Evaporative cooling is an environmentally friendly air conditioning system that operates using induced processes of heat and mass transfer, where water and air are the working fluids. It consists, specifically, in water evaporation, induced by the passage of an air flow, thus decreasing the air temperature. This paper presents three methods that can be used as reference for efficient use of evaporative cooling systems, applying it to several Brazilian cities, characterized by different climates. Initially it presents the basic operation principles of direct and indirect evaporative cooling and defines the effectiveness of the systems. Afterwards, it presents three methods that allows to determinate where the systems are more efficient. It concludes that evaporative cooling systems have a very large potential to propitiate thermal comfort and can still be used as an alternative to conventional systems in regions where the design wet bulb temperature is under 24ºC.Keywords: evaporative cooling; air conditioning; thermal comfort. Resfriamento evaporativo: água para conforto térmico RESUMOResfriamento evaporativo é um sistema de condicionamento de ar ambientalmente amigável, que opera por meio de processos induzidos de transferência de calor e massa, nos quais a água e o ar são os fluidos de trabalho. Consiste na evaporação de água, induzida pela passagem de uma corrente de ar, o que provoca uma redução na temperatura do ar. Este trabalho apresenta três métodos que podem ser utilizados como referência para a aplicação eficiente de sistemas de resfriamento evaporativo, aplicando-os a algumas cidades brasileiras, caracterizadas por condições climáticas diversas. Apresenta-se, inicialmente o princípio de operação dos sistemas de resfriamento evaporativo direto e indireto e define-se a efetividade dos sistemas. Após, são apresentados os três métodos, concluindo-se que os sistemas de resfriamento evaporativo tem grande potencial para oferecer conforto térmico, podendo ser utilizado como uma alternativa aos sistemas de condicionamento de ar convencionais em regiões onde a temperatura de bulbo úmido de projeto é menor que 24ºC.Palavras-chave: resfriamento evaporativo; condicionamento de ar; conforto térmico. CAMARGO, J. R. Evaporative cooling: water for thermal comfort.
Evaporative cooling operates using water and air as working fluids. It consists in water evaporation, through the passage of an air flow, thus decreasing the air temperature. This system has a great potential to provide thermal comfort in places where air humidity is low, being, however, less efficient where air humidity is high. A way to solve this problem is to use dehumidifiers to pre-conditioning the process air. This paper presents a system that can be used in humid climates coupling desiccant dehumidification equipment to evaporative coolers. The paper shows, initially, the main characteristics of the evaporative cooling and of the adsorption dehumidification systems. Later on the coupled systems, in which occurs a dehumidification by adsorption in a counter flow rotary heat exchanger following the evaporate cooling of the air in evaporative coolers, are analyzed. The thermodynamic equations of state are also presented. Following, this paper analyzes some operation parameters such as: reactivation temperature, R/P relationship (reactivation air flow/ process air flow) and the thermodynamic conditions of the entering air flow. The paper shows the conditions for the best operation point, with regard to thermal comfort conditions and to the energy used in the process. In addition this paper presents an application of the system in different climate characteristics of several tropical and equatorial cities
Air conditioning systems are responsible for increasing men's work efficiency as well for his comfort, mainly in the warm periods of the year. Currently, the most used system is the mechanical vapor compression system. However, in many cases, evaporative cooling system can be an economical alternative to replace the conventional system, under several conditions, or as a pre-cooler in the conventional systems. It leads to a reduction in the operational cost, comparing with systems using only mechanical refrigeration. Evaporative cooling operates using induced processes of heat and mass transfer, where water and air are the working fluids. It consists in water evaporation, induced by the passage of an air flow, thus decreasing the air temperature. This paper presents the basic principles of the evaporative cooling process for human thermal comfort, the principles of operation for the direct evaporative cooling system and the mathematical development of the equations of thermal exchanges, allowing the determination of the effectiveness of saturation. It also presents some results of experimental tests in a direct evaporative cooler that take place in the Air Conditioning Laboratory at the University of Taubaté Mechanical Engineering Department, and the experimental results are used to determinate the convective heat transfer coefficient and to compare with the mathematical model.
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