Why is it not used again and wouldn’t it be very efficient to combine with a heat pump for reuse?
Especially since water from shower or sink isn’t usually very dirty, couldn’t it be stored for a while in an isolated tank so that e.g. a heat pump can run more efficient on it than on usually colder air or colder ground water?
In: Engineering
I researched this a few years back while renovating our house.
Used hot water is called greywater.
1. It doesn’t pay off for a single household. The reason for that is the low efficiency (small amount of warm water and the relatively low temperature) and the content of fats/hair/etc from soap in the graywater forcing regular cleaning in order to maintain functionality/efficiency. To circulate two separate water circuits in order to transer heat energy also requires electricity (pumps).
2. Larger installations for multiple households can yield an overall industrial-like benefit that pays off in the long run, but it depends on several factors.
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