Solar radiant heat project begins

[jim_wilson]

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.

Thanks - I'd be interested in seeing anything you have on how you put your system together. For the moment I'm still trying to get straight in my head how to get the radiant piece working (properly) by using just the boiler. Although I would like to make sure I don't design myself into a corner in case I want to add solar later.

PM Sent.

 

[Kyle241]

Coming in late on this but I like your setup John. Nice house too!

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.

We're looking at installing grid tied PV panels in our house in Maine that will run two new mini-splits for heat and cooling. The numbers work out fairly well considering we can finance the loan for both with the offset of propane we will not use to heat with. Today the engineer comes out to work our the final specs but I am very inclined to go this route as the boiler/baseboard heat setup in the house isn't my favourite. I bought a Hearthstone woodstove last October to heat the primary section of the house but it's the wing that includes the master bedroom ensuite that isn't getting the heat and there really is no way to move it that far. So a mini-split seems like the best solution for us and A/C on the hot humid days in the summer would be nice as well as reduce the humidity we get along the coast.

Next house we build will have radiant heat, no question about it.

 

[dave1949]

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.

I'm on Central Maine Power here. There was some minimal paperwork for our grid-tied solar system. IIRC the most important issue to the utility is if the inverter being used is on their list of approved units. For lineman safety reasons, they want to know that the inverter model has passed the tests regarding shut down when no utility power is present.

The system installer provided the paperwork for us to send in so there was nothing burdensome about it, and the IN and OUT meters were promptly installed by CMP. Supposedly, the new smart meters can do the in-out with one meter but the programming is non-standard.

 

[jim_wilson]

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.

Excellent.

That makes at least one part of my system design a little bit easier. I never put probes in the floor when I had it poured. I figured if they were necessary - I could always drill. I know where the tubes are because I took pics. But I would prefer not to do that. My plan is to have two radiant heating "zones" in the barn - with two loops in each. I figure one zone will likely be kept around 40 (parking bays) - and the other zone will be kept at maybe 50 (workshop area). Because the radiant takes so long to come up to temp - I'm thinking I will add radiant panels in each of these areas as supplemental heat so I can bring them up to temp faster. Typically my usage will be something like : I will want to go out and work a few hours in the shop after work. 50 degrees isn't a bad temp to have to work in - but if I have a half hour or so the supplemental radiant panels should be able to bring the shop area up to say 60 or 65 in pretty short order.

I'd just control the supplemental radiant panels with their own thermostats.

I bought a book about radiant heating and just received it the other day: Radiant Floor Heating, Second Edition: R. Woodson: 9780071599351: Amazon.com: Books

I've only had a little bit of time to thumb thru it - but it seems pretty good so far.

One of the questions in my though is: How do you determine if it's appropriate to use a heat exhanger in a system?

From looking at your initial install - and reading about how you setup your solar panels , I understand why you have the heat exchanger installed. It isolates your solar loop from the rest of the heating system (am I correct?).

My system will be getting fed from a boiler - at least initially. I would like leave open the possibility of adding either solar or a wood boiler as an additional heat source later - but I'm not sure if I should , or where I should - add heat exchangers into this system.

Any tips?

 

[cartod]

Excellent.

That makes at least one part of my system design a little bit easier. I never put probes in the floor when I had it poured. I figured if they were necessary - I could always drill. I know where the tubes are because I took pics. But I would prefer not to do that. My plan is to have two radiant heating "zones" in the barn - with two loops in each. I figure one zone will likely be kept around 40 (parking bays) - and the other zone will be kept at maybe 50 (workshop area). Because the radiant takes so long to come up to temp - I'm thinking I will add radiant panels in each of these areas as supplemental heat so I can bring them up to temp faster. Typically my usage will be something like : I will want to go out and work a few hours in the shop after work. 50 degrees isn't a bad temp to have to work in - but if I have a half hour or so the supplemental radiant panels should be able to bring the shop area up to say 60 or 65 in pretty short order.

I'd just control the supplemental radiant panels with their own thermostats.

I bought a book about radiant heating and just received it the other day: Radiant Floor Heating, Second Edition: R. Woodson: 9780071599351: Amazon.com: Books

I've only had a little bit of time to thumb thru it - but it seems pretty good so far.

One of the questions in my though is: How do you determine if it's appropriate to use a heat exhanger in a system?

From looking at your initial install - and reading about how you setup your solar panels , I understand why you have the heat exchanger installed. It isolates your solar loop from the rest of the heating system (am I correct?).

My system will be getting fed from a boiler - at least initially. I would like leave open the possibility of adding either solar or a wood boiler as an additional heat source later - but I'm not sure if I should , or where I should - add heat exchangers into this system.

Any tips?

Thanks, just went over to amazon and bought that book. I cant wait for the movie. :laughing:

 

[jim_wilson]

Thanks, just went over to amazon and bought that book. I cant wait for the movie. :laughing:

Radiant Heating - The Movie! A tale of warmth and romance - it's a real boiler!

 

[Raspy]

Jim,

I'm really glad you are so involved in your design! Curiosity is a fine thing, but gets me in a lot of trouble too!!!

My house has settled in at about 54 degrees or so, floor temp, with only the solar running. It feels a bit chilly when I come in, but I can work in there with a tee shirt on and be very comfortable. If I was working on my book, for instance, I think I would be cold. Sheesh, Even the word "work" has to be defined!

You are right, the HX isolates the floor closed loop from the solar loop. This is needed because the solar drains down, or displaces air back up to the collectors, as I've described, while the radiant must have no air in it. They must also circulate at different times.

If you have a boiler as your only heat source for the radiant, it does not need to be isolated with a HX (heat exchanger). Circulation will go through the boiler and through the floor. A simple closed loop radiant floor system with a boiler and a pump is preferred.

Now look at a different setup: A closed loop radiant system with a boiler, as just described. But in this example we want to introduce energy from a storage tank that was heated by a solar system earlier in the day. The storage tank might be a large domestic water tank running at domestic pressure of 60 PSI and full of drinking water. The radiant is a closed loop running at 12 PSI. A heat exchanger installed in the loop can add the energy just as the boiler does. Here's the routine: The circulation starts with a call from the thermostat, the boiler fires up and heats the water a little bit on each pass until the house is warm. Or, the call from the stat starts the floor circulation and also a pump from the domestic storage tank that feeds water to the HX. The house heats the same as it would with the boiler running. Now install an aquastat on the domestic tank that monitors its temp. As the heating cycle continues the tank gets cooler until the aquastat switches (at a pre-determined lower limit temp). This "switch" shuts off the domestic pump (because the stored water is now cool), and starts the boiler burner instead. Now we have solar priority with gas backup all automatically controlled, and very simple. Aquastats can have double throw switches and the pump and boiler power can simply be fed through them. The switch flips between two positions according to temp. It is either closed on the burner circuit and open on the DHW circuit, or open on the burner and closed on the DHW circuit. All with a three terminal micro switch, controlled by temperature, and fully adjustable over your working temp range. The probe measures the storage output temp to make the decision. This function can also be accomplished with an electronic set point controller or even a solar controller that looks at the storage temp as it's "collector" input and the floor water return temp as it's "storage" temp. Then the system can be slightly more efficient than with an aquastat, but might be less responsive to heating needs. This is where it starts getting fun again as you fine tune. Then you can take the thermister sensor off the "collector" terminals and install a variable resister instead, or program the control strategy to a higher differential setting and increase the floor response time at the expense of absolute efficiency.

So, we need a HX if we have different waters that don't mix because of pressure, or toxicity or functional necessity. The heat exchanger in my example does the same thing as a boiler, it adds heat to a loop from a remote energy source. And remember, a boiler IS a heat exchanger. It's a water to air heat exchanger instead of a water to water heat exchanger. If you just put two heat sources into your loop, you can create a priority system and use your fuels in a more creative way. You might even want a third HX, or boiler, for wood or a ground source heat pump.


Once again, it's all about temperature vs efficiency with solar and temperature vs time with heating. Higher solar temp is less efficient. Lower delivery temp takes more time. You find the balance, and you favor the ideal, that fits your use. The aquastat knob, the thermostat settings and timing are your interface tools. Flow rates, storage and collector sizing are your design decisions. Heat preservation and specific delivery locations focus your available energy for the most efficient use. Always, we want maximum comfort. With solar we are trying to do it with minimal cost, as late in the year as possible, and have fun doing it. To me, it's an absolute marvel to see a good system working as temps rise. An abundance of hot water collected with a few watts driving a little circulator. Available then for domestic use or to heat a floor in the middle of the night.

My efficiency quest applies mainly to heating the house. As far as domestic hot water is concerned, the more the better. Large storage affords a lot of hot water usage, and during the warmer months there can be too much solar for the house radiant. Then, there is no need to worry about how much hot water we use. Using more is actually better because the collectors spend less time at stagnation temperatures.

 

[BitChin1]

Radiant in the home was about 4k. Geothermal was about 17k. The rebates were not enough to make a difference. Look closely at geothermal before you shell out the cash.

Can you clarify what was covered by the 4k? I used a geo system in my house at ~ 15k (cost of wells not included as they were already here for irrigation and household use) for this I get heating and cooling. I assume the 4k only covers heating cost - but does it also include the heat source or is it the cost of distribution? We contemplated adding a radiant distribution to our house but time was short and at $2800 extra we decided not to

 

[cartod]

Can you clarify what was covered by the 4k? I used a geo system in my house at ~ 15k (cost of wells not included as they were already here for irrigation and household use) for this I get heating and cooling. I assume the 4k only covers heating cost - but does it also include the heat source or is it the cost of distribution? We contemplated adding a radiant distribution to our house but time was short and at $2800 extra we decided not to

That was just the cost of the tubing.

 

[cycle_gator]

I am still very, very early in design, I have two really basic questions:

1. Why the drain back system in the collectors instead of antifreeze and just stopping circulation based on temp differential?
2. What do you do with the waste heat in the summer? I would think you could not use enough hot water to keep the collectors cool.