Solar Assist for Radiant Floor Heating System?

Tom Hughes

An Architect wants me to design a radiant floor heating system that uses a solar collector to supplement both domestic HW and the radiant system. I'm planning to use a Munchkin boiler with an indirect WH for domestic. Problem -aren't the temperatures used in a closed loop hydronic heating too high to benefit from the solar? Has anyone ever piped up something like this?

Alan(CaliforniaRadiant)Forbes

Solar

temperatures can sometimes be too high for radiant and you have to temper the water before it goes to the floor.

I don't like using solar for radiant floors for two reasons:

1) It's too difficult to control, and

2) Most of the time (at least around here), calls for heating usually come when solar gain is at a minimum (overcast, raining, etc.).

I like solar for making domestic hot water and then if you have a big enough storage tank, you could install a heat exchanger to supply your radiant floors. Now that I like. But you'll still have to have gas fired back-up for those inclement days.

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Mike T., Swampeast MO

Is the design

passively solar? i.e. South-facing glass with carefully calculated eave, MASSIVE floor? If so, lots of ideas/strategies in the "Ways to Deal with Solar Gain" for $5 at Books & More at this site. (One of the "Give & Get topics.)

Otherwise it's probably really complicated. If there is such a beast as a dual heat exchanger tank, you could use one of the HXs for the solar and the other connected to system. When temp in tank goes above supply? return? temp, draw into system. When temp in tank drops below some point but sun is shining, use the other HX to heat the water in the tank from the boiler above some point then draw off heat. Kinda' far-fetched but possibly do-able. Am certain there are a multitude of other ways as well.

Tom Hughes

Yes, I was thinking of using a Progressive Tube passive system for the domestic HW. But I'm not convinced the numbers work for space heating. I need 250 MBH of heating capacity to heat this building. That's gonna mean LOTS of storage. In any event, your dual heat exchanger concept is exactly what I was thinking I would do, except I was just going to use 2 heat exchangers. Controlling this thing will be the challenge. I might chicken out entirely.

hr

You are right, Tom

it takes lots os storage and lots of piping and controls to do it right and get much bang for you bucks. A simple DHW system with one panel and a 65 or 75 gallon tank will be money better spent. Remember DHW loads are a year 'round load. A good place to get some useable solar, in my opinion, for not much bucks.

If you go full blown solar contact Mike at Aspen Solar or others here that do it full time for the latest in what's hot and what's not. It would be worth paying them for a workable design if you go the heat/ dhw route.

I'd probably spend money on some pv before I plunged into solar radiant. Lots of new tech in that arena, fun to watch your meter spin backwards on high gain days, almost worth the price of admission just to see that happen! Maybe just enough pv to power your computer or office set up.

Either way, a thumbs up to ya for you for considering solar

hot rod

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Tom Hughes

PV is a good idea. I might sell him on Solar for DHW and some PV. I could use a dual or second heat exchanger to assist with the heating loads, but I have a hard time imagining it will provide much help during peak heating demands. It could even LOWER the return water temperature if I'm not careful with the controls.

Thanks so much to all. You've been a huge help!

Bob Gagnon plumbing and heating

must have solar info

what is pv? i was thinking of installing a secondary solar powered radiant heating system in my walls or floors that i haven't installed radiant heat in yet, no problems with controls or comfort. i have a 1500 gal. storage tank. i was wondering if anyone knows if 90 or 100 degree water will give me much heat. my box collector seems to make a lot more hot water in that temp range. can anyone tell me if the thermo- bulb collectors produce a lot more than a box collector? thanks in advance for all your help bob

Bigheadtodd

We have used

Dale Picard, Radiant engineering for design help on several projects. This guy knows solar. 406-587-6036

Viessmann, Crown, Stiebel Eltron all make double coil storage tanks.

hr

The formula would be

assuming you are using water at 8.34 lbs/ gallon. If you system could use water temperatures between 80-100 degrees you have a 20 degree delta T to work with.

1500 gallons X 8.34 X 20 = 250,200 BTUs stored in the tank to be used.

Keep in mind loss from the insulated tank and piping.

hot rod

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