60 DECEMBER 2021 WorldWide Drilling Resource® RENEW - SUBSCRIBE NOW! Too Valuable to Flush and Forget Compiled by the Editorial Staff of WorldWide Drilling Resource® Hot water flushes down drains to connected sewer pipes daily, maintaining a fairly constant temperature of around 50ºF (10ºC) as it travels from homes and businesses to treatment plants. The U.S. Department of Energy estimates 350 billion kilowatt-hours of heat energy are flushed down the drains in the United States every year - roughly enough to power 30 million homes. Sewer Heat Recovery (SHR) is fairly common in Europe and parts of Canada, but standardized SHR use agreements are just now pioneering in the United States. SHR is an alternative and sustainable energy solution reducing on-site fossil fuel combustion, lowering carbon emissions, and decreasing a buildings’ carbon footprint in facilities using hydronic (circulating water) systems for heating and cooling. The technological solution for recovering heat from sewage water is relatively simple. SHR captures heat energy from wastewater in an underground holding tank and then transfers it to a heat exchanger. This allows a heat pump to extract the energy and transport it to a connected building’s heating or cooling system. Sewage water can be utilized with district heating grids to improve the overall energy efficiency of heating and cooling systems for a city. SHRs can also be combined with heat pumps or similar heat recovery systems to utilize less energy compared to conventional heating sources, thus reducing the primary energy consumption and CO2 emissions. Different types of heat exchangers are used in combination with various heat pump types. An important factor in uti l izing sewage water as a heating source, the heat exchanger system affects how efficient the heat pump will be. The two main technical solutions for heat recovery from sewage water are sewer-external heat exchangers and insewer heat exchangers, each with advantages and disadvantages. Both systems are well suited for a variety of applications, including office buildings, district heating projects, swimming pools, industries, and schools. Sewer-external exchangers are limited by the sewage water flow, the water temperature, and the area available for the installation of the equipment. They do have high technical flexibility, as well as ease of installation and accessibility for maintenance. In sewer-external exchangers, waste water is removed from the sewer into a so-called wet well fromwhere it can be used in various ways. The actual heat exchange process takes place outside the sewer, either by using the sewage water, usually treated, in an intermediate circuit to the heat pump or pumped directly to the evaporator of the heat pump. In-sewer exchangers are mostly limited by the state of the existing sewer system, the length of straight runs and slopes, as well as the sewage water flow. This system requires a lower auxiliary power consumption compared to the sewer-external systems. In an insewer exchanger, the heat exchange process takes place within the sewer. The exchanger is installed either on the bottom of the sewer pipe to transfer WTR Too Valuable to Flush continued on page 62
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