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
Temperature gradient, the ELI5 is heat energy always moves to equilibrium that is to a balance where it won’t move anymore, the greater the difference in temperatures the greater the function through a heat exchange. The shower water you use is only about 10⁰c hotter than your body by the time it hits the drain it loses a couple more degrees, by the time it would be collected from a drain and recirculated through a heat exchange it would only be a few degrees above ambient air temperature and would barely heat your home at all. The hot water used in water heating systems is much hotter than the water used in your shower and is circulated directly off the boiler and back to the boiler, this water stays clean. Combining the shower water with the boiler water would only lower the temperature of the water from the boiler it would also turn the hot water into waste water, this means a grey water heat recirculating system has to operate on its own loop, it’s a high infrastructure cost for an extremely low return, it probably exists somewhere but for larger scale applications than the shower in a single residential home.
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