Snow-melt, Sab radiant heat

[MstrCarpenter]

First, Happy New Years to all!

This past summer I built a carport behind my shop. Mostly because I already had it, I added a single length of 3/4" oxy. barrier pex with the loops about 12" O.C.. in the 16'x20' slab. I'm at the point that I want to heat the slab. I've installed a few snow-melt systems with a plate exchanger, circulators, exp. tank, etc.etc.etc.. It's a lot of pieces but I know how and how it works. But that's not what I need because the entire F.H.W system in the shop has anti-freeze. I have a dedicated circulator and return for this already plumbed to the boiler. Now what????

I think I may need another pump to recirculate some of the return back thru the slab loop to reduce the temperature and provide some indication of slab temp and/or some type of mixing valve that's designed for this purpose. Any suggestions or experiences are truly appreciated.

[blackhat]

What is your heat source / boiler?

[jteneyck]

Yes, Happy New Year to all.  

I'm not sure I understand your question, but if it relates to controlling the temperature of the water going to the slab there are mixing valves to do that.  I have one installed on the under floor loop for my kitchen.  Pretty simple setup with a separate pump, mixing valve, thermometer, and return loop.  

John

[MstrCarpenter]

What is your heat source / boiler?

Yes, forced hot water (F.H.W.) by oil. Three zones with separate circulators. It has a tankless coil in it but I don't need hot water often so I just shut down the system when I'm not heating. I don't need this zone to be automated, in that I plan to manually turn it on and off, possibly with a simple timer. I know it's not good to send 200 deg. water to the concrete or 25 deg water to the boiler so a three or four way mixing valve is probably needed, but only for that zone (not the whole system). so do I need an additional circulator on the loop side or will a scoop tee suffice? I will be doing some type of geothermal when I have more time (i.e. retire) so the supply will be down around 180-160 deg,s.

[MstrCarpenter]

Yes, Happy New Year to all.  

I'm not sure I understand your question, but if it relates to controlling the temperature of the water going to the slab there are mixing valves to do that.  I have one installed on the under floor loop for my kitchen.  Pretty simple setup with a separate pump, mixing valve, thermometer, and return loop.  

John

John, are there two circulators moving the water? One between the boiler supply and return and another just for the loop? If so, I assume the thermostat (which in my case will be a timer) turns on both circulators and also connects to the boiler ZC terminal. Also do you have a three way or four way mixing valve? I keep asking about this because there is a price and availability difference. (I have a few three-way valves.) I'm also not sure if either will temper the water returning to the boiler at start-up. The loop temp. will be ambient outside air temp. at that time.

[jteneyck]

John, are there two circulators moving the water? One between the boiler supply and return and another just for the loop? If so, I assume the thermostat (which in my case will be a timer) turns on both circulators and also connects to the boiler ZC terminal. Also do you have a three way or four way mixing valve? I keep asking about this because there is a price and availability difference. (I have a few three-way valves.) I'm also not sure if either will temper the water returning to the boiler at start-up. The loop temp. will be ambient outside air temp. at that time.

Here's a diagram I found for radiant heat in a concrete slab:  Link

My underfloor radiant system is plumbed pretty much like this:  Link2

Both operate the same way; a pump and a mixing valve that controls the temperature of the water going to the radiant loop by adjusting the ratio of boiler vs. cool water coming back from the radiant loop.  

They are 3 way mixing valves.  The one I have is adjustable for the control temperature.  When the thermostat calls for heat the zone valve for that loop opens and then the mixing valve controls the temperature of the water going to the loop.  If you need to control the temperature of the return water to the boiler you likely need a system like in Link 2.  

I noted in the diagram for the concrete slab that temperature is controlled below 110F.  

John

[MstrCarpenter]

Here's a diagram I found for radiant heat in a concrete slab:  Link

My underfloor radiant system is plumbed pretty much like this:  Link2

Both operate the same way; a pump and a mixing valve that controls the temperature of the water going to the radiant loop by adjusting the ratio of boiler vs. cool water coming back from the radiant loop.  

They are 3 way mixing valves.  The one I have is adjustable for the control temperature.  When the thermostat calls for heat the zone valve for that loop opens and then the mixing valve controls the temperature of the water going to the loop.  If you need to control the temperature of the return water to the boiler you likely need a system like in Link 2.  

I noted in the diagram for the concrete slab that temperature is controlled below 110F.  

John

Thank-you. "Link2" with two mixing valves will keep the return temperature from getting too low. It also doesn't just partially close the supply circulator creating more"head pressure". (I'm not sure if that would consume more electrical energy or not.) This design doesn't need an additional expansion tank, plate exchanger, check valves, or any other special valves or fittings. It also looks much simpler to install than the thought process involved to understand how it addresses all of my concerns.  Thanks John. 

If there's any other input, I'm ready to learn.