The EcoDrain heat exchanger makes good use of warm waste water
The idea of using heat from waste water is an obvious one, but it presents a number of challenges.
Firstly, it only makes sense to heat the cold domestic water, which requires a thermostat-controlled mixer tap so that you do not have to constantly adjust the mixing ratio as the cold domestic water is heated by the waste water.
Secondly, the design of the heat exchanger must take into account that gravity alone ensures the passage of the waste water through the exchanger, and that the waste water may be contaminated with hair and other solid particles. It is possible to utilise some of the cold domestic water’s pressure to drive a turbine that forces the waste water through the heat exchanger, but this would reduce the pressure of the shower water.
Thirdly, complex technical installations beneath the floor are not desirable. The necessary connections must not be carried out in an inaccessible location, so in practice there must be an accessible access panel beneath the shower cubicle.
The idea is good, but hardly practical in an ordinary home..
Quote from Engadget:
‘File this one directly in the “why didn’t I think of that?” folder. As bathrooms become increasingly eco-friendly, the EcoDrain is stepping in to make use of all the hot water that goes to waste every time you shower. Put simply, this user-installed heat exchanger transfers heat from hot shower waste water to cold incoming water, essentially reducing water heater usage by as much as 40 per cent. Of course, we’ve never seen a plumbing job that was anything close to simple, but for savings like this, it may just be worth the trouble.[Via Inh [...]’