Q: What are the advantages of using a wastewater heat exchanger versus conventional heating and cooling?
A: Recycling heat energy from wastewater saves costs. Energy costs for heating and cooling can be reduced by up to 80 percent when compared with conventional methods.
Sewer heat exchangers improve sustainability and are eco-friendly. Using a wastewater heat exchanger reduces the use of fossil fuels. This improves the environment by reducing emissions and lowering a building’s carbon footprint. These systems also save water that would otherwise evaporate in cooling towers, and no cooling tower cleaning chemicals are polluting the environment.
Sewer heat exchangers can be space-saving, giving customers more latitude with their building design. Installation is quick and and easy.
The supply of wastewater is virtually unlimited. Wastewater is a free, local, and decentralized heat source. There is little interference to the existing sewer system, and minimal construction required to access the wastewater.
Q: Do grit, rags, and debris in the wastewater affect the operation of the system?
The wastewater is prescreened prior to being pumped to the heat exchanger. This prevents debris from affecting system operation. Screenings are returned to the wastewater stream.
Q: Does the raw sewage come into contact with the cooling water?
A: The cooling water does not contact the raw wastewater. The heat exchanger is constructed of welded stainless steel. Horizontal carrier medium pipe modules are arranged in parallel. The pipe modules are made of stainless steel to achieve maximum heat transfer efficiency. The pre-screened wastewater flows through the heat exchanger and, via the compactly arranged pipes, gives off its thermal energy to the cooling water.
Q: Are there negative effects from the wastewater as it flows through the heat exchanger, such as a buildup of sediment or biofilm on the pipes?
A: Due to the chemical and biological properties of wastewater, a biofilm builds up on the heat transfer surfaces. This can impair heat transfer. To prevent negative effects, an automatic solids removal mechanism provides preventive cleaning of the heat exchanger surfaces. Solids settle on the tank floor, are removed by a screw conveyor, and are returned to the sewer along with the wastewater.
Q: Is there a minimum sewage supply and temperature needed for this type of system?
A: A continuous wastewater flow of at least 1.3 gallons per second (5 liters per second) is required to ensure efficient heat recovery. The wastewater temperature should not fall below 50 °F (10 °C).
Q: What is the minimum system size (in kW) that such a system would be used for?
A: For economic heat recovery, the minimum output of useful heat is about 20 kW.
Q: How close must the facility be to the wastewater pipeline to remain economical?
A: The distance from the facility will be unique to the project. However, the distance from the sewer system to the heat station and building should be as short as possible to minimize capital and operating costs.
Q:Can other waste liquids be used for heating and cooling, such as industrial wastewater or wastewater treatment plant effluents?
A: Commercial and industrial facilities may have warm water discharges. On-site wastewater treatment can often be combined with heat recycling technology for cost savings and environmental sustainability. These solutions would be site-specific.
Treated wastewater effluent heat recovery provides several advantages: Considerable heat potentials are available due to the huge water volumes. Effluent cooling has no negative effects on the receiving water.
HUBER Technology has a compact, self-cleaning RoWin Heat Exchanger that can be installed directly in the effluent channel.
Sewage treatment plants often have a high demand for heat. In addition to heating and cooling buildings, recovered heat can be used to enhance sludge drying in HUBER’s Solar Dryer.
Filtrate from wastewater dewatering is also ideal for producing heat energy that can be used for heating digesters, for drying sludge, or heating and cooling buildings.
Q: What type of projects are in place that use this technology?
A: Due to the many advantages discussed, the use of wastewater as a heating and cooling source is catching on. HUBER has a variety of installations, including a system for the Museum of Bavarian History, a new ministry building in Stuttgart, Germany, and a 28-story high-rise in Switzerland.
HUBER is also proud to have its ThermWin® system supply heating and cooling for the first “net-zero” building in Washington, D.C. A net-zero building generates all the energy it needs for itself. The American Geophysical Union (AGU), a non-profit organization of over 58,000 geophysicists, is building their new headquarters with net-zero technology. The 5-story building will include LED lights, vertically planted green walls, a greywater reuse system, and coolable ceiling structures. HUBER’s ThermWin system will use wastewater from the sewer system to provide 500 kW cooling capacity and 220 kW heat output for the building.