Thermodynamics and economics of liquid desiccants for heating, ventilation and air-conditioning – An overview

Abstract

In an effort to minimise electricity consumption and greenhouse gases emissions, the heating, ventilation and airconditioning sector has focused its attention on developing alternative solutions to electricallydriven vapour-compression cooling. Liquid desiccant airconditioning systems represent an energyefficient and more environmentally friendly alternative technology for dehumidification and cooling, particularly in those cases with high latent loads to maintain indoor air quality and comfort conditions. This technology is considered particularly efficient in hot and humid climates. As a matter of fact, the choice of the desiccant solution influences the overall performance of the system. The current paper reviews the working principle of liquid desiccant systems, focusing on the thermodynamic properties of the desiccant solutions and describes an evaluation of the reference thermodynamic properties of different desiccant solutions to identify which thermodynamic, physical, transport property influences the liquid desiccant process and to what extent. The comparison of these thermodynamic properties for the commonly used desiccants is conducted to estimate which fluid could perform most favourably in the system. The economic factors and the effect of different applications and climatic conditions on the system performance are also described. The paper is intended to be the first step in the evaluation of alternative desiccant fluids able to overcome the problems related to the use of the common desiccant solutions, such as crystallization and

Design of quaternary ammonium type-ionic liquids as desiccants for an air-conditioning system

“…A significant interest has been paid to developing a liquid desiccant-type air conditioner [ [3] , [4] , [5] , [6] , [7] , [8] , [9] ]; it is estimated that the liquid desiccant air conditioner has at least a 20% lower electric energy versus the conventional compressor-type air conditioners [ [4] , [5] , [6] ]. Furthermore, the liquid desiccant-type air conditioner can be driven with continuous ventilation during the air-conditioning process; this property is expected to avoid the epidemic of the flu, tuberculosis, and any new types of corona virus diseases among people who share the same room during working or living; the liquid desiccant-type air conditioner is a favorable air-conditioner system for schools, hospitals, nursing homes, and supermarkets [ [3] , [4] , [5] , [6] , [7] , [8] , [9] ]. However, the present liquid desiccant-type air conditioniner has a serious weak point that it uses a lithium chloride (LiCl) aqueous solution as the desiccant source [ [3] , [4] , [5] , [6] , [7] , [8] , [9] ].…”

“…Furthermore, the liquid desiccant-type air conditioner can be driven with continuous ventilation during the air-conditioning process; this property is expected to avoid the epidemic of the flu, tuberculosis, and any new types of corona virus diseases among people who share the same room during working or living; the liquid desiccant-type air conditioner is a favorable air-conditioner system for schools, hospitals, nursing homes, and supermarkets [ [3] , [4] , [5] , [6] , [7] , [8] , [9] ]. However, the present liquid desiccant-type air conditioniner has a serious weak point that it uses a lithium chloride (LiCl) aqueous solution as the desiccant source [ [3] , [4] , [5] , [6] , [7] , [8] , [9] ]. The LiCl aqueous solution is very caustic to iron or copper, and it easily crystallizes when different salts are added for enhancing the dehumidification ability; this requires expensive corrosion-resistance pipes and prohibits its wide use.…”

Desiccant solutions, membrane technologies, and regeneration techniques in liquid desiccant air conditioning system

“…The Table also reflect that 45 wt% of LiCl possesses about 9 mPa.s and 1.4 kPa, viscosity and vapor pressure respectively at 20 C. In terms of specific heat capacity, LiBr is found to have the least value with about 1750 J/(kg K) while LiCl has the best heat capacity up to 2700 J/(kg K). 51 Having established hygroscopic capability of calcium chloride (CaCl 2 ), though lower than that of LiCl, the salient benefit of this desiccant is based on its low cost and availability. 35 Other regular halide salt solution desiccants investigated in the literature are magnesium chloride (MgCl 2 ), 36 potassium formate (KCOOH), 48 and triethylene glycol (TEG).…”

Thermodynamic Analysis of Irreversible Desiccant Systems

“…Low exergetic level heat (60–90 °C) (Tu et al [ 3 ]), rather than electricity, can be used as the main energy source, enabling the use of renewable sources (Jani et al [ 4 ]) and waste heat recovery (Ge et al [ 5 ]). A higher system reliability (Giampieri et al [ 6 ]) can be ascribed to the absence of a compressor. Desiccant-cooling systems employ a sorptive material that undergoes a cycle of thermodynamic transformations by sequentially facing the process air and the regeneration stream, thus realising the necessary heat and mass exchanges.…”