Design Temperature Help Needed

coalmaster wrote:just curious, how many R's did you put under the slab?

I am not sure, whatever 2 inch Styrofoam has for R's.

Olllotj wrote:I did not know that you could run water temp that high in a slab

I had no idea what it was either; this was what was printed in my Taco 705-2 PLC Controller manual on setting up the computer parameters.

CoaledSweat was not far off in his thinking because while that is the maximum temperature allowed, the manual suggests a slab-on-grade situation have a Design temperature Mix of 140 degrees. Radiant heat with wooden joists would be 160 degrees. Fin tubes would be 200 degrees, etc.

Keep in mind the Design Temperature Mix is not actual water temperature running through the floor, that is variable, however it is the maximum temperature the water will reach. Basically by fussing with the Design temperature Mix I am calibrating the computer for degree days.

This is also the temperature that is governed by cold weather by pass I believe. I can adjust this temperature too, but right now it is set at 10 below zero (f). When the outside temperature gets to that point, there is little need to try and adjust the slab to outside temperature in order to conserve propane. At that temp it is just plain cold, so the computer bypasses the minute by minute analysis and flows the maximum set water to heat the floor. As long as it stays below 10 below zero (f) the floor gets 145 degree water.

NoSmoke,
Have you ever considered running lower water temps through the floors and running constant circulation? I'm not sure if your controls can adjust mixed water temps to the floors on the fly ,based on outside and inside temps, but if it can, you may want to consider trying constant circulation! Just a thought. It's how I heat my home and garage, 4500 sq ft.
Jesse

Well that is kind of what I have been asking all along, where do you set the design temperature mix to get that balance?

Now what you are talking about may be different then what I am talking about. I am referring to letting the computer control the temperature of the room via its many sensors, outside temp and cumperterized degree day mapping. You might be talking about what my friend does. He has his boiler set up on a timer where every hour for 15 minutes, hot water is pumped through his floors, and it keeps his garage and house quite warm. If you mean that, then no I do not do that at all.

I kind of got my answer though; my new mudroom does not have enough floor to adequately heat it. I basically have two options to cure this; lessen the loss as much as I can with a variety of control methods. If that does not work then I can add supplemental heat (say a radiator). Putting its pex tubing on its own manifold would work as well, but a last resort due to cost.

Big ole' rad to dry the boots and mittens...
Keep the temp low on it...
Then you can open up to great room...