The Mark I used garden hose as the storage/ heating element weaved over the front of a wooden palette with an old bathroom mirror mounted in the back. This was (really) unsuccessful on two fronts:
- A 18-long ID 12mm hosepipe has a storage capacity of ~2 litres…not a lot. A water-frugal shower runs at around 8L/min, giving you 15 seconds of heat before the cold water comes through.
- Our high main pressures plus pressure build-up in the pipe (as the temperature rises) caused all sorts of issues, emanating in the pipe becoming riddled with pin holes after a few use cycles.
Mark II is made of 40mm white uPVC pipe (36mm ID) painted black with car bumper spray – I figured this would adhere to the PVC. I would have used black uPVC if I could have found it. On a whim, I mounted some shiny mini-corrugated galvanised sheet to the back of the unit. I am not sure how effective this is but found that the heat being reflected of it into my face when I was installing it was impressive, so I guess it may contribute a bit to reflecting light back out onto the back of the pipe.
The pipe, which you can get in 2m lengths from the DIY store, is arranged in a concertina with U-bends connecting the ends to form a continuous 8m run. This gives a storage capacity of >8.1 litres (~1 minute). I mounted pipe system horizontally on the wall of the house in a north-facing (in New Zealand) sun spot near the shower unit.
The shower element is made from thick gauge 25mm dia galvanised steel pipe – the type that screws together. There is a valve-type tap. I was after the industrial type look so I mounted it on a piece of old rusted steel sheet I had.
The shower head (shower rose) is actually just an aluminium gardening spray head; I was lucky to find one that had a thread that matched the pipe. I attacked the head with sander to give it a tarnished look. I used that PTFE plumber’s tape stuff on all the joints to make them watertight.
The shower unit connects to the heating/storage unit with garden hose and standard garden hose connectors. Likewise the heating/storage units connects into the tap from the mains with standard garden hose.
I was pretty stoked with the first time I tried the shower. I turned it on at the mains and left it for around half an hour to heat This was on a really hot day (28C and blue skies – intense sun). When I stood under the shower the water was as warm as a regular bathroom shower and ran warm for 30 seconds or so.
In theory, one leaves the garden tap on all the time – its function is deferred to the valve on the shower. When you turn on the shower valve, the mains pressure pushes the heated water out of the storage pipes through the showerhead, back-filling the storage at the same time. An additional advantage, I hypothesis, in leaving the garden tap on, is the system remains ‘open’. As the water heats in the PVC pipes it will try and expand. If the system is closed (by closing the shower valve at one end and the garden tap at the other) the contained volume is fixed, the water cannot expand un-restained so it exerts pressure on the inside of the pipes. This increases as the temperature rises and I suspect could become very high, potentially splitting the pipework or the joints (Spoiler – its does!Its a problem). Leaving the system open (maybe!) means that this pressure buildup is equalised into the mains so the pressure on the pipework remains moreorless constant, regardless of temperature. During my first few days use of the shower my less-than-100% confidence in my theory, together with my suspicion of some of my PVC pipe joints (I did not want to come home after work and find something had failed and water had been spewing out the tap all day) meant that I shut the system off at the wall when not in use. As suspected the buildup does cause issues – a very slow dripping leak has developed in a joint at the top of the PVC pipe which seems now to work something like a pressure valve. I will fix it at some stage – need to talk a a plumber friend about how they deal with it in hot water systems. You must be able to buy a valve. UPDATE HERE.
If I were to make a Mark III, I would like to make the heating unit a little more industrial looking. I think using wide bore metal pipes to replace the PVC would be prohibitively expensive (not that PVC pipe is particularly cheap!), but the fixtures could be made to look a little more industrial, and the hosepipe between the unit tidied up or replaced. I might add in a thermometer too (UPDATE – I did!).