WO1999036733A1 - Desiccant assisted air conditioning system - Google Patents

Desiccant assisted air conditioning system Download PDF

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Publication number
WO1999036733A1
WO1999036733A1 PCT/JP1999/000076 JP9900076W WO9936733A1 WO 1999036733 A1 WO1999036733 A1 WO 1999036733A1 JP 9900076 W JP9900076 W JP 9900076W WO 9936733 A1 WO9936733 A1 WO 9936733A1
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Prior art keywords
air
desiccant
regeneration
temperature
aluminum phosphate
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PCT/JP1999/000076
Other languages
French (fr)
Inventor
Kensaku Maeda
Yoshiro Fukasaku
Shoji Yamanaka
Original Assignee
Ebara Corporation
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Publication date
Application filed by Ebara Corporation filed Critical Ebara Corporation
Priority to AU18893/99A priority Critical patent/AU1889399A/en
Publication of WO1999036733A1 publication Critical patent/WO1999036733A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F3/00—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems
    • F24F3/12—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling
    • F24F3/14—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by humidification; by dehumidification
    • F24F3/1411—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by humidification; by dehumidification by absorbing or adsorbing water, e.g. using an hygroscopic desiccant
    • F24F3/1423—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by humidification; by dehumidification by absorbing or adsorbing water, e.g. using an hygroscopic desiccant with a moving bed of solid desiccants, e.g. a rotary wheel supporting solid desiccants
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/26—Drying gases or vapours
    • B01D53/261—Drying gases or vapours by adsorption
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/26—Drying gases or vapours
    • B01D53/28—Selection of materials for use as drying agents
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F5/00—Air-conditioning systems or apparatus not covered by F24F1/00 or F24F3/00, e.g. using solar heat or combined with household units such as an oven or water heater
    • F24F5/0007—Air-conditioning systems or apparatus not covered by F24F1/00 or F24F3/00, e.g. using solar heat or combined with household units such as an oven or water heater cooling apparatus specially adapted for use in air-conditioning
    • F24F5/001—Compression cycle type
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F2203/00—Devices or apparatus used for air treatment
    • F24F2203/10—Rotary wheel
    • F24F2203/1016—Rotary wheel combined with another type of cooling principle, e.g. compression cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F2203/00—Devices or apparatus used for air treatment
    • F24F2203/10—Rotary wheel
    • F24F2203/1028—Rotary wheel combined with a spraying device
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F2203/00—Devices or apparatus used for air treatment
    • F24F2203/10—Rotary wheel
    • F24F2203/1032—Desiccant wheel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F2203/00—Devices or apparatus used for air treatment
    • F24F2203/10—Rotary wheel
    • F24F2203/104—Heat exchanger wheel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F2203/00—Devices or apparatus used for air treatment
    • F24F2203/10—Rotary wheel
    • F24F2203/1056—Rotary wheel comprising a reheater
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F2203/00—Devices or apparatus used for air treatment
    • F24F2203/10—Rotary wheel
    • F24F2203/1072—Rotary wheel comprising two rotors
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F2203/00—Devices or apparatus used for air treatment
    • F24F2203/10—Rotary wheel
    • F24F2203/1076—Rotary wheel comprising three rotors
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F2203/00—Devices or apparatus used for air treatment
    • F24F2203/10—Rotary wheel
    • F24F2203/1084—Rotary wheel comprising two flow rotor segments

Definitions

  • the present invention relates in general to dehumidifying air conditioning systems, and relates in particular to a desiccant assisted air conditioning systemto provide continuous processes of desiccant-assisted dehumidification and desiccant-regeneration using a heat source.
  • Figure 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 altematingly 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.
  • 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 humidity ratio, and is passed through the desiccant wheel 103 to desorb the moisture from the desiccant member .
  • 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) as disclosed in a United States Patent 5,052,188, in which the latter is classified as a modified zeolite in Breuner type 1, and it is disclosed that those materials having an isothermal separation factor in the range of 0.07-0.5 are most suitable as a desiccant member in those systems designed to carry out desiccant regeneration by using some combustible gas as heat source.
  • silica-gel and zeolite known as molecular sieve
  • lower regeneration temperatures 65-75 °C
  • 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 Figure 11.
  • Figure 11 is an adsorption isotherm of zeolite disclosed in USP 5,052,188.
  • humidity ratio in summer is estimated to be about 20-21 g/kg (g moisture/kg air) for design purposes.
  • humidity ratio 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 altematingly contacts process air and regeneration air, respectively, at 50 % and 3 % humidity ratio.
  • Figure 12 shows the configuration of a desiccant-assisted air conditioning system disclosed in Figure 3 in a Japanese
  • Laid-open Patent Publication, 1997-196482 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 fromthe moisture-laden desiccant member 103 , arranged in such a way that regeneration air and process air altematingly 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.
  • Figure 13 shows a psychrometric chart to show the operation of the system shown in Figure 12.
  • the temperature of supply air SA (state N) can be lowered below that of the room (state K) as shown in Figure 13. Therefore the humidifier 105 used in the conventional system shown in Figure 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.
  • 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 where a humidity ratio is 20 %, as shown in Figure 13 (when the adsorption heat is high as in zeolite, humidity ratio of 20 % is reached at a slightly higher humidity ratio value of 8 g/kg) .
  • the humidity ratio of dehumidified process air is equal to the humidity ratio of regeneration air before regeneration (for example, refer to reference material p23-25 of TC 3.5/short course seminar, US ASHRAE Society Annual Meeting, 1997). Therefore, outdoor air can be heated to a temperature to lower its humidity ratio so as to be used as regeneration air to regenerate the desiccant member.
  • humidity ratio in summer is generally about 15 g/kg, therefore, such an air, when heated to 50 °C having a 20 % humidity ratio, can be used as regeneration air.
  • Humidity ratio can reach a value of 20 g/kg on rare occasions, but even such an air can be heated to 55 °C and used for dehumidifying the process air to less than 8 g/kg moisture. Therefore, it is desirable for such an air conditioning system to have a desiccant material which provides a high moisture removal capacity at regeneration temperature of 50-70 °C, but the conventional zeolite shows a low capacity for moisture content difference between its absorption and desorption state. Thus, low capacity must be compensated by increasing the mass of the desiccant. This will be explained in more detail below.
  • Figure 14 is a graph, calculated from the adsorption isotherm of Figure 11, showing the relationship between adsorption capacity of zeolite and temperature of air in contact therewith for various parametric values of the humidity ratio of the air.
  • Point A is the adsorption-start point where the moisture content of zeolite is in equilibrium with process air
  • points D50 and D70 are the desorption- or regeneration- start points where the moisture content of zeolite is in equilibrium with regeneration air at 50 and 70 °C, respectively.
  • This graph also shows that the differential adsorption capacity is 0.05 and 0.11 kg/kg, respectively, for 50 °C-regeneration and 70 °C-regeneration.
  • an energy-efficient and compact air conditioning system can be provided.
  • the porous aluminum phosphatematerial may be produced by reacting a hydrated alumina and phosphoric acid in a thermally dissociatable template agent.
  • a desiccant member that can be regenerated at a temperature in a range of 50-70 °C can be produced, thereby enabling to provide an energy-efficient and compact air conditioning system.
  • porous aluminum phosphate material is represented by a formula, AlP0 4 -5, and having a characteristic X-ray powder diffraction pattern including at least d-spacing data listed in Table 1 shown below: Table 1
  • porous aluminum phosphate material is represented by a formula, AlP0 4 -8, and having a characteristic X-ray powder diffraction pattern including at least d-spacing data listed in Table 2 shown below:
  • porous aluminum phosphate material is represented by a formula, AlP0 4 -ll, and having a characteristic X-ray powder diffraction pattern including at least d-spacing data listed in Table 3 shown below:
  • porous aluminumphosphatematerial is represented by a formula, A1P0 4 -16, and having a characteristic X-ray powder diffraction pattern including at least d-spacing data listed in Table 4 shown below:
  • the porous aluminum phosphate material is represented by a formula, AlPO 4 -20, and having a characteristic X-ray powder diffraction pattern including at least d-spacing data listed in Table 5 shown below: Table 5
  • AlP0 4 -n having fine pores whose diameters are substantially the same as those of water molecules , as a desiccant member enables to produce an energy-efficient and compact air conditioning system.
  • the desiccant member may be regenerated at a temperature of less than 70 °C.
  • a desiccant assisted air conditioning system whose humidity is controlled by a desiccant that can be regenerated at lower temperatures relative to conventional desiccant materials, can be operated by a thermal source that can be driven at correspondingly lower temperatures, thereby providing an energy-efficient air conditioning system.
  • process air that has been removed of moisture may be cooled by a low-temperature heat source in a heat pump, and regeneration air that prior to regeneration of the desiccant member may be heated in a high-temperature heat source of the heat pump.
  • a heat pump is used to cool the dehumidified process air, and the heat is then recycled to raise the temperature of regeneration air, to provide not only a multi-use of heat energy but also a minimization of temperature lift for the heat pump, thereby providing an energy-efficient dehumidifying air conditioning system.
  • the present desiccant assisted air conditioning system is based on dehumidifying the process air using a desiccant member made of a porous aluminum phosphate material (known by a chemical formula AlP0 4 -n by Union Carbide and in academic societies ) produced by reacting a hydrated alumina (for example, aluminum hydride, boehmite, pseudo- boehmite) with phosphoric acid using a thermally dissociatable template agent (organic base group such as tripropylamine, for example).
  • a thermally dissociatable template agent organic base group such as tripropylamine, for example.
  • the resulting desiccant material exhibits a large differential adsorption capacity, and can be regenerated at relatively low temperatures .
  • There is no need to use a bulky desiccant thereby enable to provide a compact system that can offer high energy efficiency at low operating cost.
  • Figure 1 is a graph showing an adsorption isotherm of molecular sieve made with a porous aluminum phosphate system (AlP0 4 -5);
  • Figure 2 is a graph showing a relation between the temperature of air in contact with the desiccant and water content of desiccant AlP0 4 -5;
  • Figure 3 is a schematic diagram of a second embodiment of the air-conditioning system of the present invention.
  • Figure 4 is a psychrometric chart showing the operational states in the system shown in Figure 3;
  • Figure 5 is a schematic diagram of a third embodiment of the air-conditioning system of the present invention.
  • Figure 6 is a psychrometric chart showing the operational states in the system shown in Figure 5;
  • Figure 7 is a graph showing an adsorption isotherm of molecular sieve made with a porous aluminum phosphate system (AlP0 4 -5);
  • Figure 8 is a schematic diagram of a fourth embodiment of the air-conditioning system of the present invention.
  • Figure 9 is a psychrometric chart showing the operational states in the system shown in Figure 8;
  • Figure 10 is a schematic diagram of a conventional air conditioning system
  • Figure 11 is a graph of adsorption isotherm for zeolite
  • Figure 12 is a schematic diagram of another conventional air conditioning system
  • Figure 13 is a psychrometric chart showing the operational states in the system shown in Figure 12; and Figure 14 is a graph showing the relation between air contacting the desiccant and adsorption capacity of zeolite desiccant according to adsorption isotherm shown in Figure 11.
  • the first embodiment is a dehumidifying air conditioning system shown in Figure 12, in which molecular sieve is used as a desiccant material, which is made of porous aluminum phosphate produced by reacting a hydrated alumina (for example, aluminum hydride, boehmite, pseudo-boehmite) with phosphoric acid using a thermally dissociatable template agent (organic base group such as tripropylamine, for example) of an essential skeletal structure having a chemical formula where "k" is expressed in a mol ratio:
  • a hydrated alumina for example, aluminum hydride, boehmite, pseudo-boehmite
  • a thermally dissociatable template agent organic base group such as tripropylamine, for example
  • This molecular sieve is generally designated as AlP0 4 -5 by Union Carbide Co. in a Japanese Patent Publication, 1989-57041 or in academic societies. The present inventors measured adsorption characteristics of this molecular sieve called AlP0 4 -5, and obtained the following results.
  • Figure 1 shows a graph of adsorption isotherm of the porous aluminum phosphate group molecular sieve (AlP0 4 -5).
  • the horizontal axis represents humidity ratio RH and the vertical axis represents relative water content ratio (relative water adsorption amount) defined by a ratio of the measured adsorbed amount W and the amount of adsorption W max (maximum uptake) when humidity ratio is 90 %.
  • This material shown in Figure 1 behaves in a similar manner to the desiccant material disclosed in the above-mentioned Japanese Patent Publication, 1989-57041, Example 55, where the moisture adsorption is 4.6 kg/kg at 24 °C at a pressure of 4.6 torr (humidity ratio 20 %) and the moisture adsorption is 26.4 kg/kg at 23 °C at a pressure of 18.5 torr (humidity ratio 88 % ) .
  • Notable feature is that the water content increases rapidly between the values of humidity ratio at 20 and 40 %.
  • Figure 2 shows the relationship, according to the adsorption isotherm shown in Figure 1 , between adsorption capacity of the porous aluminum phosphate group molecular sieve (AlP0 4 -5) and temperature of contacting air with humidity ratio as a parameter.
  • point A represents the adsorption-start point of the molecular sieve in equilibrium with indoor air
  • points D50 and D70 represent the desorption-start points of the molecular sieve in equilibrium with regeneration air at 50 °C and 70 °C.
  • Figure 2 shows that the differential adsorption/desorption amounts are 0.17 and 0.19 kg/kg, respectively, for 50 °C-regeneration and 70 °C- regeneration.
  • Process air (state K) flows through the desiccant wheel 103 which adsorbs moisture from the process air (state L), and in flowing through the first sensible heat exchanger 104, transfers heat to the regeneration air (state Q) and is cooled (state M) , and is further cooled (state N) in the low-temperature heat source 240 of the heat pump, and returns to the conditioning space 101 as supply air SA.
  • regeneration air is admitted from outdoors (state Q) into the first sensible heat exchanger 104 to receive heat from the process air (state L) thereby raising its temperature (state R) , and enters into the second sensible heat exchanger 121 to receive heat from the post-desiccant regeneration air (state U) thereby raising its temperature (state S), and is further heated in the high- temperature heat source 220 of the heat pump to raise its temperature (state T), and is then flows through the desiccant wheel 103 to desorb the moisture thereby regenerating the desiccant.
  • Post-desiccant regeneration air (state U) transfers heat (state V) in the second sensible heat exchanger 121 to the regeneration air exiting from the first sensible heat exchanger 104, and is discarded as waste gas.
  • the desiccant assisted air conditioning system operates by generating a differential humidity ratio DX and a differential enthalpy DQ between the indoor air (state K) and the supply air (state N) to provide a dehumidification and cooling effect of the conditioning space.
  • the driving energy for the system is afforded by the differential heat obtained by subtracting the afore-mentioned heat DQ from the heat input DG to heat the regeneration air so that desiccant regeneration is carried out utilizing the waste heat generated in a sensible heat treatment process from state M to state N, thereby providing an excellent energy efficiency for the system.
  • desorption temperature for regeneration air (state T) can be selected in the range of 50-55 °C, and therefore, the operating temperature (condensing temperature) of the high-temperature heat source 220 of the heat pump can be lowered, and the power required to operate the heat pump can also be lowered.
  • Present system is overall much more energy conserving, and is more compact compared with the conventional systems.
  • molecular sieve based on porous aluminum phosphate is represented by AlP0 4 -5, however, as recited in the afore-mentioned Japanese Patent, 1989-57041, there are various isomers of A1P0 4 represented by a general formula AlP0 4 -n. It is known that moisture adsorption by molecular sieve is performed by trapping water molecules at adsorption sites whose cavity size is larger than the diameter of the water molecules. Trapping force is also affected by the presence of metallic ions at the adsorption sites.
  • AlP0 4 -5 is reported to have a strong I/I 0 peak in a range of d-spacing between 3.93-4.51 angstroms according to Table 2 in the afore-mentioned Japanese Patent 1989-57041, and other isomers that have such characteristics are also disclosed as follows.
  • FIG 3 shows the system configuration in a second embodiment.
  • the air conditioning system shown in Figure 3 is a hybrid system combining a desiccant and a heat pump as in Figure 12, but without the first sensible heat exchanger 104, and the desiccant wheel 103 uses the porous aluminum phosphate molecular sieve, represented by the so-called AlP0 4 -n formula.
  • process air and regeneration air do not exchange heat so that the process air is supplied at higher temperatures. Therefore, this type of system is most suitable when the use is primarily dehumidification involving low sensible heat ratios .
  • the operation of this system will be explained with reference to the psychrometric chart shown in Figure 4 related to the system shown in Figure 3.
  • Process air (state K) flows through the desiccant wheel 103 which adsorbs moisture (state L), and is cooled (state M) in the low-temperature heat source 240 of the heat pump and returns to the conditioning space 101.
  • regeneration air which is outdoor air (state Q) enters into the sensible heat exchanger 121 to receive heat from the post-desiccant regeneration air (state U) thereby raising its temperature ( state S ) , and is f rther heated in the high- temperature heat source 220 of the heat pump to raise its temperature (state T) , and then flows through the desiccant wheel 103 to desorb the moisture.
  • Post-desiccant regeneration air (state U) transfers heat (state V) to the regeneration air in the sensible heat exchanger 121, thereby returning heat to the system and is discarded as waste gas .
  • the desiccant assisted air conditioning system performs its functions by generating a differential humidity ratio DX and a differential enthalpy DQ between the indoor air (state K) and the supply air (state M) .
  • the temperature of supply air is higher and is close to room air temperature, and therefore, it is most suitable when the conditioning load is primarily humidity lowering ( latent heat load) .
  • the temperature difference between regeneration air at 50 °C and supply air is only 23 °C, so that the temperature lift, i.e., temperature difference between the low- and high-temperature heat sources of the heat pump will be 33 °C by adding 10 °C to 23 °C.
  • the heat pump can be operated at a much lower temperature lift, thereby enabling to conserve energy. Because a dew drainage is not needed, the facility becomes simpler, and as in the first embodiment system, small amount of desiccant member is needed to treat a large amount of moisture so that the desiccant wheel can be made compact. Therefore, the overall system exhibits superior energy efficiency and a compact arrangement is effective for equivalent performance.
  • Figure 5 shows the system configuration in a third embodiment.
  • the air conditioning system shown in Figure 5 is also a hybrid system similar to the one shown in Figure 3, but the difference is that the process air is a mixture of outdoor air and indoor return air while the regeneration air is a mixture of indoor exhaust air and outdoor air.
  • a passage 161 and a blower 160 are provided between a process air passage 107 and an outdoor air admittance passage 124 for mixing outdoor air with return room air
  • a passage 162 is provided between a regeneration air passage 124 and a return air passage 107 for mixing the return room air with outdoor air.
  • Post-desiccant regeneration air (state U) transfers heat to the regeneration air(state V) in the sensible heat exchanger 121, thereby returning heat to the system and is discarded as waste gas .
  • the desiccant assisted air conditioning system performs its functions by generating a differential humidity ratio DX and a differential enthalpy DQ between the indoor air (state K) and the supply air (state M) .
  • this system based on mixing indoor air with outdoor air is most suitable for maintaining a certain level of comfort in the indoor environment. Assuming that, on a typical mid-summer day, indoor air is at 27 °C with a 50 % humidity ratio (RH) and outdoor is at 33 °C with a 63 % RH, then, pre-desiccant process air is mixed with outdoor air having a humidity ratio of 20 g/kg to become process air at a dry-bulb temperature of 29 °C and a humidity ratio of 13 g/kg as shown in Figure 6.
  • RH 50 % humidity ratio
  • pre-desiccant process air is mixed with outdoor air having a humidity ratio of 20 g/kg to become process air at a dry-bulb temperature of 29 °C and a humidity ratio of 13 g/kg as shown in Figure 6.
  • process air moves along the isenthalpic line to a humidity ratio of 7 g/kg at state L having a humidity ratio of about 10 % (more accurately 11 %). Therefore, the temperature of regeneration air for desorption-start is 65 °C, as described before, according to the intersection point of the humidity ratio line at 10 % and the humidity ratio line at 17 g/kg.
  • pre-desiccant regeneration air is at dry bulb temperature of 31 °C and a humidity ratio of 17 g/kg because of mixing with return air having a humidity ratio of 10 g/kg.
  • the desiccant condition at the desorption-start point (state T) is at a dry-bulb temperature of 65 °C and a humidity ratio of 17 g/kg.
  • the differential adsorption capacity of the desiccant member, given by the difference between the adsorption-start state F (dry-bulb temperature at 29 °C and humidity ratio of 13 g/kg) and the regeneration-start state T (dry-bulb temperature at 31 °C and humidity ratio at 17 g/kg) is 0.19 g/kg as indicated in Figure 7 for this material.
  • the moisture adsorption capacity is as large as what was shown in Figure 2.
  • the operation of the various devices for process air and regeneration air is the same as in the second embodiment, and will not be repeated.
  • the temperature of regeneration air can be set low (state T), so that the operating temperature (condensation) of the high temperature heat source 220 of the heat pump is lowered, thereby lowering the drive power for the compressor of the heat pump.
  • FIG 8 shows the system configuration in a fourth embodiment of the invention.
  • This system is similar to the so-called desiccant-assisted air conditioning system without the heat pump shown in Figure 10. The difference is that dehumidified process air is cooled in the heat exchanger 104 by means of heat exchange with the outdoor air which is humidified in a humidifier 105, thereby eliminating heat exchange between process air and regeneration air.
  • regeneration air is first humidified to lower its dry-bulb temperature and is then subjected to heat exchange with process air, but in such a process, humidity ratio of the regeneration WO 99/36733 ..
  • Process air (state K) flows through the desiccant wheel 103 and is removed of its moisture (state L), and is further cooled (state M) in the cooler 104 by the humidified outdoor air and returns to the conditioning space 101.
  • regeneration air is admitted from outdoors (state Q) and enters into the sensible heat exchanger 121 to receive heat from the post-desiccant regeneration air (state U) thereby raising its temperature (state S), and is further heated in the heater 220 (state T), and then flows through the desiccant wheel 103 to desorb the moisture.
  • Post-desiccant regeneration air (state U) transfers heat, in the sensible heat exchanger 121, to the incoming regeneration air (state Q) , and the cooled regeneration gas (state V) is discarded as waste gas.
  • cooling air which is outdoor air (state Q) is admitted into the humidifier 105, so that its temperature is lowered (state D) by the heat of vaporization of water, and then it is mixed in the heat exchanger 104 to remove heat from the process air (state L) to produce supply air (state M) , and the warmed cooling air (state E) is discarded as waste gas.
  • a humidity ratio difference DX is generated between room air (state K) and supply air (state M) to provide a dehumidifying effect.
  • the supply air temperature is lower and is closer to the room air temperature, sensible heat load of the room air is not increased, so that the system is suitable when a conditioning load requires primarily dehumidification (latent heat load) .
  • Outdoor summer temperature is generally around 28 °C, which is not much different than indoor air temperature, so that room dehumidification can be achieved without increasing the sensible heat load by using the present system in which no humidifier is provided in the process air passage.
  • latent heat load can be processed by using low temperature heat source at 50-70 °C such as waste heat or solar heating instead of using vapor compression cycle type cooling system.
  • a small amount of desiccant member is sufficient to process a large amount of moisture, thereby providing a compact desiccant wheel. Therefore, compared with the conventional system, the present system offers superior energy efficiency with a compact air conditioning system.
  • the present invention is advantageous as an air conditioning system used in general dwelling houses or larger buildings used as supermarket or business offices.

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Abstract

A compact and energy efficient air conditioning system is operated with a desiccant material having a high differential adsorption capacity even at lower regeneration temperatures than those in the conventional system. The desiccant assisted air conditioning system comprises a process air path for flowing process air to adsorb moisture from the process air by a desiccant member, and a regeneration air path for flowing regeneration air heated by a heat source to desorb moisture from the desiccant member. The desiccant member is arranged so that the process air or the regeneration air flows alternatingly through the desiccant member. The desiccant member comprises a porous aluminum phosphate material having an essential skeletal structure with a general chemical formula, Al2O3k(P2O5), where k = 1.0±0.2, expressed in a mol ratio.

Description

DESCRIPTION
DESICCANT ASSISTED AIR CONDITIONING SYSTEM
Technical Field
The present invention relates in general to dehumidifying air conditioning systems, and relates in particular to a desiccant assisted air conditioning systemto provide continuous processes of desiccant-assisted dehumidification and desiccant-regeneration using a heat source.
Background Art
Figure 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 altematingly 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 humidity ratio, 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) as disclosed in a United States Patent 5,052,188, in which the latter is classified as a modified zeolite in Breuner type 1, and it is disclosed that those materials having an isothermal separation factor in the range of 0.07-0.5 are most suitable as a desiccant member in those systems designed to carry out desiccant regeneration by using some combustible gas as heat source. Other publications, such as United States Patent 3,844, 737, also mention zeolite as a desiccant material in air conditioning systems using combustible gases for heating regeneration air, but, no prior publications other than USP 5,052,188 give any suggestions regarding the 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 the substrate.
In air conditioning technologies based on combustible gas heating of regeneration air, as mentioned above, regeneration temperature is reported as 101 °C (215 °F) in USP 5,052,188 and 143 °C (290 °F) in USP 3,889,742. It is recited in USP 5,052,188 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 Figure 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 Figure 11.
Figure 11 is an adsorption isotherm of zeolite disclosed in USP 5,052,188. 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 humidity ratio drops to about 3.0%. On the other hand, humidity ratio 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 altematingly contacts process air and regeneration air, respectively, at 50 % and 3 % humidity ratio. Equilibrium moisture content in zeolite in contact with regeneration air at 3 % humidity ratio is found to be X=0.236 from Figure 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=l ) , the difference in desorption and adsorption is the same as the difference in the humidity ratio 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.
Figure 12 shows the configuration of a desiccant-assisted air conditioning system disclosed in Figure 3 in a Japanese
Laid-open Patent Publication, 1997-196482, 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 fromthe moisture-laden desiccant member 103 , arranged in such a way that regeneration air and process air altematingly 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. Figure 13 shows a psychrometric chart to show the operation of the system shown in Figure 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 Figure 13. Therefore the humidifier 105 used in the conventional system shown in Figure 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 where a humidity ratio is 20 %, as shown in Figure 13 (when the adsorption heat is high as in zeolite, humidity ratio of 20 % is reached at a slightly higher humidity ratio value of 8 g/kg) . It is known by those skilled in the art that the humidity ratio of dehumidified process air is equal to the humidity ratio of regeneration air before regeneration (for example, refer to reference material p23-25 of TC 3.5/short course seminar, US ASHRAE Society Annual Meeting, 1997). Therefore, outdoor air can be heated to a temperature to lower its humidity ratio so as to be used as regeneration air to regenerate the desiccant member.
In other words , humidity ratio in summer is generally about 15 g/kg, therefore, such an air, when heated to 50 °C having a 20 % humidity ratio, can be used as regeneration air. Humidity ratio can reach a value of 20 g/kg on rare occasions, but even such an air can be heated to 55 °C and used for dehumidifying the process air to less than 8 g/kg moisture. Therefore, it is desirable for such an air conditioning system to have a desiccant material which provides a high moisture removal capacity at regeneration temperature of 50-70 °C, but the conventional zeolite shows a low capacity for moisture content difference between its absorption and desorption state. Thus, low capacity must be compensated by increasing the mass of the desiccant. This will be explained in more detail below.
When the regeneration air at humidity ratio of 15 g/kg is heated to 50 °C, its humidity ratio is about 20 % (18.9 % accurately). Therefore, equilibrium moisture content of zeolite of separation factor R=0.1 in contact with regeneration air is X=0.71 for P=0.2 when humidity ratio is 20 % as shown in the graph in Figure 11. On the other hand, equilibrium moisture content of zeolite in contact with spent process air exhausted from the room is X=0.91 at P=0.5 as before. Therefore, by flowing regeneration air heated to 50 °C, the desiccant can adsorb moisture of 0.05 kg/kg, obtained by multiplying the differential adsorption capacity 0.20 (=0.91-0.71) with the maximum uptake of 0.25 kg/kg for zeolite. Comparing this value 0.05 with the previous value 0.169 kg/kg, gives a ratio as 1/3.4, which means that the size of the zeolite desiccant needs to be 3.4 times larger.
Figure 14 is a graph, calculated from the adsorption isotherm of Figure 11, showing the relationship between adsorption capacity of zeolite and temperature of air in contact therewith for various parametric values of the humidity ratio of the air. Point A is the adsorption-start point where the moisture content of zeolite is in equilibrium with process air, and points D50 and D70 are the desorption- or regeneration- start points where the moisture content of zeolite is in equilibrium with regeneration air at 50 and 70 °C, respectively. This graph also shows that the differential adsorption capacity is 0.05 and 0.11 kg/kg, respectively, for 50 °C-regeneration and 70 °C-regeneration. These values confirm that the desiccant size must be increased by 1.5-3.4 times the size of a desiccant regenerated at higher temperatures.
On the other hand, if a material such as silica-gel is used, whose adsorption isotherm is linear (separation factor R=l ) , the differential adsorption capacity is 0.3 (=0.5-0.2) for 50 °C-regeneration( humidity ratio 20 %), similarly to the differential humidity ratio, so that, adsorbed amount is 0.09 kg/kg, obtained by multiplying 0.3 with the maximum uptake of 0.3 kg/kg for silica-gel. For 70 °C-regeneration (humidity ratio 7.5 %), the adsorbed amount is 0.127 kg/kg, obtained by multiplying the differential adsorption capacity 0.425 (=0.5-0.075) with the maximum uptake of 0.3 kg/kg for silica-gel. These values (0.09, 0.127) are higher than those for zeolite type 1 (0.05, 0.11), but even in these cases, it is clear that the desiccant size must be increased compared with the high-temperature regeneration process which produces an adsorption amount of 0.14 kg/kg.
It can be seen, therefore, that the conventional desiccant technology is not adaptable to low-temperature regeneration (50-70 °C), and the necessity for a larger desiccant leads to a large air conditioning system and high operating cost.
Disclosure of Invention
It is an object of the present invention to provide a compact and energy efficient air conditioning system that is operated with a desiccant material having a high differential adsorption capacity even at lower regeneration temperatures than those in the conventional system.
The object has been achieved in a desiccant assisted air conditioning system comprising: a process air path for flowing process air to adsorb moisture from the process air by a desiccant member; and a regeneration air path for flowing regeneration air heated by a heat source to desorb moisture from the desiccant member, the desiccant member being arranged so that the process air or the regeneration air flows altematingly through the desiccant member; wherein the desiccant member comprises a porous aluminum phosphate material having an essential skeletal structure with a general chemical formula, Al203k(P205) , where k = 1.0±0.2, expressed in a mol ratio.
By using such an aluminum phosphate compound as a desiccant member which can be regenerated at a temperature in a range of 50-70 °C, an energy-efficient and compact air conditioning system can be provided.
It is an aspect of the invention that the porous aluminum phosphatematerial may be produced by reacting a hydrated alumina and phosphoric acid in a thermally dissociatable template agent.
By using an aluminum phosphate compound thus prepared, a desiccant member that can be regenerated at a temperature in a range of 50-70 °C can be produced, thereby enabling to provide an energy-efficient and compact air conditioning system.
It is another aspect of the invention that the porous aluminum phosphate material is represented by a formula, AlP04-5, and having a characteristic X-ray powder diffraction pattern including at least d-spacing data listed in Table 1 shown below: Table 1
2 θ d 100XI/I0
7.4-7.6 11.9-11.6 100
14.8-15.3 5.97-5.83 13-43
19.7-20.1 4.51-4.42 39-92
20.8-21.2 4.27-4.19 37-87
22.3-22.7 3.99-3.93 62-118
25.9-26.3 3.44-3.39 22-35
It is still another aspect of the invention that the porous aluminum phosphate material is represented by a formula, AlP04-8, and having a characteristic X-ray powder diffraction pattern including at least d-spacing data listed in Table 2 shown below:
Table 2 2 θ d 100XI/I0
5.3-5.4 16.7-16.4 80-100
6.50-6.65 13.6-13.3 30-100
19.7-19.8 4.51-4.48 8-29
21.2-21.3 4.19-4.17 46-82
21.8-21.9 4.08-4.06 14-56
22.4-22.9 3.97-3.88 35-39
It is still another aspect of the invention that the porous aluminum phosphate material is represented by a formula, AlP04-ll, and having a characteristic X-ray powder diffraction pattern including at least d-spacing data listed in Table 3 shown below:
Table 3
2 θ d 100XI/I0
9.4-9.5 9.41-9.31 31-49
20.5-20.6 4.33-4.31 34-53
21.00-21.25 4.23-4.19 100
22.15-22.25 4.01-4.00 12-58
22.50-22.70 3.95-3.92 47-75
23.15-23.50 3.84-3.79 10-68
It is still another aspect of the invention that the porous aluminumphosphatematerial is represented by a formula, A1P04-16, and having a characteristic X-ray powder diffraction pattern including at least d-spacing data listed in Table 4 shown below:
Table 4 2 θ d 100XI/I0
11.3-11.5 7.83-7.69 59-63
18.70-18.85 4.75-4.71 48-54
21.9-22.2 4.06-4.00 100
26.55-26.75 3.36-3.33 23-27
29.75-29.95 3.00-2.98 26-30
it is still another aspect of the invention that the porous aluminum phosphate material is represented by a formula, AlPO4-20, and having a characteristic X-ray powder diffraction pattern including at least d-spacing data listed in Table 5 shown below: Table 5
2 θ d 100XI7I0
13.9-14.1 6.37-6.28 40-55
19.8-20.0 4.48-4.44 40-48
24.3-24.5 3.66-3.63 100
28.2-28.3 3.16-3.15 12-25
31.4-31.7 2.85-2.82 11-18
34.6-34.8 2.59-2.58 15-18
Using such an aluminum phosphate compound represented by a general chemical formula, AlP04-n, having fine pores whose diameters are substantially the same as those of water molecules , as a desiccant member enables to produce an energy-efficient and compact air conditioning system.
It is still another aspect of the invention that the desiccant member may be regenerated at a temperature of less than 70 °C.
Accordingly, a desiccant assisted air conditioning system, whose humidity is controlled by a desiccant that can be regenerated at lower temperatures relative to conventional desiccant materials, can be operated by a thermal source that can be driven at correspondingly lower temperatures, thereby providing an energy-efficient air conditioning system.
In a final aspect of the invention, process air that has been removed of moisture may be cooled by a low-temperature heat source in a heat pump, and regeneration air that prior to regeneration of the desiccant member may be heated in a high-temperature heat source of the heat pump.
Accordingly, a heat pump is used to cool the dehumidified process air, and the heat is then recycled to raise the temperature of regeneration air, to provide not only a multi-use of heat energy but also a minimization of temperature lift for the heat pump, thereby providing an energy-efficient dehumidifying air conditioning system. Accordingly, the present desiccant assisted air conditioning system is based on dehumidifying the process air using a desiccant member made of a porous aluminum phosphate material (known by a chemical formula AlP04-n by Union Carbide and in academic societies ) produced by reacting a hydrated alumina (for example, aluminum hydride, boehmite, pseudo- boehmite) with phosphoric acid using a thermally dissociatable template agent (organic base group such as tripropylamine, for example). The resulting desiccant material exhibits a large differential adsorption capacity, and can be regenerated at relatively low temperatures . There is no need to use a bulky desiccant, thereby enable to provide a compact system that can offer high energy efficiency at low operating cost.
Brief Description of Drawings
Figure 1 is a graph showing an adsorption isotherm of molecular sieve made with a porous aluminum phosphate system (AlP04-5);
Figure 2 is a graph showing a relation between the temperature of air in contact with the desiccant and water content of desiccant AlP04-5;
Figure 3 is a schematic diagram of a second embodiment of the air-conditioning system of the present invention;
Figure 4 is a psychrometric chart showing the operational states in the system shown in Figure 3;
Figure 5 is a schematic diagram of a third embodiment of the air-conditioning system of the present invention;
Figure 6 is a psychrometric chart showing the operational states in the system shown in Figure 5; Figure 7 is a graph showing an adsorption isotherm of molecular sieve made with a porous aluminum phosphate system (AlP04-5);
Figure 8 is a schematic diagram of a fourth embodiment of the air-conditioning system of the present invention; Figure 9 is a psychrometric chart showing the operational states in the system shown in Figure 8;
Figure 10 is a schematic diagram of a conventional air conditioning system; Figure 11 is a graph of adsorption isotherm for zeolite;
Figure 12 is a schematic diagram of another conventional air conditioning system;
Figure 13 is a psychrometric chart showing the operational states in the system shown in Figure 12; and Figure 14 is a graph showing the relation between air contacting the desiccant and adsorption capacity of zeolite desiccant according to adsorption isotherm shown in Figure 11.
Best Mode for Carrying Out the Invention Preferred embodiments will be presented in the following with reference to the drawings .
In the first embodiment is a dehumidifying air conditioning system shown in Figure 12, in which molecular sieve is used as a desiccant material, which is made of porous aluminum phosphate produced by reacting a hydrated alumina (for example, aluminum hydride, boehmite, pseudo-boehmite) with phosphoric acid using a thermally dissociatable template agent (organic base group such as tripropylamine, for example) of an essential skeletal structure having a chemical formula where "k" is expressed in a mol ratio:
Al203kP205 (k = 1.0±0.2) and having a X-ray powder diffraction pattern including at least d-spacing shown in Table 1. This molecular sieve is generally designated as AlP04-5 by Union Carbide Co. in a Japanese Patent Publication, 1989-57041 or in academic societies. The present inventors measured adsorption characteristics of this molecular sieve called AlP04-5, and obtained the following results.
Figure 1 shows a graph of adsorption isotherm of the porous aluminum phosphate group molecular sieve (AlP04-5). The horizontal axis represents humidity ratio RH and the vertical axis represents relative water content ratio (relative water adsorption amount) defined by a ratio of the measured adsorbed amount W and the amount of adsorption Wmax (maximum uptake) when humidity ratio is 90 %. This material shown in Figure 1 behaves in a similar manner to the desiccant material disclosed in the above-mentioned Japanese Patent Publication, 1989-57041, Example 55, where the moisture adsorption is 4.6 kg/kg at 24 °C at a pressure of 4.6 torr (humidity ratio 20 %) and the moisture adsorption is 26.4 kg/kg at 23 °C at a pressure of 18.5 torr (humidity ratio 88 % ) . Notable feature is that the water content increases rapidly between the values of humidity ratio at 20 and 40 %. This feature also has been reported in institutionary meetings, for example in Figure 4 in an article "Adsorption Properties of Microporous Aluminum phosphate AlP04-5" in "New Developments in Zeolite Science and Technology", pp.539-546, published for International Zeolite Conference, 1986.
Figure 2 shows the relationship, according to the adsorption isotherm shown in Figure 1 , between adsorption capacity of the porous aluminum phosphate group molecular sieve (AlP04-5) and temperature of contacting air with humidity ratio as a parameter. In Figure 2, point A represents the adsorption-start point of the molecular sieve in equilibrium with indoor air, and points D50 and D70 represent the desorption-start points of the molecular sieve in equilibrium with regeneration air at 50 °C and 70 °C. Figure 2 shows that the differential adsorption/desorption amounts are 0.17 and 0.19 kg/kg, respectively, for 50 °C-regeneration and 70 °C- regeneration. These values are larger than those attainable by zeolite or silica-gel regenerated at these temperatures, and show that the present desiccant material can produce essentially the same degree of dehumidification at lower regeneration temperatures as zeolite regenerated at over 100 °C, using about the same weight for both materials. Next, the operation of the present desiccant assisted air conditioning system shown in Figure 12 will be explained using the psychrometric chart shown in Figure 13.
Process air (state K) flows through the desiccant wheel 103 which adsorbs moisture from the process air (state L), and in flowing through the first sensible heat exchanger 104, transfers heat to the regeneration air (state Q) and is cooled (state M) , and is further cooled (state N) in the low-temperature heat source 240 of the heat pump, and returns to the conditioning space 101 as supply air SA. In the meantime, regeneration air is admitted from outdoors (state Q) into the first sensible heat exchanger 104 to receive heat from the process air (state L) thereby raising its temperature (state R) , and enters into the second sensible heat exchanger 121 to receive heat from the post-desiccant regeneration air (state U) thereby raising its temperature (state S), and is further heated in the high- temperature heat source 220 of the heat pump to raise its temperature (state T), and is then flows through the desiccant wheel 103 to desorb the moisture thereby regenerating the desiccant. Post-desiccant regeneration air (state U) transfers heat (state V) in the second sensible heat exchanger 121 to the regeneration air exiting from the first sensible heat exchanger 104, and is discarded as waste gas. Accordingly, the desiccant assisted air conditioning system operates by generating a differential humidity ratio DX and a differential enthalpy DQ between the indoor air (state K) and the supply air (state N) to provide a dehumidification and cooling effect of the conditioning space. The driving energy for the system is afforded by the differential heat obtained by subtracting the afore-mentioned heat DQ from the heat input DG to heat the regeneration air so that desiccant regeneration is carried out utilizing the waste heat generated in a sensible heat treatment process from state M to state N, thereby providing an excellent energy efficiency for the system. In this system, because the supply air temperature (state N) can be made lower than the indoor air temperature (state K) , there is no need to cool the air using the humidifier 105. On the other hand, in the conventional air conditioning systems, because it removes sensible heat from the process air, liquid water is added to the process air after it is dehumidified to cool the process air, therefore, it is necessary to remove more moisture than is truly required based on the difference in the humidity values of supply air and room air. As can be seen in Figure 12, humidifier is not used in the present system, and the net moisture to be removed by the desiccant is low, and therefore, the same degree of dehumidifying and cooling can be achieved by using a smaller amount of desiccant member relative to the amount required by the conventional systems . Accordingly, in the present system, high capacity desorption can be obtained even at low regeneration temperatures , and a small amount of desiccant is sufficient to remove a large amount of moisture, thereby enabling to use a smaller desiccant wheel. Also, desorption temperature for regeneration air (state T) can be selected in the range of 50-55 °C, and therefore, the operating temperature (condensing temperature) of the high-temperature heat source 220 of the heat pump can be lowered, and the power required to operate the heat pump can also be lowered. Present system is overall much more energy conserving, and is more compact compared with the conventional systems.
In the present embodiment, molecular sieve based on porous aluminum phosphate is represented by AlP04-5, however, as recited in the afore-mentioned Japanese Patent, 1989-57041, there are various isomers of A1P04 represented by a general formula AlP04-n. It is known that moisture adsorption by molecular sieve is performed by trapping water molecules at adsorption sites whose cavity size is larger than the diameter of the water molecules. Trapping force is also affected by the presence of metallic ions at the adsorption sites. But, such metallic ions offering a strong attractive force (which may be alkali metals or alkaline earth metals such as sodium or potassium, for example) do not exist in the adsorption sites in the so-called AlP04-n materials . Therefore, these materials are extremely sensitive to the pore size. It is obvious, therefore, that any AlP04-n porous aluminum phosphate isomers having similar fine pore sizes can be used as an variation of the desiccant material used in this embodiment.
For example, AlP04-5 is reported to have a strong I/I0 peak in a range of d-spacing between 3.93-4.51 angstroms according to Table 2 in the afore-mentioned Japanese Patent 1989-57041, and other isomers that have such characteristics are also disclosed as follows.
(1) In Table 4, it is reported that AlP04-8 has a strong I/I0 peak between 4.17-4.19 angstroms, and exhibits a strong moisture adsorption behavior in Example 62-A.
(2) In Table 8, it is reported that AlP04-ll has a strong I/I0 peak between 4.19-4.23 angstroms, and exhibits a strong moisture adsorption behavior in Example 63. (3) In Table 13, it is reported that A1P04-16 has a strong I/I0 eak between 4.00-4.06 angstroms, and exhibits a strong moisture adsorption behavior in Example 60.
(4) In Table 19, it is reported that AlPO4-20 has a strong I/IQ peak between 3.63-3.66 angstroms, and exhibits a strong moisture adsorption behavior in Example 58.
Figure 3 shows the system configuration in a second embodiment. The air conditioning system shown in Figure 3 is a hybrid system combining a desiccant and a heat pump as in Figure 12, but without the first sensible heat exchanger 104, and the desiccant wheel 103 uses the porous aluminum phosphate molecular sieve, represented by the so-called AlP04-n formula. In this system, process air and regeneration air do not exchange heat so that the process air is supplied at higher temperatures. Therefore, this type of system is most suitable when the use is primarily dehumidification involving low sensible heat ratios . The operation of this system will be explained with reference to the psychrometric chart shown in Figure 4 related to the system shown in Figure 3. Process air (state K) flows through the desiccant wheel 103 which adsorbs moisture (state L), and is cooled (state M) in the low-temperature heat source 240 of the heat pump and returns to the conditioning space 101. In the meantime, regeneration air, which is outdoor air (state Q), enters into the sensible heat exchanger 121 to receive heat from the post-desiccant regeneration air (state U) thereby raising its temperature ( state S ) , and is f rther heated in the high- temperature heat source 220 of the heat pump to raise its temperature (state T) , and then flows through the desiccant wheel 103 to desorb the moisture. Post-desiccant regeneration air (state U) transfers heat (state V) to the regeneration air in the sensible heat exchanger 121, thereby returning heat to the system and is discarded as waste gas . Accordingly, the desiccant assisted air conditioning system performs its functions by generating a differential humidity ratio DX and a differential enthalpy DQ between the indoor air (state K) and the supply air (state M) . Compared with the first embodiment, the temperature of supply air is higher and is close to room air temperature, and therefore, it is most suitable when the conditioning load is primarily humidity lowering ( latent heat load) . If the supply air temperature is adjusted to 27 °C which is about the same as room air temperature, the temperature difference between regeneration air at 50 °C and supply air is only 23 °C, so that the temperature lift, i.e., temperature difference between the low- and high-temperature heat sources of the heat pump will be 33 °C by adding 10 °C to 23 °C. Compared with the conventional vapor compression type air conditioning systems, the heat pump can be operated at a much lower temperature lift, thereby enabling to conserve energy. Because a dew drainage is not needed, the facility becomes simpler, and as in the first embodiment system, small amount of desiccant member is needed to treat a large amount of moisture so that the desiccant wheel can be made compact. Therefore, the overall system exhibits superior energy efficiency and a compact arrangement is effective for equivalent performance.
Figure 5 shows the system configuration in a third embodiment. The air conditioning system shown in Figure 5 is also a hybrid system similar to the one shown in Figure 3, but the difference is that the process air is a mixture of outdoor air and indoor return air while the regeneration air is a mixture of indoor exhaust air and outdoor air. For this reason, in addition to the system configuration shown in Figure 3 , a passage 161 and a blower 160 are provided between a process air passage 107 and an outdoor air admittance passage 124 for mixing outdoor air with return room air, and a passage 162 is provided between a regeneration air passage 124 and a return air passage 107 for mixing the return room air with outdoor air. In such a system, because the humidity ratio of the process air at the adsorption-start point of the desiccant is higher than that specified in the Japanese Industrial Standards ( JIS) for indoor comfort, regeneration air must be heated to a higher temperature in order to maintain the humidity at 7 g/kg as in the previous embodiment; however, the same benefits as before are accrued using the desiccant member of the present invention. In the following, the operation of the system based on A1PO.-5 material will be explained with reference to the psychrometric chart shown in Figure 6, and the relation of air temperature and moisture adsorption at varying humidity ratio levels shown in Figure 7. Mixed process air (stateF) comprised by outdoor air (state Q) and indoor return air (state K) flows through the desiccant wheel 103 which adsorbs moisture (state L) , and is further cooled (state M) in the low-temperature heat source 240 of the heat pump and returns to the conditioning space 101. In the meantime, regeneration air is also a mixture (state G) comprised by outdoor air (state Q) and return indoor air (state K) enters into the sensible heat exchanger 121 to receive heat from the post- desiccant regeneration air (state U), thereby raising its temperature (state S), and is further heated in the high- temperature heat source 220 of the heat pump to raise the temperature (state T) , and flows through the desiccant wheel 103 to desorb the moisture. Post-desiccant regeneration air (state U) transfers heat to the regeneration air(state V) in the sensible heat exchanger 121, thereby returning heat to the system and is discarded as waste gas . Accordingly, the desiccant assisted air conditioning system performs its functions by generating a differential humidity ratio DX and a differential enthalpy DQ between the indoor air (state K) and the supply air (state M) .
Compared with the second embodiment system, this system based on mixing indoor air with outdoor air is most suitable for maintaining a certain level of comfort in the indoor environment. Assuming that, on a typical mid-summer day, indoor air is at 27 °C with a 50 % humidity ratio (RH) and outdoor is at 33 °C with a 63 % RH, then, pre-desiccant process air is mixed with outdoor air having a humidity ratio of 20 g/kg to become process air at a dry-bulb temperature of 29 °C and a humidity ratio of 13 g/kg as shown in Figure 6. After being dehumidified by adsorption in the desiccant member, process air moves along the isenthalpic line to a humidity ratio of 7 g/kg at state L having a humidity ratio of about 10 % (more accurately 11 %). Therefore, the temperature of regeneration air for desorption-start is 65 °C, as described before, according to the intersection point of the humidity ratio line at 10 % and the humidity ratio line at 17 g/kg. On the other hand, pre-desiccant regeneration air is at dry bulb temperature of 31 °C and a humidity ratio of 17 g/kg because of mixing with return air having a humidity ratio of 10 g/kg. Therefore, the desiccant condition at the desorption-start point (state T) is at a dry-bulb temperature of 65 °C and a humidity ratio of 17 g/kg. The differential adsorption capacity of the desiccant member, given by the difference between the adsorption-start state F (dry-bulb temperature at 29 °C and humidity ratio of 13 g/kg) and the regeneration-start state T (dry-bulb temperature at 31 °C and humidity ratio at 17 g/kg) is 0.19 g/kg as indicated in Figure 7 for this material. The moisture adsorption capacity is as large as what was shown in Figure 2. The operation of the various devices for process air and regeneration air is the same as in the second embodiment, and will not be repeated.
As demonstrated in this embodiment, even when it is necessary to raise the regeneration temperature slightly about 65 °C because of mixing with outdoor air, differential adsorption capacity of the material remains high so that a small amount of material is needed to perform an equal degree of dehu idification, thereby enabling to provide a compact desiccant wheel. Also, the temperature of regeneration air can be set low (state T), so that the operating temperature (condensation) of the high temperature heat source 220 of the heat pump is lowered, thereby lowering the drive power for the compressor of the heat pump. The overall system is thus energy efficient and compact.
Figure 8 shows the system configuration in a fourth embodiment of the invention. This system is similar to the so-called desiccant-assisted air conditioning system without the heat pump shown in Figure 10. The difference is that dehumidified process air is cooled in the heat exchanger 104 by means of heat exchange with the outdoor air which is humidified in a humidifier 105, thereby eliminating heat exchange between process air and regeneration air. In the conventional systems, regeneration air is first humidified to lower its dry-bulb temperature and is then subjected to heat exchange with process air, but in such a process, humidity ratio of the regeneration WO 99/36733 .. PCTΛJP99/00076
air becomes elevated, and in order to attain the same level of humidity ratio in the regeneration air as in the dehumidified process air, it is necessary to heat the regeneration air to a high temperature. But the present system avoid this difficulty by providing a separate cooling path for cooling the process air. The operation of the system shown in Figure 8 will be explained using a psychrometric chart given in Figure 9.
Process air (state K) flows through the desiccant wheel 103 and is removed of its moisture (state L), and is further cooled (state M) in the cooler 104 by the humidified outdoor air and returns to the conditioning space 101. In the meantime, regeneration air is admitted from outdoors (state Q) and enters into the sensible heat exchanger 121 to receive heat from the post-desiccant regeneration air (state U) thereby raising its temperature (state S), and is further heated in the heater 220 (state T), and then flows through the desiccant wheel 103 to desorb the moisture. Post-desiccant regeneration air (state U) transfers heat, in the sensible heat exchanger 121, to the incoming regeneration air (state Q) , and the cooled regeneration gas (state V) is discarded as waste gas. In a separate thermal circuit, cooling air which is outdoor air (state Q) is admitted into the humidifier 105, so that its temperature is lowered (state D) by the heat of vaporization of water, and then it is mixed in the heat exchanger 104 to remove heat from the process air (state L) to produce supply air (state M) , and the warmed cooling air (state E) is discarded as waste gas.
Accordingly, a humidity ratio difference DX is generated between room air (state K) and supply air (state M) to provide a dehumidifying effect. Compared with conventional systems, because the supply air temperature is lower and is closer to the room air temperature, sensible heat load of the room air is not increased, so that the system is suitable when a conditioning load requires primarily dehumidification (latent heat load) . Outdoor summer temperature is generally around 28 °C, which is not much different than indoor air temperature, so that room dehumidification can be achieved without increasing the sensible heat load by using the present system in which no humidifier is provided in the process air passage. Therefore, latent heat load can be processed by using low temperature heat source at 50-70 °C such as waste heat or solar heating instead of using vapor compression cycle type cooling system. As in the first embodiment system, a small amount of desiccant member is sufficient to process a large amount of moisture, thereby providing a compact desiccant wheel. Therefore, compared with the conventional system, the present system offers superior energy efficiency with a compact air conditioning system.
Industrial Applicability The present invention is advantageous as an air conditioning system used in general dwelling houses or larger buildings used as supermarket or business offices.

Claims

1. A desiccant assisted air conditioning system comprising: a process air path for flowing process air to adsorb moisture from said process air by a desiccant member; and a regeneration air path for flowing regeneration air heated by a heat source to desorb moisture from said desiccant member, said desiccant member being arranged so that said process air or said regeneration air flows altematingly through said desiccant member; wherein said desiccant member comprises a porous aluminum phosphate material having an essential skeletal structure with a general chemical formula, Al203k(P205) , where k = 1.0┬▒0.2, expressed in a mol ratio.
2. A system according to claim 1, wherein said porous aluminum phosphate material is AlP04-n.
3. A system according to claim 1 , wherein said porous aluminum phosphate material is produced by reacting a hydrated alumina and phosphoric acid in a thermally dissociatable template agent.
4. A system according to claim 1, wherein said porous aluminum phosphate material is represented by a formula, AlP04-5, and having a characteristic X-ray powder diffraction pattern including at least d-spacing data listed in Table 1 shown below:
Table 1 2 ╬╕ d 100XI/I0
7.4-7.6 11.9-11.6 100
14.8-15.3 5.97-5.83 13-43
19.7-20.1 4.51-4.42 39-92
20.8-21.2 4.27-4.19 37-87
22.3-22.7 3.99-3.93 62-118
25.9-26.3 3.44-3.39 22-35
5. A system according to claim 1, wherein said porous aluminum phosphate material is represented by a formula, AlP04-8, and having a characteristic X-ray powder diffraction pattern including at least d-spacing data listed in Table 2 shown below:
Table 2 2 ╬╕ d 100XI/I0
5.3-5.4 16.7-16.4 80-100
6.50-6.65 13.6-13.3 30-100
19.7-19.8 4.51-4.48 8-29
21.2-21.3 4.19-4.17 46-82
21.8-21.9 4.08-4.06 14-56
22.4-22.9 3.97-3.88 35-39
6. A system according to claim 1, wherein said porous aluminum phosphate material is represented by a formula, A1P04-11, and having a characteristic X-ray powder diffraction pattern including at least d-spacing data listed in Table 3 shown below:
Table 3
2 ╬╕ d 100XI/I0
9.4-9.5 9.41-9.31 31-49
20.5-20.6 4.33-4.31 34-53
21.00-21.25 4.23-4.19 100
22.15-22.25 4.01-4.00 12-58
22.50-22.70 3.95-3.92 47-75
23.15-23.50 3.84-3.79 10-68
7. A system according to claim 1, wherein said porous aluminum phosphate material is represented by a formula, A1P04-16, and having a characteristic X-ray powder diffraction pattern including at least d-spacing data listed in Table 4 shown below: Table 4
20 d 100XI/I0
11.3-11.5 7.83-7.69 59-63
18.70-18.85 4.75-4.71 48-54
21.9-22.2 4.06-4.00 100
26.55-26.75 3.36-3.33 23-27
29.75-29.95 3.00-2.98 26-30
8. A system according to claim 1, wherein said porous aluminumphosphatematerial is represented by a formula, AlPO4-20, and having a characteristic X-ray powder diffraction pattern including at least d-spacing data listed in Table 5 shown below:
Table 5 2 ╬╕ d 100XI/I0
13.9-14.1 6.37-6.28 40-55
19.8-20.0 4.48-4.44 40-48
24.3-24.5 3.66-3.63 100
28.2-28.3 3.16-3.15 12-25
31.4-31.7 2.85-2.82 11-18
34.6-34.8 2.59-2.58 15-18
9. A system according to claim 1, wherein said desiccant member is regenerated at a temperature of less than 70 ┬░C.
10. A system according to claim 8, wherein process air that has been removed of moisture is cooled by a low-temperature heat source in a heat pump, and regeneration air that prior to regeneration of said desiccant member is heated in a high- temperature heat source of said heat pump.
PCT/JP1999/000076 1998-01-14 1999-01-13 Desiccant assisted air conditioning system WO1999036733A1 (en)

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