1:5:10:365 EcoTip Blog

May 23, 2008

:144 Heat Recovery

Filed under: :144 Heat Recovery — Tags: , , , , — John Banta @ 12:40 am

Welcome to today’s 1:5:10:365 Tip for becoming a better steward for our home and planet.

1:5:10:144 EcoTip: As hot water goes down the drain it carries about 80–90% of the energy used to heat water in a home with it. A Drain-water (or grey-water) heat recovery systems can capture the energy and preheat cold water before it enters the water heater or goes to other hot water fixtures.


Illustration of a drain-water heat recovery system. Water flows from a  faucet down the drain, which is wrapped with a copper coil called a heat exchanger. Cold water flows through the coil and is heated by the hot water going down the drain. The heated water then flows to the plumbing fixture and hot water heater where it then flows through the faucet, and down the drain where it then heats new clean cold water in the coil.


Additional Information:

According to the U.S. Department of Energy:

 Drain-water heat recovery technology works well with all types of water heaters, especially with demand and solar water heaters. Also, drain-water heat exchangers can recover heat from the hot water used in showers, bathtubs, sinks, dishwashers, and clothes washers. They generally have the ability to store recovered heat for later use. You’ll need a unit with storage capacity for use with a dishwasher or clothes washer. Without storage capacity, you’ll only have useful energy during the simultaneous flow of cold water and heated drain water, like while showering.

Some storage-type systems have tanks containing a reservoir of clean water. Drain water flows through a spiral tube at the bottom of the heat storage tank. This warms the tank water, which rises to the top. Water heater intake water is preheated by circulation through a coil at the top of the tank.

Non-storage systems usually have a copper heat exchanger that replaces a vertical section of a main waste drain. As warm water flows down the waste drain, incoming cold water flows through a spiral copper tube wrapped tightly around the copper section of the waste drain. This preheats the incoming cold water that goes to the water heater or a fixture, such as a shower.

By preheating cold water, drain-water heat recovery systems help increase water heating capacity. This increased capacity really helps if you have an undersized water heater. You can also lower your water heating temperature without affecting the capacity.

Prices for drain-water heat recovery systems range from $300 to $500. You’ll need a qualified plumbing and heating contractor to install the system. Installation will usually be less expensive in new home construction. Paybacks range from 2.5 to 7 years, depending on how often the system is used. http://www.eere.energy.gov/consumer/your_home/water_heating/index.cfm/mytopic=13040

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