Cooling of schools – results from a demonstration project using adiabatic evaporative cooling with harvested rainwater

This paper reports on a demonstration project where a section of a school building with eight classrooms and three other rooms was retrofitted with a mechanical balanced ventilation system with an integrated evaporative cooling unit. The floor area was 537 m2. Especially in temperate climates, evaporative cooling has unreleased potential as an alternative solution to conventional cooling technologies, and by combining it with harvesting of rainwater, the solution aligns well with a future with higher cooling needs, need for climate adaptation, and the overall sustainability agenda. The cooling unit works by storing, filtering and spraying rainwater into the return air. The water evaporates, cools the return air, and through an innovative corrosion-resilient plastic heat exchanger, the return air then absorbs heat from the supply air. In this way indoor climate problems caused by humidification of the indoor air are avoided. The demonstration was running in the May and June 2019. The results show that the specific fan power increased approx. 500 J/m3 when the evaporative cooling pumps were activated and that the available cooling power – depending on the moisture content of the return air – was fluctuating in the range 20-30 W/m2. The peak rainwater consumption was approx. 1 m3/day. The results show that implementation of evaporative cooling with harvested rainwater is an attractive and sustainable alternative to mechanical compressor cooling