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The IUP Journal of Mechanical Engineering
Implementation of Nocturnal Radiative Cooling System with Different Thickness Radiators for Indian Climate: A Feasibility Study
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The paper evaluates the feasibility of implementing nocturnal radiative cooling system for air comfort application. Mechanical air conditioners are conventional in creating thermal comfort but are energy-intensive and hence harmful to the ecological system. Therefore, passive cooling can be adopted as a viable alternative to conventional cooling system. Heat flow through the roof contributes to the total heat gain of a building. The contribution becomes more severe for single story houses covered by metal sheet roofing. An aluminum nocturnal radiator thickness of 0.44 mm and 0.55 mm, painted with an appropriate white paint, was established on the roof. The lightweight metallic radiator was used for cooling the ambient air below its initial temperature. Consequently, this environment-friendly and highly-efficient system can reduce the use of mechanical vapor compression systems. Roofs of buildings radiate heat day and night at a rate of up to 75 W/m2. Generally, most locations can provide net night sky radiation above 60 W/m2, while the nocturnal coolers have the potential of reducing space temperatures by 2 to 4 °C and can yield 14-48% savings in the energy demand of a building.

 
 

The problem of climatic change due to consumption of fossil fuels combined with the resources’ depletion leads to a growing need for replacement of conventional energy consumption activities with those that use natural means. Cooling or heating of indoor spaces in order to achieve indoor favorable conditions demand a great amount of energy as cooling or heating loads. The demand for cooling loads, particularly, may be remarkably increased for urban buildings because of the ‘‘heat island’’ effect, so the use of techniques for cooling combined with physical processes—passive techniques—is an attempt to sufficiently restrict the energy consumption in the buildings’ sector. Passive cooling of buildings can achieve remarkable thermal comfort during summer with a great reduction of cooling loads. Heat dissipation techniques are based on the transfer of a building’s excess heat to a lower temperature environmental sink, as the ambient air, water, ground and sky. In case, the sink is sky, heat dissipation is carried out by a longwave radiation from a building to the sky (radiative cooling) (Frank, 2011). The sky temperature is usually lower than the temperature of most objects on the earth, so any ordinary surface that ‘‘sees’’ the sky has a net longwave radiant loss. Despite this radiative loss, the surface does not obtain lower temperature throughout the 24 h daily cycle, as the incoming solar radiation during the daytime is greater than the net longwave radiation loss.

 
 

Passive cooling, Energy conservation, Human comfort, Nocturnal, Sky radiation.