Quote:
Originally Posted by GaryGary
Hi,
Interesting idea -- kind of like a small batch heater, but simpler to build.
The ID of 3/4 pex is 0.671 inches, so 300 ft of 3/4 pex holds:
(0.671)^2*0.785*12*300/231 = 5.5 gallons -- so, best make that shower fairly quick 
I'd use polyiso insulation rather than the pink xps -- its very easy to melt the xps -- I've made a lot of xps thermal sculptures
I think that the 4 inches is probably overkill -- no matter what you do to the back, the front is still only R2, so once you get the back up to (say) R8, nearly all the heat is being lost out the front.
I did a PEX collector: The $1000 Solar Water Heating System
This worked fine, but even with a tilt of 70 degrees (nearly vertical), and only single glazing, there were times when the collector temperature got up to 230F. You will really have to keep an eye on the stagnation temperature in the summer and fall. In my collector, the PEX was not pressurized, so 230F once in a while was OK, but in your case the PEX will be under full mains pressure, and you will have to keep the temperature lower.
If you have not bought your PEX yet, PEXUniverse.com has good prices and free shipping -- $115 (I think) for 300 ft of 3/4.
Gary |
Hey Gary , I picked up some 1/2" thick Polyiso with aluminum covering yesterday at Lowes -- Im going to lay down a full inch for the bottom then put a thick sheetmetal plate painted high temp. Flat Black on top of that ., then the Pex Coil will lay on top of that wrapped in h.d. tin foil also painted high temp. Flat Black. Once placed in the box, the Pex Coil will have 2" on all sides to expand (if need be) . I had Lowes order me a Double pane Low E Window (by Pella) having no strips inside the panes, so, i expect that to work exceedingly well. In fact, I plan on placing a sheetmetal plate over the top of the window and regulate it based on the seasons --- in summer months, it will probably be fully covered to prevent full suns rays and just rely on conduction warming the Pex water .
5-6 gallons of 140 f. water will more than satisfy my low hot water useage each time ...and even at that ill have to dilute it with the cold water faucet.
Any problems with your Pex expanding and contracting ? If so, how much ?
For the time being, im going to introduce the Collector water directly into the hot water supply pipe off the water heater for useage...but, I may change it over to a THermosyphon operation (heating the Water Heater ) since the Collector will be on the ground and the water heater is 8' higher.
Ill take a look at your Pex collector install. Thanks.