Low Temperature (Solar) Hot Water Heat

Have you looked into radiant floor heating?

Tubes ran through cement or epoxy in the floor or even attatched to the under side of subfloor flow heated water to increase room temperature. This may work better than a radiator/forced air system

http://www.radiantcompany.com/

these guys may give you the idea better than I can

This site gives some good info, as well as some different alternatives.http://mb-soft.com/solar/intake.html

farmatt

I think you missed the point of the question

Although the UK is probably warmer on average than Minnesota, that is because of the gulf stream: the insolation here is probably quite a lot less:-

(as your over towards the east of the continent I guess your cloud cover is probably lower than the UK.)

However solar panels here produce reasonable quantities of very hot water. I'm certainly not aware of anyone having to increase the size of their radiators to compensate for temperature deficiencies.

See Del the Cat's solar panel project http://cr4.globalspec.com/blogentry/4969/DIY-Solar-Hot-Water-Panels

I'm in Michigan and we probably get less insolation than Minnesota. You may want to investigate evacuated tube collectors. They're more efficient in the colder climes than other types of collectors. That said, I too, am looking for solid information on how many BTU's can be extracted. My workshop 20x32 workshop has R30 in the ceilings, R19 wall and R10 under the slab. Anyone have real world data, not just theoretical?

I have been working on a hot water heating system for some time now and have come to the following conclusions regarding areas where conditions are as you report. The problem of heating is a 24/7 issue and can only be addressed by figuring out just how to save the suns energy for use when it is not shining( ie at night and during those long dog days of winter when you never see the sun). For me the answer is to store the heat in a buried tank with glauber's salt as the storage medium.

Glauber's salt ( a phase change material)can store 80 calories per gram as compared to water at 1 calorie per gram. That means you can store great quantities of energy for later use. The phase change is at 90 degrees f, something you can easily get with a solar collector of most any type. In my fastest calculation possible I have estimated you can store 12000 btu's in 800 gallons of glaubers salt. That is enough to last quite a while. Your power bill will tell you the btu's you burn daily and with that you can determine just how long your ground storage would last before using the grid again.

90 degree water is not hot by any standard but it is sufficient to heat floors via radiant heat. You might also consider using a parabolic collector to generate hotter water when the sun does shine.

Friend,

Glauber's salt has been a viable phase-change storage medium for many years. You do have to watch out for its changing hydrate status. There are some additives that were promoted back in the earlier solar heyday of the 1970's, to avoid this problem. I don't have details now, but just a caution for you.

--John M.

I am aware of the additives. I read an article about them. On is Borax and the other I don't recall, so I will have to re read the article. The only issue I have with Glauber's salt is that I can only get 90 degree water back, but lots of it. At least that is what I gathered from the article. I would rather have another PCM to use that will give me a higher temperature for my hot water. The base board heat is fine with 90 degrees except it will take longer to heat the area.

It has been (as usual) a great discussion and I appreciate all the comments that were submitted.

I had heard of Glauber's salt and would appreciate anything beyond Google news about it.

A few people missed the concept that lower temperature radiators can be compensated by having larger radiators. It is part of the Q=CA(t2-t1) thing, the A for area being the big deal.

You are welcome, as usual I learned from the people who posted answers.

Let us know what your final results are, I know I am always curious what the final outcomes end up being.

Yes Dear,

I have been working on solar thermal storage systems for quite some time.

The suggestions given at#6 are quite workable. How ever I would like to add that - which ever type of solar collector you decide to deploy is OK, but the point to consider is to see that there should atleast two glass covers on the collectors. As the working temperature goes up, the losses from the collector top become quite high and hence net heat collection goes down. To collect heat at 90 degrees it is must to have atleast two glass covers to reduce top heat losses in case you are not using concentrating collectors.

-Dr N P Singh

What is the incoming temperature of your source water, GPM flow rate and desired temperature rise?

http://www.completeheating.ca

Any possibility of installing massive quantities of glass in the south wall of the building? (Called Passive Solar Heating) That would allow the sun to heat the building during the day. Perhaps it would get too hot, to say 90 degrees. So what, wear less clothing. At night, place insulated covers over the windows (I'm thinking on the inside of the house, but if they could be made water proof, they would work on the outside also. Watch for condensation if using them on the inside.) The temp in the house will drop over the night, but if the walls, roof, floor are well insulated, it should not be excessive. When the sun comes up, remove the window covers and start soaking up the sun. The more insulation in the walls, roof, floor, windows, etc the better this will work. No moving parts (except movable insulation).

I'm sure there are MANY solar companies that can help you with numbers. How about this: Forget storage it's a pain in the butt. Pump the water from the solar collector into the house and through a finned coil with air blown over it. Do that as long as the water is warmer than the air temperature of the room where the fan-coil is located. As soon as the panel isn't heating the water, the pump should shut off. Apply insulation to the windows as described above at that point. Use FDA approved propylene glycol antifreeze so if there is a spill it will not be toxic to pets that like to drink it. That way no need to drain it down at night to prevent freezing. Would that work? Just a thought. Need calcs. What would I use for a fan-coil? Anything cheap with a low power fan. A modine unit heater perhaps, or a car heater coil and fan powered by a 12V photovoltaic panel maybe.

Guest,

Your questions show a lot of interest--have you considered registering and becoming a member of the site? The massive quantities of glass in the south wall was first done in modern architecture, if I remember correctly, in a building in the upper midwest of the USA in the 1940's. (Note how nebulous I am about this.) Workers found while finishing it that it was too hot even on winter days, and too cold then on nights. This shows a need for balancing the solar gain with thermal mass to avoid excessive swings in temperature. A Trombe wall (French design) puts dark colored thermal mass on the inside of the glazing (examples are solid concrete blocks or tubes of water, etc.). This will soak up the heat and then liberate it by radiation and convection later. A simple rule of thumb for this is 1" or 2.5cm thickness for each hour of delay from when the sunlight starts to heat the outside until the heat reaches the inside.

Look up "passive" versus "active" solar systems. Passive generally means the thermal energy is collected, stored, and used in the same location; while active means that these three functions are in different locations with a separate source of energy being used to move the thermal energy around. Obviously, the passive is simpler and potentially more efficient. However, active systems can work in many applications where passive is not possible. Your 12v car heater fan/coil thought is good.

Solar has had a number of incarnations in the USA--southwest pueblo construction centuries ago, hot water in Florida in the early 1900's, the 1970's, etc. It is very significant and helpful in many other countries also.

--John M.