Abstract
Increasing of occupant comfort demands are leading to rising requirement for air conditioning, but deteriorating global energy and environment crisis are starving for energy saving and environmental protection. The need to come up with the new energy saving as well as environmental friendly air conditioning systems has been more urgent than ever before. In hot and humid areas, the liquid desiccant air-conditioning systems based on evaporative cooling was proposed as an alternative to the traditional vapor compression systems due to its advantage in, removing the air latent load, friendly to environment, removing of pollutants from the process air and reduction of the electrical energy. In this project, recent researches and development activities in liquid desiccant dehumidification systems combined with evaporative cooling technologies are surveyed. Following that, such a liquid dehumidifier is fabricated. In this system, CaCl2 salt solution is used for dehumidification of air. Strong solution is internally cooled to minimize heating up of the solution which causes reduction in its absorbing capacity. Evaporative cooling that follows is more effective because dehumidified air flows over cooling water spray. Weak solution is regenerated by an electric heater. Finally air gets cooled and dehumidified. Heating for regeneration can be done using any cheap heat source like waste heat, solar energy. Direct evaporative cooling gives good effect in dry areas. Its effectiveness is not much in humid areas. To be suitable for such high humidity conditions in this system air is dried first, using cacl2 salt solution. Heat is generated during dehumidification. Cooling water is circulated to absorb this heat. Evaporative cooler also cools the salt solution after it got regenerated by heating.
Highlights
Liquid desiccants are solutions that have a high affinity for water vapor
The liquid desiccants used in these systems commonly are very strong solutions of the ionic salts lithium chloride and calcium chloride
These ionic salts have the attractive characteristic that the salts themselves have essential zero vapor pressure, and so vapors of the desiccant will not appear in the air supplied by the liquid desiccant air conditioning
Summary
Liquid desiccants are solutions that have a high affinity for water vapor. This property is the key to creating cooling systems that dehumidify air without over-cooling [1]. One approach to limiting the impact of the heat released when the desiccant absorbs water vapor is to flow desiccant at a sufficiently high rate that its temperature rise is limited (i.e., in the preceding example, if the desiccant's concentration changed only 0.1 point, its temperature would rise only be 4 F) This approach, which was first used in the liquid-desiccant systems of the 1930s and is still used in many liquid desiccant air conditioning s today, requires that the liquid desiccant is first cooled before it is delivered to the top of a bed of porous contact media. Thermal energy, at a temperature as low as 40–50°C required for regenerating of the liquid desiccant can efficiently obtained using a heater (Figure 1)
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