ITRM20090672A1 - INTEGRATED AIR-CONDITIONING AND DEHUMIDIFICATION PLANT. - Google Patents

Description

Integrated air conditioning and dehumidification system.

The present invention relates to an integrated air conditioning and dehumidification system.

More specifically, the invention concerns a system for air conditioning and dehumidification for civil or industrial environments, for the air conditioning of means of transport, hygrometric control of confined spaces, suitable for applications in the refrigerated transport and refrigeration sector. The proposed system is compact so that it can be installed even in small spaces, allowing at the same time significant energy savings compared to traditional techniques.

As is well known, currently air dehumidification can also be carried out by "chemical" method, using solid or liquid drying substances (for example, aqueous solutions of LiCl, CaCl2, etc.). This approach, as known, compared to the more traditional technology that uses a refrigeration cycle to dehumidify the air by cooling it below the dew point, allows the control of specific humidity regardless of the temperature. Therefore, it is possible to obtain significant energy savings compared to the traditional process, especially when it is necessary to face high latent loads and at the same time a source of thermal energy is available to regenerate the desiccant.

In general, this type of system is mainly used in the industrial field for the dehumidification of the air in devices that provide for direct contact between the air and the desiccant solution, both in the absorption phase and in the regeneration phase.

Under normal operating conditions, of course, a continuous regeneration of the desiccant solution is required to remove the absorbed water, which would gradually dilute the desiccant solution, weakening its dehumidifying action.

Generally, regeneration is carried out thermally both by boiling the desiccant at atmospheric pressure, and by using various systems in direct air-solution contact. In the first case, in order to carry out effective regeneration it is necessary to have thermal energy at temperatures above 130-140 ° C. In the second case, the following drawbacks occur:

(a) considerable size of the regeneration system, as it includes, in addition to the actual regenerator, delivery and return ducts for the regeneration air and a fan for moving it;

(b) entrainment of desiccant droplets in the treated air;

(c) reduced possibility of varying air flow and desiccant independently;

(d) progressive pollution of the solution by atmospheric dust.

In addition, said systems are very problematic to use on means of transport subject to accelerations / decelerations.

Air conditioning systems are also known that integrate dehumidification systems in direct contact with steam compression refrigeration cycles. In these systems, called hybrid systems, the refrigeration unit can operate at a higher evaporation temperature than in a traditional system with higher coefficients of performance (COP). The regeneration is carried out by exploiting the thermal energy transferred to the condenser of the refrigeration cycle and therefore these systems do not need additional thermal energy. The overall energy savings compared to traditional air conditioning systems using refrigeration cycles can reach up to 30-35% with further improvements in the case of high latent loads. Obviously, hybrid systems also share the drawbacks of direct contact mentioned above.

Recently, technical evolutions of air conditioning and dehumidification systems have been proposed with liquid desiccants (traditional and hybrid) which avoid direct air-desiccant contact by inserting a thin hydrophobic membrane impermeable to the liquid phase and permeable to vapor between the two phases. which carry out the necessary energy and mass exchanges both to achieve the absorption of the vapor (ie the dehumidification of the air) and its desorption, ie the regeneration of the desiccant solution. For this purpose it is possible to use components called “membrane contactors” or “membrane contactors” equipped with well-known hydrophobic membranes, for example microporous membranes of polymeric materials (polytetrafluoroethylene PTFE, polyvinylidenefluride PVDF, polypropylene PP, etc.). Research and development to increase the performance of membranes and contactors in multiple application sectors is undergoing strong development all over the world.

Today's diaphragm contactors (plane symmetry, spiral and hollow fiber) allow high exchange surfaces per volume unit with low pressure drops both on the air side and on the solution side and can be used on transport vehicles.

Hybrid systems using membrane contactors have also been found to have limitations. For example, the air-desiccant solution contactors can present reliability problems especially when they operate in the regeneration phase, i.e. at higher temperatures. Furthermore, the size of the regeneration system remains high both because the regeneration contactor must be sized to dispose of all the sensible and latent load of the system towards the outside air and due to the presence of the delivery and return ducts for the supply air. regeneration and the fan for handling it. These aspects penalize the compactness of the entire plant (an aspect of great importance especially in the sector of means of transport such as cars, buses, trucks, train carriages and the like).

These and other technical problems are solved by means of an integrated air conditioning and dehumidification system which provides for the combination of refrigeration means with a cycle a operating with liquid desiccants, which uses a further contactor for air conditioning and dehumidification. air-desiccant membrane, and provides means for the regeneration of the desiccant solution provided with a membrane distiller of the liquid / liquid type.

The purpose of the present invention is, therefore, to provide an integrated air conditioning and dehumidification system that is more energy efficient than the traditional process based solely on the use of the refrigeration cycle.

Another purpose of the invention is to provide an integrated air conditioning and dehumidification system that is compact in size.

A further purpose of the present invention is to provide a system capable of both conditioning the air, cooling and dehumidifying it, or just dehumidifying it.

Therefore, the specific object of the present invention is an integrated air conditioning and dehumidification system, comprising a heat source, an air conditioning / dehumidification unit, for cooling and dehumidifying the air by means of a desiccant solution, refrigeration means, connected to said conditioning / dehumidification unit, designed to cool, by controlling its temperature, said desiccant solution at a predefined temperature, and then introduce it into said conditioning / dehumidification unit, a tank, connected in a loop circuit to said conditioning / dehumidification unit and to said refrigeration means, in which a reserve of said desiccant solution coming from said conditioning / dehumidification unit is collected, and regeneration means of said desiccant solution, connected to said tank, said regeneration means being adapted to reconcentrate said diluted desiccant solution. i coming from said conditioning / dehumidification unit, extracting water from it using thermal energy obtained from said thermal source, to return it to said tank, characterized in that said regeneration means comprise a membrane still of the liquid / liquid type.

Always according to the invention, said membrane still can be of the direct contact membrane type or DCMD (Direct Contact Membrane Distillation), and interposed between a first desiccant regeneration circuit, in which a first exchanger is connected in series. with said thermal source for heating the desiccant solution, a pump and a second circulation circuit of the collection water, in which means are connected in series for the cooling of said water and a further pump, said circuit for the circulation of the collection water being also provided with a drain for the distilled collection water.

Still according to the invention, said cooling means can comprise a second heat exchanger for cooling said water or a water-air hydrophobic membrane contactor capable of exchanging not only thermal energy but also water vapor with the ambient air. so as to cool the water below the outside air temperature. In the latter case, to keep the circuit always full of water, it will be necessary to simply top up the water from the outside.

Advantageously according to the invention, said membrane still can be an air-gap membrane distillation (AGMD - Air-Gap Membrane Distillation) with thermal recovery, and by the fact of comprising a heat exchanger with said thermal source, connected to said membrane still, and a distilled water discharge duct.

Further according to the invention, said refrigeration means can comprise an evaporator, a lamination valve, a condenser and a compressor.

Preferably according to the invention, said thermal source can coincide with said capacitor.

Still according to the invention, said system can comprise a sensor for detecting the concentration of the solution and / or the solution level contained in the tank, suitable for activating the operation of said regeneration means when the dilution of the solution has exceeded the expected limit.

Still according to the invention, said tank can be connected to said refrigerating means by means of a first pump and to said regeneration means by means of a first delivery duct, in which a second pump is provided, and a return duct.

Further according to the invention, said regeneration means can be connected, preferably interposed, between said tank and said refrigeration means.

Advantageously according to the invention, said plant can comprise an economizer interposed between said tank and said regeneration means.

The present invention will now be described for illustrative but not limitative purposes, according to its preferred embodiments, with particular reference to the figures of the attached drawings, in which:

Figure 1 shows an architecture of an air conditioning / dehumidification system which uses a first embodiment of an integrated air conditioning / dehumidification system, according to the present invention;

Figure 2 shows an air conditioning / dehumidification system architecture that uses a second embodiment of an integrated air conditioning / dehumidification system, according to the present invention; And

Figure 3 shows on the psychrometric diagram (Ashrae diagram) the transformations of the process air as they occur in the system of Figures 1 and 2.

In the various figures similar parts will be indicated with the same numerical references.

Referring to Figure 1, an integrated system 1 is observed for the conditioning and dehumidification of the air of an environment A, such as a vehicle interior such as cars, buses, trucks, train vans and the like.

The air in the thermodynamic state (m), resulting from the mixing of the fresh air (e) and the recirculated air (a '), is cooled and dehumidified by means of the integrated system 1 according to the present invention up to the conditions of release (s) in the conditioned environment A.

The system 1 comprises an air conditioning / dehumidification unit 20 which provides for the cooling and dehumidification of the fresh air (e) and the recirculation air (a '), and a tank 30 connected to it for collecting the solution desiccant.

The plant 1 further comprises refrigeration means 40, provided with an evaporator 41, a lamination valve 42, a condenser 43 and a compressor 44. Said evaporator 41 is connected to said tank 30 by means of a first pump 51.

The plant 1 also comprises an economizer 31 connected by means of a pair of outward and return pipes in which circulation is facilitated by a second pump 52. Said economizer 31 can also be connected in a loop between the tank 30 and the evaporator 41. Furthermore, regeneration means 60 are connected to said economizer 31, comprising a membrane still 61, arranged between the regeneration circuit of the desiccant 62 and the circulation circuit of the distilled water 63.

The regeneration means 60 are adapted to reconcentrate said diluted desiccant solution coming from said conditioning / dehumidification unit 20, extracting water from it using thermal energy obtained from a thermal source, to return it to said tank 30.

In a preferred embodiment, said thermal source coincides with waste thermal sources or it can also coincide with the condenser 43. In the latter case, the system has the advantage of not requiring external inputs of thermal energy.

Furthermore, said circuit 62 a first heat exchanger 64 and a pump 65 are connected in series. A second heat exchanger 66 and a further pump 67 are connected in series in said collection water circulation circuit 63. the collection water circulation circuit 63 also has a water drain 68.

Advantageously according to the invention, the heat exchanger 66 can be replaced by a water-air hydrophobic membrane contactor 20 capable of exchanging not only thermal energy but also water vapor with the ambient air, thus obtaining the advantages of a greater flow of distillate per unit of membrane area or, given the same, to carry out the process with heat at a lower temperature from said second heat source 66.

As can be seen, said membrane still 61 is of the liquid / liquid type, and in particular of the direct contact membrane type or DCMD (Direct Contact Membrane Distillation).

This type of contactor is currently applied in the desalination of sea water for the production of drinking water and in the concentration of aqueous solutions. These DCMD direct contact membrane stills operate a distillation by passing sea water at a higher temperature on one side of the membrane and water at a lower temperature on the other side, thus carrying out the distillation process by preventing the mixing of the phases.

The cause of the transport process through the membrane is the difference in partial pressure of the vapor on both sides of the membrane, which in turn is caused by a difference in temperature. Distillation is therefore carried out at ambient pressure using thermal sources at moderate temperatures (maximum 90-95 ° C).

These processes represent an alternative sector to the more common desalination processes such as traditional distillation and reverse osmosis.

Operation occurs as follows. In the conditioning / dehumidification unit 20 (for example also the dehumidification contactor) a heat and mass exchange takes place simultaneously so that the hygroscopic solution, which enters the cold and concentrated component 20 (conditioning / dehumidification unit), exits more hot and diluted. Because of this, the solution must be cooled and regenerated to keep the temperature and the concentration at the inlet to the conditioning / dehumidification unit 20 constant. The temperature control (cooling) of the absorbent solution is carried out by the refrigeration cycle carried out by said refrigeration means. , while the restoration of the concentration takes place by means of said regeneration means 60. The solution circuit can be considered composed of two parts which operate between two different levels of temperature and concentration: the absorption circuit (dehumidification), where the solution is kept cold and at the required concentration, and the regeneration circuit, made by said regeneration means 60, in which said solution is kept hot and more concentrated.

The heat economizer 31 operates between the two circuits in order to pre-heat the solution pumped by said pump 52 diverted to the regeneration circuit, and pre-cool the return solution from said desiccant regeneration circuit 2. The distillation process of the steam from the solution at a higher temperature to the water circulating in the distilled water circulation circuit 63, which is at a lower temperature than the regeneration circuit 62, is carried out by means of the membrane still 61. In particular, the The water vaporizes from the solution on the warm side of the membrane of the membrane still 61, passes through the membrane in the vapor phase and condenses into the water at a lower temperature on the other side of the membrane. The thermal energy necessary for the distillation process is supplied to the solution through said first heat exchanger 64. In circuit 63 the water is cooled by means of an exchange coil (i.e. the second heat exchanger 66), operating with external air or water of well. The volumetric excess of condensed water is conveyed to the outside through the drain 68. The regeneration process can operate continuously in parallel to the absorption circuit or be enslaved to the signal of a sensor dependent on the concentration of the solution, or to the solution level in the tank 30.

The system allows to achieve considerable energy savings since, as already observed, allowing the refrigeration cycle, made by said refrigeration means 40, to operate more advantageously from a thermodynamic point of view. In fact, with a higher evaporation temperature, the cycle achieves more favorable coefficients of performance (COP) with lower mechanical energy demands on the compressor 44. This latter aspect becomes more evident if we consider a common plant as a term of comparison. hydronic air conditioning instead of direct expansion (i.e. for medium-large sized systems comprising an intermediate circuit of chilled water from the refrigerator evaporator that feeds the battery through which the air is cooled and dehumidified).

The system according to the invention also makes it possible to avoid post-heating of the air, which is necessary in traditional systems to control the internal hygrometric conditions.

Figure 2 shows a second embodiment of the plant 1 'according to the present invention, which differs from the previous embodiment both in that it does not provide the economizer 31, and because the regeneration means 70 comprise a membrane still 71 of the liquid / liquid type but of the air-gap membrane or AGMD (Air-gap Membrane Distillation) type, therefore connected to a single heat exchanger 72, the membrane distiller 71 equipped with a water drain 73.

Air gap or AGMD membrane stills are also currently applied in the salt water purification sector. In this case, salty water at a higher temperature is passed on one side of the membrane, while on the other side there is a thin layer of air (air-gap) which, in turn, is in contact with a wet waterproof sheet. on the other side by sea water at a lower temperature. The vapor passing through the membrane condenses on the waterproof sheet. Compared to the case of the DCMD still described in the previous embodiment, there is a significant heat recovery by internal exchange between the two seawater streams and a greater compactness of the system.

The plant 1 described above, therefore, has a simplified regeneration circuit, making the system considerably more compact, thanks to the membrane still 71 with heat recovery.

An advantage that follows from the heat recovery that takes place inside the membrane still 71 is to significantly reduce the heat energy demand for regeneration and therefore also the enslaved heat exchanger 72 can be very compact in construction. On the other hand, the mass flows achievable in AGMD modules are lower than in the DCMD case and their construction is less simple. By way of example, DCMD processes allow vapor flux densities across the membrane of the order of 20-40 [kg / (hm <2>)] while in the case of AGMD the flows, although still conspicuous, are smaller 2-5 [kg / (hm <2>)]).

The process air transformations of both systems of the embodiments described in Figures 1 and 2 do not differ from each other and are represented in the Ashrae psychrometric diagram of Figure 3.

The main technical advantages of the plants according to the present invention when thermal recovery energy is available are listed below:

- they can be easily integrated / used in existing systems (for example of the direct contact type);

- unlike what happens in the case of hybrid systems that regenerate the solution using all the heat transferred to the condenser of the refrigerator, this system can also operate the regeneration independently of the absorption circuit, for example, using waste heat (engine on vehicles ) and that is, it can concentrate the solution even when the fridge is not working. In other words, the system according to the invention can operate in dehumidification only mode as well as in dehumidification and cooling mode;

- in the summer regime they allow significant mechanical / electrical energy savings (30-40%) compared to traditional steam compression plants;

- in the intermediate seasons it is possible to dehumidify the air without necessarily having to cool it to below the dew point with therefore considerable savings in mechanical / electrical energy;

- allow you to create compact systems characterized by dimensions of the same order of magnitude as traditional ones thanks to the high efficiency of energy exchanges and the mass allowed by modern membrane component technology.

Among other things, it should be added that the plant according to the invention allows to achieve significant commercial advantages both in the civil sector and in that of means of transport. For example, it can be observed that in modern cars the power demand for air conditioning now represents a very significant fraction of fuel consumption as a result of the progress made in engine efficiency and the increase in glass surfaces (higher loads solar), which distinguishes the current cars. As an indication, a car with an engine with a maximum power of 70-80 kW can absorb a mechanical power of approximately 4-5 kW for summer air conditioning. This energy demand assumes a significant percentage importance if we consider that, under normal conditions of use, the power delivered by the engine is much lower (about 18 kW). It can also be observed that in the intermediate seasons or on rainy days, to avoid problems of fogging of the glass, only the dehumidification of the air is required and not its simultaneous cooling, and the system according to the invention allows, as mentioned, to exclude the operation of refrigeration vehicles.

The present invention has been described for illustrative, but not limitative purposes, according to its preferred embodiments, but it is to be understood that variations and / or modifications may be made by those skilled in the art without thereby departing from the relative scope of protection, such as defined by the attached claims.

Claims (10)

CLAIMS 1. Integrated system (1, 1 ') for air conditioning and dehumidification, including a heat source, a conditioning / dehumidification unit (20), for cooling and dehumidifying the air by means of a desiccant solution, refrigeration means (40), connected to said conditioning / dehumidification unit (20), suitable for cooling, controlling the temperature, said desiccant solution at a predefined temperature, and then introduced it into said air conditioning / dehumidification unit (20), a tank (30), connected in a loop circuit to said conditioning / dehumidification unit (20) and to said refrigeration means (40), in which a reserve of said desiccant solution coming from said conditioning / dehumidification unit (20) is collected , And regeneration means (60; 70) of said desiccant solution, connected to said tank (30), said regeneration means (60; 70) being able to reconcentrate said diluted desiccant solution coming from said conditioning / dehumidification unit (20), extracting from it water using thermal energy obtained from said thermal source, to return it to said tank (30), characterized in that said regeneration means (60; 70) comprise a membrane still (61; 71) of the liquid / liquid type. 2. Integrated plant (1 ') according to claim 1, characterized in that said membrane distiller (61) is of the direct contact membrane type or DCMD (Direct Contact Membrane Distillation), and interposed between a first regeneration circuit of the 'desiccant (62), in which a first heat exchanger (64) with said thermal source for heating the desiccant solution, a pump (65) and a second circulation circuit of the collection water (63) are connected in series ), in which means (66) for cooling said water and a further pump (67) are connected in series, said collection water circulation circuit (63) also being provided with a water drain of distilled collection (68). 3. Integrated plant (1) according to claim 2, characterized in that said cooling means comprise a second heat exchanger (66) for cooling said water or a water-air hydrophobic membrane contactor capable of exchanging with the ambient air not only thermal energy but also water vapor, so as to cool the water below the temperature of the outside air. 4. Integrated plant (1) according to claim 1, characterized in that said membrane still (71) is an air-gap membrane distillation (AGMD - Air-Gap Membrane Distillation) with heat recovery, and by the fact that it comprises a heat exchanger (72) with said thermal source, connected to said membrane still (71), and a distilled water discharge duct (73). 5. Integrated plant (1, 1 ') according to any one of the preceding claims, characterized in that said refrigerating means (40) comprise an evaporator (41), a lamination valve (42), a condenser (43) and a compressor (44). 6. Integrated system (1, 1 ') according to claim 5, characterized by the fact that said heat source coincides with said capacitor (43). 7. Integrated system (1; 1 ') according to any one of the preceding claims, characterized in that it comprises a sensor for detecting the concentration of the solution and / or the solution level contained in the tank (30), suitable for activating the operation of said regeneration means (60; 70) when the dilution of the solution has exceeded the foreseen limit. Integrated plant (1; 1 ') according to any one of the preceding claims, characterized in that said tank (30) is connected to said refrigerating means (40) by means of a first pump (51) and to said regeneration means (60; 70) by means of a first delivery duct, in which a second pump (52) is provided, and a return duct. Integrated plant (1; 1 ') according to any one of claims 1 - 7, characterized in that said regeneration means (60; 70) are connected, preferably interposed, between said tank (30) and said refrigeration means (40 ). 10. Integrated system (1; 1 ') according to any of the previous claims, characterized by the fact of comprising an economizer (31) interposed between said tank (30) and said regeneration means (60; 70).