Refrigeration – Processes – Circulating external gas
Reexamination Certificate
2000-06-19
2002-01-01
Bennett, Henry (Department: 3744)
Refrigeration
Processes
Circulating external gas
C062S069000, C062S271000
Reexamination Certificate
active
06334316
ABSTRACT:
TECHNICAL FIELD
The present invention relates in general to dehumidifying air conditioning systems, and relates in particular to a desiccant assisted air conditioning system to provide continuous processes of desiccant-assisted dehumidification and desiccant-regeneration using a heat source.
BACKGROUND ART
FIG. 10
shows a conventional dehumidifying air conditioning system having a process air path for dehumidifying air by passing the air through a desiccant, and a regeneration air path for desorbing moisture from the desiccant by passing heated air through the desiccant, arranged in such a way to flow the process air and regeneration air alternatingly through the desiccant. The system comprises: a process air path A; a regeneration air path B; a desiccant wheel
103
; two sensible heat exchangers
104
,
121
; a heater
220
; and a humidifier
105
. Process air is dehumidified in the desiccant wheel
103
, and, in this process, is heated by the heat of adsorption of moisture in the desiccant member, and is cooled next by passing through a first heat exchanger
104
by exchanging heat with the regeneration air. Process air is further cooled in the humidifier
105
before being supplied to the conditioning space (room) supply air SA. In the meantime, outside air (OA) serving as regeneration air is admitted into the first sensible heat exchanger
104
which raises the temperature of regeneration air by transferring heat from the dehumidified process air, and the heated regeneration air is further heated by a heat source
200
in the heating device
220
to lower its relative humidity, and is passed through the desiccant wheel
103
to desorb the moisture from the desiccant member. In the conventional system, sensible heat portion in the post-regeneration regeneration air is recovered by heat exchange with unheated regeneration air in the second sensible heat exchanger
121
, before exhausting the regeneration air to outside (EX). This type of system is known as a desiccant-assisted air conditioning system, and is an important practical technique to provide control over conditioning space humidity.
Desiccant materials which can be used in such desiccant-assisted air conditioning systems are known to include silica-gel and zeolite (known as molecular sieve), which are classified as a modified zeolite in Breuner type
1
. It is said that those materials having an isothermal separation factor in the range of 0.07~0.5 are most suitable as a desiccant member which is used in those systems designed to carry out desiccant regeneration by using some combustible gas as heat source. U.S. Pat. No. 3,844,737 mentions zeolite as a desiccant material in air conditioning systems using combustible gases for heating regeneration air, but, no prior publications give any suggestions regarding the suitable adsorption characteristics of zeolite. Although lithium chloride has also been used as a moisture adsorbing material, its use has gradually been discontinued because of deliquescence tendency when exposed to high humidity to fall out from a rotating frame of the desiccant wheel.
In air conditioning technologies based on combustible gas heating of regeneration air, as mentioned above, regeneration temperature is reported as 101° C. (215° F. ) or 143° C. (290° F.). It is said that zeolite is suitable for regeneration at such temperatures, and in particular, zeolite having an isothermal separation factor R between 0.07~0.5 as exemplified by R=0.1 in
FIG. 11
is most suitable. However, if other types of heating sources are considered for desiccant regeneration, lower regeneration temperatures (65~75° C.) offer more available choices, such as waste heat and solar heating. But, in such a case, zeolite materials in Breuner type
1
class and having a separation factor in the range of 0.07~0.5 are not always an optimum material for desiccant. The reason will be explained with reference to FIG.
11
.
FIG. 11
is an adsorption isotherm of conventional zeolite. When outdoor air is used as regeneration air in a desiccant-assisted air conditioning system, humidity ratio in summer is estimated to be about 20~21 g/kg (g moisture/kg air) for design purposes. When such an air is heated to a desiccant desorption temperature of 110° C. mentioned above, its relative humidity drops to about 3.0%. On the other hand, relative humidity of process air to be dehumidified can be estimated to be about 50% based on general room conditions where dry-bulb temperature is 27° C. and wet-bulb temperature is 19° C. as specified in JIS(Japanese Industrial Standard)-C9612, for example. The desiccant member thus alternatingly contacts process air and regeneration air, respectively, at 50% and 3% relative humidity. Equilibrium moisture content in zeolite in contact with regeneration air at 3% relative humidity is found to be X=0.236 from
FIG. 11
, using a functional relation X=P/(R+P−R×P) for a separation factor R=0.1 and P=0.030.
On the other hand, equilibrium moisture content in zeolite in contact with process air exhausted from a room can be found, similarly, to be X=0.910 for separation factor R=0.1 and P=0.5. Therefore, in the case of heating the regeneration air to 101° C. for desorbing zeolite, the amount of moisture which can be adsorbed by the desiccant member is 0.169 kg/kg, which is obtained by multiplying the difference in the relative adsorbed amount (0.910−0.236=0.674) with the maximum uptake 0.25 kg/kg (kg water per kg zeolite). If a material such as silica-gel is used, whose characteristic adsorption isotherm is linear (isothermal separation factor R=1), the difference in desorption and adsorption is the same as the difference in the relative humidity values, 0.500−0.030=0.470, and a corresponding value drops to 0.140 kg/kg, which is obtained by multiplying the maximum uptake (usually 0.3 kg/kg for silica-gel) with 0.470. Therefore, zeolite is more effective in this case. This example shows that, when the desorption temperature is as high as 101° C. as in the conventional air conditioning apparatus, the use of zeolite is clearly more advantageous. However, when similar calculations are performed for the range of desorption temperatures of 50~70° C. as desired in the present invention, superiority of zeolite is not certain and the differential adsorption capacity (difference in desorbed/adsorbed amount) is significantly decreased. This will be explained in more detail below with reference to FIG.
12
.
FIG. 12
shows the configuration of a desiccant-assisted air conditioning system disclosed the inventor, comprised by a process air path for dehumidifying and a regeneration air path for flowing air which is first heated in a heating source before desorbing moisture from the moisture-laden desiccant member
103
, arranged in such a way that regeneration air and process air alternatingly flow through the desiccant member
103
. Dehumidified process air is cooled in a low-temperature heat source
240
of a heat pump, and pre-desiccant regeneration air is heated in a high-temperature heat source
220
of the heat pump.
FIG. 13
shows a psychrometric chart to show the operation of the system shown in FIG.
12
.
Accordingly, by cooling the dehumidified process air in the low-temperature source
240
of the heat pump, the temperature of supply air SA (state N) can be lowered below that of the room (state K) as shown in FIG.
13
. Therefore the humidifier
105
used in the conventional system shown in
FIG. 10
becomes unnecessary so that dehumidified cooled process air and supply air SA have the same humidity ratio, thus providing a higher cooling effect than the conventional system. Those skilled in the art know that, for summer air conditioning, supply air is generally at less than 8 g/kg (moisture per kg of air), therefore, by setting the humidity ratio of the supply air, i.e., dehumidified process air at 7 g/kg, the process air changes its state from the room state along an isenthalpic line until it reaches 7 g/kg wh
Fukasaku Yoshiro
Inaba Hideo
Maeda Kensaku
Nishida Rosuke
Oouchi Toshiaki
Armstrong Westerman Hattori McLeland & Naughton LLP
Bennett Henry
Ebara Corporation
Shulman Mark
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