Heat Recovery (031-DP-6)
Discussion Paper Summary
Wastewater that exits homes and buildings in the CRD travels at an average temperature of 16 degrees Celsius, which is often significantly higher that ambient air temperatures. If wastewater travels unimpeded to outfalls, this heat energy is lost. Heat recovery involves the extraction of this heat from wastewater or effluent, and use of the extracted energy to heat homes, hot water heaters and provide for district heating in urban areas. The CRD is exploring heat recovery as an option for integrated resource management in the Core Area.
Heat Recovery Technology
Heat is recovered from wastewater through the use of heat exchangers, which transfers heat from wastewater to a refrigerant. Two types of heat exchangers are available: in-tank heat exchangers, which are more efficient, but require additional technology when used with raw wastewater, and in-pipe or in-trench heat exchangers, which are far less efficient.
Raw wastewater heat exchangers require screening measures to reduce fouling of the exchanger tubes. Systems which use this technology are being built in Vancouver, BC and are in operation in Switzerland and Norway.
Treated effluent heat exchangers do not require screening mechanisms, however, to be useful the treatment plant must be located near the potential users of the heat. A district heating system in Whistler, BC’s athlete’s village is being built which will use heat recovered from wastewater effluent. Similar facilities are located in Göteborg and Stockholm, Sweden.
Heat Recovery Potential & Concerns
Effluent temperature can have an effect on treatment plants, the receiving environment and aquatic life. Low temperatures can prevent dilution and dispersion of effluent, cause fats oils and grease to congeal in sewer lines and harm aquatic life. The amount of heat taken by a heat exchanger must be balanced, therefore, by minimum temperature requirements.
In the CRD, it is theorized that, using a flat plate heat exchanger, approximately 2,950 GJ/d of heat energy, rising to 4,970GJ/d in 2065, could be harvested. This energy could supply space heating for 18,500 households, or 31,300 households in 2065, with adjustments for seasonal fluctuations. Recovery of the heat will depend on the proximity of each plant to potential users.
© Image courtesy of Evan Leeson