Comfort levels in evaporatively cooled buildings

Abstract

A medium sized office building is modeled for centralised evaporative air cooling together with modified cooling tower, cooling coils, saturation pad and evaporatively cooled roof. The tower exit air is used to pre-cool the tower inlet air thereby reducing the latter's wet bulb temperature. Cooling load of the building is estimated by Cooling Load Temperature Difference – Cooling Load Factor (CLTD – CLF) method with respect to time for various indoor temperatures. Cooling capacity of the evaporative cooling system is also calculated for various indoor temperatures leading to equilibrium indoor temperature for any time. Knowing the latent load on the space and the prevailing ambient conditions, the indoor humidity is predicted. For the assumed activity level, clothing and air velocity, PMV and PPD are estimated. The positive values of PMV the resulting PPD are integrated over the time to get PMV – hours and PPD – hours which give the cumulative dissatisfaction levels for each month. The developed evaporative cooling model is applied for five representative cities in India, namely Ahmedabad, Bangalore, Jodhpur, Nagpur and New Delhi. While for Bangalore (cool and dry) the comfort is achieved throughout the year satisfactorily, discomfort prevailed for few months around July for Jodhpur (hot and dry). The maximum value of discomfort felt is about 50 PMV-Hours in the month of July. For other cities, much less discomfort is felt for shorter duration. The analysis reveals that centralised evaporative air cooling is feasible for human comfort especially in hot and dry climates. Modified cooling tower and roof evaporative cooling further widen its scope to bring the indoor conditions within the extended comfort zone.