Solar Radiant Floor Heat.

flashheatingand

How practical is a Radiant floor system that were to use solar heating as primary source and boiler as a secondary source? I know it isn't kids play, but as a concept, is it feasable?

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TimNJ

You're going to have to collect and store the hot water for the radiant during the day when the sun is out and most likely use it at night when you will have a higher demand for heat. Doesn't seem too practical.
I have radiant and it works fine hooked up to a wood fired boiler and zoned with a Boilermate. The Biolermate lets me zero in the water temp. going out to slab to compensate for warmer weather in spring vs coldest part of winter.

DavidC

I think it's a good match, but you probably should have a back up for extended cold spells or cloudy days. Try searching on www.builditsolar.com, one I remember has built a complete solar setup and claims it heats his home 100%, including temps that dip to-30f. I'll be trying something similar to his but will include wood backup. I want to believe but need to see it.

Tim, I'm curious if your system is open or closed? I currently use a wood boiler that is open.

Good Luck
Dave

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TimNJ

It's half and half. The closed zone for my kitchen area is operating off the Boilermate. It consists of 4 loops and is approx. 450 sq. ft. The second zone is running directly from the boiler with a mixing valve to temper the water down. This zone is approx. 1,000 sq. ft. and consists of 5 loops. I have thermometers on the each zone's in/out manifolds so I can monitor the water temps going in and coming out of the slab. I also have a ball valve on each individual loop to regulate the flow in different areas of the rooms if need be.
I would like to take the second zone off the boiler and put it on another Boilermate but I'm not really motivated to do it right now.

thom

I did this on my own home when I built it in 1984. It works just fine. This winter will be the 24th year I've heated my house with it. I have 576 square feet of collectors heating my home. The house is 3000 square feet, 1700 square feet on the first floor, 1300 square feet on the second floor.

The storage is the slab. I poured a 6" slab over 2" styrene. The slab is isolated from the foundations (footings and stemwalls) with 1" styrene. Even the interior bearing walls have footings and stems so they could be properly isolated from the slab to inhibit heat loss into the earth.

The system is entirely automated. When rooftop collector temperatures reach 110F the pump turns on pumping water through the collectors then through the slab. When the collector temperature drops to 95F the pump shuts off, the system drains down into a plastic 55 gallon drum. The liquid is tap water. I replace the water annually but it always comes out perfectly clean.

The back up boiler heats the same in-slab piping but works through zone valves. Each room is a separate zone. I installed a 100,000 btuh heater but turned it down to 1/3 capacity because it tended to overheat, boil the water, and whine. The back up boiler is an off-the-shelf tankless water heater.

The upstairs gets its primary heat from rising heat from the first floor. Each upstairs room has hot-water baseboards for auxiliary heat. These rooms are also individually zoned and work off the same boiler.

Most of the time there is no need for auxiliary heat. Our Albuquerque climate is fairly moderate with lots of sun. When heated up, the system will make it through the night, the following cloudy day, and that following night. If the second day is cloudy it will probably make it through that second cloudy day but not the subsequent night.

Getting the system to work well was a struggle. There were (are?) no technical specifications for doing this. The tankless water heaters are designed to work on a pressurized system but the drain-down system I built cannot work if pressurized.

nhmaster3015

If you're just looking for someplace to throw money away, I can give you my address.

DavidC

I asked about open or closed system because my current system is an outdoor wood boiler that is open. The boiler itself is rusting out, I'm noticing corrosion on the copper pipes and have had to replace a couple of iron heaters due to leaks. My most recent understanding of the problem is that being an open system allows a continuous supply of oxygen into the system, thus feeding the rust.

The collectors I have in mind sound the same as what Thom described in his system, definately open. I'm thinking all plastic lines (for the transfer from the collector to the storage tank) and isolating the collectors from the rest of the system with a heat exchanger in the storage tank. Then the rest could be pressurized with an expansion tank and remain closed.

Any thoughts from the resident experts?

Good Luck
Dave

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nhmaster3015

www.caleffi.com download idronics 3 read thouroughly.

DavidC

Thanks for that link. I've only scanned breifly through so far and haven't spotted the system I'll be building. I will be going back to the PDF for a closer read later.

Good Luck
Dave

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TimNJ

That is an interesting set up. I have my slab set up basically the same. I have 2 zones of HWBB on the second floor. My house is oriented to capture maximum passive solar benefits and for the most part the heating sysytem doesn't operate during the day. That was why I put in my initial reply about the storage problem. In my case I would be overheating the house with the combination of solar gain and the slab being heated at the same time.

thom

Which is the reason for the 6" slab. It stores more heat. Yes, we do tend to solar overheat. We walk around in shorts and bare feet in the winter, oftentimes leaving the doors open. It does not overheat to the extent that the floors get uncomfortably hot. There are times, especially in the early and late winter when I will turn the system off for a day or two.

TimNJ

Here in NJ, I usually don't need to use heat until mid to late Nov. and that is because Nov & Dec tend to be cloudy. By Jan, Feb. we get more sunny days and we too will open up some windows to release some of the excess solar heat.
With all the south facing window area the wife gets to lay out in her bikini in the living room and tan in Jan.

flashheatingand

Thanks for the info. There seems to be quite a bit of work/knowlege that one should have, but, imagine the benefits if you could actually heat the house with the sun (at least x percent of the winter).

Again, thanks for the link.

flashheatingand

So, about how much do you spend to heat your homes?

TimNJ

It's hard to tell now. I use propane, wood, and passive solar. The propane price has fluctuated wildly for the past couple years so it's hard to figure.
I use about 500 gallons propane a year which is 2nd fl HWBB and also DHW. 3000 sq ft. 1500 in HWBB and the other 1500 in radiant.

thom

On mine I'm not sure. I heat 3000 square feet and my gas bill increases by about $75 for the coldest month, $50 for the other few cold months, BUT I use gas to heat the spa also.

In addition to gas for back-up, there's the cost of the pump to run the solar.

orson

I read an article a while ago about building solar radiant floor heating system.

The storage method was to build a shed to house an insulated storage tank and make the south facing wall of the shed the collector.

The author trenched and ran water lines below the frost line and insualted them from the shed to the house.

He had some type of dual thermostat system set up.

He claimed the water in the tank would register at over 130deg F on a
-20deg F sunny day.

I'll see if I can dig up the article.

Edit: found the link quicker than I thought: http://www.builditsolar.com/Projects.../solarshed.htm

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DavidC

Good find. That's the model I intend to use for my setup. I have it bookmarked on the home 'putor.

Good Luck
Dave

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sawyerEd

Why did you have your collectors set to drain down at 95 F? Modern radiant systems are set to operate at about that temperature, wouldn't 75F be better. Why did you isolate your slab from the soil beneath the structure? You're problems stem from not having enough trombe mass to store the excess heat or your collector area was too large. You may have been exceeding the ability of the materials to transfer the heat properly, specific heat. Circulation problems caused by too rapid flow or undersized piping? What kind of circ pump did you use?

joasis

What do you guess for actual slab temperature average? Did you run the loop directly on the EPS or up in the slab?

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