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Solar Hot Water Heater

11K views 41 replies 8 participants last post by  DangerMouse 
#1 ·
i'm building a solar hot water supplement system, similar to the one shown. except mine will be taller and thinner. about 6 feet upright. will also have boiler type temp and pressure gauge and temp/pressure relief valve outside on unit.

A: i'm wondering if cpvc (made for hot water) in 2" size with primer and glue will stand up to possible excessive heat and expansion and not leak?

(i know, copper....but i hate copper sweating, and it's cost prohibitive.)

B: another option is 2" black steel with hi-temp dope or teflon tape, but my concern there would be rust in the HWH.

my preference would be cpvc though.

any suggestions here would be helpful, thanks!

DM
 

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#2 ·
Generally, I think PVC/CPVC has a max temp rating of something like 140F. Seems low to me as a HW heater can put out 140..

http://www.engineeringtoolbox.com/pvc-cpvc-pipes-pressures-d_796.html

Ran across this company which makes high temp/pressure CPVC that may work.. I'm sure other cos. make it too, but not sure of cost, availability, etc.. http://www.harvel.com/piping-cpvc.asp

PEX I think is usually rated 180F. Also saw this blog entry on PEX w/aluminum.. http://www.pmengineer.com/CDA/Articles/Breaking_News/BNP_GUID_9-5-2006_A_10000000000000435978 Probably expensive though.

I'm no expert here, but thought that might help.. You'd probably want/need at least a 200F rating, and a higher PSI than normal CPVC.

Black steel with definately rust.. Even galvi would probably not do so well for ya..

PS - No idea how reputable any of those links are, but I'm sure someone will jump in..
 
#3 · (Edited)
Copper. That is the only way to go. Temperature in these systems can exceed 210 degrees and that will melt pex which has a maximum of 200 degrees @ 60psi. CPVC will dry out and crack. You can go galvanized if you want to but that is harder to work with unless you have the equipment to make your own lengths.

Yes copper is expensive.

Barrier pex (aluminum liner) will not work as it will still soften the poly.

You will also need a pressure tank (5 gallon will work for large systems and 3 for smaller systems), pressure/temperature release valve, steam vent, air scoop, pressure gauge, hight temperature pump, Delta T differential relay, valves to isolate the system for maintenance and flow restriction for the pump, and a high point to putting more fluid in the system.

If you are building the collector use copper for sure and you can get some snap on aluminum panels that will help gather more heat that are designed for pex. Put in glass to keep the heat in and change the heat from radiation to convection. Insulate behind the pipe to keep the heat in. Use board insulation. Seal it as best as you can but not totally sealed as it needs some air movement.
 
#6 ·
You will also need a pressure tank (5 gallon will work for large systems and 3 for smaller systems), pressure/temperature release valve, steam vent, air scoop, pressure gauge, height temperature pump, Delta T differential relay, valves to isolate the system for maintenance and flow restriction for the pump, and a high point to putting more fluid in the system.
thankx Marvin, please elaborate on this paragraph?
got pictures of these things? p/t valve i know, pressure gauge i know, why a pressure tank? and the rest?

DM
 
#5 ·
I am not aware of any copper aluminum connections that would work for this situation.

These expand at different rates and don't think they would survive the expansion contraction process.

There are options like SolarFlex but that is really expensive and makes copper look like CPVC in comparison.
 
#9 ·
Could you use soft copper instead of rigid? With a cheap conduit bender you could save some using so many fittings.

DM, does Michigan have a lot of bright sunshine? Here in Ohio we have mostly overcast days throughout the year. Something like 13 days of clear blue sky a year.

I'd consider solar if we had more bright sunny days and the cost of running a pump would be off-set by the electric/gas saved heating the water.

Did you run any numbers as to what your projected savings might be?
 
#12 ·
? huh? won't work? why not? sun heats tubes, water called from faucet/shower, cold goes into batch heater, hot goes into inside water heater. water already hot, no elec. needed to heat it. i don't follow....

DM
 
#15 ·
? huh? won't work? why not? sun heats tubes, water called from faucet/shower, cold goes into batch heater, hot goes into inside water heater. water already hot, no elec. needed to heat it. i don't follow....

DM
Ok, I'm not understanding your diagram. How many feet of tubing are you running inside your solar heater? If the volume of your tubing is big enough, sitting in the sun, waiting for you to turn the faucet on, and that tubing goes to your hot water tank, then yes that will work.

If that volume of water is going into a separate tank and then into your hot water heater your not gonna gain much. In other words, your not raising the temperature of the (holding tank) water by circulating solar heated water through it.
 
#14 ·
I bet your ambient to sun light ratio is going to make that batch system not work so well. The batch tank will be cold most of the time. If it's cool out, you need some way to collect solar heat without letting the cool ambient air just steal it away. You need proper solar collectors and a well insulated tank.
 
#18 ·
Clutch, so far i only intend to use it for 3 seasons, disconnect for freezing weather. however, if i bury lines, keep from freezing, add the insulated cover i already designed.......who knows? anyways, my case is long and thin to fit it where i need it to get the most sun, so bending copper at that sharp of an angle i think would be a nono. but if i gotta sweat it, so be it. still cheaper than paying for elec. i will need to pay a bit more because i want the copper as large a diameter as i can get to hold more water. i'm also thinking i will need a plumbing permit b4 hooking it up, yes? i do all work by the book, don't need hassles there!

DM
 
#19 ·
Keep the copper as small as you can get it. It will heat faster since there is a larger amount of copper versus the amount of water. Run more of it.

Second, why wouldn't you want to heat water in the winter? This is when you need it the most. I use my system more in the winter than at any other time.

To make the system work like you want it to you would have to have a lot of panels. If you have the water on it will go through the system so fast that there will not be any time to heat it up.

Since the system is outside any water in the pipes will get colder than the ground temperature thereby costing you more money to heat it up. If your ground temperature is 55 (very common near the 45 latitude) and the outside temperature is 45 you will lose 10 degrees and your delta T will increase.

The goal of solar heating is to reduce delta T.
 
#20 ·
ideally, i'd like to make it permanent. this will mean running pipes underground as i build that section of the home. i need some way of draining for the winter though, an inline pump of some sort maybe? i also am making an insulated cover for cooler weather and to keep debris, raccoons, etc. off it at night. it's 7 feet long by 12". i am sectioning off three areas to drop in custom cut glass panes. i have tons of old windows, but none 10 1/2" wide by 7 ft.! lol so 3 sections it is. easier to access and/or replace broken pane. the area gets full sun from about 9 A.M. till dusk.

DM
 
#21 ·
thin pipe is a fine idea. i can run 6 or 7 runs up and down the box easy enough. now that i think about it, any cooler water in a 1/2" line will go into the tank pretty fast then change to the hot. winter demands more freezing line consideration and protection than 3 season. although if i can figure it out, i certainly won't mind opening the cover in the A.M. and closing it at night! free is free! (though an automatic open/close lid system would be great!) how about painting the copper black? hi-temp automotive flat black do the trick ya think? =o)

DM
 
#22 ·
Painting it black is good. Also consider using 3/8" or even 1/4" pipe. Much faster heating of the water.

If you don't go with the aluminum panels then put a sheet of reflective ducting material behind the pipe to reflect heat back to the pipe. Or you could put some tiled mirrors in there.

As for your design it is way more work that I would want to do. The standard systems out there are designed to work when you are not there. Mine runs in the background and hardly ever needs fixing or tinkering. I just sit inside knowing that my heat is free.

There is something therapeutic about that.
 
#23 ·
do you have pics of yours? are there any links to these 'standard systems' i can look at? the shape is predetermined by available space, but everything else is wide open still! i'd still love to have it year round too! i already have 1" insulate foam and foil for reflection. can double up the foam too if needed.

DM
 
#27 ·
One inch should be fine. It just helps keep the heat from radiating out the back.

I posted some links to standard systems.

You can make it all if you want to. No need to use commercial products.

A heat exchanger can be an old 275 gallon fuel oil tank. Just shove in 2 separate sections of copper pipe. One to bring in the hot water from the panel and one to take the hot water away to your house. The water bath in the tank will be the heat storage. Insulate the tank real well to keep the heat in.

Cost is about $100, $75 for the pipe and $25 for the tank. I have several that I got for free.

One element of the system is now done.
 
#30 ·
ok, i saw those. i'm still leaning toward the simplicity of the pic in post #8. it gets hot pulled in when in use and keeps elec. as backup if cloudy and solar is not enough. either way, i believe it WILL cut my overall costs, be easy and fun to make and setup. still have the two questions.... permit needed? (most likely) and 180 degree copper fittings? are they out there? kinda like a horseshoe?
and what about burying those lines while it's open and i'm building? i can drop them straight down into the well pit, (won't freeze there either!) then underground into the new crawl space and up. but i need to be able to clean and drain them. hmmmm...

DM
 
#31 ·
Use soft copper and get a bender. No fittings at all except at the end.

If you bury it make sure it is insulated well. Don't want it cooling down and it will cool down fast.

Of course you know that on cold days you will actually increase your energy use, right? I guess I already said that.

I feel like a dog chasing his tail.
 
#38 · (Edited)
gp, dark cloudy days is why i'm leaving it electric too. and freezing is why i still have not decided to leave it hooked up in winter. if i can get help figuring out how to, or simply figure it out myself, i will. i already pay next to nothing to heat, perhaps i can pipe some of that to the box and my well pit? hmmmmm
Marvin, feel free to comment or not, this is a free forum, and thankfully, we live in America.

tnkz to all for input.

DM
 
#39 ·
gp, dark cloudy days is why i'm leaving it electric too.
Yeah, the electric back up will ensure you still get warm water in the house, but the water in the roof tank may get colder, not warmer, which means it will cost you more to bring the temperature back to to ground temperature, and then up to set point, in the main tank.

If you heat the water some before it gets to your main tank, it will cost less to heat it to set point.

If you chill the water some before it gets to your main tank, it will cost you more to heat it to set point.

I'll look for my crayons :whistling2:
 
#40 · (Edited)
what roof??? it's going to be on my well pit cover (post #30) ...... and, "freezing is why i still have not decided to leave it hooked up in winter. if i can get help figuring out how to, or simply figure it out myself, i will. i already pay next to nothing to heat, perhaps i can pipe some of that to the box and my well pit" (post #38) .....
DM
 
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