Recently, solid desiccant air conditioning system has been proposed as an alternative to the conventional vapor compression refrigeration air conditioning systems for efficient control over humidity of conditioned air especially in hot and humid areas. The solid desiccant cooling can be more favorable over the traditional vapor compression refrigeration air conditioners, because it assures more accessible, economical and cleaner air conditioning. It is still more important when it is powered by free energy sources like solar energy and waste heat with temperatures of between 60°C and 80°C. In addition, it can significantly reduce the operating cost as well as save energy. In the present paper, principle of solid desiccant cooling system is recalled and its technological applications and advancements are discussed. Through a rigorous literature review, different configurations of desiccant cooling cycles, conventional and hybrid desiccant cooling cycles, different types of mathematical models of rotary desiccant dehumidifier, performance evaluation of desiccant cooling system, technological improvement and the advantage it can offer in terms of energy and cost savings are highlighted. This paper also gives a detailed account of the general features and performance of the solid desiccant cooling system when it is powered by solar energy or industrial waste heat for regenerating the desiccant. This review is useful for making opportunities to further research of solid desiccant cooling system and its feasibility which is becoming common in the coming days.

Solid desiccant air conditioning – A state of the art review

In the solid desiccant wheel air-conditioning system, the performance of the desiccant wheel is critical to the capability, size and cost of the whole system. Constructing mathematical model is an effective method for analyzing the performance of the rotary wheel as well as the system. The model can also be used to guide system operation, interpret experimental results and assist in system design and optimization. The overall objective of this paper is to provide a review of various efforts that researchers have made to mathematically model the coupled heat and mass transfer process occurring within the wheel. The paper first briefly describes desiccant wheel including fundamental principle, heat and mass transfer mechanism and the method of model establishment. Then various models consisting of ideal assumptions, governing equations, auxiliary conditions, solution methods and main results are presented. The models can be classified into two main categories: (1) gas-side resistance (GSR) model; (2) gas and solid-side resistance (GSSR) model which can be further subdivided into pseudo-gas-side (PGS) model, gas and solid-side (GSS) model and parabolic concentration profile (PCP) model. It shows that GSSR models are higher in precision and more complex compared with GSR models. In addition, the simplified empirical models based on measured data are briefly discussed. This review is useful for understanding the evolution process and status quo of the mathematical model and highlighting the key aspects of model improvement such as taking account of pressure loss or air leakage.

A review of the mathematical models for predicting rotary desiccant wheel

Analysis of heat and mass transfer in porous sorbents used in rotary regenerators

Solar desiccant-based air-conditioning has the potential to significantly reduce cost and/or greenhouse gas emissions associated with cooling of buildings Parasitic energy consumption for the operation of supply fans has been identified as a major hindrance to achieving these savings The cooling performance is governed by the trade-off between supplying larger flow-rates of cool air or lower flow-rates of cold air The performance of a combined solid desiccant-indirect evaporative cooler system is analysed by solving the heat and mass transfer equations for both components simultaneously Focus is placed on varying the desiccant wheel supply/regeneration and indirect cooler secondary/primary air-flow ratios Results show that for an ambient reference condition, and 70 °C regeneration temperature, a supply/regeneration flow ratio of 067 and an indirect cooler secondary/primary flow ratio of 03 gives the best performance with COPe > 20 The proposed cooling system thus has potential to achieve substantial energy and greenhouse gas emission savings

Optimisation of a desiccant cooling system design with indirect evaporative cooler

Numerical and experimental performance analysis of rotary desiccant wheels

A mathematical model describing the heat and mass transfer processes that occur during sorption of water vapor in a dehumidifier consisting of parallel channels lined on either side width desiccant felt, is presented. The model includes both gas-side and solid-side resistances for thermal and mass transport. The moisture transport in the desiccant is expressed by considering both gas phase diffusion and surface diffusion. The heat and mass transfer in the desiccant matrix occurs simultaneously and is coupled by an equilibrium sorption relation which is applied locally within the desiccant. Solutions are obtained by using an explicit finite-difference scheme. The effect of heat and mass transfer Biot numbers and other system parameters on the performance of an adiabatic open-cycle cooling system are investigated.

D. Charoensupaya

Papers

Effect of adsorbent heat and mass transfer resistances on performace of an open-cycle adiabatic desiccant cooling system