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Thread: Hydronic radiant heat stat

  1. #16
    DIY scratch-pad engineer leejosepho's Avatar
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    Quote Originally Posted by crater View Post
    So I'll want to get a Stat that has an internal high-limit circuit that reads the sensor in the floor? Can I ask my plumbing supply place for just that and they'll know what I'm talking about?
    I do not know anything about your plumbing supply place, but I am using one of these:

    http://www.aubetech.com/products/pro...133&noLangue=2

    Click on "hydronic" on the left, and look for an "AF" stat, meaning it reads both "air" and "floor" temperature.

    Quote Originally Posted by crater View Post
    Also with 3 zones I would assume that I would need 3 Stats and 3 floor sensors? 1 for each zone
    Yes, as far as I know.

    Quote Originally Posted by crater View Post
    And is the floor sensor supplied with the stat or is it like a Johnson Control that sends a low voltage signal to the stat?
    My only experience is with the Aube stats, and the sensors come with them.

    Quote Originally Posted by crater View Post
    ... last year it cost me $700.00 for 1 months electric bill trying to get it up and running and never really did work. Now this fall after some re-plumbing and starting it before it was -30d it seems to work but just needs some tweeking.
    If I were you, I would just turn the system on with a low boiler (water temp) setting (such as possibly 100*) and let it run for a couple of days in one or more zones so the floor temp can spread and stabilize ... then watch to see how much or how often the boiler runs to maintain whatever temperature has been achieved ... and you can read that temperature by placing a thermometer under a piece of foil and covered with a folded towel (or some other kind of insulation) in the middle of the floor. Since your electricity is so expensive, maybe you should just try to hold the floor around 80* and let your forced air do the rest.

    Quote Originally Posted by crater View Post
    ... with the recovery rate of the electric boiler I am beginning to wonder if it was a good decision for my application.
    Again, I would begin with an output temp of about 100*, and with a low (turn-on) setting just a few degrees below that ... then decide about raising both after a couple of days. The idea here is like placing small sticks on a cooking fire to maintain a desire temperature rather than just tossing in another log ... then decide whether you can afford to purchase more sticks.

  2. #17
    Computer Programmer Bill Arden's Avatar
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    Quote Originally Posted by crater View Post
    ok I get the gist now.

    And it makes sence to do exactly that, now will drilling a hole in the concrete and inserting the sensor work, or will there be to much heat loss for the sensor to be acurate?

    Also my forced air is GEO Thermal so one of the burning questions is: Is running the combination of the GEO and the radiant as or just as efficient as just heating with the GEO?

    NOTE: my GEO is not the heat source for the radiant. The radiant has a seperate 15KW (50k btu) electric boiler as it's heat source.
    Then I would just heat the slab a small amount since a ground source heat pump is 300% to 500% efficient. (COP 3-5 compared to electric heat)

    I'm not sure why you need a in-floor sensor. you could just measure the temperature of the return pipe and the electric boiler also has a temperature limit you could set.

    in-floor sensors are mainly needed for in floor heating wires.
    Important note Ė I donít know man made laws, just laws of physics
    Disclaimer: I'm a big fan of Darwin awards.

  3. #18

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    Quote Originally Posted by Bill Arden View Post
    Then I would just heat the slab a small amount since a ground source heat pump is 300% to 500% efficient. (COP 3-5 compared to electric heat)

    I'm not sure why you need a in-floor sensor. you could just measure the temperature of the return pipe and the electric boiler also has a temperature limit you could set.

    in-floor sensors are mainly needed for in floor heating wires.
    OK so heat the slab to 80* (the point where thermal mass will radiate heat)
    then let the Geo take care of the air temp rise? So I'd have a higher electric bill to have warm feet but not necessarily a warm room (due to the radiant).

    Measuring the return temp. would assume that the liquid was the same temp as the thermal mass would'nt it?

    IE: If return is = or > 80* then system shut off OR if return is < or = 79* then system stay on

    Is the aquastat the limit selector you are mentioning? It limits how hot the boiler will get before modulating.

  4. #19
    Computer Programmer Bill Arden's Avatar
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    Quote Originally Posted by crater View Post
    OK so heat the slab to 80* (the point where thermal mass will radiate heat)
    then let the Geo take care of the air temp rise? So I'd have a higher electric bill to have warm feet but not necessarily a warm room (due to the radiant).

    Measuring the return temp. would assume that the liquid was the same temp as the thermal mass would'nt it?

    IE: If return is = or > 80* then system shut off OR if return is < or = 79* then system stay on

    Is the aquastat the limit selector you are mentioning? It limits how hot the boiler will get before modulating.
    I'm not sure where it would be located, but the boiler must have a temperature sensor already to measure the water temperature.

    if you have an aquastat, then yes, that is what you would use.
    Important note Ė I donít know man made laws, just laws of physics
    Disclaimer: I'm a big fan of Darwin awards.

  5. #20

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    With a 30* Delta-T, I would think I would need to have the Aquastat set at 110* to maintain the thermal mass(concrete floor) at 80*
    So I could regulate floor temp at the return line. Setting return line stat to be satisfied at 80* and if I wanted to heat with the floor then set a air temp stat at say 72* then if the floor was 80* but the room was 70 system would be running and if the room temp was 73* but the floor temp dropped below 80* the system would start and heat the floor back up to 80* but would't that require a constant flow to get a real floor temp. not just a drop in temp at the sensor?

  6. #21
    Computer Programmer Bill Arden's Avatar
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    Quote Originally Posted by crater View Post
    With a 30* Delta-T, I would think I would need to have the Aquastat set at 110* to maintain the thermal mass(concrete floor) at 80*
    So I could regulate floor temp at the return line. Setting return line stat to be satisfied at 80* and if I wanted to heat with the floor then set a air temp stat at say 72* then if the floor was 80* but the room was 70 system would be running and if the room temp was 73* but the floor temp dropped below 80* the system would start and heat the floor back up to 80* but would't that require a constant flow to get a real floor temp. not just a drop in temp at the sensor?
    I guess I was assuming a continuously on pump. The Delta-T would drop as the pump continues to run with the resulting Delta-T being dependent on how much heat the slab looses.
    Important note Ė I donít know man made laws, just laws of physics
    Disclaimer: I'm a big fan of Darwin awards.

  7. #22

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    I would think a embeded floor sensor could do the same thing without have a pump running continously

  8. #23

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    The way my system is set up is as such:
    Stat--->24v 3 zone control panel--> low voltage to boiler and high voltage to corrisponding zone pump
    so when zone 1 calls for heat the zone panel sends low voltage to boiler to start it and also high voltage to the #1 zone pump to start the flow

    I am using 3 zone pumps instead of zoning valves and 1 pump

  9. #24
    Like an engineer alternety's Avatar
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    I know this is not an answer to your question but comments on the overall system fundamentals and assumptions. I hate it when people do that.http://www.terrylove.com/forums/imag...es/biggrin.gif Anyway, there are several issues.

    You should not need radiant and air. Radiant just makes you feel warm. No source, no breezes, etc. I have it; I feel no need at all to have any additional system. Most everyone that walks in comments about the absolutely uniform and sourceless comfort. I have never seen a recommendation for dual systems.

    Heat pumps tend to be poor sources for hot air heating because they do not get the air comfortable enough for the draft the system causes. Geothermal pumps can be better than air based systems. The temperature available from the geothermal system is very well matched with radiant floor; not so well with air heating systems.

    Some assumptions include, sufficient insulation under a slab. Floors that are ceilings of other heated spaces need to be insulated from each other. You should have had a heating calculation before building things. If you can supply the full loses from the heat pump, you could go that route. If there is a backup resistive heater in the heat pump system, you would be no worse off than you are now for capacity and cost to operate.

    There is probably nothing you can do with your existing heat pump if has a direct air exchanger in the furnace. You might ask the manufacturer if it can be converted to provide only hot water. If it could, use the radiant as you only heating source. Do a heat loss analysis of the house. Find required fluid temperatures, required flow, if you tubing is adequate in layout and flow capacity. The floor tubing is the only imutable given.

    I know "you should have done it this way" is annoying. Just think over what you have and how you might be able to use the pieces. A single system would most likely give you much better comfort. Certainly couse less headaches for controlling things.

    The thermostat for the floor should be capable of dealing with the thermal mass of the floor. I suspect thermostats not designed to be smart will not be real helpful. I had one of those systems a long time ago. Constant over and undershoot.

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