snootsandfruits wrote: ↑Wed Jan 05, 2022 8:46 pmThat being a WWHR unit, or just the waste pipe?
At the moment just the building layout - assumed WWHR, but not yet confirmed.
Adokforme wrote: ↑Wed Jan 05, 2022 9:29 pmCollecting waste heat from bath water might be a different proposition but I remember working at a research establishment in the seventies where a whole section was dedicated to waste heat recovery of such whereby a bladder was used to capture waste water from the bath prior to heat being taken and the water then finally drained. It was controlled by timers and monitoring equipment etc whereby the bath was "filled" and drained twice a day but I'm not aware of any such heat recovery system being marketed as a result!
I've seen a few homebrew systems (one in Oxford springs to mind), but dealing with the gunk (soap scum, hair, etc.) which accumulates is a bit of a problem.
Adokforme wrote: ↑Wed Jan 05, 2022 9:29 pmI can only imagine that for any usable heat to be retained an inline preliminary thermal store would be required for the incoming cold to pass through prior to be drawn through the actual heated thermal store. But each to their own and good luck to anyone thinking of installing one.
That's exactly how it works - they're installed vertically with the incoming cold water travelling upwards and the outgoing warm waste flowing downwards (surface tension holding it to the pipe). That gives a very good counter-flow heat exchanger. The pre-heated cold water can then go either to the cold inlet of the shower, the water heater cold inlet, or both in parallel.
snootsandfruits wrote: ↑Wed Jan 05, 2022 10:35 pmTypical shower head water temperatures of 41ºC measured in the laboratory by Liverpool John Moores University (ref 7, figure 17 for mixer showers) indicate water temperature falls by 5.9ºC in the shower, giving a drain temperature of 35.1ºC, say 35ºC for simplicity.
35C water contains quite a lot of energy.
Incoming cold water is at ~10°C (12 month average), hot water to shower is 40°C and warm water to drain is at 35°C. This means that (40-35) / (40-10) = 83% of the heat in the shower water is going straight down the drain. That's the critical calculation -