The phenomenon of evaporative cooling is a common process in nature, whose applications for cooling air are being used since the ancient years. In fact, it meets this objective with a low energy consumption, being compared to the primary energy consumption of other alternatives for cooling, as it is simply based in the phenomenon of reducing the air temperature by evaporating water on it. This process can be an interesting alternative to conventional systems in these applications where no very low temperatures are needed, like the case of air-conditioning during the summer. However, the risk of contamination by legionnaire’s disease, commonly related to evaporative cooling systems, has led in recent years to the substitution of these devices in the industry by less-efficient systems, like the case of cooling towers or evaporative condensers substituted by air-condensing refrigerating processes. Therefore, these systems based in the evaporative cooling are rarely used for cooling buildings. Toreduce this risk, evaporative cooling is produced from humid surfaces, in such a way that water evaporates due to the difference of vapor pressure between the surface and the air, and thus minimizing the generation of aerosols, responsible for the spread of legionnaire disease. Aerosols are nevertheless produced in conventional systems where water is sprayed or directly in contact with the stream of air; and the problem worsens if the water, which is re circulated, has been still in any moment or its temperature is adequate for the bacteria proliferation. This paper aims to introduce the thermodynamic basis in which the process is based, as well as the commercial evaporative systems and the problem associated to legionnaire’s disease in this kind of systems. Furthermore, three different experimental devices based in evaporative cooling are described, which have been designed and manufactured in the Thermal Engineering Research Group of the University of Valladolid., describing their characteristics of operation and providing the experimental results obtained during their characterization, for outside air conditions typical of hot and dry summers. Keywords: Direct evaporative cooling, Air-conditioning, Energy efficiency, Legionnaire’s disease. 1. Introduction
The environmental impact associated to the use of energy from conventional fossil origin, the energetic and economic dependency on non-renewable sources, lead to the necessity of reducing the energy consumption, maintaining the current targets and necessities of each activity that require the use of energy. Figures about the energy consumption by fields show that from 20% to 40% of the total energy demand in developing countries is generated in buildings, depending on the climatic conditions . Moreover, due to the high number of users of the building sector, an improvement on the energy efficiency of the systems leads to an important decrement on the energy consumption, thus being this sector one of the most interesting fields to focus the activity to improve the energy efficiency. However, not only the economic savings have to be considered in the study of the improvements in energy efficiency, whose profitability is commonly uncertain, but also the reduction in the environmental impact or in the misused of natural resources implied . Despite the fact that the priority of the new dispositions introduced for energy management, new devices and generators among others, is to reduce the energy consumption in buildings, they must ensure a proper comfort level and well being of their users . Consequently, it should be considered the introduction of systems that permit condition the hydro thermal environment of the rooms, maintaining an adequate indoor air quality and thermal comfort, with low energy requirements, when providing energetic viable solutions to obtain a proper thermal environment in buildings. There are many sustainable alternatives in the...
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