Trouble with infloor heat

[ketas47]

I have a 26' x 38' x 10' garage with 2"x6" walls.Walls and ceiling insulated and 2" under floor and 1 " along outside edge. 2 8'x10' over head door and 1 service door.
I have a Navien on demand HW heater(210a)17000-17500btu that I hooked up to the infloor system(temp/pressure gauges, pressure tank, air elimanator, pressure relief safety valve,pump) and I am having trouble getting a delta t of 20 degrees.
I had temp going out @ 120 and coming back @ 65. Called plumber and thought air in system or to small of a pump. Circulated each line(4 250') 15 minuted to get air out,still low temp coming back and heater seems to be starving for more flow(stays on low heating cycle).
Replaced pump(grundos ups 15-58) with stiebel eltron cp3s26-110fc running on medium speed.
Temp return now up to 75 degrees, but still cant get Delta t of 20 and seemed to take about a hour to raise Temp 1 degree.
Also heater is modulating higher since I installed bigger pump.
I did clean all filters and strainers and found some blockage.
My Questions Why such a big Delta t and why is my floor heating so slow.?How do you know all the air is out of system? Floor temp is @ 60. Thanks
The floor is @ about 60 degrees

 

[sands35]

Concrete has a lot of thermal mass. It's not going to to change 20* in a hour. 60*F is about right.

If you had a delta T of 20*F then your concrete would eventually get to 90-100*F. Not sure that's what you want.

 

[jack stand]

60* is about where I have my shop set at (air temp) and this results in (about) a 75* slab temp using a cheap HDepot IR thermom. I have a Techmar t stat that uses a slab sensor along with the room temp reading (that I don't quite understand) but it keeps me comfy. Check out http://www.greenbuildingtalk.com/Forums/tabid/53/afv/topicsview/aff/12/Default.aspx or maybe badgerboiler will help out. I'm not sure if I know how your'e using the delta-t term but if that's the difference of your water temps leaving and returning to your heat source after going through your slab, that is about what mine shows as well.

 

[Sureshot]

Be sure to give it time. I wait 24 hrs after making small adjustments to see the effect.

Over time as the slab temp stabilizes the delta should come down. If your slab is at 60 and the return is 75 it seems to me the slab temp is not stabilized or the circ speed is too high. 2 cents.

 

[tdkkart]

What's the delta after the system has been running for an hour??

1*/hr would not be unusual, neither is the large delta. You simply cannot change the temp of 40,000lbs of concrete in 5 minutes.

BTW, the air in your system at this point is in the form of micro-bubbles. Getting them out will take time, as in hours or days, not 15 minutes.

 

[jlckmj]

I had temp going out @ 120 and coming back @ 65.

That is about what my system runs also. I enter the manifold at 120* and return between 60 and 70 when the system first fires up, the return goes up to 70 to 75 after it has run for 10-12 minutes. I usually have an average garage floor temp of about 60*. (taken with cheap infrared thermometer)

My garage is about the same size as yours, I also have 4 loops of between 220 and 250 feet, using a tank type water heater, and I think my system is working very well at this point. I'm no expert, but the way I see it, if you are not loosing heat into the concrete, you are pumping water through the pipes too quickly and not letting the concrete retain the heat.

Someone please enlighten me if I am wrong.

Jim

 

[ketas47]

First, thanks to all the replies.
I left the system alone for about 2 days now and am @ 115 degree water leaving on demand water heater and returning @ 75 degrees. It was off for about 14 hours before thermostat turned system back on. But then it ran for about 3 hours before thermostat shut system off.Temp rise of about 3-4 degrees.
Does this seem normal? Seems to be down along time before thermostat restarts system and then seems to run quite a long time and over shoots set temp.
Thermostat is cheap honeywell mounted on a 2x4 on outside wall about 4ft above floor.
Thanks again for input

 

[sneezer41]

If it is overshooting then the water temp is too high. If you can turn it down, you will have longer runs and less overshoot. Otherwise your only option is to turn down the thermostat. I don;t believe any thermostat has enough built in anticipation for a concrete radiant system,but I have used electronic setback thermostats that did pretty good

 

[jlckmj]

ketas

Since day one my thermostat has been set at about 50* and my system always overshoots that temperature. Like I said in my earlier post, I usually have floor temp of about 60* I just consider it to be one of the things that happens with this type of system.

Jim

 

[Randy in Maine]

It sounds to me like it is working like it is supposed to.

My floor used 21 cubic yards of concrete = 42 tons of thermal mass to heat up and cool down.