Instead of, or in addition to a heat squirrel, how about sending the domestic hot water (DHW) waste via a coil in the thermal store?
It should be easy to have a thermostat that checks if hot water being “thrown away” is above the temperature of the lower section of the thermal store, and if so, sends the water through a heating coil in the thermal store, so it passes over some of it’s heat before it goes down the drain.
- water leaving the shower head at 42 deg C will have cooled to around 37 deg C by the time it gets to the drain.
- The 5 deg heat loss will already have been recovered to the house (assuming effective MVHR on the shower room exhaust).
- The heat squirrel holds 120 litres of hot waste water, to pre-heat any incoming cold water that is heading to the heat store.
- By holding the hot water, there is more time for the heat transfer to any incoming cold water, especially any that sits in the coil inside the heat squirrel.
- Hopefully this 120 litres of water is regularly self flushing as “grey water very quickly turns manky when stored, even for short periods.”
Hot Tub Hot Water Heat Recovery
One key thing here, is my plan to have a log fired hot tub.
- I’m looking at hot tubs that use logs to get the water up to temp and then keep the temp there.
- BUT to accelerate getting it up to temp after it has been left a while, I want the option to top it up with hot water from the domestic hot water supply.
- Reading elsewhere, hot tubs tend to run around 36° degrees. Although friends with hot tubs say they tend to run theirs between 37° degrees and 39° degrees.
- I also want the option of taking water from the hot tub, when it’s not going to be used for a while and sending this via a heat recovery option back to the heat store.
- I accept that sending “lumps” of less than 120 litres at a time will optimise this in terms of giving the water time to transfer it’s heat to the heat store / cold water coming in to the house.