Over the past few year I've been thinking alot about greywater heat recycling.
As showers use a lot of energy it would be sensible to try to get back some of the heat washed down the drain.
Anyway here is a brief summary of the project:
Instead of feeding the water from my recycler to to the inlet of my water heater I opted to just run it to the cold water. The thermostat in the shower should regulate the water so that less water from the water heater is used when running the recycler.
I also opted to run the copper coil inside the drain pipe in direct contact with the grey water as opposed to making a new grey water drain pipe out of copper as I believe this is more efficient.
I used compression fittings so no soldering was involved.
Diagram of my greywater recycler
6 meters of 12mm copper pipe was coiled to form the heat exchanger inside my 75mm plastic drain pipe. This coil was made by filling the pipe with salt and then wrapping it around a pipe.
The coil was put inside 75mm drain pipe with y splits for the inlet and outlet of the coil.
View inside the heat exchanger
Heat exchanger in place
Cold water line connections to the bathroom. Inlet on left side outlet on right. I also made a bypass valve so I could disconnect the heat exchanger while still having a functioning water supply.
As of now I have not done any measurements of the efficiency of the system, but while running the shower the water in to the heat exchanger is very cold ~7C and the output is warm ~20C.
Lars