U.S. patent application number 09/772306 was filed with the patent office on 2001-06-21 for high-efficiency air-conditioning system with high-volume air distribution.
Invention is credited to Kopko, William L..
Application Number | 20010003902 09/772306 |
Document ID | / |
Family ID | 26724184 |
Filed Date | 2001-06-21 |
United States Patent
Application |
20010003902 |
Kind Code |
A1 |
Kopko, William L. |
June 21, 2001 |
High-efficiency air-conditioning system with high-volume air
distribution
Abstract
This invention provides a fundamentally new approach to air
conditioning. In a conventional air-conditioning system air the
full volume of air is cooled below the dew point to provide both
sensible and latent cooling. In the new system, dehumidification
and sensible cooling functions are preferably separate. The
separate dehumidification allows for much higher supply air
temperatures, preferably within about 10.degree. F. of the space
temperature. Low-velocity air distribution through a ceiling plenum
or a vent into the space allows for very low fan static pressures,
which greatly reduces fan energy use compared to conventional
ducted systems. The low static pressures and high supply-air
temperatures allow the use of existing drop ceiling construction
with little modification. The system can also include low-cost
thermal storage. Latent thermal storage is in the form of a
concentrated liquid desiccant solution. Chilled water storage is
another option. The result is a major improvement in energy
efficiency and comfort while reducing installed cost and peak
electrical demand of the system.
Inventors: |
Kopko, William L.;
(Springfield, VA) |
Correspondence
Address: |
William L. Kopko
8705 Cromwell Drive
Springfield
VA
22151
US
|
Family ID: |
26724184 |
Appl. No.: |
09/772306 |
Filed: |
January 29, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09772306 |
Jan 29, 2001 |
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09331758 |
Jun 25, 1999 |
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6185943 |
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60046676 |
May 16, 1997 |
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Current U.S.
Class: |
62/89 ; 62/411;
62/426 |
Current CPC
Class: |
F24F 2003/003 20130101;
F24F 2003/144 20130101; F24F 3/1417 20130101; F24F 3/00 20130101;
F24F 3/14 20130101; F24F 2011/0006 20130101; F24F 1/00075 20190201;
F24F 13/072 20130101 |
Class at
Publication: |
62/89 ; 62/411;
62/426 |
International
Class: |
F25D 017/06 |
Claims
I claim:
1. A method for air conditioning a building space comprising:
Cooling, dehumidifying, and blowing air to produce a supply air
stream with a volumetric flow rate of at least about 5000 cubic
feet per minute with a temperature that is above about 63.degree.
F. with a relative humidity of less than 90%; Supplying said supply
air stream in an approximately horizontal direction above an
occupied portion of the building space at a maximum speed of less
than about 1000 feet per minute; and Mixing air from said supply
air stream into air in the occupied portion of said building
space.
2. The method for air conditioning a building space of claim 1
further comprising drawing at least a portion of air that is cooled
to produce said supply air stream as a return air stream from the
occupied portion of said building space.
3. The method for air conditioning a building space of claim 2
wherein said supply temperature is at least about 67.degree. F.
4. The method for air conditioning a building space of claim 3
wherein the air speed is less than about 500 feet per minute.
5. The method for air conditioning a building space of claim 4
wherein the supply relative humidity is less than about 75
percent.
6. The method for air conditioning a building space of claim 5
wherein the method of supplying air comprises supplying air through
a ceiling plenum to vents in a suspended ceiling, and then into the
building space.
7. The method for air conditioning a building space of claim 5
wherein the method of supplying air comprises delivering air to
said building space in an approximately horizontal direction
through a vent located above the occupied portion of said building
space.
8. The method of claim 1 wherein said dehumidifying is accomplished
by direct contact between air and a liquid desiccant.
9. The method of claim 8 further comprising cooling said liquid
desiccant.
10. The method of claim 8 further comprising regenerating said
desiccant using heat from a condenser.
Description
[0001] This application is a continuation-in-part of application
Ser. No. 09/331,758 filed on Jun. 25, 1999. Applicant claims
benefit of co-pending provisional U.S. application Ser. No.
60/046,676 that was filed on May 16, 1997.
BACKGROUND
[0002] Air-conditioning manufacturers, architects, and professional
design engineers have expended huge efforts in optimizing the
design of building air-conditioning systems. Annual sales of
equipment amount to tens of billions of dollars and annual energy
use for heating and cooling have similar values. In addition the
costs associated with reduced productivity of workers because of
uncomfortable environmental conditions may be several times these
figures, although difficult to quantify. Yet despite this effort
the fundamental process for air conditioning buildings has remained
essentially the same since the introduction of the first air
conditioners in the 1920's. Conventional approaches to air
conditioning have inherent problems that severely limit their
efficiency, raise installed cost, and frequently produce poor
comfort conditions in the building space. Solving these problems
requires major changes in the basic configuration of
air-conditioning systems.
[0003] Conventional air-conditioning systems use a relatively small
volume of air for cooling. The typical arrangement uses a
vapor-compression refrigeration system to cool a mixture of return
air and outside air to approximately 55.degree. F. and then
distribute the cooled air through ducts to the building space. The
low supply air temperatures are a result of the need to cool air
below its dew point to remove moisture. The low air temperatures
are also necessary to meet the sensible cooling needs of the space
without excessively large ducts.
[0004] There are several important problems with this approach. The
first is related to fan energy use. Since air flow is through
relatively restrictive ductwork, fan static pressures are quite
high. Typical pressures range from less than 0.5 inches of water
for residential systems to as much as 5 to 10 inches of water for
large commercial cooling systems. These high static pressures
result in large energy use from the fan, which also adds to the
cooling load for the rest of the system. In many commercial
systems, the fan heat accounts for as much as 20 to 30 percent of
the total cooling load for the building. The net result is a very
inefficient cooling system.
[0005] A second problem is with high compressor energy required.
The low supply air temperatures mean even lower evaporating
temperatures, typically 40 to 50 F for the compressor system. The
low evaporating temperatures create more work for the compressor,
which further reduces the efficiency of the system.
[0006] A third problem is poor indoor air quality associated with
high duct humidity. Conditions over 70% relative humidity allow the
growth of mold and fungus in ductwork. The relative humidity in the
supply ducts for conventional systems is frequently over 90%. In
addition water from wet coils wets drain pans and can also wet
nearby ductwork. These wet conditions create a potential breeding
grounds for many types of microbes that can cause health and odor
problems.
[0007] A fourth issue is high noise levels with conventional
systems. The high static pressure creates a need for a powerful fan
that usually is quite noisy. In addition, metal ducts transmit the
noise quite well. Common fixes for the noise problem include the
use of fiberglass duct liners. Unfortunately these liners increase
cost and pressure drop and also can contribute to problems with
molds given the high relative humidity in most ducts.
[0008] A fifth problem is the potential for drafts with
conventional cooling systems. The low supply air temperatures and
high velocities create the possibility of extremely uncomfortable
conditions near the vents. Designers must take special care to
ensure adequate mixing of room air and supply air to reduce drafts
to acceptable levels.
[0009] A sixth problem is the need for simultaneous heating and
cooling. Most office buildings have a single air handling system
for the interior and exterior zones. In cold weather the interior
zones still need cooling because of heat from people, lights,
equipment, etc., while the exterior needs heat. The usual solution
is to supply cool air to the entire building in order to satisfy
the cooling needs of the interior. Perimeter heaters or heaters in
the ducts servicing the exterior zones then provide the heat
necessary to satisfy the heating load and overcome the cooling from
the supply air.
[0010] The objective of the present invention is to improve energy
efficiency and to reduce or eliminate the problems associated with
existing air conditioning systems.
SUMMARY OF THE INVENTION
[0011] The invention uses a fundamentally different approach to air
conditioning. The approach involves the use of a large volumetric
flow rate of air with a temperature that is close to that of the
building space for space heating and cooling. A separate
dehumidification system is used in humid climates. In one preferred
embodiment, a ceiling plenum is used as for the supply air and air
returns through the space. In another preferred embodiment, supply
air enters the space through a vent near the ceiling along one wall
and returns near the floor along the same wall. Pressure drops are
kept very low because of the low air velocities. The low pressure
and small temperature difference between the supply air and the
room air allow for very low energy use and improved comfort.
DESCRIPTION OF THE FIGURES
[0012] FIG. 1 shows a preferred embodiment that uses a ceiling
plenum to distribute supply air.
[0013] FIG. 2 is a preferred embodiment that returns air through a
channel in a window.
[0014] FIG. 3 is a preferred embodiment for buildings without
ceiling plenum.
[0015] FIG. 4 is an alternate embodiment that uses a cooled liquid
desiccant for both cooling and dehumidification.
[0016] FIG. 5 is another alternate embodiment that uses liquid
desiccant for dehumidification.
DESCRIPTION OF THE INVENTION
[0017] Preferred embodiment: FIG. 1 shows a preferred embodiment of
the invention. Fan, 1, draws air across coil, 2, where it is cooled
or heated to create a supply air stream 40. Ceiling, 3, defines the
bottom of a ceiling plenum, 4, that serves as a flow path for air
leaving the fan. Vents, 5, provide openings into that allow supply
air to mix with air in an occupied portion of the building space,
6. Vent, 7, provides an opening to allow air, 8, to return through
a partition 42 in the space. A separate ventilation system, 9,
provides dehumidified outside air, 10, to the space and recovers
energy from exhaust air, 11.
[0018] The fan may be a propeller or centrifugal fan. It would have
to provide only a small static pressure, typically less than 0.2
inches of water. The low static pressures favor the uses of
low-speed fans, which should help to reduce fan sound levels and
should reduce fan energy use.
[0019] The coil can contain water or brine or a refrigerant. The
supply air temperature for cooling would normally be greater than
about 63.degree. F. and preferably about 68 to 70.degree. F. The
high temperatures prevent unwanted heat transfer through the
ceiling and help to keep the relative humidity in the plenum below
70%. The coil temperature should be a least a few degrees above the
dewpoint of the return air and preferably as close as practical to
that of the supply air temperature. The high coil temperatures
minimize the compressor energy required for cooling and eliminate
problems associated with wet coils.
[0020] The ceiling would normally be a suspended ceiling. The tiles
should sufficiently rigid to withstand the pressure of the plenum,
which would normally be less the 0.1 inches of water. The low
static pressures in the plenum reduce the loads on the tiles and
reduce the problems associated with leaks around the edge of the
tiles. The tiles should provide sufficient resistance to leakage
and conduction to prevent undesirable heat transfer between the
plenum and the space. In many cases, existing suspended ceilings
would meet these requirements without any significant
modification.
[0021] This configuration preferably uses very low velocities for
the supply air compared to conventional duct systems. According to
the ASHRAE Handbook 1985 Fundamentals for a conventional
"low-velocity" duct with at least 10,000 CFM flow rate, the duct
would have a velocity of 1300 to 2600 feet per minute. For the
present invention at similar volumetric flow rates, the maximum
supply air velocity would be less than about 1000 feet per minute
and preferably about 100 to 400 feet per minute. This lower
velocity is readily achievable because of the huge flow area
available in a ceiling plenum compared to conventional ductwork.
The low velocities assure low flow noise. They also provide very
low pressure drops, which helps to assure proper air distribution
to the entire building.
[0022] The vents, 5, are designed to handle a large volume of air
with a minimal pressure drop, typically only a few hundredths of an
inch of water. Adjustment may be manual or automatic. The vents
should introduce sufficient mixing so as to prevent undesirable
drafts.
[0023] Vents, 7, that allow air to move between zones should be
able to handle the required airflow with pressure drops that are
smaller than the pressure drop across the ceiling vents. In
buildings with raised floors, another option is return air though
the space under the floor.
[0024] Ideally the vents would have a control mechanism that is
responsive to space temperature without need of a source of outside
power. For example wax actuators and shape-memory actuators are
capable of producing significant motion in response relatively
small changes in space temperature and could be used to control air
flow through the vents. Co-pending provisional U.S. application No.
60/077008 describes a roller damper mechanism that can work with
these types of actuators.
[0025] While this drawing shows the ventilation air entering the
ceiling plenum, the exact location where the air is added to the
building is somewhat arbitrary, so long as the air temperature is
close to that of the space. Likewise the exhaust air can be drawn
from anywhere in the building and normally at least a portion would
come from toilet exhaust. The ventilation/dehumidification system
should incorporate an enthalpy wheel or other heat recovery device,
and would preferably be a desiccant-based system capable of
providing low dewpoints. The temperature of the air should be close
to that of the building space, although this is not required if the
air is mixed into the supply air. The ventilation system should
also provide a small positive pressure for the building space to
reduce possible of infiltration of outside air.
[0026] While the preferred dehumidification system is combined with
a heat recovery ventilation system, many other configurations are
possible. For example, the dehumidification system can simply
further cool a portion of the air leaving the cooling coil so that
its temperature drops below the dewpoint. A heat pipe or other
device for exchanging heat between the air on the coil and the air
leaving the coil can increase the amount of moisture remove
compared to sensible cooling, which can reduce energy use. This
arrangement is acceptable in cases where adequate outside air is
available to the space from infiltration or other sources. Numerous
other dehumidification systems that appear in the prior art could
be used in the new system. The ASHRAE Handbooks describe many of
these dehumidification options.
[0027] In dry climates the dehumidification system can be
eliminated, although sensible heat recovery may still be a valuable
option. There is also potential for eliminating the need for a
compressor, with sensible cooling provided with an indirect
evaporative cooler or cooling tower.
[0028] The table below shows the massive energy advantages of the
invention when compared to a conventional air-conditioning system
in handling the sensible cooling load:
1 Comparison of Energy Use for a Conventional Cooling System and
New Invention new conventional high-flow units zone sensible load
20 20 btu/hr/ft2 supply air temperature 55 70 deg F room
temperature 75 77 deg F cfm/ton of total sensible load 556 1587
cfm/ton fan static pressure 6 0.2 inches H2O fan static efficiency
70% 50% motor efficiency 90% 80% fan power (hp/1000 CFM) 1.349
0.063 hp/1000 cfm fan power (w/CFM) 1.12 0.06 w/cfm fan heating
3.53 0.19 deg F fan heat (% of sensible load) 18% 3% coil load 23.5
20.5 btu/hr/ft2 chilled water temperature 45 65 deg F chiller
energy use 0.6 0.3 kw/coil ton chiller energy use 0.706 0.308
kw/building ton fan energy use 0.528 0.091 kw/building ton total
energy use 1.234 0.399 kw/building ton percent energy saved
67.7%
[0029] This analysis shows that the new system can save over two
thirds of the energy used for sensible cooling at design
conditions. At off-design conditions the savings can be even larger
because of the increased availability of free cooling because of
the much high chilled water and supply air temperatures. This free
cooling option means that the chiller may be shut down for a large
portion of what is normally the cooling season.
[0030] The system should also have a major advantage in handling
latent load. The use of an enthalpy wheel or other suitable heat
exchanger can reduce loads associated with bringing in outside air
by 80%. Heat recovery also greatly reduces heating requirements.
For most office and retail buildings, the outside air is the main
source of moisture. Use of a gas-driven desiccant system also gives
the opportunity to greatly reduce electric demand charges while
efficiently handling the ventilation load. Electrically driven
systems are also an option.
[0031] Use of a separate dehumidification system also greatly
reduces the need to run the whole system when the building is
unoccupied. Current systems frequently require continuous operation
during conditions of high humidity in order to prevent excessive
accumulation of moisture in building materials during off periods.
The present invention allows the operation of the dehumidification
system alone, which greatly reduces operating costs while providing
good moisture control.
[0032] Embodiment with Alternate Return-Air Configuration: FIG. 2
shows a variation of the first embodiment that is designed to
greatly reduce the need for heating. The basic idea is to move a
large volume of air from the interior toward the exterior of the
building. The system also draws return air from the building
envelope. Return air, 13, is drawn upward through channel, 19, that
is formed between exterior glazing, 12, and interior glazing, 17 of
a window 44. This arrangement effectively removes any cold air
associated with heat loss through glazing, 12 and an exterior wall,
18. The return air then moves into channel, 14. Fan, 15, draws air
from the channel through coil, 16, and then discharges the
conditioned air into the ceiling plenum 4 as a supply air stream
41.
[0033] This configuration several advantages that greatly reduce
winter heating requirements. The first is that it removes cold from
the building envelop before it enters the conditioned space. The
second is that it then moves this air toward the interior so as to
provide necessary cooling. Third it then uses the air returning
from the interior to provide as source of warm air for the exterior
zones. This system should not require any significant amount of
heat so long as the interior heat generation exceeds the exterior
heating load. Proper insulation of windows and walls can
effectively eliminate the need for heat in most larger buildings
even in the most severe climates. The only time that heat would
normally be required, would be if the building were unoccupied for
a long period of time with limited sunlight. Under these
circumstances, the coils provide heat to warm the entire
building.
[0034] FIG. 3 shows a third preferred embodiment of the invention.
This configuration is suitable in retail space or similar
applications with large open areas and few obstructions near the
ceiling. Fan, 23, moves supply air, 20, from coil, 24, through
vent, 25, to mix with air in building space, 6. The air returns
through register, 21, and return duct, 22, back to coil, 24. As
with the other embodiments, a separate dehumidification system
supplies outside air and recovers heat from exhaust air.
[0035] A key feature of this embodiment is the combination of high
air volume, high temperature, low velocity, and low relative
humidity of the supply air compared to conventional systems. The
preferred velocity of the air flowing through the vent is low, less
than 1000 feet per minute and preferably about 100 to 500 feet per
minute. The air volume flow requirements are large, typically over
twice that of convention systems per unit of cooling capacity,
which corresponds to at least 10,000 CFM for a small commercial
building (5 to 10-ton load). For a typical retail building (50,000
to 100,000 square feet) the volumetric flow rate amounts to over
100,000 CFM. A preferred supply air temperature is high, at least
about 63.degree. F. and preferably 68 to 70.degree. F. The relative
humidity of the supply air is low compared to conventional systems,
less than about 90 percent and preferably about 75 percent or
lower. The combination of low velocity, high air volumetric flow
rate, and high supply air temperature allows for a very long throw
of 100 feet or more without risk of cold, high-velocity drafts. The
low relative humidity of the supply air assures proper humidity
control in the space. These supply-air conditions provide comfort
in the building space in addition to providing great opportunities
for energy savings.
[0036] The large volumetric flow rates and relatively warm
temperatures of the supply air allow for very long throws that may
be necessary to supply air to a large space. The higher supply
temperatures also greatly reduce the risk of uncomfortable drafts
in the space. As with the other embodiments, this system has a
large advantage in efficiency because of the high coil temperatures
and low fan static pressures. It should have a major first cost
advantage since it virtually eliminates the need for ductwork. One
disadvantage is that it does not provide local temperature control
within the building space, which may limit its application.
[0037] Cooled-Desiccant Embodiment: FIG. 4 shows an embodiment that
uses a cooled liquid desiccant for both cooling and
dehumidification for comfort air conditioning in a building 140.
This embodiment uses two chillers. A water-cooled chiller 100
includes a water-cooled condenser 102 and a desiccant cooler 104. A
condenser water pump circulates cooling water through the condenser
102 to a cooling tower 106.
[0038] The second chiller is a desiccant-cooled chiller, 110. It
comprises a desiccant-cooled condenser 112 and a desiccant cooler
114. A condenser pump 118 circulates a liquid desiccant through the
condenser to a cooling tower 116. The waste heat from the condenser
cools heats the desiccant fluid, which cause water to evaporate out
of the desiccant and creates concentrated desiccant. The desiccant
cooling tower should be of special design to ensure material
compatibility and prevent excessive loss of desiccant material.
[0039] A desiccant loop provides sensible and latent cooling to a
building 140. The desiccant loop comprises a cooled-desiccant pump
120 the pumps desiccant through the desiccant coolers 114 and 104.
A supply desiccant line 130 supplies the cooled desiccant to an air
handler 138. A return desiccant line 132 returns the desiccant from
the air handler to the cooled-desiccant pump 120 to complete the
loop.
[0040] The air handler 138 uses cooled desiccant to cooled and
dehumidify a mixed air stream 156. The mixed-air stream 156 is a
mixture of outside air 152 and return air 154 that is moved by a
fan 150. A portion of the mixed-air stream leaves the building as
exhaust air 154. The remaining mixed-air stream enters a filter 158
and then goes through a first, second, and third direct-contact
heat exchangers 160, 162, and 164 respectively. The direct-contact
heat exchangers allow simultaneous heat and mass transfer between
the air and the cooled desiccant and are preferably arranged in a
counter-crossflow configuration.
[0041] The first direct-contact heat exchanger receives desiccant
from a first sump pump 168. A first sump 174 collects desiccant
that drains off of the first direct-contact heat exchanger.
Likewise the second direct-contact heat exchanger receives
desiccant from a second sump pump 166 and has a second sump 172.
The desiccant collected in the second sump 172 supplies the first
sump pump 168. A third direct-contact heat exchanger 164 receives
desiccant from the supply desiccant line 130. Air flows through the
first then the second and the third direct-contact heat exchangers
so as to approximate a couterflow configuration. This setup allows
for a close approach temperature. While three passes of cooling are
shown in FIG. 4, other numbers a possible and may be desirable
depending on the details of the design of the air handler. The
preferred number is between 1 and 5 passes.
[0042] A supply air stream 180 exits in an approximately horizontal
direction from the air handler 138. As with the previous
embodiments as for example FIG. 3, the supply air has a relatively
high temperature, low speed, and low relative humidity compared to
conventional designs. The preferred values for these conditions are
similar to those for the earlier embodiments. The supply air stream
gradually slows as it moves away from the air handler and mixes
into the air in an occupied portion 142 of the building 140.
[0043] The preferred desiccant material is calcium chloride,
although other materials such as various glycols, lithium chloride,
or lithium bromide are possible. The advantages of calcium chloride
include its low-cost, availability, and very low toxicity. Its long
history of use as a brine for refrigeration applications means that
compatibility with materials of construction is well known. Because
the required relative humidity is relatively high (about 70%)
compared to the low values required in most other desiccant
applications (typically about 30% or less), the relatively high
equilibrium vapor pressure of calcium chloride solutions is not a
problem.
[0044] Alternate liquid desiccant embodiment: FIG. 5 shows an
embodiment with liquid-desiccant dehumidification with a single
chiller. The chiller 200 comprises a liquid cooler 214 that
evaporates refrigerant and supplies refrigerant vapor to a
compressor 215. While the chiller is shown outside, it can also be
located inside a building to be cooled. The discharge of the
compressor goes into an auxiliary condenser 212 the heats
desiccant. The refrigerant leaving the auxiliary condenser then
goes into a main condenser 202 that exchanges heat with condenser
water. Liquid refrigerant leaves the main condenser through a
liquid line 217 that includes valve, orifice, or other pressure
drop.
[0045] The main condenser is part of a cooling tower loop. A
condenser-water pump 208 moves water through the condenser to a
cooling tower 206, which normally cools the water by evaporation
into the atmosphere. Dry cooling towers are also an option.
[0046] The auxiliary condenser is used to heat liquid desiccant. A
desiccant pump 218 move desiccant through the auxiliary condenser
to a direct-contact heat exchanger 216 that is a type of cooling
tower. The direct-contact heat exchanger evaporates water from the
warm desiccant. The majority of desiccant leaving the heat
exchanger returns through a control valve 282 to the desiccant
pump. The rest goes through line 284 to a desiccant storage tank
234. The desiccant storage tank keeps a supply of desiccant for
dehumidification when the auxiliary condenser is not operating.
[0047] The operation of the condenser pumps allows for efficient
production of chilled water and concentrated desiccant. To produce
concentrated desiccant, the chiller is run with the desiccant pump
218 is on, and the condenser water pump 208 turned off. The chiller
then runs with a relatively high condensing temperature (about 100
to 130.degree. F.) to regenerate the desiccant. When additional
concentrated desiccant is not required, the desiccant pump is
turned off; and the condenser water pump 208 is turned on, which
allows the chiller to run with a lower condensing temperature
(typically less than 105.degree. F.). When no chilled water is
required, the chiller is turned off. While FIG. 5 shows a series
refrigerant flow configuration for the condensers, the condensers
can also share a common shell (shellside refrigerant) with separate
tube bundles and liquid connections.
[0048] The storage tank is preferably sized to provide desiccant
for at least an hour or two of operation. Storage capacity with at
8 to 12 hours of storage allows for significant demand shifting.
The volume of storage required is small since because the desiccant
uses the heat of vaporization of water as the storage mechanism.
Latent energy storage of several hundred Btu/lbm is possible. The
storage capacity of the desiccant related primarily to
concentration of solution, not temperature, so insulation of the
tank is not normally required.
[0049] A desiccant pump 290 draws desiccant from the bottom of the
storage tank, which normally contains the most-concentrated
desiccant, and move the desiccant through a desiccant supply line
292. The desiccant supply line adds concentrated desiccant to a
warm desiccant line 300 that is part of fluid circuit includes a
direct-contact heat exchanger 302 in an air handler 238. The warm
desiccant flows into a heat exchanger 296 that cools the desiccant
using chilled water. The desiccant then flows through a
cooled-desiccant line 298 to the direct-contact heat exchanger 302.
A sump 306 collects warm desiccant from the direct-contact heat
changer 302. Most of the desiccant then enters a desiccant pump 304
that pumps it through the warm-desiccant line 300 to complete the
loop. A portion of the desiccant drains from the sump 306 through a
diluted-desiccant line 294, which returns it to the desiccant
storage tank 234, preferably at a location near the top liquid in
the tank.
[0050] The air handler 238 also comprises fan 250 and a coil 260.
The fan 250 draws return air 254 and outside air 252 into the air
handler. A portion of a mixed air stream 256 leaving the fan exits
as an exhaust air stream 254. The rest of the air stream goes
through a filter 258 to a coil 260 and then through the
direct-contact heat exchanger 302, which dries the air with the
desiccant. The air leave the air handler as a supply air stream
280, which flows in a roughly horizontal direction at low speed as
in the earlier embodiments. The supply air 280 mixes with air in an
occupied portion of a building space 242.
[0051] Cooling water from the coil come from the chiller. A chilled
water supply line 230 leaves the water cooler 214 and enters the
heat exchanger 296 that cools the desiccant. The chilled water then
enters the coil 260 and returns to a chilled-water pump 220 through
return line 232. The chilled-water pump 220 pumps the water through
the cooler 214 to complete the chilled-water circuit.
[0052] Some features can be changed while keeping the basic
function of the system. For example, the heat exchanger 296 for
cooling desiccant can be eliminated. Another possibility is to
place the desiccant upstream of the cooling coil. These changes
would increase the desiccant concentration and lower chilled water
temperature necessary to achieve a given supply air temperature and
relative humidity. Another possibility is to uses the auxiliary
condenser as a desuperheater that operates at the same time as the
main condenser. This change is possible with refrigerants that
produce a high discharge temperature, such as R-22, but it is not
normally an option with R-123, which has little superheat. While
the chiller and associated equipment is shown outside, it can also
be located inside the building to be cooled or in a separate
structure.
[0053] Yet another option is to incorporate a heat-recovery heat
exchanger or enthalpy recovery wheel to reduce ventilation energy
requirements. This approach reduces energy use, but may be feasible
in every case depending on the ability to economically recover
energy from the exhaust air. These changes or similar changes or
combinations of changes do not affect the basic function of the
system
[0054] Other possible configurations: There are many possible
variations of these embodiments. For example, through not
preferred, a conventional heat-pipe reheat system with air cooled
below the dewpoint can provide similar supply-air conditions.
Mixing return air and supply air to achieve a high supply air
temperature is also an option, though not preferred.
[0055] Other systems for regenerating desiccant using heat from
combustion or heat from solar energy is another option. The solar
option is explore more fully in a co-pending application entitled,
"Solar air conditioner." Other configurations of chillers or heat
pumps are also possible for supplying heat to regenerate a
desiccant.
[0056] Thermal storage using chilled water is another possibility.
This option is discussed in a co-pending application entitled, "Air
conditioner with thermal storage."
[0057] Summary of the Advantages: To sum up, here are the
advantages of the invention:
[0058] 1. reduced fan energy,
[0059] 2. less compressor energy,
[0060] 3. less ductwork required,
[0061] 4. smaller space requirements,
[0062] 5. reduced heating requirements,
[0063] 6. individual room control possible,
[0064] 7. dry coils (reduced maintenance),
[0065] 8. better indoor air quality,
[0066] 9. low noise,
[0067] 10. no cold drafts,
[0068] 11. increased economizer use possible
[0069] 12. ability to use thermal storage for demand shifting,
and
[0070] 13. efficient dehumidification using liquid desiccant.
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