multiple valves that
allow the reheat coil to function as either a subcooling coil or a
partial condenser. Thus the system can maintain specified indoor
temperature and humidity conditions even at times when no heating
or cooling is needed. The system may have an outdoor condensing
unit including a compressor and a condenser operably connected via
refrigerant lines to an indoor unit to form a "split system"
refrigerant loop.
Inventors: |
Springer, David A.;
(Winters, CA) ; Hoeschele, Marc A.; (Davis,
CA) ; Berman, Mark J.; (Davis, CA) ; Phillips,
James H.; (Sacramento, CA) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
DAVIS ENERGY GROUP, INC.
Davis
CA
|
Family ID: |
35135029 |
Appl. No.: |
11/115188 |
Filed: |
April 27, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60565532 |
Apr 27, 2004 |
|
|
|
Current U.S.
Class: |
62/186 ;
62/513 |
Current CPC
Class: |
F24F 3/153 20130101;
F25B 40/02 20130101 |
Class at
Publication: |
062/186 ;
062/513 |
International
Class: |
F25D 017/06; F25D
017/04; F25B 041/00 |
Claims
What is claimed is:
1. A system for controlling indoor environmental conditions,
comprising: a vapor-compression refrigerant loop with a compressor,
a condenser, a reheat coil, an expansion device, and an evaporator
coil; an air mover that drives an indoor air stream sequentially
across the evaporator and a reheat coil; a plurality of valves
disposed within the vapor-compression loop; and a controller
operably connected to the vapor-compression loop, the air mover and
the plurality of valves, wherein the condenser discharges heat to
an outdoor environment, and the controller controls a plurality of
dehumidification stages including a stage that causes refrigerant
to condense in the reheat coil.
2. The system of claim 1, wherein the refrigerant loop includes a
receiver for refrigerant volume control.
3. The system of claim 1, wherein one of the plurality of
dehumidification stages minimizes dehumidification of indoor air by
operating the air mover at a normal speed and directing a
refrigerant in the refrigerant loop to bypass the reheat coil by
operating at least one of the plurality of valves.
4. The system of claim 1, wherein one of the plurality of
dehumidification stages increases dehumidification of indoor air by
reducing a speed of the air mover to reduce a velocity of the
indoor air stream across the evaporator and the reheat coil.
5. The system of claim 1, wherein at least one of the plurality of
dehumidification stages protects the condenser from low refrigerant
pressures by reducing a rate at which the condenser discharges heat
to the outdoor environment.
6. The system of claim 1, wherein the condenser is cooled by a
second air stream driven by at least one condenser fan and a flow
rate of the second air stream is controlled by controlling the at
least one condenser fan.
7. The system of claim 6, wherein the at least one condenser fan
operates at a single speed and is cycled on and off to reduce a
heat exchange rate of the second air stream.
8. The system of claim 1, wherein the controller is operably
connected to an indoor temperature sensor, an indoor humidity
sensor, at least one of the plurality of valves, and the controller
includes control logic that controls the air mover, the condenser,
and the at least one of the plurality of valves based on input from
at least one of the indoor temperature sensor and the indoor
humidity sensor.
9. The system of claim 2, wherein the refrigerant receiver is
located between the condenser and the evaporator.
10. The system of claim 2, wherein the reheat coil is located in a
first parallel path between the condenser and the expansion device,
and the receiver is located in a second parallel path between the
condenser and the expansion device.
11. The system of claim 10, wherein a first bypass path is provided
between an outlet of the reheat coil and an inlet of the
receiver.
12. The system of claim 11, wherein a second bypass path is
provided between an inlet of the reheat coil and an outlet of the
receiver.
13. The system of claim 12, wherein the plurality of valves
includes first and second refrigerant valves placed in the second
parallel path between the condenser and the expansion device and
wherein the first refrigerant valve is placed between the condenser
and the receiver, and the second refrigerant valve is placed
between the receiver and the expansion device.
14. The system of claim 13, wherein the first bypass path joins the
second parallel path between the condenser and the expansion device
at a location between the first refrigerant valve and the receiver,
and the plurality of valves includes a check valve located in the
first bypass path to prevent refrigerant flow from the inlet of the
receiver to the outlet of the reheat coil.
15. The system of claim 14, wherein the plurality of valves
includes first and second pressure-reducing check valves located in
the first parallel path between the condenser and the expansion
device, and wherein the first pressure-reducing check valve is
located between the condenser and the reheat coil, and the second
pressure-reducing check valve is located between the reheat coil
and the expansion device.
16. The system of claim 15, wherein the second bypass path joins
the first parallel path between the first pressure-reducing check
valve and the reheat coil, and the first bypass path joins the
first parallel path between the reheat coil and the second
pressure-reducing check valve.
17. A system for controlling indoor environmental conditions,
comprising: an outdoor condensing unit including a compressor and a
condenser operably connected via refrigerant lines; an indoor unit
operably connected to the outdoor condensing unit to form a
refrigerant loop, the indoor unit comprising: an evaporator coil, a
reheat coil, an expansion device, a refrigerant receiver for
refrigerant volume control, an expansion device, and a plurality of
valves, operably connected via refrigerant lines; an air mover that
drives a first air stream sequentially across the evaporator coil
and the reheat coil; and a controller operably connected to the
outdoor condensing unit and the indoor condensing unit, wherein the
condenser discharges heat to outdoor air, the reheat coil is
located downstream of the evaporator coil in the first air stream,
and the controller controls a plurality of dehumidification
stages.
18. The system of claim 17, wherein the plurality of
dehumidification stages includes a stage that causes refrigerant in
the refrigerant loop to condense in the reheat coil.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/565,532, filed on Apr. 27, 2004.
BACKGROUND
[0002] The subject matter of this disclosure relates to providing
building cooling, dehumidification, and fresh air ventilation
through a range of outdoor and indoor conditions.
[0003] New U.S. homes that are built in compliance with ASHRAE
Standard 90.2, Energy Star, and other energy efficiency programs
have lower cooling loads than in the past, and because they are of
tighter construction, they frequently require mechanical
ventilation as prescribed by ASHRAE Standard 62.2. In humid
climates the ventilation air often requires more dehumidification
than can typically be provided by air conditioners, because typical
air conditioners in energy-efficient homes have short run times
during many cooling load hours. Short run times typically limit
latent cooling capacity. Failure to control excessive indoor
humidity has contributed to problems with indoor mold. This issue
has become increasingly expensive for homeowners and builders, as
mold-related property damage and class action lawsuits have risen
steadily.
[0004] Vapor compression cooling systems (air conditioners) that
are in use in most homes and other buildings provide a mix of
sensible cooling (lowering the air temperature) and latent cooling
(removing moisture). Typically, the sensible heat ratio ("SHR", the
sensible cooling capacity divided by the total capacity) for most
residential cooling systems ranges from 0.7 to 0.8. In humid
conditions this SHR is often too high to maintain temperature and
relative humidity in the ideal ranges of 74.degree.-78.degree. F.,
and 40-60%, respectively. Some vapor compression cooling systems
lower the airflow rate through the evaporator coil to reduce the
SHR under humid conditions, but re-evaporation of condensate
retained on the coil at system shutdown still limits the SHR,
particularly when systems cycle frequently, as they do under low
load conditions. Such residential cooling systems are "split
systems", with an outdoor condensing unit that includes the
compressor, condensing coil, and condenser fan, and a separate
indoor unit that includes an evaporator coil, expansion device, and
system blower. Two refrigerant lines join the outdoor and indoor
components.
[0005] Furthermore, a stand-alone dehumidifier is frequently used
in humid climates to control indoor humidity. Because heat from the
condenser is added to indoor air, the dehumidifier often increases
the sensible cooling load, the air conditioner run time, and the
amount of energy consumption. A preferred approach to
dehumidification in the cooling season is to dehumidify indoor air
by rejecting condenser heat to outside air instead of to the indoor
space.
[0006] In the prior art, various strategies have been proposed to
control both temperature and humidity. For example, U.S. Pat. No.
6,170,271 B1 shows a concept with two separate refrigerant loops; a
first loop with the evaporator in the supply air stream and the
condenser outdoors, for sensibly cooling the air stream, and a
second "latent cooling" loop with the evaporator just downstream of
the first evaporator, and with the condenser downstream of the
second evaporator. This approach is similar to combining an air
conditioner and a dehumidifier, but with the added benefits of
requiring only one indoor blower and cabinet, and a smaller second
evaporator can be used because the air has been pre-cooled in the
first evaporator. However, all heat from the second loop is added
to the supply air, with associated energy penalties. In the
embodiment, having the dehumidifier condenser located outside the
supply air stream, the system is still penalized by the cost of
requiring dual compressors, additional refrigerant piping, and
condensers. Various other design configurations appear in the
patent literature and are aimed at more precisely controlling both
sensible and latent loads.
[0007] Another strategy having dual refrigerant loops is shown in
U.S. Pat. No. 6,705,093 B1 and uses two condensing units that share
an evaporator coil whose tubing pattern maintains separation of the
two loops. One of the two loops has a sub-cooling coil. This
approach adds substantial cost to a conventional system with a
single refrigerant loop. Another approach to increasing latent
cooling is shown in U.S. Pat. No. 6,427,454 B1. This design
selectively causes a portion of the return air to bypass the
evaporator coil, which lowers the coil temperature and increases
moisture condensation on the coil. However, this approach is
unlikely to succeed in the market, as it is comparable to lowering
the blower speed, but with higher initial costs and without the
energy savings associated with reducing blower speed.
[0008] U.S. Pat. No. 6,123,147 shows a retrofit system that adds a
hot water reheat coil connected to a residential water heater
located downstream of the evaporator. Like other "reheat" designs,
this approach decreases the SHR by making the cooling system run
longer. However, the economics of such a system will be poor
because gas water heating is substituted for waste heat already
available from the condensing side of the refrigerant system. Thus,
this approach is like driving a vehicle using the accelerator and
brake simultaneously. Other strategies, such as that disclosed in
U.S. Pat. No. 5,791,153, apply desiccant-based enthalpy wheels to
increase latent cooling. These designs require added components to
recharge the desiccant and therefore may not be cost-effective.
[0009] Of the major product lines in the U.S. marketplace, only the
Carrier.RTM. Infinity.TM. series and the Lennox.TM.
SignatureStat.TM. controller claim features that control both
temperature and humidity. However, both products can only control
humidity by varying fan and compressor speed. There are no added
components designed to respond to conditions with high humidity and
low cooling loads. Thus, these systems cannot maintain a specified
temperature/humidity set through a wide range of conditions.
[0010] In the "packaged" air conditioning market with products
usually applied to non-residential buildings, Lennox.TM. markets a
patented Humiditrol.RTM. line that includes refrigerant control
valves and a "hot gas" reheat coil for more precise humidity
control. Carrier.RTM. markets the MoistureMiser.TM. that uses a
"sub-cooling" coil for the same purpose. In both cases the strategy
is to add some heat from the condenser side of the refrigerant
system back into the supply air stream (downstream of the
evaporator) to reduce the net cooling rate. Such systems must run
longer to satisfy the cooling load, and the longer run time removes
more moisture at the evaporator. Adding more length to the coil on
the condenser side also reduces the liquid refrigerant temperature
into the evaporator, which increases evaporator capacity and
therefore drops the evaporator temperature, increasing the rate of
moisture removal. Lennox.TM. claims superior dehumidification
performance because the higher heat output of the "hot gas"
approach causes longer cooling cycles, thus removing more moisture
compared to the sub-cooling approach.
[0011] These non-residential products use a "single-package"
configuration, and no "split system" units currently include the
"reheat coil" features described above. In fact, the Lennox.TM. hot
gas approach is only workable in a single package device, as the
system would require an extra pair of refrigerant lines to be
applied in a "split system" configuration because refrigerant must
flow first to the indoor reheat coil, then back to the condenser,
then to the indoor expansion device. The Carrier.RTM. sub-cooling
approach would not require an extra line set in a split system
configuration because the refrigerant flows directly from the
sub-cooling coil to the expansion device. However, the approach
only provides two stages of dehumidification, and therefore cannot
sufficiently control humidity when sensible loads are very low and
latent loads are high.
[0012] Although the vapor compression systems disclosed above, and
others, use hot gas and sub-cooling reheat coils to reduce the SHR
in single-package units, no known systems dynamically combine
features that, by applying multiple dehumidification stages in a
split system configuration, can maintain desired temperature and
humidity conditions even in the absence of cooling loads, through
the full range of climatic conditions in the U.S. and
elsewhere.
SUMMARY
[0013] The most desirable indoor comfort system for humid climates
would use minimal added components to a conventional split air
conditioning system, but would have the capability of dehumidifying
even in a "neutral" condition wherein the building needs neither
heating nor cooling. Using a single refrigerant loop with a
supplemental reheat coil to achieve this condition would require
that the evaporator and the reheat coil have equal and opposite
heat transfers to the air stream. The outdoor coil is then
rejecting a heat quantity equal to the compressor input energy. A
low indoor airflow rate is desirable to maximize latent cooling,
using care not to freeze the evaporator coil.
[0014] In various exemplary embodiments, the systems and methods of
this invention provide automatic, dynamic control of indoor
relative humidity and temperature to achieve specified conditions
by applying multiple stages of dehumidification. Various aspects of
the exemplary embodiment include the capability to remove moisture
from outside ventilation air supplied to maintain indoor air
quality at times when no heating or cooling is needed. Still
another aspect is the ability to maintain a specified indoor
relative humidity through a wide range of climates and seasonal
conditions. For economic viability, such systems should readily
integrate with conventional heating and cooling components,
applying the fan, coil, and condensing unit to both sensible
cooling and dehumidification functions.
[0015] In various exemplary embodiments, the systems and methods of
this invention surpasses the efficiency of air conditioners
combined with stand-alone dehumidifiers, by rejecting condenser
heat developed in the dehumidification process to outdoors instead
of indoors.
[0016] In various exemplary embodiments, the systems and methods of
this invention efficiently and effectively dehumidifies outside
ventilation air supplied to buildings for the purpose of
maintaining indoor air quality.
[0017] In various exemplary embodiments, the systems and methods of
this invention combines indoor cooling and dehumidification
components into a single unit to facilitate installation and reduce
cost.
[0018] These and other objects and advantages will be apparent to
those skilled in the art in light of the following disclosure,
claims and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The invention will be described in detail with reference to
the following drawings in which like reference numerals refer to
like elements and wherein:
[0020] FIG. 1 is a schematic diagram of the refrigeration and
control components of the invention showing alternate refrigeration
flow paths for the various dehumidification stages;
[0021] FIG. 2 is a schematic diagram of the refrigeration and
control components of the invention showing alternate refrigeration
flow paths for the various dehumidification stages; and
[0022] FIG. 3 is a schematic diagram of the refrigeration and
control components of the invention showing alternate refrigeration
flow paths for the various dehumidification stages.
DETAILED DESCRIPTION OF EMBODIMENTS
[0023] An exemplary embodiment of the systems and methods described
in this disclosure comprises a set of vapor compression cooling
components that can respond to a wide range of sensible and latent
cooling loads, and control components with appropriate logic for
automatically maintaining indoor temperature and relative humidity
within close tolerances. The embodiment can condition either
re-circulated indoor air, outside ventilation air supplied to
buildings to maintain indoor air quality, or a mixture of the two.
Exemplary components of such a system include a compressor, a
condensing coil, a condenser fan, an indoor blower, an evaporator
coil, a reheat coil, a refrigerant receiver, a thermostatic
expansion valve, solenoid valves for switching refrigerant flow, a
check valve, "pressure-differential check valves" (PDCV's),
temperature and humidity sensors, and controls for selecting an
operating mode based on sensed conditions.
[0024] With reference to FIG. 1, an integrated dehumidification
system 100 comprises an outdoor-condensing unit 1, an indoor unit
40, refrigerant lines 7 and 13 that connect the condensing unit 1
and the indoor unit 40, and a control system 30.
[0025] The condensing unit 1 includes a compressor 2, condensers 3,
a cabinet 4, and a condenser fan 5 driven by a condenser fan motor
6. Major components of the indoor unit 40 includes an evaporator
coil 12, a reheat coil 8, a blower 21 driven by motor 22, automatic
valves 14 and 15, and an enclosing cabinet 41. The indoor unit also
includes PDCV's and refrigerant lines as will be discussed with
respect to the specific dehumidification stages. The control system
30 includes a thermostat and logic board 33, switching/relay boards
34 in the indoor unit and 35 in the outdoor condensing unit 1, and
indoor air sensors for temperature 31 and humidity 32, and an
optional coil freeze sensor 37.
[0026] In an exemplary embodiment, the integrated dehumidification
system 100 includes four dehumidification modes. In an exemplary
embodiment, a "Stage 1 dehumidification" mode has the lowest latent
cooling capability and the highest SHR and may use a refrigerant
flow schematic similar to that for a conventional split air
conditioning system. Low pressure refrigerant vapor is compressed
to a superheated, high pressure vapor state in the compressor 2 of
the outdoor condensing unit 1. The vapor then passes through the
condenser coils 3 where the vapor condenses to a liquid state,
giving up heat, before leaving the outdoor condensing unit 1
through the refrigerant line 7. During this process, the condenser
fan 5, driven by the fan motor 6, induces outdoor airflow across
the condenser coils 3 to discharge heat to outdoor air. Although
FIG. 1 shows two condenser coils 3 in parallel, one "wrap-around"
coil may be used as well.
[0027] After the liquid refrigerant enters the indoor unit 40
through the refrigerant line 7, the liquid refrigerant passes
through an open automatic control valve 14. In the exemplary
embodiment, there are multiple parallel paths through lines 9, 17,
19, and 42, toward the evaporator coil 12. But all of these paths
are blocked by either a check valve 36 or PDCV's 16a, 16b that have
pressure drop settings higher than the downstream pressure drops
between the entering refrigerant line 7 and an expansion device 11.
After passing through the automatic control valve 14, the
refrigerant flow proceeds through the line segment 23 into the
liquid receiver 10, then through another open automatic control
valve 15 via the line segment 20, and on through the expansion
device 11. The expansion 11 restricts refrigerant flow and causes
the high pressure liquid to begin a change of state from a liquid
to a low pressure gas. From the expansion device 11, the
refrigerant enters the evaporator coil 12 where the change of state
is completed. As the refrigerant evaporates at the evaporator coil
12, the refrigerant absorbs heat from the air stream 26 driven
through the air path 18 across the evaporator coil 12 by the indoor
blower 21 powered by the blower motor 22. The heat absorbed by the
refrigerant results in cooling of the air stream 26. If the
surfaces of the evaporator coil 12 are cooler than the dew point
temperature of the air stream 26, moisture will condense on the
coil 12 and drip into a drain pan 27 from which it can be drained
through condensate drain 28. From the evaporator 12 the low
pressure refrigerant vapor returns through the refrigerant line 13
to the compressor 2 of the outdoor condensing unit 1.
[0028] With continuing reference to FIG. 1, "Stage 2
dehumidification" mode of the exemplary embodiment uses a "reduced
air flow" strategy. In Stage 2, the speed of the blower motor 22 is
reduced, thereby reducing the flow rate of the air stream 26. The
reduced speed of the blower motor 22 increases air stream residence
time and causes a reduction of the evaporating temperature in the
evaporator coil 12, thereby increasing dehumidification. The
control system 30 is programmed with staged thresholds for indoor
relative humidity. For example, when a first user-selected
threshold is exceeded, the control system 30 will shift the
operating speed of the blower motor 22 from a normal speed to a
programmed lower speed. If indoor humidity later drops slightly
below the first user-selected threshold, the control system 30
returns the operating speed of the motor 22 to the normal
speed.
[0029] FIG. 2 shows the refrigerant flow in the indoor condensing
unit 40 when a second humidity threshold is exceeded. In this
"Stage 3 dehumidification" mode the automatic control valve 14
remains open, and the refrigerant flow passes through the receiver
10 as in Stages 1 and 2. In Stage 3 the refrigerant then flows
through the line 42 toward the reheat coil 8, rather than through
the line 20 toward the evaporator coil 12, because the automatic
control valve 15 in the line 20 is now closed. A PDCV 16a that
requires approximately 5 psi of pressure to overcome its spring
force is located between the refrigerant line 7 and the
intersection of the lines 42 and 9 to prevent the refrigerant from
flowing directly into the reheat coil 8 in the first three
dehumidification stages. A check valve 36 in the line 19 prevents
bypassing of the reheat coil from the line 23 above the receiver 10
to the line 17 toward the expansion device 11. From the exit of the
reheat coil 8, all refrigerant flows through the line 17 and
through PDCV 16b to the expansion device 11 and the evaporator coil
12 before completing the circuit back to the compressor 2 of the
outdoor condensing unit 1 through the refrigerant line 13. In this
circuit, the liquid refrigerant from the condenser 3 (see FIG. 1)
is sub-cooled in the reheat coil 8. This process increases
dehumidification mostly by adding heat back into the air stream 26
downstream of the evaporator coil 12, which reduces the cooling
delivery rate and causes the dehumidification system 100 to run
longer to satisfy the cooling load. Longer operation with a
constant surface temperature pattern for the evaporator coil 12
results in more moisture removal as long as part of the surface of
the evaporator coil 12 is colder than the dew point temperature of
the entering air stream 26. This circuit offers an additional
dehumidification benefit by sub-cooling the liquid refrigerant
below the condensing temperature to lower the evaporating
temperature and thus increase the rate of moisture removal. The
control system 30 (see FIG. 1), implements Stage 3 dehumidification
by closing the automatic control valve 15 when a second
user-selected threshold is exceeded.
[0030] If the humidity sensor 32 (see FIG. 1) indicates that a
third user-selected threshold has been exceeded, the control system
30 will initiate a "Stage 4 dehumidification" mode operation as
shown in FIG. 3. In Stage 4 mode, the automatic control valve 15 is
opened and the automatic control valve 14 is closed so that the
incoming refrigerant flow from the outdoor condensing unit 1 (see
FIG. 1) is forced through the line 9 with a PDCV 16a into the
reheat coil 8. The flow then proceeds through a low pressure drop
check valve 36 in line 19 before entering the receiver 10. The PDCV
16b imposes a greater pressure drop in line 17 than the sum of the
pressure drops in the lines 19, 20, the receiver 10, and the open
valve 15. As a result, flow is forced through the receiver 10. From
the receiver 10 the refrigerant flow proceeds through the open
automatic control valve 15 in the line 20 and through the expansion
device 11 before entering the evaporator coil 12. With the receiver
10 downstream of the reheat coil 8, the refrigerant can partially
condense in the reheat coil 8 because the refrigerant will
preferentially condense in the coldest available location. Because
the reheat coil 8 is in the low temperature air stream 26 leaving
the evaporator coil 12, the reheat coil 8 will be typically be
cooler than the condensing coil 3 (see FIG. 1) located in outdoor
air. As a result the refrigerant partially condenses in the reheat
coil 8, delivering more reheat than was available in Stage 3
dehumidification mode.
[0031] In an exemplary embodiment, it is possible to operate in the
Stage 4 dehumidification mode without either cooling or heating the
supply air stream. In this "neutral" dehumidification case,
sufficient condensing occurs in the reheat coil 8 to balance the
cooling delivered at the evaporator coil 12, and the heat being
discharged at the condensing unit 1 equals the equivalent heat
input of the compressor 2 (see FIG. 1). In contrast, a conventional
dehumidifier adds all heat, including the compressor input heat, to
the space in which it is enclosed. Without applying controls at the
condensing unit, there are two ways to accomplish the neutral
dehumidification state. One is to combine a relatively small
condensing coil 3 (FIG. 1) and a relatively large reheat coil 8.
This sizing approach will probably compromise Stage 1 (normal
cooling) operation. The other is to combine a normally-sized
condenser coil 3 with a large reheat coil 8, and operate the blower
motor 22 at a sufficiently low speed that air leaving the
evaporator coil 12 is just above freezing temperature. (An
evaporator coil surface temperature sensor 37 (see FIG. 1) should
be used to increase the airflow rate when there is danger of
freezing moisture on the evaporator coil 12.) This strategy
maximizes dehumidification, and causes the lowest possible
temperature entering the reheat coil 8, increasing the amount of
refrigerant condensation that occurs in the reheat coil. However,
this strategy may drop refrigerant pressures sufficiently to trip
the low pressure cut-out-typically included in the condensing unit
1. Thus, care must be used in sizing the coils and compressor.
[0032] An aspect of such a dehumidification system is that no
control interaction with the condensing unit is required. The
system may also be coupled with any available condensing unit.
However, applying added controls to the condensing unit components
offers improved dehumidification control. Such condensing unit
controls provide two additional strategies or stages of
dehumidification that can further reduce the SHR without penalizing
Stage 1 cooling operation. For example, a first strategy may be to
couple the air handler 40 (see FIG. 1) with a two-speed condensing
unit 1. A two-speed condensing unit typically includes a two-speed
compressor 2 and a two-speed condenser fan motor 6. Control access
to these components offers the opportunity for additional
dehumidification benefits. For example, if a one-speed compressor
moves into an unacceptably low pressure operating regime in the
Stage 4 dehumidification mode, a solution may be to select a
two-speed condensing unit and shift to low speed for the Stage 4
operation. Another potential benefit of control access to the
condensing unit is the opportunity to reduce the speed of the
condenser fan motor 6 to reduce condenser heat transfer in the
Stage 4 dehumidification mode. In an extreme case, the condenser
fan motor 6 can be disabled so that most of the condensation occurs
in the reheat coil. The system will then operate nearly like a
packaged dehumidifier, causing a net heat addition to the
space.
[0033] With the multiple stage dehumidification strategies
described here, it is possible to satisfy both temperature and
humidity targets in indoor spaces through a full range of outdoor,
indoor, and ventilation conditions. When control access to the
condensing unit is available, the system can even dehumidify in the
absence of cooling loads, or can deliver heat while dehumidifying
if desired. In each stage of the dehumidification operation, the
system can operate at maximum potential efficiency by rejecting the
most heat possible to the outdoor environment while satisfying the
indoor temperature and humidity targets.
[0034] Although the invention has been shown and described with
respect to a preferred embodiment thereof, it should be understood
by those skilled in the art that various changes and omissions in
the form and detail thereof may be made therein without departing
from the spirit and scope of the invention. For example, the system
has been described assuming an air-cooled condenser, which is
currently the most common condenser type. However, the multi-stage
dehumidification strategies described here may as easily be applied
with water-cooled condensers or storage-type condensers such as
hydronic or direct refrigerant ground-loops.
* * * * *