Solar radiant heat project begins

[Raspy]

great to know! You said to maintain 62 in home you have 130 degrees set at the valve. Is that maxed out? What temp does the basement stay at?

I don't think that's exactly what he meant, but he can correct me if I'm wrong. The thermostat controls it such that it only runs for an hour and stays off for six hours. This is very typical and makes sense. Sounds like a good system. And it doesn't mean the floor is 130 degrees in order to maintain 62. There's a big difference between delivery temp, floor temp and air temp. Don't take all these numbers too literally. Time, tube spacing and actual delivery temp vs max delivery temp all factor in. There are exceptions, but usually the average floor temp is not above 80 or 85 and often only about 70-75. Early in the heating cycle, there might be a 90 directly over the tube and 65 between the tubes. If the floor is driven up too fast, there will be an overshoot because the thermostat reading lags and by the time it shuts off the floor is hot enough to bring the temp on up an extra ten degrees. This is where high limits and programming become important.

Rick, Thanks for the numbers

 

[Raspy]

Well, if you are correct and rooms need "zones" and there "own loops" it was all for nothing because I didn't do that.
I heated the entire basement and was hoping that the basement transfers the warmth to the entire home.
The basement has separate zones but those separate zones on the floor below won't transmit to "zones" on the main floor. I can always add tubing under the main floor in the floor joists but I'm gonna give it a year with just a hot basement first. I sure hope this was not all for nothing.

Keep in mind also that my outdoor wood boiler is 500,000 btu's designed to heat 10,000 sq ft. The indoor backup boiler is 300,000 BTU's.

Hope it works this way!

Your basement looks very well designed and installed. Should do just what you want it too. And by the way, that is one beautiful home!

 

[IXLR8]

John, Thank you for your detailed response... gives me a bunch more to think about.

 

[jim_wilson]

I should explain, the mixing valve comes preset to 130 (changeable if required). The boiler output is 170 degrees which is too hot for the floor. The pump is controlled by a thermostat on the wall, set to 70F/20C. When the air temp drops below 20C, the pump starts pushing 130 degree water through the floor until the air temp increases, causing the thermostat to shut off the pump. Remember, 130 is just a little hotter than your body temp (98.6) so it feels warm but not hot. Seems to run about an hour then shut down for about 6 hours. Hope that helps.

Sorry John, didnt mean to hijack your thread.

Is a regular wall-mount thermostat sufficient to control a radiant slab floor? I'm wondering because I've seen installs where there's a temperature probe buried in the concrete. That's one thing I didn't do before I had them do the concrete pour for my floor.

 

[rmorey]

Is a regular wall-mount thermostat sufficient to control a radiant slab floor? I'm wondering because I've seen installs where there's a temperature probe buried in the concrete. That's one thing I didn't do before I had them do the concrete pour for my floor.

I bought a fan control from taco (basically a relay controlled by a 24v thermostat) and a basic thermostat from Uponor. Got it all from PexSupply.com. When the thermostat calls for heat, the relay closes and sends 120vac to the circ pump. If you want to pm me, I can send you more detailed info of my install. pics etc.

 

[Raspy]

Is a regular wall-mount thermostat sufficient to control a radiant slab floor? I'm wondering because I've seen installs where there's a temperature probe buried in the concrete. That's one thing I didn't do before I had them do the concrete pour for my floor.

Jim,

A standard 24v or 120v programmable wall thermostat is the best way to control a radiant system. Remember, we use the thermostat not only as a temperature control, but as a timer. This way we can send a blast of heat at appropriate times regardless of the room temp. This allows us to "trick" the house into staying at a steady temp, reduce energy costs and maximize comfort. At first glance it seems counter-intuitive to program different temps and times into a radiant system, but actually, that is how we make it efficient and steady. This programming becomes even more important when we have solar involved, because as I mentioned, no solar system can keep up in the worst winter weather, so we have to maximize that energy source. This is done by making a few decisions about comfort that are slightly unconventional, but make sense with radiant.

A temp probe is used for a radiant zone that is inside a forced air zone. An example is a bathroom floor radiant in a forced air home. If you tried to use a wall thermostat in the bath, it would shut off when the forced air came on. In baths, with a floor sensor system, we can decide to hold the floor temp at 80 and just leave it there regardless of the rest of the house. The best way to install a floor sensor is to put a short piece of PEX in before the pour with the buried end taped closed. This is set between the radiant PEX and exits where you can get at it. The sensor is slid down into this tube with the wires extending out. The sensor just sits in there and can be pulled out anytime. The wires are extended to the controller. This is typically a thermostat with remove sensing capability that reads the temp and works like a conventional thermostat. There is also a much simpler way to do it with a small water heater.

You guys are probably seeing now where I'm at with all this. Radiant and solar are two very interesting heat transfer problems. Thinking outside the box and looking at heat transfer theory with conduction, radiation and convection, as well as how air and water interface in various situations, and what is really required to be comfortable, all factor in. Temperature numbers don't mean much more than an indication of trends or efficiency. For instance, 130 degrees feed temp does not mean 130 degrees floor temp. A constant thermostat setting means wild swings in room temp, but programming wild swings in set temps means a steady room temp. The supply and return temps to the slab should be close in temp, with a minimum differential, for maximum BTU delivery. Designing solar flow schemes to cool the collectors instead of heating the water leads to greater efficiency. Designing the freeze protection first, is the best approach with solar, even though that aspect produces no heat. Stuff like that is what makes it fun. It helps you come up with very good systems. Don't be afraid to be creative! Design in simplicity without giving up any function. Too often, system are far more complicated than they should be.

 

[Raspy]

I bought a fan control from taco (basically a relay controlled by a 24v thermostat) and a basic thermostat from Uponor. Got it all from PexSupply.com. When the thermostat calls for heat, the relay closes and sends 120vac to the circ pump. If you want to pm me, I can send you more detailed info of my install. pics etc.

I did the same thing in my little guest house kitchen radiant system, except I used a 120v programmable stat and ran the pump and water heater power directly from it. No relay needed. I boiled that system down to the absolute fewest parts needed and it has run well for about seven years now.

 

[fordmantpw]

When we built our house in 09', we compared a high eff boiler vs GSHP. As it turned out, the Geo was only slightly over 30% more than the boiler and w/ the 30% rebate it was an easy decision.

That's what I'm seeing as well.

Did you consider using Solar PV panels and heating the water with an electric heater in the winter, then selling the excess electricity back to the grid in the summer? This is the direction solar companies here are starting to go with the price reduction of the panels and the converters.

I discussed this with a solar representative, and since we are going geothermal, he recommended using the de-superheater in the GSHP as the heat source instead of solar hot water. Not PV, but solar hot water. I would like to include solar in our house design, and the solar would run the geothermal.

 

[IXLR8]

Designing solar flow schemes to cool the collectors instead of heating the water leads to greater efficiency. Designing the freeze protection first, is the best approach with solar, even though that aspect produces no heat. Stuff like that is what makes it fun. It helps you come up with very good systems. Don't be afraid to be creative! Design in simplicity without giving up any function. Too often, system are far more complicated than they should be.

John,
I appreciate your going all out to go with the KISS principle of design and implementation of your system. This is causing me to rethink a lot of what I was planning... thank you. Keep the details coming.

 

[IXLR8]

...... It seems now since so many solar farms popped up, the TVA, Our main source of electricity, has now stopped the rebate/credits and put in place a lot of restrictions to the type of system you can install, as well as to how much electricity you are allowed to produce. Of course, I can see the need to make sure your personal install meets the required safety concerns as well as capablity of matching the power they produce. I can not see how or why they think it necessary to limit the amount of power you can produce. Now it seems, if your intentions are to produce your own power, whether solar, hydro, wind or other means, and connect to the grid, then TVA has to be involved in the design of your home as well as the design of your power system. .......

Hmmm, maybe I will rethink moving to NC. Here in Maine I was thinking of installing grid tied PV panels. I called the local power company and they said, "give us a call when you have the system up and running and we will come install the proper meter". No permits, no approvals, no design reviews, just call us when it is running.