Patent Application
20160084541
The present invention relates to a trithermal adsorption cooling/heating method or system for refrigerating machine, using a MOF solid adsorbent, in certain specific operating ranges, depending on the MOF used.
The invention also relates to fan coil-type air-conditioning systems or cooling floor-type or cooling ceiling-type air-conditioning systems, as well as dehumidification systems, using the method or comprising the system according to the present invention.
The operating principles of refrigerating machines using solid adsorbates in a trithermal (closed) system are known. For example, the companies Vaillant, Viesman, Sortech and Mycon market such types of refrigerating machine.
In a trithermal adsorption-type system, where T0 represents the internal evaporation temperature at which the cold Q0 is produced, Tc represents the intermediate heat rejection temperature of Qc (condensation and adsorption), and finally TA represents the internal temperature of the heat source that supplies Qg for regenerating the adsorbent.
The efficiency of the method is determined by the quantity of vapour of the refrigerating fluid that can be reversibly exchanged between adsorption and desorption (coefficient of performance: COP) and by the adsorption time (specific cooling power: SCP). Cf.
Thus the efficiency of the thermal transformation method is expressed:
(i) By the coefficient of performance (COP)
COP=Q0/Qg=QEvaporation/QDesorption
The COP is directly related to the variation in mass of cycled fluid (adsorbed-desorbed) in the trithermal cycle. In general, the fluids that offer the best potentials are those that have high latent heat/heat of vaporisation such as short alcohols (methanol, ethanol) and in particular water.
(i) By the power of machine, which is expressed in terms of specific cooling power (SCP) per volume (V) or mass (m) of the apparatus (apparatus=adsorbent+adsorber)
The SCP is directly related to the speed of the transfer phenomena, i.e., the matter transfer (the time necessary for the phenomenon to occur, of which the speed of transport of the fluid in the adsorbent is an element) and the heat transfer (the time necessary for the transfer of the quantities of heat from one element to another, of which the speed of conduction/convection of the heat is an element).
The performance (SCP) of a refrigerating machine may be limited either by:
To minimise the thermal loads or the size of apparatuses for refrigerating machines, adsorbents with a high adsorption capacity under the operating conditions, and rapid adsorption and desorption kinetics, are necessary. Thus the adsorbent and the adsorber configuration have a high impact on the performance.
The adsorber typically used is silica gel. This is an inefficient adsorbent, i.e., with a low COP. The drawback of silica gel in terms of efficiency of the process is its relatively low adsorption capacity during the adsorption/desorption cycles, which requires large quantities of silica gel. This leads to bulky equipment with relatively low power (SCP) and efficiency (COP) values. (J. Bauer et al. Int. J. Energy Res. 2009; 33: 1233-1249 [1]).
The application of MOFs (Metal Organic Frameworks), which are porous coordination polymers, in particular Basolite A520, in refrigerating machines was mentioned in EP 2230288 [2] and EP 2049549 [19]).
However, MOFs are not equivalent in all applications that can be considered for adsorption-type cooling/heating systems. In particular, some MOFs are not completely suitable for some types of cooling/heating (e.g. air-conditioning systems), depending on their adsorption characterisation (isotherm profile according to IUPAC classification), operating partial vapour pressures and temperatures.
There therefore exists a need to develop trithermal adsorption cooling/heating methods and systems for refrigerating machines that are perfectly optimised, i.e. which optimise the following three criteria:
The present invention responds precisely to this requirement by selecting certain particular MOFs, for association with particular operating modes of trithermal adsorption cooling/heating methods and systems, thus affording optimised operation of these methods/systems.
According to one aspect, the present invention relates to a closed trithermal adsorption cooling/heating method or system for refrigerating machine, comprising:
a. a refrigerating fluid (F) selected from water, alcohols and hydrocarbons;
b. a condensation module (C) for condensation of said refrigerating fluid (F), in thermal connection with a water circuit (CWTmedium) in which the water temperature at the outlet from the circuit is Tc;
c. an evaporation module (E) for evaporation of said refrigerating fluid (F), in thermal connection with a water circuit (CWTlow) in which the water temperature at the outlet from the circuit is Te;
d. at least one adsorption/desorption module (AD) containing a solid adsorbent (A) composed of a porous hybrid metal-organic metal-organic material (MOF), the adsorption/desorption module (AD) being alternately in fluid connection with said condensation module (C) and then said evaporation module (E), said MOF material being able to adsorb or desorb the refrigerating fluid (F) depending on whether the adsorption/desorption module (AD) is in fluid connection with the evaporation module (E) and condensation module (C) respectively, and depending on the temperature TMOF to which the MOF material is subjected.
Advantageously, the system is used so that the module AD is put alternately in adsorption and then desorption mode.
Advantageously, the system contains two adsorption/desorption modules (AD) and (AD′), each alternately in fluid connection with the condensation (C) and evaporation (E) modules, so that when (AD) is in fluid connection with the condensation module (C) then (AD′) is in fluid connection with the evaporation module (E), and vice-versa. An example of configuration of such a system is depicted in
Advantageously, the refrigerating fluid (F) may be water, alcohol or a hydrocarbon; preferably water or an alcohol. The alcohol may be methanol or ethanol. Advantageously, the refrigerating fluid (F) may be water. Advantageously, the refrigerating fluid (F) may be methanol or ethanol.
The term “in thermal connection” as used in the present document refers to a connection means allowing exchange of heat between the elements to which it refers. For example, it may be a connection means allowing exchange of heat between the condensation module (C) and the water circuit (CWTmedium) or between the evaporation module (E) and the water circuit (CWTlow). For example, the thermal connection may be achieved by means of a heat exchanger. Alternatively, the thermal connection may be achieved by passage of the water circuit through the condensation module (C) or the evaporation module (E), thus allowing transfer of the heat given off in the condensation module (C) into the water circuit passing through it, or conversely allowing the transfer of the heat adsorbed in the evaporation module (E) into the water circuit passing through it.
The term “in fluid connection” as used in the present document refers to a connection means allowing transfer of refrigerating fluid vapour between the elements to which it refers. For example, it may be a connection means allowing transfer of refrigerating fluid vapour from an adsorption/desorption module (AD′) to the condensation module (C). It may also be a connection means allowing the transfer of refrigerating fluid vapour from an evaporation module to an adsorption/desorption module (AD) as illustrated in
Advantageously, when the system has two modules (AD) and (AD′), the two adsorption/desorption modules contain the same solid adsorbent (MOF), and are not in fluid connection with the condensation module (C) or the evaporation module (E) simultaneously.
Advantageously, in desorption mode, the MOF adsorbent is subjected to a temperature TMOF such that Tmax≧TMOF≧Tc, wherein Tc represents the temperature of the water at the outlet from the water circuit (CWTmedium) and Tmax represents the high range of the temperature at which the MOF is regenerated (i.e. the MOF desorbs the refrigerating fluid molecules). Naturally Tmax would be lower than the temperature at which the MOF may decompose or degrade. The value of Tmax depends on the MOF used. Typically, a temperature Tmax of at least 85° C. will allow to regenerate the MOFs that may be used in the context of the present invention. Advantageously, Tmax may be between 60° C. and 120° C., advantageously between 60° C. and 100° C., or advantageously between 70° C. and 90° C. One advantage of MOFs compared with the adsorbents conventionally used is that they can be regenerated at lower temperatures.
Advantageously, when the adsorption/desorption module (AD) or (AD′) is in desorption mode, the heat source for heating the MOF material at the temperature TMOF Tmax≧TMOF>Tc is selected from solar panels, atmospheric burners such as natural gas boilers, geothermal energy or free heat.
Advantageously, the thermal connection between the refrigerating fluid (F) and the water circuits (CWTmedium) and (CWTlow) of the condensation and evaporation modules respectively is provided by a heat exchanger (ET).
Hereinafter, the elements described above in the “general description” parts (F, C, CWTmedium, Tc, CWTlow, AD, A, E, AD′, etc.) are repeated in embodiments 1 to 3 that follow, adding an index (e.g. F1) to designate the embodiment concerned.
For all the variants described in part A above for the closed system (general description), the solid adsorbent (A1) may be composed of a porous hybrid metal-organic material (MOF) selected from zirconium fumarates, such as MOF-801, and aluminium aminoterephthalates, such as Al-CAU-10, and the adsorption/desorption operating parameters may be as follows:
in adsorption mode:
in which:
pe/psat (e) represents the partial vapour pressure of the refrigerating fluid (or the relative humidity when the refrigerating fluid is water) in the evaporation module (E1);
pe represents the pressure of the refrigerating fluid (F1) in gaseous phase in the evaporation module (E1); and
psat (e) represents the saturation vapour pressure of the refrigerating fluid (F1) at the temperature of absorption of said refrigerating fluid (F1) by the porous hybrid metal organic material;
in desorption mode:
in which:
pc/psat (c) represents the partial vapour pressure of the refrigerating fluid (or the relative humidity when the refrigerating fluid is water) in the condensation module (C1);
pc represents the pressure of the refrigerating fluid (F1) in gaseous phase in the condensation module (C1); and
psat (c) represents the saturation vapour pressure of the refrigerating fluid (F1) at the temperature of desorption of said refrigerating fluid (F1) from the porous hybrid metal organic material.
Advantageously, Te1 represents 5° C.±2° C. in adsorption mode, and Tc1 represents 45° C.±4° C. in desorption mode. In this operating mode, the method or system may be suitable for a fan coil-type air-conditioning system. Thus the invention also provides a fan coil-type air-conditioning system using this operating mode.
Advantageously, Te1 represents 12° C.±3° C. in adsorption mode, and Tc1 represents 50° C.±5° C. in desorption mode. In this operating mode, the method or system may be suitable for a cooling floor-type or cooling ceiling-type air-conditioning system. Thus the invention also provides a cooling floor-type or cooling ceiling-type air-conditioning system using this operating mode.
For all the variants described in part A above for the closed system (general description), the solid adsorbent (A2) may be composed of a porous hybrid metal organic material (MOF) selected from aluminium aminoterephthalates such as Al-CAU-10, and the adsorption/desorption operating parameters may be as follows:
in adsorption mode:
in which:
pe/psat (e) represents the partial vapour pressure of the refrigerating fluid (or the relative humidity when the refrigerating fluid is water) in the evaporation module (E2);
pe represents the pressure of the refrigerating fluid (F2) in gaseous phase in the evaporation module (E2); and
psat (e) represents the saturation vapour pressure of the refrigerating fluid (F2) at the temperature of absorption of said refrigerating fluid (F2) by the porous hybrid metal organic material;
in desorption mode:
in which:
pc/psat (c) represents the partial vapour pressure of the refrigerating fluid (or the relative humidity when the refrigerating fluid is water) in the condensation module (C2);
pc represents the pressure of the refrigerating fluid (F2) in gaseous phase in the condensation module (C2);
psat (c) represents the saturation vapour pressure of the refrigerating fluid (F2) at the temperature of desorption of said refrigerating fluid (F2) from the porous hybrid metal organic material.
Advantageously, Te2 represents 5° C.±2° C. in adsorption mode, and Tc2 represents 35° C.±4° C. in desorption mode. In this operating mode, the method or system may be suitable for a fan coil-type air-conditioning system. Thus the invention also provides a fan coil-type air-conditioning system using this operating mode.
Advantageously, Te2 represents 12° C.±3° C. in adsorption mode, and Tc2 represents 45° C.±5° C. in desorption mode. In this operating mode, the method or system may be suitable for a cooling floor-type or cooling ceiling-type air-conditioning system. Thus the invention also provides a cooling floor-type or cooling ceiling-type air-conditioning system using this operating mode.
For all the variants described in part A above for the closed system (general description), the solid adsorbent (A3) may be composed of a porous hybrid metal organic material (MOF) selected from zirconium aminoterephthalates such as Zr-UiO-66-NH2, zirconium methanetetrabenzoates such as Zr-UiO-MTB (MOF-814), and aluminium fumarates such as Basolite A520, and the adsorption/desorption operating parameters may be as follows:
in adsorption mode:
in which:
pe/psat (e) represents the partial vapour pressure of the refrigerating fluid (or the relative humidity when the refrigerating fluid is water) in the evaporation module (E3);
pe represents the pressure of the refrigerating fluid (F3) in gaseous phase in the evaporation module (E3);
psat (e) represents the saturation vapour pressure of the refrigerating fluid (F3) at the temperature of absorption of said refrigerating fluid (F3) by the porous hybrid metal organic material;
in desorption mode:
in which:
pc/psat (c) represents the partial vapour pressure of the refrigerating fluid (or the relative humidity when the refrigerating fluid is water) in the condensation module (C3);
pc represents the pressure of the refrigerating fluid (F3) in gaseous phase in the condensation module (C3);
psat (c) represents the saturation vapour pressure of the refrigerating fluid (F3) at the temperature of desorption of said refrigerating fluid (F3) from the porous hybrid metal organic material.
Advantageously, the solid adsorbent (A3) may be composed of a porous hybrid metal organic material (MOF) selected from zirconium aminoterephthalates such as Zr-UiO-66-NH2, and the adsorption/desorption operating parameters are as follows:
in adsorption mode:
Advantageously, Te3 represents 5° C.±2° C. in adsorption mode, and Tc3 represents 30° C.±4° C. in desorption mode. In this operating mode, the method or system may be suitable for a fan coil-type air-conditioning system. Thus the invention also provides a fan coil-type air-conditioning system using this operating mode.
Advantageously, Te3 represents 12° C.±3° C. in adsorption mode, and Tc3 represents 40° C.±4° C. in desorption mode. In this operating mode, the method or system may be suitable for a cooling floor-type or cooling ceiling-type air-conditioning system. Thus the invention also provides a cooling floor-type or cooling ceiling-type air-conditioning system using this operating mode.
Advantageously, the solid adsorbent (A3) may be composed of a porous hybrid metal organic material (MOF) selected from zirconium aminoterephthalates such as Zr-UiO-66-NH2, zirconium methanetetrabenzoates such as Zr-UiO-MTB (MOF-814), and aluminium fumarates such as Basolite A520, and the adsorption/desorption operating parameters are as follows:
in adsorption mode:
Advantageously, Te3 represents 5° C.±2° C. in adsorption mode, and Te3 represents 25° C.±4° C. in desorption mode. In this operating mode, the method or system may be suitable for a fan coil-type air-conditioning system. Thus the invention also provides a fan coil-type air-conditioning system using this operating mode.
Advantageously, Te3 represents 12° C.±3° C. in adsorption mode, and Tc3 represents 35° C.±4° C. in desorption mode. In this operating mode, the method or system may be suitable for a cooling floor-type or cooling ceiling-type air-conditioning system. Thus the invention also provides a cooling floor-type or cooling ceiling-type air-conditioning system using this operating mode.
In each of the embodiments 1 to 3, the reflecting surface may represent a reflecting floor or ceiling.
In each of the embodiments 1 to 3, the MOF adsorbent may be formed according to any method known in the field of trithermal adsorption cooling/heating systems for refrigerating machine (for example fixed bed, adhesive or composite coating). Advantageously, the MOF adsorbent may be placed on a metal heat exchanger according to a method allowing growth of the MOF directly on the surface of a metal support (i.e. without binder, adhesive or composite). It may for example be a method for growing MOF on the surface of a metal support, comprising:
(1) oxidising the surface metal of the metal support in order to cover said surface with a layer of metal oxide;
(ii) preparing a precursor solution/suspension of MOF material comprising the mixture in a polar solvent (a) of a metallic inorganic precursor which may be a metal M, a salt of metal M or a coordination complex comprising a metal ion M, wherein M is a metal ion selected from Al3+, Fe2+, Fe3+, Zn2+, Ti3+, Ti4+, Zr2+, Zr4+, Ca2+, Cu2+, Gd3+, Mg2+, Mn2+, Mn3+, Mn4+ or Si4+; preferably Zr4+ or Al3+; and (b) at least one ligand L selected from a di-, tri- or tetra-carboxylate ligand chosen from: C2H2(CO2−)2 (fumarate), C2H4(CO2−)2 (succinate), C3H6(CO2−)2 (glutarate), C4H4(CO2−)2 (muconate), C4H8(CO2−)2 (adipate), C7H14(CO2−)2 (azelate), C5H3S(CO2−)2 (2,5-thiophenedicarboxylate), C6H4(CO2−)2 (terephthalate), C6H4(CO2−)2 (isoterephthalate), C6H2N2(CO2−)2 (2,5-pyrazine dicarboxylate), C10H6(CO2−)2 (naphthalene-2,6-dicarboxylate), C12H8(CO2−)2 (biphenyl-4,4′-dicarboxylate), C12H8N2(CO2−)2 (azobenzenedicarboxylate), C6H3(CO2−)3 (benzene-1,2,4-tricarboxylate), C6H3(CO2−)3 (benzene-1,3,5-tricarboxylate), C24H15(CO2−)3 (benzene-1,3,5-tribenzoate), C6H2(CO2−)4 (benzene-1,2,4,5-tetracarboxylate, C10H4(CO2−)4 (naphthalene-2,3,6,7-tetracarboxylate), C10H4(CO2−)4 (naphthalene-1,4,5,8-tetracarboxylate), C12H6(CO2−)4 (biphenyl-3,5,3′,5′-tetracarboxylate), 2-aminoterephthalate, 2-nitroterephthalate, 2-methylterephthalate, 2-chloroterephthalate, 2-bromoterephthalate, 2,5-dihydroxoterephthalate, tetrafluoroterephthalate, tetramethylterephthalate, dimethyl-4,4′-biphenydicarboxylate, tetramethyl-4,4′-biphenydicarboxylate, dicarboxy-4,4′-biphenydicarboxylate, or 2,5-pyrazyne dicarboxylate;
(iii) immersing the oxidised metal support obtained in step (i) in the solution/suspension obtained in step (ii);
(iv) heating the mixture of step (iii) at 100°-140° C., preferably 110°-130° C., advantageously 120° C., for 24 to 36 hours, preferably 48 to 36 hours, advantageously at least 48 hours;
(v) removing the metal support from the precursor solution/suspension of MOF material;
(vi) rinsing the support with a suitable solvent;
(vii) air drying at 40°-60° C., preferably 45°-55° C., advantageously 50° C.
In step (ii), the ligand L may also represent 2,5-diperfluoroterphthalate, azobenzene 4,4′-dicarboxylate, 3,3′-dihydroxoazobenzene, 4,4′-dicarboxylate, 3,3′-diperfluoroazobenzene 4,4′-dicarboxylate, 3,5,3′,5′-azobenzenetetracarboxylate, 2,5-dimethyl terephthalate, perfluorosuccinate, perfluoromuconate, perfluoroglutarate, 3,5,3′,5′-perfluoro-4,4′-azobenzene dicarboxylate, or 3,3′-diperfluoroazobenzene 4,4′-dicarboxylate.
Advantageously, the ligand L may represent C2H2(CO2−)2 (fumarate), C6H4(CO2−)2 (terephthalate), C6H4(CO2−)2 (isoterephthalate), 2-aminoterephthalate, MTB (methanetetrabenzoate) or 1,4-benzenedicarboxylate.
Advantageously, the metal support may be made from copper or aluminium, and may be in the form of a plate, a honeycomb structure or any form used in heat exchangers, for example a flat finned tube.
Advantageously, step (i) can be performed by any means known to a person skilled in the art, for example heat or chemical treatment of the surface of the adsorber, which treatment is specific and suited to the material of the adsorber and of the adsorbent.
For example, when the metal support is made from copper, step (i) may be performed by placing the copper support in a furnace at a sufficient temperature and for a sufficient length of time to achieve the oxidation of the surface of the copper support. For example, treatment in the furnace can be carried out at 100° C. in ambient atmosphere.
In another example, when the metal support is made from aluminium, step (i) may be performed by treating the support in a solution of sodium hydroxide and in a dilute nitric acid solution (in order to deoxidise the aluminium surface), and then air drying at a sufficient temperature and for a sufficient length of time to achieve oxidation of the surface of the aluminium support. For example, the air drying may be carried out at 60° C.
The preparation of the precursor solution/suspension of MOF materials may preferably be done in the presence of energy, which may for example be supplied by heating, such as for example hydrothermal or solvothermal conditions, but also by microwave, ultrasound, grinding, a method involving a supercritical fluid, etc. The corresponding protocols are those known to a person skilled in the art. Non-limitative examples of protocols that can be used for hydrothermal or solvothermal conditions are described for example in K. Byrapsa, et al. “Handbook of hydrothermal technology”, Noyes Publications, Parkridge, N.J., USA, William Andrew Publishing, LLC, Norwich, N.Y., USA, 2001 [14]. For synthesis by microwave, non-limitative examples of protocols that can be used are described for example in G. Tompsett, et al. ChemPhysChem. 2006, 7, 296 [15]; in S.-E. Park, et al. Catal. Survey Asia 2004, 8, 91 [16]; in C. S. Cundy, Collect. Czech. Chem. Commum. 1998, 63, 1699 [17]; or in S. H. Jhung, et al. Bull. Kor. Chem. Soc. 2005, 26, 880 [18].
Hydrothermal or solvothermal conditions, the reaction temperatures of which may vary between 0° C. and 220° C., are generally implemented in glass (or plastic) receptacles when the temperature is below the boiling point of the solvent. When the temperature is higher or when the reaction takes place in the presence of fluorine, Teflon bodies inserted in metal enclosures are used [14].
Thus, advantageously, step (iv) can be performed in a Teflon body inserted in a metal enclosure (Teflon-lined stainless steel autoclave).
The solvents used in step (ii) are generally polar. In particular the following solvents can be used: water, alcohols, dimethylformamide, dimethylsulfoxide, acetonitrile, tetrahydrofuran, diethylformamide, chloroform, dichloromethane, dimethylacetamide or mixtures of these solvents. Advantageously, it may be dimethylformamide (DMF). The above solvents may also be used in the rinsing step (vi).
One or more additives may also be added during the preparation of the precursor solution/suspension of MOF material, in step (ii), in order to modulate the pH of the mixture. These additives may advantageously be selected from mineral or organic acids or mineral or organic bases. In particular, the additives may be selected from HF, HCl, HNO3, H2SO4, NaOH, KOH, lutidine, ethylamine, methylamine, ammonia, urea, EDTA, tripropylamine, pyridine, etc. Advantageously, HCl may be used.
The method described above has the advantage of allowing to obtain metal supports coated with a fine layer of MOF material, without the use of binders, adhesives or composite in order to ensure adhesion of the MOF to the surface of the support. The MOF material adheres to the layer of metal oxide generated on the surface of the metal support during step (i) of the method. In heat-exchanger applications, where the MOF material functions as an adsorbent (e.g. refrigerating machines), this formation of the MOF in a layer directly on the metal support optimises the heat-transfer speed, and reduces the mass of adsorbent layer (since no binder, adhesive or composite is necessary).
It is known that, in the case of heat exchangers with a surface coated with adsorbent, naturally the exchange surface is important but generally the surface is imposed less to provide the heat power than to provide the quantity of absorbent necessary since the thickness of the layers of adsorbent is limited. In other words, a reduction in the mass of adsorbent by a factor of 2 may result in a reduction in the exchange surfaces by a factor of close to 2 and the volume of each adsorber will also be very quickly reduced.
The above method has precisely the advantage of allowing to deposit a MOF adsorbent to form an effective coated surface with a suitable thickness of adsorbent.
Another advantage of this method is to allow optimisation of the mass of water cycled during a cycle when a heat exchanger coated with MOF according to the method of the invention is used. This is because, typically, in the regeneration heat, the sensible heat may represent one third and the latent heat two-thirds. By way of example, a reduction of the masses of adsorbent metal by a factor of 2 would give rise to a reduction in the sensible heat by a factor of 2 if the temperature conditions are the same. The gain in COP would then be between 15% and 20%, which is very appreciable.
In summary, by using this method, access is had to heat exchangers covered with MOF with advantageous performances in terms of cycled mass, COP and SCP.
According to another aspect, in each of embodiments 1 to 3, the invention also relates to use of the method or system according to the invention as described above in any of embodiments 1 to 3 for cooling or heating in a fan coil-type air-conditioning system, or in a cooling floor-type or cooling ceiling-type air-conditioning systems.
Systems for cooling by desiccation are open-cycle systems using the refrigerant in direct contact with the air. The cooling cycle consists of a combination of cooling by evaporation and dehumidification of the air by means of a desiccant material. The term “open” indicates that the refrigerant cannot be reused after having provided the desired cooling, and new refrigerant therefore has to be reinjected into the system. Under these conditions, the only refrigerant that can be used is water since it would be in contact with the air supplied to the building. Usually, this technology uses rotating desiccant wheels as the desiccant material.
Apparatuses and methods for exchanging heat and moisture between two air currents are known (see for example EP 0846923 A). Such apparatuses and methods are used for improving the ambient air, for example in small houses and buildings, i.e. for cooling and drying the external air that is introduced into a building in summer and for heating and humidifying said air during the winter before the air is transferred into the building.
However, there exists a problem when the external air is hot and humid, i.e. the temperature is above 35° C. and the external relative humidity p/psat is above 0.25, since the known apparatuses are not suitable for treating this air.
A particular design of these systems is required in the case of use for extreme climates such as for example for Asiatic coastal regions. Because of the high humidity of the ambient air, the standard configuration of this system does not suffice to reduce the humidity to a sufficient level in order then to use cooling by direct evaporation. Thus there exist other methods suited to a specific climate that are either already being used on installations or are still at the development stage.
Adsorbents of the silica gel type are usually used in the desiccant wheels of open cycles. The equipment manufacturers have selected specific adsorbents for their wheels. Overall, it can be said that, for temperate climates, the wheels are very effective and give excellent results. Nevertheless, this is not the case for humid tropical climates where the wheels are absolutely not suitable.
Thus, in
The present invention responds to this technical problem by eliminating the aforementioned problems and by proposing a method and an apparatus that functions effectively under the above conditions of high humidity.
Thus, according to another aspect, the present invention relates to an adsorption-type dehumidification method comprising the combination of a system for drying by desiccant wheel with a solid (A5) composed of a porous hybrid metal-organic material (MOF) selected from aluminium carboxylates such as Al-MIL-100, zirconium fumarates such as MOF-801 or MOF-841 (Zr-UiO-MTB), as the desiccant adsorbent.
The adsorbent (A5) disposed on the desiccant wheel dehumidifies and cools a first air flow brought from the ambient (external) air to the inside of the building, and to restore a second hot humid air flow from the inside of said building to the ambient (external) air.
This is because MOF-801, which has a high adsorption capacity up to 20% R.H. (relative humidity), appears to be promising and to be suited to such an application. Likewise, MOF-841 which has a very high adsorption capacity for a R.H. of between 100% and 25%, may be advantageous.
An example of an apparatus suited to implementing this dehumidification method is illustrated in
In summer (the heater 4-5 is not used), at (1) the hot humid external air enters the system and passes through the desiccant wheel, which is rotating slowly. In passing through this wheel (1-2), the air is dehumidified by adsorption of water. This phenomenon also involves an increase in the air temperature because of the adsorption heat. Next the air passes through another wheel, which is in fact a heat exchanger (2-3). The air is therefore cooled significantly. Finally, the air passes through a humidifier (3-4) in which its humidity is increased to its set value, and its temperature further reduced. Cool dry air is therefore obtained at (5). At (6) an air that is hotter and more humid than the distributed air is recovered. It will again be humidified in another humidifier (6-7) in order to arrive close to its saturation point. Next, the air passes through the heat exchanger (7-8), and thus this wheel will be cooled as the air heats up. The effect of this phenomenon is to “regenerate” the properties of the heat-exchanger wheel. Next, the air is further heated by means of solar energy via the heater (8-9). Lastly, the desiccant wheel is regenerated (9-10) by means of the hot air. In other words, when hot air passes, the humidity of the wheel decreases as the humidity in the hot air increases.
In winter the heater (4-5) is used to heat the air entering the building. In order to function, the system needs a relatively low temperature (50° C. to 75° C.) coming from the collectors, and thus flat collectors are sufficient, and air-type collectors may sometimes be used. A storage receiver may also be used to extend the use of the system.
Thus, according to one aspect of the invention, a method for air conditioning by exchange of heat and humidity between two air flows is proposed, one of the two being hot and humid, at least during a first part of the year, in which a first air flow is brought from the ambient air as far as the inside of a building and a second one of said air flows is brought from the inside of said building to the ambient air, by means of which said first air flow is transferred through a dehumidifier (a) and then transferred through a heat exchanger (b) before being transferred to the inside of said building, while said second air flow is cooled and then transferred through said heat exchanger (b), after which it is transferred through said dehumidifier (a), characterised in that the first air flow has a relative humidity (RH) 0.15<RH≦0.60; preferably 0.25<RH≦0.50, and the dehumidifier is an adsorption dehumidifier comprising a solid absorbent (A5) composed of a porous hybrid metal-organic material (MOF) selected from aluminium carboxylates such as Al-MIL-100 or zirconium fumarates such as MOF-801 or MOF-841 (Zr-UiO-MTB).
According to another variant, said first air flow is, at least during a second part of the year, colder and less humid in absolute terms than the second air flow.
Advantageously, the dehumidifier is a desiccant wheel. For example, it is possible to use a desiccant wheel of the Munters type.
Advantageously, the first air flow may be humidified by passing through a dehumidifier (c1) after passing through the heat exchanger (b). This step adjusts the humidity of the first air flow to a set value before it is transferred into the building.
Advantageously, the first air flow can be heated by passing through a heater (d1) after passing through the heat exchanger (b), and optionally through the humidifier (c1). This step adjusts the temperature of the first air flow to a set value before it is transferred into the building. Preferably, the heating system (d1) will be used during the cold months of the year (for example during winter) and will not be used during the summer period.
Advantageously, the second air flow can be humidified by passing through a humidifier (c2) after passing through the heat exchanger (b). This step adjusts the humidity of the second air flow to a value close to its saturation point before it is transferred to the ambient air (outside the building).
Advantageously, the second air flow can be heated by passing through a heater (d2) after passing through the heat exchanger (b), and optionally through the humidifier (c2). This step adjusts the temperature of the second air flow to a set value before it is transferred into the dehumidifier. The hot air flow regenerates the adsorbent of the dehumidifier: as the hot air passes, the humidity in the dehumidifier decreases as the humidity in the second air flow discharged to the outside increases.
Advantageously, the heating system (d1) and (d2) can be supplied by solar panels. The system can be enhanced with a storage vessel (buffer vessel) containing hot water (cf.
According to another aspect, a dehumidification system is proposed implementing a method of air conditioning by exchange of heat and humidity between two air flows according to the invention. For example, a system as illustrated in
According to another aspect, the use is proposed of a dehumidification method or system according to the invention for dehumidifying ambient air.
The MOF materials mentioned in the various embodiments described in the context of the present invention are known, and their synthesis and characterisation have been reported in the literature:
Table 1 sets out a comparison of the adsorbed quantities of water (by % of the mass of anhydrous adsorbent) of the various adsorbents with respect to the Fuji silica gel.
Table 2 sets out the comparative results of example 1.
Some MOF solids that are porous coordination polymers show advantageous adsorption/desorption capabilities for certain adsorption and desorption conditions, in particular at low water vapour pressure. These performances stem from the particular so called “S” isotherm profile (type V in the UIPAC nomenclature). Adsorption isotherms of MOFs advantageously used in the context of the present invention have been reported in the literature:
In summary, the MOFs mentioned are characterised by
However, the “S” adsorption character implies of an adsorbent that it is effective only in a narrow partial pressure range. Thus Zr-terephthalate (UiO66) allows to cycle only a quantity of water of less than 5% at an RH of between 10% and 30% whereas the Fuji silica can cycle a quantity of water greater than 10%. Reference for UiO-66=D. Wiersum, Asian J. 2011, 6, 3270-3280).
The performances of several adsorbents have been compared in various operating modes. These comparative results are set out table 1.
In this study, four operating modes P/Psat were considered, where P/Psat (or the relative humidity, RH) is the ratio between the pressure in the evaporator (or the condenser) and Psat is the saturation vapour pressure corresponding to the adsorption temperature—which is assumed to be equal to the condensation temperature—(or desorption temperature). The heat rejection temperature depends on the type of cooling: with water (in which case 25° C. is optionally possible) or air, and in the latter case the temperature depends on the cooling quality (cooling tower or simple cooling tower).
Table 1 presents a comparison, for the five P/Psat conditions studied, with respect to the Fuji silica gel (Fuji Davison RD silica gel), of the quantities of water adsorbed by the various adsorbents, the properties of which have been given. When the quantity adsorbed by the adsorbent is close to that of the Fuji silica gel, the = sign is used, when it is less good the minus (−) sign is then adopted and when it is a little better the + sign is used, and if it is approximately double, ++ is used, and approximately 3 times better the symbol +++ is used.
The adsorbents mentioned in table 1 and
Silica gel Fuji: Fuji Davison RD silica gel
Analysing these comparative results allowed to select the trinomials (relative humidity)/(Te/Tc)/MOF that are most suitable for optimum functioning in various applications of implementation of refrigeration machines of the adsorbent type. The results of this analysis are set out in table 2 (Te=evaporator temperature, Tc=condenser temperature).
The adsorption properties of the Zr-UiO-66-NH2 MOF make it a good candidate for applications in cooling floor-type air conditioning systems (operating modes number 3a and 3b).
In addition, its desorption properties as a function of temperature demonstrate that its desorption is very effective between 60° C. and 70° C., which makes it an excellent candidate in terms of cycled quantity. The result is that the quantity cycled by UiO66-NH2 is 3 times that of silica gel.
A copper sheet (50×50 mm) was blasted on both faces, treated (etched) in a sodium hydroxide solution (pH>12), deoxidised in dilute nitric acid (4<pH<6) and air dried at 60° C. A solution containing 15.12 g (64.0 mmol) of ZrCl4, 10.8 g (65.2 mmol) of benzene-1,4-dicarboxylic acid and 11.44 ml of HCl was stirred in 200 ml of dimethylformamide (DMF) until the solution was completely transparent. The copper sheet was then immersed in the solution in a stainless steel autoclave with a wall covered with Teflon (Teflon-lined). The mixture was heated at 120°-160° C. (preferably) for 48 hours. After cooling, the Cu sheet was carefully removed, rinsed three times in DMF and twice in EtOH and finally air dried at 50° C.
UiO-66 powder was synthesised by successively adding 3.78 g of ZrCl4 (16.2 mmol), 2.86 ml of 35% HCl (32.4 mmol) and 2.70 g of 1,4-benzene dicarboxylic acid (16.3 mmol) to 100 ml of N,N′-dimethylformamide. The mixture was then stirred until the solution was completely transparent, before being transferred and sealed in a stainless steel autoclave with a Teflon-lined wall, where the mixture was heated at 220° C. for 20 hours. The resulting microcrystalline powder was separated from the solvent by centrifugation and dried for one night in an oven set at 60° C.
The UIO-66 powder was dispersed in DMF in order to form a homogeneous white dispersion (15 mg ml−1) under ultrasound for 2 hours. Next, 1270 it of UIO-66 dispersion was added to a poly (MAA-co-EDMA) precursor containing 35 μl of MAA monomer (methyl methacrylate), 400 it of EDMA crosslinking agent and 400 mg of porogenic PEG 6000. After the above mixture was subjected to ultrasound for 0.5 hours, 10 mg of AIBN initiator was added, and another treatment for 5 minutes under ultrasound was necessary to dissolve the AIBN.
A copper metal sheet (50×50 mm) was covered with the polymerisation mixture using a syringe. After polymerisation at 60° C. for 24 hours, the whole was washed with methanol in order to eliminate the porogen and the monomer that had not reacted.
The untreated samples of UiO-66 were synthesised by successively adding 3.78 g of ZrCl4 (16.2 mmol), 2.86 ml of 35% HCl (32.4 mmol) and 2.70 g of 1,4-benzene dicarboxylic acid (16.3 mmol) to 100 ml of N,N′-dimethylformamide. The mixture was then stirred until the solution was completely transparent, before being transferred and sealed in a stainless steel autoclave with a Teflon-lined wall, where the mixture was heated at 220° C. for 20 hours. The resulting microcrystalline powder was separated from the solvent by centrifugation and dried for one night in an oven set at 60° C.
The coating was prepared by a strip-pouring method. 0.3 g of 6FDA-ODA was dissolved in 10 ml of chloroform and the solution was filtered in order to eliminate the undissolved matter and the particles of dust. The solvent was evaporated in order to obtain a polymer solution of 10% to 12% by weight. The UiO-66 powder was added to 5 ml of chloroform and subjected to sonication for 1-2 minutes. Approximately 10% of the polymer solution was then added to the suspension of MOF UIO-66. The suspension was stirred for 6 hours. After good homogenisation, the remaining quantity of the polymer solution was added to the suspension and the final suspension was stirred once again for 1 day. The suspension was next transferred into a vacuum oven for 30 minutes in order to degas, and then poured onto a copper plate and covered in order to delay evaporation of the solvent. After 48 hours, the cover was removed in order to evaporate the residual chloroform for 24 hours. The supported layers were then placed in a vacuum stove at 230° C. for annealing for 15 hours, and the membranes obtained were finally cooled slowly to ambient temperature in the oven and stored in driers.
A copper sheet (50×50 mm) was washed with ethanol for 30 minutes and then five times with water under ultrasound in order to clean the surface, and was next placed in a stove at 100° C. for oxidation.
A solution containing 15.12 g (64.0 mmol) of ZrCl4, 11.81 g (65.2 mmol) of 2-amino-benzene-1,4-dicarboxylic acid and 11.44 ml of HCl in 200 ml of dimethylformamide (DMF) was stirred until the solution was entirely transparent.
The copper sheet was immersed in the solution in a stainless steel autoclave with a Teflon-lined wall. The mixture was heated at 120° C. for 48 hours.
After cooling, the sheet of Cu was carefully removed, rinsed five times in DMF and finally air dried at 50° C.
A sheet of aluminium (50×50 mm) was treated in a solution of sodium hydroxide (pH>12), deoxidised in dilute nitric acid (4<pH<6) and then air dried at 60° C.
A solution containing 4.82 g (20.7 mmol) of ZrCl4 and 10.29 g (62 mmol) of fumaric acid in 200 ml of dimethylformamide (DMF) was stirred until the solution was completely transparent.
The aluminium sheet was immersed in the solution in a stainless steel autoclave with a Teflon-lined wall. The mixture was heated at 120° C. for 48 hours.
After cooling, the aluminium sheet was carefully removed, rinsed five times in DMF and EtOH and finally air dried at 50° C.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14 290281.6 | Sep 2014 | EP | regional |
| 14 61273 | Nov 2014 | FR | national |
