Abstrict An air-conditioning system for a cabin of a motorized vehicle comprising
of an evaporator and desiccant, where said desiccant is downstream
of evaporator, and said desiccant is a rotor that uses nearby excess
heat to regenerate the desiccant.
Claims What is claimed is:
1. An air-conditioning system for a cabin of a motorized vehicle
comprising of an evaporator and desiccant, where said desiccant
is downstream of evaporator, and said desiccant is a rotor that
uses vehicle's excess heat to regenerate the desiccant.
2. An A/C system as set forth in claim 1 wherein the source of
regeneration heat for the desiccant is hot air coming off the radiator
that is routed into the rotor housing.
3. An A/C system as set forth in claim 1 wherein the source of
regeneration heat for the desiccant is engine coolant exiting the
engine block that is routed to a liquid-to-air heat exchanger to
heat the regeneration air prior to entering the radiator.
4. An A/C system as set forth in claim 1 wherein the source of
regeneration is hot engine exhaust, which after catalytic conversion
which is routed to an air-to-air heat exchanger.
5. An A/C system as set forth in claim 1 wherein the source of
regeneration is excess heat generated by a fuel cell.
6. A method of air-conditioning for a cabin of a motorized vehicle
comprising of an evaporator and desiccant, where said desiccant
is downstream of evaporator, and said desiccant is a rotor that
uses vehicle's excess heat to regenerate the desiccant.
Description BACKGROUND
[0001] This invention relates to dehumidification and cooling in
an enclosed area, in particular, a method and system for climate
control in a motorized vehicle.
BACKGROUND OF THE INVENTION--DESCRIPTION OF PRIOR ART
[0002] This invention relates to dehumidification and cooling in
an enclosed area, in particular, a method and system for climate
control in a motorized vehicle. There exists a strong need for dehumidification
in the enclosed area of a motor vehicle; for safety reasons, i.e.
the windshield can fog up during high humidity conditions, resulting
in reduced driver visibility; comfort of the passengers; and if
the humidity of the cabin can be lowered by thermally activated
means, the compressor power consumption and the size of the direct
expansion (DX) air-conditioning system can be reduced. If the load
on the DX system is reduced through addition of a light component
(i.e. a small desiccant rotor), the benefits include; fuel savings,
reduced shaft horsepower required to operate the compressor, and
possibly weight reduction. With such potential benefits, a design
study of such a system is warranted.
[0003] Different methods of systems to dehumidify and cool air
in motor vehicles have been previously described. U.S. 2002/0002833
A1 describes an A/C system including an evaporator, a desiccant
dryer (located downstream of the evaporator, and a compressor fluidly
connected to the evaporator.) The desiccant dehumidifier in this
system is of the carousel type. This patent explicitly states that
the only sufficient heat source existing in a motorized vehicle
for the regeneration of the desiccant is from the engine exhaust
air, and states that this heat source is undesirable due to safety
reasons. The safety concerns are founded: If the catalytic converter
and the seals separating the process and regeneration air on the
desiccant dryer were to simultaneously fail, the result would be
unburned hydrocarbons and carbon monoxide entering the cabin. However,
the statement that this is the only sufficient heat source is not
true for U.S. 2002/0002833 A1 or for the present invention due to
the configuration of these systems. The other sufficient sources
of regeneration heat for systems of these configurations (desiccant
dryer downstream of evaporator) are the engine coolant leaving the
engine block (185-200 deg F.) and the hot air leaving the radiator
(estimated to be approximately 130 deg F.). These sources of heat,
while unacceptable for systems requiring regeneration temperatures
in excess of 200 deg F. (where the desiccant dryer is upstream of
the evaporator), are acceptable for U.S. 2002/0002833 A1 or for
the present invention since the regeneration temperature requirements
are estimated to be approximately 100-130 deg F.
[0004] U.S. 2002/0092419 A1 describes an air desiccant system for
climate control in a motor vehicle. This system uses a vacuum method
for desiccant regeneration. The desiccant dryer in this system is
of the cartridge type. The only heat source that this patent mentions
in a motorized vehicle for the regeneration of the desiccant is
from the exhaust, and states that this heat source is undesirable.
This patent overlooks the other sources of heat for desiccant regeneration,
as previously stated. Furthermore, there are disadvantages to using
a vacuum for the regeneration of the desiccant. They will be presented
in the following paragraph.
[0005] In any desiccant system that uses low pressure regeneration
air and ambient pressure process air, the seals that separate the
process side from the regeneration side have to be very sturdy,
well-mated to the dryer face and also wear resistant over time.
If the seals don't have these characteristics then the potential
exists for unacceptable amounts of higher ambient pressure air to
leak into the low pressure regeneration side. In other words, there
has to be an excellent seal mating or the desiccant performance
will suffer adversely.
[0006] Another disadvantage of the vacuum from engine method is
that such a system will require redesign of the engine's intake
manifold in order to gain access to the required low pressure air.
[0007] U.S. Pat. No. 5514035 describes a desiccant based windshield
defog system including an evaporator, a desiccant dryer (located
upstream of the evaporator), and a compressor fluidly connected
to the evaporator. The desiccant dryer in this proposed system is
a rotor. This system is not optimized because the desiccant dryer
is located upstream of the evaporator. A model was developed to
simulate these systems and identify the optimum configuration. The
results are shown in FIG. 1. FIG. 1 shows that the compressor power
consumption reduction is overall larger and more uniform when the
desiccant dryer is placed after the evaporating coil.
BRIEF SUMMARY OF THE INVENTION
[0008] This invention presents a method and apparatus for dehumidification
and cooling in an enclosed area. In particular, it is a method and
system for climate control in a motorized vehicle. The air conditioning
system includes an evaporator and desiccant dryer located downstream
of the evaporator, and a compressor fluidly connected to the evaporator.
The desiccant dryer in this system is of the rotor type, and the
heat source used to regenerate the desiccant is the excess heat
generated by the motor. The engine heat can be used to regenerate
the desiccant by one of the following 3 methods:
[0009] 1. Hot air coming off the radiator routed directly into
the rotor housing (approx. 130 deg F.)
[0010] 2. Engine coolant, exiting the engine block (approx 190
deg F.), routed to a liquid-to-air heat exchanger to heat the regeneration
air.
[0011] 3. Hot engine exhaust, after catalytic conversion, routed
to an air-to-air heat exchanger.
[0012] The advantages of this system include:
[0013] 1. As FIG. 1 shows, placing the desiccant rotor upstream
of the evaporator will not necessarily reduce shaft power to the
compressor. But for the present invention, electric energy requirements
are uniformly displaced with "free" thermal energy requirements.
Thus the cooling efficiency, measured by electric power consumption,
is higher.
[0014] 2. The present invention is simple, and reduces compressor
power consumption and cooling load on the evaporator. Reduced cooling
load on the evaporator means that compressor, condenser and evaporator
coils will be smaller and lighter. Note that the desiccant rotor
itself is very light, weighing on the order of two pounds. Some
additional fan power to drive process and regeneration air through
the desiccant dryer is required, but this amount is more than offset
by the reduced power consumption of the compressor.
[0015] 3. The temperature method of desiccant regeneration provides
a simpler, less problematic solution to desiccant regeneration than
the vacuum method: The sealing system will be less expensive and
require little or no maintenance. In addition, upon failure, the
system performance changes are expected to be small since the similar
pressures on the process and regeneration side will result in minimal
leakage rates.
[0016] 4. In contrast with the systems where the desiccant rotor
is upstream of the evaporator, there is sufficient excess heat produced
in a motor vehicle for the present invention.
[0017] 5. If the system is so designed, the additional dehumidification
capability provided by the desiccant rotor will improve comfort
to the passengers and the defog capacity of the air-conditioning
system.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 2 depicts the preferred embodiment of the invention.
REFERENCE NUMERALS IN DRAWINGS
[0019] 11--Intake air (from cabin or ambient)
[0020] 12--After filter and fan, entering evaporator coil
[0021] 13--Leaving evaporator coil, entering desiccant rotor
[0022] 14--Leaving evaporator coil (to cabin)
[0023] 15--Regeneration air inlet
[0024] 16--Regeneration air outlet
[0025] 17--Discharge air
DETAILED DESCRIPTION OF THE INVENTION
[0026] FIG. 2 is an illustration of the configuration of the invention
where the desiccant rotor is downstream of the evaporator coil.
The air being processed passes through the filter, the fan, and
the evaporator coil where the air is cooled and dehumidified, then
through the desiccant rotor where the air is dried and heated.
[0027] An analysis was performed on the configuration of this invention
(evap-rotor) vs. a configuration where the desiccant is placed upstream
of the evaporator (rotor-evap).
[0028] A model developed by Chant and Jeter (1995) for rotary desiccant
wheels was used to simulate the desiccant rotor. In addition to
the validation performed on the model described in the paper, the
model was adapted to the Engelhard HexCore rotor and validated with
data collected at the National Renewable Energy Laboratory in 1998.
The model's latent capacity predictions for HexCore's hexagonal
passage, Nomex core coated with titanium silicate desiccant were
within +/-10% and the outlet dry bulb agreement followed the latent
agreement. The model was used in the HexCore selection software
until Engelhard Corporation closed the HexCore business in 2001.
Since then, the model has been adapted by NovelAire technologies
for design work and eventual integration into their selection software
for their wound silica gel and molecular sieve series desiccant
rotors. The model's predictions for Novelaire's rotor were also
validated with NREL data and gave agreement of latent capacity errors
between +/-10%. The NREL data is confidential.
[0029] Two rotor-evaporator coil configurations were under study.
For each system, the rotor type, size and operating conditions were
selected. These design selections are merely typical operating conditions
for commercial desiccant wheels, with no optimization involved.
The source of regeneration air is not addressed.
[0030] For the performance calculations included in this report,
the inlet air state was constant at 95 deg F., while the inlet humidity
was varied (117 100 80 and 67 grns/lb). For each of the four
inlet humidities considered, the integrated systems were operated
to supply 70 deg F., 60 grns/lb air to the cabin. The vapor compression
system's capacity and the desiccant rotor's regeneration temperature
and wheel speed were varied to produce the desired supply condition.
Thus the performance calculations were performed for a constant
sensible load and varying latent load. This approach was used in
order to produce some parametric results with which to demonstrate
the systems' characteristics.
[0031] In the case of the Rotor-evap system, the rotor was operated
to remove the entire latent load, while the DX system performed
only the sensible cooling. Thus the latent and sensible loads are
handled independently. The VC system must remove the original sensible
load plus the heat of adsorption. For Case 1--where the ambient
humidity is 1117 grns/lb--this sensible load on the DX system is
greater than the conventional system load and DX system tonnage
required is more than the conventional system. Thus the Rotor-evap
system will result in increased power consumption during periods
of high humidity. Note that this is a typical summer operating condition
for many regions of the United States, such as the entire East Coast
and much of the Midwest. FIG. 3 shows a psychrometric plot for the
rotor-evap system.
[0032] The rotor in the Evap-rotor system serves to handle a portion
of the latent load, heating the air in the process and eliminating
the need for reheat. The desiccant rotor's capacity increases with
process inlet relative humidity, so the desiccant rotor's performance
is well served by this configuration. The VC system was operated
in each case to bring the air to a 58.5 deg F. dew point. The desiccant
rotor's capacity was roughly constant since it was bringing the
air from 58.5 deg F., 71 grns/lb to 70 deg F., 60 grns/lb. FIG.
4 shows a psychrometric plot for the rotor-evap system.
[0033] A rotor comprised of silica gel desiccant in a high temperature
fiber substrate, was simulated. The rotor is 12 inches in diameter,
and 4 (Evap-rotor system) or 6 (Rotor-evap system) inches deep.
The wheel's rotation speed is between 12 and 45 revs/hour. A 50/50
face split, balanced flow design was used. The particular rotor
simulated, excluding the housing, is estimated to be 2 to 3 lbs.
However, there are similarly performing, light-weight rotors that
could be evaluated for this application which would weigh about
1 lb. The regeneration temperature ranged from 110 to 205 deg F.
In an actual installed system, these parameters would not be varied,
but set at design time to handle a pre-defined extreme load. The
system components would then be cycled as needed during part-load
conditions.
[0034] Evaporator performance was estimated based on "typical"
cooling coil performance. Latent cooling was initiated at about
80% RH.
[0035] The latent capacity (amount of dehumidification cooling
performed) characteristics of a desiccant rotor as a function of
regeneration temperature and relative humidity are shown in FIG.
5. FIG. 5 shows that the latent capacity of the rotor increases
with increasing regeneration temperature and increasing process
inlet relative humidity. For the system where the rotor is upstream
of the evaporator, the rotor will need high capacity (in order to
handle the entire latent load) and will be processing air at moderate
relative humidities. Thus such a system, using thermal reactivation,
requires regeneration temperature in the range of 220 deg F. This
quality of thermal energy is only available from the engine's exhaust
air. In the case of the system where the rotor is downstream of
the evaporator and only handling a portion of the latent load, the
rotor requires only moderate capacity and--since it is downstream
of the evaporator--is processing nearly saturated air.
[0036] Thus results of the analysis completed so far have shown
that the current invention is a good match with the low grade, safe
thermal energy available from the engine coolant and radiator exhaust
air. The results also indicate that compressor power consumption
reduction is higher and more uniform when the desiccant dryer is
placed after the evaporating coil. |