radiant floor problems

Wayco Wayne_2

Customer having problem with an in slab radiant floor not recovering fast enough from when he turns it back at night. I tell him he shouldn't really be trying to set back with an in slab radiant floor but he says he has another smaller room with radiant in slab that it works just fine. I measure room. about 370 sq feet with a 10 foot ceiling and several french doors and windows. I then go to the boiler room. This room has one loop going to it. I check the numbers on the side of the tubing and the loop is about 250 feet long, of 1/2 in Pex. I'm amazed it works at all. He has 140 degree water coming off a thermostatic mixing valve and a grundfos circ 14-42 that is split by 2 zone valves, one going to the sun room in question and the other going to another smaller room. ("The one that works") The only ways of bolstering this radiant floor that I can think of is higher temperature and higher flow. Changing to constant circulation might help. Any feedback from the peanut gallery? BTW you should see the boiler piping. Don't get me started. WW

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Mike T., Swampeast MO

You might want to measure the delta-t of that loop while it's struggling to recover after setback. If already very high you might start hitting that wall of diminishing return with more pumping ability...

Can't convince the HO to use less setback, eh? That would certainly be my first suggestion.

Weezbo

guess you are going to break out the crystal ball on this one

for it will need that minimum....one thing easy to try is lower water temps say 85¡ãF off the mixer....then choke down the flow on the sun room that"Works"...constant circ and low temps is always the better way to fly...bang boom is just not worth considering.the garage doesnt need to be 92 in the shade.lower temp constant flow vs higher temps and pump the heck out of her....pumping the heck outta her 'Sounds', Like a Great idea however thats getting pump happy.instead try picking up the boiler pressure constant flow with the mixer squeezed down to the lowest setting for a day. so you can see what you are able to do without upsetting the guy. hes probably happy as a clam that he Has heat...and is counting his blessings at that.

Mike Reavis_2

140 degrees sounds a little high

for water in a concrete slab. I don't think that higher water temp is an option.

It isn't taking the path of least resistance is it?

quick look at a radiant heat system program, w/ assumptions says 2 loops, 205ft+ leaders, 88 degree water flowing @1.4 gpm. less than 7k btu's.

disconnect the pipe and check flow- Kinks?

no high water table?

best of luck
Mike

Weezbo

Mike...I need to send you some $ for the programme.

I have been buzy as heck....so, i will send you a few extra bucks for the Viessmann:) i just got some calleffi controls and i havent even had time to look at the program you wrote or thiers...Wayne, you might consider this mike's programm, my apprentice went thru it and i asked him a few questions ,either he learned something from it or his ability to learn stuff thru osmosis has improved lately:)

Mike T., Swampeast MO

No problem. Glad you enjoyed--even if those instructions were written in stream-of-consciousness and only lightly proofread.

Am looking forward to somewhat colder weather with daytime highs below 45° or so to see just how close theory relates to reality. So far, it looks good. Was happy and a bit shocked when I plugged in a steady supply temp from the boiler and it produced the measured return temp!

Had a person from North Pole, AK join the club I manage this week--now I've seen that town name twice!

hr

Do a heat load calc first

you need to know the number you have to hit. Without the actual load number we will just be guessing at a fix

You may get there with the 18" oc loop. It's the surface temperature that matters. You may be able to crank up the temperature and get above the normal 83- 85 surface temperature. It may get a little warm and uncomfortable right on top of the tube, and the wide OC spacing will produce noticable temperature spread... But it may still heat the room.

hot rod

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