My experiences with solar hot water radiant heat.

I purchased 9 4'x 8' used hot water panels and a 400 gallon fiberglass storage tank. I'm guessing these were first installed in the 80s. The panels are of quality construction and still look good. I did have one panel that had a leak on one of the brazed joints where the 1/2" tube connected to the 3/4" header. I tried patching it but the only way I got it to seal was to cut out the brazed joint and put in a copper T.
 
My house is situated to take advantage of the view and not really optimal for solar. So I mounted 4 panels vertically on the side of the garage which faces south easterly and the other 5 were set at a 70 degree angle around the corner. The sun hits the 4 panels as soon as it comes up and within a half hour I'm getting hot water until about 2:30 PM. The other 5 panels start producing at about 10:20AM and run until sundown.
 
I've done all of the work myself, well except for placing the panels because they weigh 190#s each. The house is built with Form-Tech ICFs from the footers to the eaves. The basement walls have 8" concrete and the main floor walls are 6" thick.   R50 insulation in the attic.

The basement is a walk out and I put 3/4" PEX tubing on 12" centers in the slab. The slab took 35 yards of concrete and is poured on top of 2 inches of ridgid foam insulation. I had about 10 yards of gypcrete poured on the main floor and used 1/2" PEX tubing on it. The wife wanted wide plank eastern pine on about half the main floor so I put in 2x4 sleepers on 12" centers and ran the PEX between them. The non wood covered floors have just the solid gypcrete with PEX.

I've only had the system running for about 2 months now but I'm thrilled so far with its performance. My goal was to cut my propane usage by at least 200 gallons per year and reduce my electric hot water heating costs.

Last year I used 530 gallons of propane for heating and 2 fireplaces that are mostly for "viewing pleasure".
The Stats:
Square footage: 2400 on each floor (Thats real not the tax mans #, I'm not counting the exterior walls)
Elevation: 7000 ft
Location: Front range of Colorado about middle of state east to west and 17 miles south of the Wyoming border.
Heat exchange fluid: 50/50 propylene glycol/water (It gets cold here)
Solar controllers: TK-SC6 2 of them one for each bank of panels
Pumps: Grundfos on the 5 panel drain back sytem, Taco 006 on the 4 panel pressurized system, and a Taco 006 to circulate thru the floors.
Heat exchanges: 20 plate on the 4 panel, 40 plate on the 5 panel. They both have the option to run through a 3/4" copper coils into the 400 gallon tank.
I run staight water in the floors. I do have radiant in the garage that would need antifreeze but it is not hooked up yet.

I have a flow meter on the 5 panel system and use a ball valve to limit the flow to 2 gallons a minute. That seems to give me hot enough water coming out of the panels to do useful work. The plate heat exhangers are in series and the circulation pump comes on when either set of panels is pumping. I was using the 4 panel unit just for heating the storage tank, but that wasn't getting the full potential out of them. We just couldn't use that much hot water. So I added the second heat exchanger for the radiant heat. I heat the tank to 120 then switch it over to the floors.

On the 5 panel heat exchanger I've gotten up to a 40 degree temperature differential.
(Delta T)x(GPM)x(Lbs/gallon)x(Specific heat 50/50)x(minutes/hour)=BTU/hour
 40x2x8x.85x60=32,640 BTU/hour

That's been about the peak so far during the winter. A gallon of propane contains 91,600 BTU x 90% eff. furnace=82,440 BTU On a sunny day I figure that I'm saving 1.5 to 2 gallons of propane. I have a 1000 gallon tank so I only fill it in the fall and this year it was a $1.49/gallon. That was a pretty good deal compared to a lot of locations. That's why I'm figuring it on gallons of propane rather than $.

In the summer I will probably shutter the 5 panel system because we can't use all the hot water. I did valve it so I can turn off 3 panels and just run with 2. I'm running a high effieciency furnace too because you can't count on the sun every day. I set the thermostat to 65. On a sunny day the house will get to 70 (20-30 outside temp) and the furnace may not run overnight unless the wind is blowing harder than normal. The basement feels warmer in the mornings because of the much bigger thermal mass. Right now I'm running all zones open and adjust the ball valves so that the return temps are about the same. The basement has 4 zones and 2 on the main. The basement is comfortable in stocking feet. I can't really tell on the carpet or wood floor other than with a IR thermometer.
 
I was originally planning on a Munchkin boiler for the radiant but the wife insisted on forced air. I don't think I can justify buying a boiler now. With the forced air I can add some humidity to the dry air for the wood floors sake.

Enough rambling for now.

Very nice!

I built an air heater and have had it running for about 2 or 3 weeks.  26" x 8' gets about a 10 degree temp rise since I have a fairly strong fan on it.  It is making a difference,though it will take thru  next winter to figure how much.

 

I have it sited to reduce visibility,so I probably get 4 hours a day.  But I figure it is better than nothing,and an interesting project.

why are all the panels not just heating the storage tank?

how much was the initial tank/panel setup, roughly? I'm curious about economics of this.

glad to hear you're successfully using some sun!

s. kellly, I had 2 4'x8' hot air panels on the house I had built in 1983. They worked well but they would get the house so hot the wife or kids would open windows to cool off and then wouldn't shut them until it got to cool. I fixed this by adding a duct to blow all the hot air down the basment. I made a sliding switch box and put the pull cords in a closet. That way you could run it up stairs until comfortable then switch it down to the basement. Good luck with yours.

NRT.Rob, I'm not sure I understand your question, I can only get the storage tank so hot. The 4 panel system came on line last fall. I have a clock on it that counts time that the panels are pumping, over 3 months they only clocked about 60 hours total. Once the tank gets over 125 I don't get a lot of heat transfer from the panels. By running it into the floor the panels start pumping at 85 degrees and will run 5 to 6 hours a day. The panels are plumbed so that they can all heat the storage tank and that's what they'll do when I don't need heat in the house. I'm just using the storage tank to preheat water for the electric water heater. The wife likes hot baths and used to complain about running out of hot water, fixed that problem with the solar. This house building has been going on for about 6 years now. I wanted to take showers before we had the propane and furnace in. That's why I have an electric water heater.

I bought the panels and tank for $1000. I've got roughly another $1500 in copper pipe, pumps, controllers, propylene glycol, mounting hardware, and so on. I did the labor myself, if I had to buy new and pay someone to install it the price would be at least 10x. That would be hard to justify.

you can draw heat out of the storage tank with the floor. no need to choose, really, and frankly your floor could probably draw the tank down to room temp by morning, leaving the tank good and thirsty for solar.

you'd have less for DHW, but if you used the BTUs, you used them. colder tank = more solar. cool that tank down!

Rob, Now I understand, you want me to risk running out of hot bath water! There's some things not worth taking a chance on. Currently I have to flip a switch to heat the tank or the floor. Right now the tank gets heated by the 4 panel system one day a week. It's pretty well insulated. I do understand what you're saying but if we had a couple cloudy days the tank would be cold. I think my flat plate heat exchangers are more efficeint than the copper coils I have in the tank too.

Thx, MT6

well, maybe I'm missing something. when you flip over to the floor, your circulation is floor to panel through a heat exchanger? does this ever STOP, or are you gobbling all the solar BTUs you get at that point, from both arrays? If so, then I'm full of it and you should ignore me.

but if you're not heating with both arrays, or the solar sometimes has to stop transfer because your mass is charged, then you're definitely missing out on some benefit you could reclaim with a tank based design.

Rob, When I'm heating the 400 gallon tank the return water to the collector is a few degrees above the tank temp so I am loosing some heat there, but if I don't return hot water to the collectors it doesn't come back hot enough to heat the tank. I got a deal on 24 volt valves from a guy who took out a floor board system so he could put in AC. The switch selects which valve opens when the pump starts, either the tank or the heat exchanger. The switch also selects which RTD to use, the one in the tank or the one for the flloor.

I'm in the investigation stage now for computerizing this. It would be nice to know how much heat I'm getting and the most efficeint way to extract as much as possible. Also in the spring and fall I wont be able to use all the heat so I could dump it to the garage floor. The garage is also ICFs and the floor is 600 sq ft. There is no insulation under the slab tho. Should make a good thermal dump.