Municipal steam district heating services such as New York City’s Consolidated Edison’s have no recirculation system. The waste heat, usually in the form of steam condensate and hot water, is mixed with and cooled by municipal potable water. Since 2006, The Center for Innovation and Applied Technology and The Laboratory for Energy Reclamation and Innovation at the Cooper Union have been developing a system to use this thermal pollution to heat the growth medium of green roofs. The authors have also constructed three geothermal heated gardens systems in Iceland. American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) specifications for heated sidewalks were referenced in all locations.
The heated green roofs have the potential to save more than 2,000,000 cubic meters of potable water if applied to 40% of Consolidated Edison’s steam customers. Plant growth is often accelerated by 20% or more in all locations.