WO2013054322A1

WO2013054322A1 - Dehumidifier and method of use thereof

Info

Publication number: WO2013054322A1
Application number: PCT/IL2012/000353
Authority: WO
Inventors: Gad Assaf
Original assignee: Agam Energy Systems Ltd.
Priority date: 2011-10-11
Filing date: 2012-10-09
Publication date: 2013-04-18
Also published as: JP6165150B2; IL215720A; IL215720A0; KR20140081785A; JP2014532160A

Abstract

A dehumidifier (10) includes a desiccant reservoir (14) having an inlet (16) for adding concentrated liquid desiccant and an outlet (18) for removing less concentrated liquid desiccant. An air inlet (20) downstream of a vapor condenser (22) receives humid air and an air exit (24) upstream of the vapor condenser (22) emits dry air into an enclosure (12). A pump (26) coupled to the outlet (18) pumps liquid desiccant from the reservoir through spray nozzles (28) on to the vapor condenser (22), which absorbs water vapor from the humid air and heats the liquid desiccant. A regenerator (30) removes water from the less concentrated liquid desiccant and replenishes concentrated liquid desiccant to the reservoir (14). A cooling element (32) cools the liquid desiccant in the dehumidifier and/or the condensing water in the regenerator, and a heat sink (36) recovers the heat of condensation.

Description

Dehumidifier and Method of Use Thereof

FIELD OF THE INVENTION

The present invention relates to dehumidification systems and methods, and more particularly, to a liquid desiccant regenerator (LDR) for the dehumidification of air in an enclosure, and to a method for dehumidification.

BACKGROUND OF THE INVENTION

US Patent No. 6,266,975 discloses a desiccant (brine) regenerator based on a vapor compressor. The regeneration maintains the desiccant as a concentrate, since effective vapor sinks even in humid conditions. US Patent No. 6,463,750 discloses a system for dehumidification of air in an enclosure which includes an air brine heat exchanger for heating cold fresh air introduced into the heat exchanger from the outside and for dehumidifying the air within the enclosure by vapor condensation.

US Patent No. 4,355,683 discloses an air conditioning system and/or a heating system in combination with a solar pond, wherein it is important to maintain a concentration of salt which increases with the depth of the pond. The pond is regenerated, that is, the salt concentration gradient is maintained, by components of the air conditioning system, or by special concentrator towers wherein moisture is removed from brine that is circulated to the towers from the pond.

US Patent No. 4,205,529 discloses a hybrid air conditioning system that combines a solar powered LiCl dehumidifier with a LiBr absorption chiller. The desiccant dehumidifier removes the latent load by absorbing moisture from the air, and the sensible load is removed by the absorption chiller. The desiccant dehumidifier is coupled to a regenerator and the desiccant in the regenerator is heated by solar heated hot water to drive the moisture therefrom before being fed back to the dehumidifier. The heat of vaporization expended in the desiccant regenerator is recovered and used to partially preheat the driving fluid of the absorption chiller, thus substantially improving the overall COP of the hybrid system. WO 03/004937 in the name of the present Applicant discloses an air conditioning system for an environment within an enclosure, the system including an air/water cooling tower in fluid flow communication, via a heat exchanger, with a brine/air heat exchanger, and a brine regenerator in fluid flow communication with the brine/air heat exchanger, the brine/air heat exchanger having an air outlet to the enclosure and an air inlet.

US Patent No. 7,938,888 in the name of the present Applicant discloses a liquid desiccant regenerator dehumidification system, including a desiccant/air heat exchanger having a first desiccant inlet and a desiccant reservoir. The reservoir has a first desiccant outlet, a second desiccant outlet and a second desiccant inlet. The first desiccant inlet and the first desiccant outlet are connectable to a heat source, the second desiccant inlet conducts diluted desiccant of the reservoir and the second desiccant outlet conducts concentrated desiccant from the reservoir. The second desiccant inlet and the desiccant outlet are connected to a desiccant/desiccant heat exchanger for applying heat to the diluted desiccant flowing into the reservoir. The desiccant air heat exchanger and the desiccant reservoir are both exposed to air. The system dehumidifies by pumping concentrated liquid desiccant from the desiccant reservoir to the heater and returning heated concentrated liquid desiccant from the heater to the first desiccant inlet at a rate such that the mass flow rate of the desiccant flow into the regenerator is at least twice the mass flow rate of the condensed water. The desiccant regenerator exchanges diluted desiccant flowing into the regenerator via the inlet with concentrated desiccant discharging from the regenerator via the first desiccant outlet, and the temperature of the concentrated desiccant is higher than the temperature of the diluted desiccant, so as to introduce heat from the regenerator to a vapor condenser, and the heat elevates the temperature of the diluted desiccant, which functions as a vapor sink.

In the dehumidifier of US Patent No. 7,938,888 dry warm air exits from the dehumidifier at the same enthalpy as the cold humid air introduced therein. This is achieved by virtue of the fact that the humidity in the air condenses on the brine, the condensation heats the brine and the brine heats the air. In other words the adiabatic humidifier converts the latent heat of the water vapor in the air to sensible heat, i.e. the air temperature rises. In the dehumidifier of US Patent No. 7,938,888 desiccant is sprayed on to humid air so as to absorb water vapor from the air and dry it. In doing so, the water vapor in the air changes phase so that its latent heat is converted to sensible heat and the desiccant becomes heated. Heat from the desiccant will be passed to the surrounding air until a point of equilibrium is reached where the temperature of the desiccant is just sufficiently high to release all the latent energy back to the air as sensible heat. In the constant enthalpy dehumidifier described in US Pat. No. 7,938,888 this imposes an effective limit on the amount of water that can be removed, as will now be explained. 1 gram of water has a latent heat of 2,500 Joules. The specific heat of air is 1,000 Joules/kg/°C. Consequently, in order to maintain constant enthalpy of the air when condensing 1 gram of water vapor in a mixture of 1kg of air, the air temperature must be elevated by 2.5°C. This heat can only be provided by the desiccant which must therefore be warmer than the air by at least this amount This imposes a limit on the amount of water vapor in the air that can be removed since the more water vapor that is condensed from the air the higher must be the temperature gradient between the desiccant and the air. However, the hotter the desiccant becomes, the less effective it becomes as a drying agent.

Likewise, as the desiccant absorbs water vapor it becomes more dilute and less effective and, to this end, a regenerator is provided which serves to remove the absorbed water vapor from the desiccant and return the concentrated desiccant to the reservoir of the dehumidifier. Here, too, there is a practical limit to the concentration of the desiccant since, on the one hand, the more concentrated the desiccant, the greater is the efficiency of the dehumidifier, while on the other hand, the more concentrated the desiccant, the harder it is for the regenerator to remove the absorbed water vapor.

By way of example, in the constant enthalpy (i.e. adiabatic) dehumidifier disclosed in US Pat. No. 7,938,888, to remove 3 gram of water vapor per kilogram of air the desiccant activity in the dehumidifier must be approximately 30%, i.e. the partial vapor pressure of the desiccant in the dehumidifier should be 0.3 and its temperature should be approximately 30°C. Even then it is to be noted that at this activity many desiccants may crystallize, thereby rendering it impossible to remove the required humidity and those desiccants such as LiCl and LiBr which do not crystallize at this activity are expensive. Moreover, the desiccant that is evaporated in the regenerator is more concentrated than the desiccant in the dehumidifier and therefore its partial vapor pressure is less, e.g. 25%. To evaporate desiccant at this activity requires high temperature of the desiccant and low temperature of the water in the regenerator thereby rendering it practically impossible to remove the heat from the water. One possible solution to avoid crystallization of the desiccant as suggested in US Pat. No. 7,938,888 is to ensure that the mass flow rate of the desiccant flow in the regenerator is at least twice the mass flow rate of the condensed water in the dehumidifier.

It would therefore be desirable to find an alternative approach to drying the air which would allow much higher quantities of humidity to be removed from the air while not requiring highly concentrated desiccant so as to facilitate effective regeneration without the risk of crystallization of the desiccant.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a dehumidifier that allows higher quantities of humidity to be removed from the air than hitherto-proposed systems while not requiring highly concentrated desiccant.

In accordance with the present invention, there is provided a dehumidifier for dehumidifying air inside an enclosure, said dehumidifier comprising:

a desiccant reservoir inside the enclosure having a desiccant inlet for adding concentrated liquid desiccant and a desiccant outlet for removing less concentrated liquid desiccant;

an air inlet within the enclosure downstream of a dehumidifier vapor condenser for receiving humid air and an air exit within the enclosure upstream of the dehumidifier vapor condenser for exiting dry air into the enclosure,

a pump coupled to the desiccant outlet for pumping liquid desiccant from the reservoir through spray nozzles on to the dehumidifier vapor condenser so as to absorb water vapor from the humid air and heat the liquid desiccant, whereby the air exiting through the air exit is drier than the air entering the air inlet, and

a regenerator coupled to the desiccant inlet and to the desiccant outlet of the desiccant reservoir for removing water from the less concentrated liquid desiccant conveyed out of the desiccant outlet and replenishing concentrated liquid desiccant to the desiccant reservoir via the desiccant inlet; characterized by:

a cooling element for cooling the liquid desiccant in the dehumidifier and/or the condensing water in the regenerator by absorbing latent heat of condensation of the liquid desiccant in the dehumidifier and/or of condensing water in the regenerator, and a heat sink for recovering said heat of condensation.

In accordance with another aspect of the invention, there is provided a method for dehumidifying air in an enclosure, the method comprising:

conveying humid air in the enclosure to an air inlet of an dehumidifier vapor condenser that is coupled to a desiccant reservoir,

pumping liquid desiccant from the desiccant reservoir through spray nozzles on to the dehumidifier vapor condenser so as to absorb water vapor from the humid air and heat the liquid desiccant, whereby the air exiting through an air exit of the dehumidifier vapor condenser is drier than the air entering the air inlet,

using a regenerator to remove water from less concentrated liquid desiccant conveyed out of the desiccant reservoir and replenishing concentrated liquid desiccant to the desiccant reservoir;

characterized by:

cooling the liquid desiccant in the dehumidifier and/or the condensing water in the regenerator by absorbing latent heat of condensation of the liquid desiccant in the dehumidifier and/or of condensing water in the regenerator, and

recovering said heat of condensation by a heat sink.

As will be explained below, the dehumidifier according to the invention is not adiabatic (i.e. constant enthalpy) but, to the contrary, is a varying enthalpy system.

In some embodiments, the invention cools the desiccant in the dehumidifier since cooling the desiccant to e.g. 15°C where the air in the enclosure is 20°C makes it is possible for the desiccant to have an activity of 60% in the dehumidifier. The activity of the desiccant in the regenerator will then be approximately 55%, which allows the temperature of desiccant in the regenerator to be only 60°C while the temperature of the water can be as low as 40°C, thus making it possible to remove the heat from the water. Furthermore, this permits all common desiccants such as MgCl and CaCl to be used, which are much less expensive than LiCl and LiBr without the risk of crystallization. BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

Figs. 1 to 5 are schematic views of a dehumidifier according to different embodiments of the present invention; and

Fig. 6 is a psychometric chart useful for explaining operation of the dehumidifier.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description of some embodiments, identical components that appear in more than one figure or even in the same figure or that share similar functionality will be referenced by identical reference symbols.

Fig. 1 shows schematically a dehumidifier 10 for dehumidifying air inside an enclosure 12, comprising a desiccant reservoir 14 inside the enclosure having a desiccant inlet 16 for adding more concentrated liquid desiccant and a desiccant outlet 18 for removing less concentrated liquid desiccant. Also provided within the enclosure 12 are an air inlet 20 downstream of a dehumidifier vapor condenser 22 for receiving humid air and an air exit 24 upstream of the dehumidifier vapor condenser 22 for releasing dry air into the enclosure 12. A pump 26 is coupled to the desiccant outlet 18 for pumping liquid desiccant from the desiccant reservoir 14 through spray nozzles 28 on to the dehumidifier vapor condenser 22 so as to absorb water vapor from the humid air. In doing so the water vapor gives up latent heat, which heats the liquid desiccant, whereby the air exiting through the air exit 24 is drier than the air entering the air inlet 20. A regenerator 30 is coupled to the desiccant inlet 16 and to the desiccant outlet 18 of the desiccant reservoir 14 for removing water from the less concentrated liquid desiccant conveyed out of the desiccant outlet 18 and replenishing concentrated liquid desiccant to the desiccant reservoir 14 via the desiccant inlet 16. A cooling element 32 is disposed between the desiccant outlet 18 and the dehumidifier vapor condenser 22 for cooling the liquid desiccant prior to its reaching the dehumidifier the dehumidifier vapor condenser 22 by absorbing latent heat of condensation of the liquid desiccant thereby reducing the temperature of the liquid desiccant in the dehumidifier vapor condenser 22. The latent heat of condensation is recovered by a heat sink 34 coupled to the cooling element 32.

In the embodiment shown in Fig. 1, the cooling element 32 is constituted by an evaporator 36 connected in series with a compressor 38, which together function as a heat exchanger that removes heat from the liquid desiccant to a refrigerant, which may be a chlorofluorocarbon such Freon™ or to a hydrofluorocarbon and then conveys the removed heat from the refrigerant to a condenser 40 in series with the compressor 38. Freon is a trademark of E. I. du Pont de Nemours and Company. An expansion valve 42 controls the amount of refrigerant flow into the evaporator 36 thereby controlling the superheating at the outlet of the evaporator 36. Although the condenser 40 is shown within the enclosure it may equally well be outside the enclosure.

As noted above, the function of the regenerator 30 is to remove water from the less concentrated liquid desiccant and replenish concentrated liquid desiccant to the desiccant reservoir 14. The exact construction of the regenerator 30 is not a feature of the invention as long is it is capable of realizing this function. The regenerator 30 may be constructed in a similar manner to that employed in our US Patent No. 7,938,888 as will now be described with reference to Fig. 1.

Thus, by way of example, the regenerator 30 is shown as a closed loop dual stage evaporator comprising an interconnected evaporator 44a and condenser 44b each including a respective reservoir 46a, 46b, a respective air inlet 48 a, 48b and a respective air outlet 50a, 50b. The reservoir 46a contains desiccant while the reservoir 46b contains water. The air outlet 50a of the evaporator 44a is coupled to the air inlet 48b of the condenser 44b to form a closed loop while the air outlet 50b of the condenser 44b is coupled to the inlet 48a of the evaporator 44a also to form a closed loop. Diluted desiccant in the reservoir 14 at ambient temperature, e.g. 20°C is pumped by the pump 26 to the desiccant reservoir 46a in the regenerator 30. Since the regenerator 30 requires that the desiccant be at an elevated temperature, e.g. 65°C, the desiccant reservoir 46a of the regenerator 30 is preferably coupled to the desiccant reservoir 14 of the dehumidifier 10 via a desiccant/ desiccant heat exchanger 52, which heats the diluted desiccant flowing from the dehumidifier 10 to the regenerator 30 and cools the concentrated desiccant flowing from the regenerator 30 back to the dehumidifier 10. A desiccant/air heat exchanger 54 coupled to a heater 56 has a desiccant inlet 58 coupled to the desiccant reservoir 46a. A pump 60 conveys desiccant from the desiccant reservoir 46a to the desiccant/air heat exchanger 54, which conveys heated diluted desiccant via a desiccant outlet 62 through spray nozzles 64a on to the evaporator 44a. Air entering the air inlet 48a is heated on contact with the evaporator 44a and is thereby 5 able to hold more water, which it absorbs from the diluted desiccant, thereby increasing its concentration. The concentrated desiccant is returned to the reservoir 14 of the dehumidifier 10 via the desiccant/desiccant heat exchanger 52. Having absorbed heat from the diluted desiccant, the air exiting from the air outlet 0a of the evaporator 44a is now both hotter and wetter than the air entering the air inlet 48a. The hot moist air

10 circulates through the closed loop to the air inlet 48b of the condenser 44b, which condenses water from the air and conveys the condensed water into the reservoir 46b. The heat of condensation is recovered by a heat regenerating system 66 which serves as a heat sink 34 that receives hot water from the reservoir 46b via a pump 68, which it radiates to the enclosure 12. This cools the water which is then returned through spray

15 nozzles 64b on to the condenser 44b.

Fig 2 shows a second embodiment where the cooling element 32 comprises a heat exchanger 70 which removes heat from the desiccant in the dehumidifier vapor condenser 22 and conveys the removed heat to cold water 72 in a reservoir, for example, an aquifer or swimming pool 74. The cold water at a temperature of around

20 5°C is pumped to the heat exchanger 70 by a pump 76 and may further be transmitted to the vapor condenser 44b in the regenerator 30 where the cold water is further heated and returned to the aquifer or swimming pool 74 as warm water 78 at a temperature of around 35°C for other uses such as space heating and the like.

Fig. 3 shows a third embodiment of a hybrid system where the cooling element

25 32 is effectively shared between the dehumidifier 10 and the regenerator 30. Thus, a heat exchanger comprising an evaporator 36 in series with a compressor 38 is connected between the reservoir 14 of the dehumidifier 10 and the reservoir 46a of the regenerator 30, and removes heat from the liquid desiccant to a refrigerant and then conveys the removed heat from the refrigerant to a condenser 40 in series with the compressor 38.

30 An expansion valve 42 controls the amount of refrigerant flow into the evaporator 36 thereby controlling the superheating at the outlet of the evaporator 36. Although the condenser 40 is shown within the enclosure 12 it may equally well be outside the enclosure. The condenser 40 is connected between the reservoir 46a evaporator 44a of the regenerator 30. The evaporator 36 cools the desiccant in the dehumidifier vapor condenser 22 by removing heat which is then conveyed to the condenser and transferred to the desiccant in the regenerator 30. The heat sink 34 is realized by an aquifer or swimming pool 74. Cold water 72 from the aquifer or swimming pool 74 is directed on to the condenser 44b so as to absorb moisture from the hot moist air reaching the air inlet 48b of the condenser 44b, thereby making the air drier. The condensed water is warmed by the latent heat of condensation and flows into the reservoir 46b from where it is pumped by a pump 76 as hot water 78 back to the aquifer or swimming pool 74. The cold water 72 and the hot water 78 may be stored in separate tanks.

In the embodiments shown in Figs. 1 to 3, the cooling element 32 cools liquid desiccant in the dehumidifier vapor condenser 22, since the colder the liquid desiccant in the dehumidifier 22, the more effectively it is able to absorb water vapor from the air in the enclosure 12.

Fig. 4 shows a fourth embodiment where the cooling element 32 comprises an evaporator 36 connected between the reservoir 46b and the condenser 44b in the regenerator 30 for removing heat from the liquid desiccant in the condenser 44b. The heat thus removed is conveyed by a compressor 38 to a condenser 40 connected between the reservoir 46a and the evaporator 44a in the regenerator 30. Heat is removed from the condensed water and fed to the desiccant evaporator 44a. In this way the water at the regenerator condenser is kept cold which enhances the regenerator effect. Although not shown in the figure, an additional heat pump may be coupled to the dehumidifier 10 similar to the arrangement shown in Fig. 1 and comprising an evaporator for removing heat from the desiccant vapor condenser 22 and a condenser for conveying the removed heat to the air in the enclosure 12.

Fig. 5 shows a fifth embodiment where the heat sink 34 is realized by an aquifer or swimming pool 74. Cold water 72 from the aquifer or swimming pool 74 is directed on to the condenser 44b so as to absorb moisture from the hot moist air reaching the air inlet 48b of the condenser 44b, thereby making the air drier. The air is condensed by the condenser 44b and the cold condensed water flows into the reservoir 46b from where it is pumped by a pump 76 as hot water 78 back to the aquifer or swimming pool 74. In order better to appreciate the improvement of the varying enthalpy dehumidifier according to the invention over the adiabatic (i.e. constant enthalpy) dehumidifier described in US Pat. No. 7,938,888, we will first consider operation of the adiabatic dehumidifier with reference to the psychometric chart shown in Fig. 6, which plots desiccant activity for varying conditions of temperature and relative humidity. Moreover, since the components of the adiabatic dehumidifier exist also in the varying enthalpy dehumidifier 10 shown in Fig. 1, we will refer to these components with reference to Fig. 1.

Liquid desiccant is characterized by vapor pressure, which is low, compared with the vapor pressure of water at the same temperature. The ratio of desiccant vapor pressure to water pressure at the same temperature is defined as the "activity" a. Thus, for example, the desiccant LiCl, at a concentration of S=25%, is characterized by vapor pressure which is half that of water at the same temperature and has an activity of =50%. At S=40%, the activity -25%. At a given concentration the desiccant will follow the relative humidity curve on the psychometric chart. For example, for lithium chloride (LiCl) having a salt concentration of 40% the activity ratio is 20%, while at a salt concentration of 30% the activity is about 40%. At a concentration of 20% the activity becomes 60%. At the same ambient temperature lithium chloride and lithium bromide remain liquid at an activity a=20% or so. Yet common inexpensive liquid desiccants like CaCl and MgCl will crystallize when their salt concentration corresponds to an activity below 40% or so.

With reference to the adiabatic dehumidifier disclosed in US Pat. No. 7,938,888 and the psychometric chart shown in Fig. 6, air enters the adiabatic dehumidifier vapor condenser 22 at a temperature of 20°C and vapor content of 12 gram/kg marked 1 in Fig. 6 and exits at a temperature of 25 °C and 10 gram vapor/kg. In other words, only 2 gram of water vapor per kg air has been removed from the air. This means that while in the adiabatic dehumidifier all the latent heat is converted to sensible heat, the dehumidification rate is only 2 gram vapor to 1 kg air. The liquid desiccant interface in this example remains at a relative humidity of 40%, with vapor concentration of 9 g kg and T= 27.5°C. In the process, the desiccant collects 2 gram water for each kg of air that is introduced into the dehumidifier. Applying this to the dehumidifier 10 in Fig. 1, to maintain the concentration at steady state, the regenerator 30 must remove water from the desiccant at the same rate that the cold desiccant at the dehumidifier vapor condenser 22 shown in Fig. 1 collects the water vapor.

Assuming that the concentration of liquid desiccant LiCl in the dehumidifier vapor condenser 22 is 30% with =40%, the desiccant concentration in the regenerator 5 30 will be higher, say 35% LiCl with =35%. At the regenerator 30, low activity desiccant requires a high desiccant temperature at the evaporator 36 Fig. 1 which evaporates "dry steam" at high temperature and low vapor pressure. To be an effective condenser of dry steam, cold water should be introduced from the heat sink 34 to the water condenser 44b. However when the water at the pump 66 is too cold, the heat sink

10 34 cannot transmit heat to the enclosure 12.

It may be concluded that the constant enthalpy dehumidifier disclosed in US Pat. No. 7,938,888 cannot remove more than 2 gram water/kg air and requires costly desiccants which do not crystallize at low activity.

Now let us compare operation of the dehumidifier 10 according to the present

15 invention where the desiccant has an activity ratio of a=50% and yet it is effective as dehumidifier with heat recovery.

Thus, reverting to the first embodiment shown in Fig. 1, the improvement results from cooling the desiccant in the dehumidifier 10 by the cooling element 32 and conveying the heat removed from the desiccant either to the air or for other needs.

20 In the psychometric chart shown in Fig. 6, the desiccant interface will follow the curve of relative humidity of 50% while being cooled from 22°C to 17°C by the evaporator 36 in Fig. 1 or the evaporator 70 in Fig. 2. The air will follow the isothermal line from vapor content of 12 gram to 8.5g which reduces the humidity by 3.5 gram kg. as compared with a maximum 2 gram depletion in the adiabatic dehumidifier.

25 The desiccant is heated by the air vapor condenser 44b from 17°C to 22°C. The vapor content depletion of air exiting the varying enthalpy dehumidifier according to the invention is therefore 3.5 gram/kg since air enters at 12 gram/kg and exits at 8.5 gram/kg as compared with vapor content depletion of 2 gram/kg in the adiabatic dehumidifier.

30 Thus the varying enthalpy dehumidifier according to the invention is more effective in removing water vapor from the air than the adiabatic dehumidifier. The air temperature is elevated in the adiabatic dehumidifier from 20°C to 25°C i.e. by 5°C as compared with constant temperature in this example or only small temperature variation of air in the varying enthalpy dehumidifier according to the invention. Thus while in the adiabatic dehumidifier all the latent heat is converted to air heating, a large portion of the latent heat in the varying enthalpy dehumidifier is used to heat the cold desiccant.

Furthermore, it should be noted that the relationship between the diluted desiccant flowing into the regenerator and the concentrated desiccant flowing out of the regenerator could be controlled by a circulating pump disposed in the system to propel the desiccant into the regenerator. Also, in order to improve the efficiency of the desiccant/air heat exchangers, the Reynolds number of air inside the filling substance used in the heat exchanger should preferably be smaller than 2000.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrated embodiments. The scope of the invention is to be determined only by the appended claims.

Claims

CLAIMS:

1. A dehumidifier (10) for dehumidifying air inside an enclosure (12), said dehumidifier (10) comprising:

a desiccant reservoir (14) inside the enclosure having a desiccant inlet (16) for adding concentrated liquid desiccant and a desiccant outlet (18) for removing less concentrated liquid desiccant;

an air inlet (20) within the enclosure downstream of a dehumidifier vapor condenser (22) for receiving humid air and an air exit (24) within the enclosure upstream of the dehumidifier vapor condenser (22) for exiting dry air into the enclosure, a pump (26) coupled to the desiccant outlet for pumping liquid desiccant from the desiccant reservoir through spray nozzles (28) on to the dehumidifier vapor condenser (22) so as to absorb water vapor from the humid air and heat the liquid desiccant, whereby the air exiting through the air exit (24) is drier than the air entering the air inlet, and

a regenerator (30) coupled to the desiccant inlet (16) and to the desiccant outlet

(18) of the desiccant reservoir (14) for removing water f om the less concentrated liquid desiccant conveyed out of the desiccant outlet (18) and replenishing concentrated liquid desiccant to the desiccant reservoir (14) via the desiccant inlet (16);

characterized by:

a cooling element (32) for cooling the liquid desiccant in the dehumidifier and/or the condensing water in the regenerator by absorbing latent heat of condensation of the liquid desiccant in the dehumidifier and/or of condensing water in the regenerator, and

a heat sink (36) for recovering said heat of condensation.

2. The dehumidifier according to claim 1, wherein:

the regenerator (30) comprises an interconnected evaporator (44a) and condenser (44b) each including a respective reservoir (46a, 46b), a respective air inlet (48a, 48b) and a respective air outlet (50a, 50b),

the reservoir (46a) of the evaporator (44a) is fluidly coupled to the desiccant reservoir (14) of the dehumidifier, and the heat sink (34) is adapted to direct cold water on to the condenser (44b) so as to absorb moisture from hot moist air reaching the air inlet (48b) of the condenser (44b) thereby making the air drier.

3. The dehumidifier according to claim 1 or 2, wherein:

the heat sink (34) is realized by an aquifer or swimming pool (74) configured for directing cold water (72) on to the condenser (44b) and for releasing hot water into the reservoir (46b), and

a pump (76) for pumping hot water (78) back to the aquifer or swimming pool

(74).

4. The dehumidifier according to claim 3, wherein the aquifer or swimming pool (74) includes separate tanks for storing the cold water (72) and the hot water (78).

5. The dehumidifier according to any one of claim 1 to 4, wherein the cooling element (32) is configured for cooling liquid desiccant in the dehumidifier vapor condenser (22).

6. The dehumidifier according to claim 5, wherein the cooling element (32) comprises:

an evaporator (36) connected between the reservoir (46b) and the condenser (44b) in the regenerator (30) for removing heat from the liquid desiccant in the condenser (44b), and

a compressor (38) for conveying the heat to a condenser (40) connected between the reservoir (46a) and the evaporator (44a) in the regenerator (30).

7. The dehumidifier according to claim 5, comprising an additional heat pump for removing heat from the desiccant vapor condenser (22) and conveying the removed heat to air in the enclosure (12).

8. The dehumidifier according to any one of claims 1 to 7, wherein the cooling element (32) comprises a heat exchanger (70) which is adapted to remove heat from the desiccant in the dehumidifier vapor condenser (22) and convey the removed heat to cold water (72) stored in a reservoir (74).

9. The dehumidifier according to claim 8, wherein the reservoir is an aquifer or swimming pool (74).

10. The dehumidifier according to claim 8 or 9, including a pump (76) for pumping cold water (72) at a temperature of around 5°C to the heat exchanger (70) and to the vapor condenser (44b) in the regenerator (30) where the cold water is further heated and returned to the reservoir (74) as warm water (78) at a temperature of around 35°C for other uses such as space heating.

11. The dehumidifier according to any one of claims 1 to 10, wherein the cooling element (32) is shared between the dehumidifier (10) and the regenerator (30).

12. The dehumidifier according to claim 11, comprising:

an evaporator (36) in series with a compressor (38) and a condenser (40) connected between the reservoir (46a) of the evaporator (44a) in the regenerator (30), said evaporator being connected between the reservoir (14) of the dehumidifier (10) and the reservoir (46a) of the regenerator (30) and adapted to remove heat from the liquid desiccant to a refrigerant and convey the removed heat from the refrigerant to the condenser (40).

13. The dehumidifier according to claim 12, wherein the condenser (40) is outside the enclosure (12).

14. The dehumidifier according to any one of claims 1 to 13, further including a desiccant/desiccant heat exchanger (52) coupled between the dehumidifier (10) and the regenerator (30) and being adapted to heat diluted desiccant flowing from the dehumidifier to the regenerator and to cool concentrated desiccant flowing from the regenerator back to the dehumidifier.

15. A method for dehumidifying air in an enclosure, the method comprising:

conveying humid air in the enclosure to an air inlet (20) of an dehumidifier (22) that is coupled to a desiccant reservoir (14),

pumping liquid desiccant from the desiccant reservoir through spray nozzles (28) on to the dehumidifier (22) so as to absorb water vapor from the humid air and heat the liquid desiccant, whereby the air exiting through an air exit (24) of the dehumidifier (22) is drier than the air entering the air inlet,

using a regenerator (30) to remove water from less concentrated liquid desiccant conveyed out of the desiccant reservoir (14) and replenishing concentrated liquid desiccant to the desiccant reservoir (14);

characterized by:

cooling the liquid desiccant in the dehumidifier (22) and/or the condensing water in the regenerator (30) by absorbing latent heat of condensation of the liquid desiccant in the dehumidifier and/or of condensing water in the regenerator, and

recovering said heat of condensation by a heat sink (36).

16. The method according to claim 15, further including removing heat from the condensed water and feeding the removed heat to the desiccant evaporator (44a).

17. The method according to claim 15 or 16, wherein in respect of air flowing through the desiccant/air heat exchanger the Reynolds number is smaller than 2000.