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How do I wire up a thermostat, heater and a pump?

post #1 of 9
Thread Starter 
I'm considering fitting a heated floor to my workshop conversion project. I've pulled permits and am within code to heat any way I like. This is considered a 'shop conversion'.

I'd like some help with how to wire thermostats, a heater and a pump to 110V. Only electric is available to the detached shop to heat the water and ideally the heater and pump will be cheap and easy to replace. Controls would ideally be off the shelf items I can wire up with little modification.

Here's a diagram of what I think might accomplish this in a simple way.


T - thermostat
P - pump
H - Heater
Tank is just an insulated water storage tank.
The tube of fluid is to supply under floor heating to a concrete thermal mass, that is to mantain a constant temperature in a room.

Basic logic
------------
- T1 detects a drop in temp and starts the heating process by turning on H.
- The water begins to heat until T2 reaches the target temp and turns on power to P beginning circulation.
- When the cooler return water fills the tank T2 will fall below target temp and stop circulation. This ensures cold water is not circulated.
- The cycle continues until T1 reaches it's target temp switching off the heater. It could optionally turn off the pump as well at this point to prevent the residual heat in the tank being circulated causing the room to overheat.


Another possible solution is to use hot tub parts for the heater and pump. They might be easy to source at little (or no) cost, second hand, but I think the heater would have to run with the pump, which is OK if it will work. It would then only require the T1 to detect the room temp drop and turn on both the heater and pump until the target temp is reached. The concrete thermal mass will help to regulate the temperature. This method would still require a tank, just to allow for expansion. If this is reasonable it should be easier to install and maintain.

Using a large tank has the advantage that a solar heating panel could be retrofitted to supplement the system. Colorado is sunny for most of the winter but I first need a reliable solution.

I served a mechanical apprenticeship that involved some electronics and circuit diagrams, but I'm more than a little rusty.

Of course the lower the cost the better. Any input would be appreciated.
post #2 of 9
Comments & points:

Member whirnot is from your general area - he just built a solar air heater which looks great and is working well - you might drop him a line asking for advice.       www.ecohuddle.com/forum/thread/1975/new-design-for-solar-air-heater-reposted

1) İt will not be all that cheap of heat when using 100% electric - solar panels would help and don't have to be fancy
2) There needs to be serious insulation under the slab and the slab should be thermally isolated from the foundations - expecially in Colorado
3) Design hot water temp - approx 40 degrees C (104 deg F)?
4) To add a solar panel connection later, the tank will need to have a coil (heat exchanger) in it - can always change out the tanks
5) The 'basic logic' seems OK - the second version would depend on the heat load/heater capacity being matched which they will normally not be
6) İ doubt the hot tub pump has the head to supply the floor coils
7) You need to get someone to calculate the water flow (and head) needed for your worst case (coldest) - that will also set the minimum heater capacity


 
post #3 of 9
Thread Starter 
Thanks for the reply, I'll reply to your numbers below.

Quote:
Originally Posted by Russ View Post

Comments & points:

Member whirnot is from your general area - he just built a solar air heater which looks great and is working well - you might drop him a line asking for advice.       www.ecohuddle.com/forum/thread/1975/new-design-for-solar-air-heater-reposted

1) İt will not be all that cheap of heat when using 100% electric - solar panels would help and don't have to be fancy
2) There needs to be serious insulation under the slab and the slab should be thermally isolated from the foundations - expecially in Colorado
3) Design hot water temp - approx 40 degrees C (104 deg F)?
4) To add a solar panel connection later, the tank will need to have a coil (heat exchanger) in it - can always change out the tanks
5) The 'basic logic' seems OK - the second version would depend on the heat load/heater capacity being matched which they will normally not be
6) İ doubt the hot tub pump has the head to supply the floor coils
7) You need to get someone to calculate the water flow (and head) needed for your worst case (coldest) - that will also set the minimum heater capacity


 

1, The plan is to add panels but we need to make the decision on what kind of heating to use soon as next thing is to put in the floor. If we do go with underfloor heating solar panels can be retrofitted to supply hot water easily enough. Radiant floor will be nice for my wife as she intends to use the space to teach her yoga classes. We expect the warm floor to bring in additional customers so would likely pay for itself with the additional revenue. Warm air solar would keep the overall heating costs down too but we'd lose the benefit of the warm floor. If we decide not to use radiant floor, just warm air, then we'll also add warm air solar. Warm air solar is easier compared to warm water, I think.

2. There is already a slab under the building which is on a monolithic foundation. Would I just need insulation between the slabs? How much would you think I need and what type? Would the slab holding the pipes have much of an issue with expansion and would this tear or crush up the insulation.

3. 40C sounds OK

4. Retrofit is a good idea. I'll be back when I get to that part of the project :)

5. not sure what you mean by 'heat load/heater capacity'.

6/7 How do I begin to calculate the requirements for the pump?

Thanks again for taking the time to reply.
post #4 of 9
Since you already have the slab what İ would do is use a layer of Dow XPS closed cell foam (or equivalent) - probably 50mm thick on top the slab - also insulate between the edge of the new layer which will hold the radiant system and the walls. You need to minimize heat loss to the ground and exterior walls.

The Pex tubing would be fixed to the insulation layer during construction.

The final layer needs to be good concrete (using small stone) as that is what holds everything together plus you want efficient heat transfer into the floor. 

Any covering over the final concrete acts as an insulating barrier making your system less efficient - tile is preferred.

The tubing should be a Pex A or B with an oxygen barrier - forget Pex C 

İ prefer PPRC pipe to the steel and copper that is often offered. İt is fusion welded but otherwise easy to work with and long life - no corrosion concerns. After initial pressure testing there are no concerns of a leak with fusion welding.

Depending on the size of the heated area you might want more than one zone - the site İ am giving has diagrams of different types of systems. Radiant Company does excellent at providing information - about the best İ have found. Please note that İ am not connected with them in any way nor have İ bought from them. http://www.radiantcompany.com/

The heat load/heater capacity is how much heat you want to provide for the area and along with operating temperature tells you the pump size. Radiant can help with this.

 
post #5 of 9
İ found the Radiant Company site when İ was digging for information for our new homes. Hope you find the information useful. Being located rather distant from them İ bought everything here where this type of system is common.

To many companies and governments (all of Europe is really bad about this) try to keep all information commercial - pay and get it type of thing.  
post #6 of 9
Thread Starter 
Russ that site is excellent. It's answered so many questions already. I'll have a good read of the info there. The leger method looks right for my situation and is going to be easy to install myself which should save hundreds from the total cost.

Thanks again! I really appreciate you taking the time to help.

Simon
post #7 of 9
Glad to be of assistance! When they talk of styrofoam the material has little to do with a styrofoam cup though some companies try to sell the cheap material to you.

This is closed cell, extruded board type material. The cheaper styrofoam (like the cup) becomes water logged and loses it's insulation value.

What İ used here was Dow XPS extruded foam board - fashionable pink in color though after installation you can't see it. 
post #8 of 9
Thread Starter 
Concrete quote was over a grand (I think my wife said $1500 poured), sand is $114 delivered! This means we can  go ahead and install the tubing and revisit the issues of heating after we have a floor in. Heaters in the meantime but at least the project can now progress! I'm going to post a new thread regarding flooring but I'm one happy dude right now! :)
post #9 of 9
What they use here is a mix using only sand and cement of about 50mm thickness over the foam board. That gives a cover everywhere (over the tubing) of at least 25mm. İt is doubtful there is insulation under the slab as there would have probably been no reason to do so. This means the foam over the slab and under the tubing is important to prevent excessive heat loss.

 Your final floor covering goes on top of that. All floor coverings act as an insulator with tile being the minimum and carpet being the maximum.
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