Analyzing the Performance of Passive Downdraught Evaporative Cooling (PDEC) Applied to a Small Air-Conditioned Office Building in Phoenix, AZ
The demand for cooling in residential and commercial buildings is increasing worldwide, causing more reliance on conventional vapor compression cooling techniques and thereby exacerbating the environmental impact. Passive cooling and energy efficient designs have proven to substantially reduce this adverse impact and their widespread application would be highly desirable.
Direct evaporative cooling has been recognized as an efficient energy method for cooling spaces in hot and dry climates. In this study we specifically investigate the applicability of using Passive Downdraught Evaporative Cooling (PDEC) in a DOE prototype building, small office, air conditioned, Commercial building 511m2, one floor story located in Phoenix, Arizona.
The initial strategy involved exploring the possibility of cooling the building only by a passive method, using a PDEC system. Such an approach proved to be unpractical for Phoenix; therefore, the research investigated the possibility of combining PDEC with a conventional HVAC system. It focused on analyzing the performance and the potential energy savings of the proposed hybrid system on an hourly basis for the cooling months from April to October, using commercially available PHDC software. Water consumption related to the evaporative cooling was also evaluated. Further, the research addressed potential improvements to the system such as adding wind catchers or mechanical fans.
The results indicate that there is substantial temperature reductions associated with the use of a PDEC during the cooling months ( about 18-20° C) , and a 23 % and a 37% decrease in the cooling loads of the HVAC system when setting the indoor thermostat to 24°C and 27°C respectively. However, this study showed less than 10% savings in the cooling loads during July and August proposing the possibility of using the Cool Tower as a Pre-Cooling system during these months as a way of reducing the overall cooling loads of the conventional system since.”