Passive Hydrothermal Air Conditioning: Thermal Comfort at a Low Cost, Environmentally and Economically
At Meadows Primary School, NOWarchitecture have designed an air conditioning system that takes advantage of the consistent ground temperature, in conjunction with the thermal capacity of stored water, to provide a comfortable indoor environment which saves on energy, materials and resources.
The project commenced design in 2008 and was completed in 2011, now operating ‘successful learning environments for ages 0 – 12 in state of the art facilities. These include a full size gymnasium, performing arts hall, Stephanie Alexander kitchen, canteen and breakfast club kitchen, and a synthetic athletics track/sports field.’ 1
Conceived holistically, the design approach sought to create an interconnection of elements defined by the site-specific environmental factors. The implemented Passive Hydrothermal Air Conditioning system derives from 30 years of research and practice by NOWarchitecture directors Judith North and Neville Cowland.
Diagrammatic detail section
Passive Hydrothermal Air Conditioning System
Passive Hydrothermal Air Conditioning works by circulating air through plastic pipes, which sit in water and between water tanks embedded in the soil. The tanks are structured from load-bearing plastic void formers inside a membrane, so water fills the space within and between the tanks and around the ventilation pipes. The water in the tanks is ground-coupled so the water temperature is maintained at around 15 degrees Celsius. After the exchange of heat, the cooled air is delivered via convection at low level into the class room through floor grilles.
Diagrammatic cross section of a classroom
The water tanks have an additional purpose forming part of the footing system. It is estimated that over 400 cubic metres of concrete is saved as a result. The benefit of using water to cool the air, states Cowland, is that ‘the thermal capacity of water is over five times that of clay soil and four times that of concrete.’ To ensure that they can always provide some cooling effect, the tanks are regulated so that 30 per cent of the water is retained at all times. The toilet flushing and ground irrigation system switches over to mains water if the water level drops to 30 per cent.
Diagrammatic long section of a classroom
‘This design provides excellent thermal comfort and air quality with energy inputs 75 per cent lower than typical systems. As hot, stale air rises and is expelled through clerestory louvre windows, fresh air is induced through floor grilles.’ Judith North
This inter-linked air conditioning system works on many levels. It saves energy, materials and resources, stores harvested water (720,000 litre storage capacity), and provides a comfortable environment for users. In addition to the Passive Hydrothermal Air Conditioning system, other environmental elements include:
Louise Mackenzie has a background in architecture and film, and co-curates the annual Cinecity International Film Project.
1. http://www.meadowsps.vic.edu.au/ accessed 9 March 2014
Roderic Bunn, ‘Pool Resource’ pp 8-12 in Delta T Magazine June 2010, http://nowarchitecture.com/images/media/DELTA T June 2010.pdf
Roderic Bunn, ‘Water wise?’ pp 22-26 in Equilibrium October 2010, http://www.airah.org.au/imis15_prod/Content_Files/EcoLibrium/2010/October/2010_10_F03.pdf