overheating slab

Randy Tibbits

I was chatting with a contractor from a nearby community. They don't reccomend radiant infloor heat. They have problems with the heat coming on at night and then midmorning the slab is overheating and causing the ac to come on. Basicaly both systems are fighting one an other. I've not seen this on my jobs. What can be done to cure this problem? Either at the time of the original install or now as a retrofit. This is a interesting development for me. I've been thinking about marketing that area and with the locals reccomending forced air now is the time.

Mark Hunt

Wrong control strategy


This can and does happen on underfloor applications as well.

Thermostatic or fixed mixing controls will allow design day temp water to shoot through the system. Now your floor is a charged thermal battery with a bunch of BTU's looking for a place to go. Now we have a room that is 75 or 80 degrees!

Best approach is to control water temps with motorized valves or variable speed injection. Outdoor sensors to make the system responsive to what's happening outside, or indoor sensors to make the system responsive to what is happening inside. Or a mixture of both.



Mark H

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Waylon Lowery

Mark is...

right on target. You need weather responsive controls (outdoor reset mixing or injection) and or smart t-stats.

Unknown

PWM thermostats

Pulse Width Modulation (PWM) thermostats work on a setpoint and a cycle length. The use of a floor sensor helps control the large flywheel effect of high mass systems.

tekmar Control Systems makes a GREAT thermostat to control just what you are experiencing. Take a look at their 510,511 and 512 programable thermostats. Their 512 controls heating & cooling and it's programing helps prevent whats happening to your system.

I like these thermostats a lot and will never again use an air sensing on/off stat to control a radiant mass. Wirsbo offers these same controls under their name and it's sometimes cheaper than under the tekmar name.

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Kal Row

couldnt agree more - it's theeee stat for radiant

http://www.tekmarcontrols.com/acrobat/d510.pdf

Weezbo

go With the flow....

low temp water, variable speed with outside ,room ,responsive control is a quick fix for that ,however....it all depends on what you are dealing with....some things may LOOK right and the control not be there,some things may seem right have great controls and have hidden Features as to the way they behave..you may not be able to Rescue all systems, may be the more succint way of saying that. joe home owner will probably think you are working with god just to have low water temps on some Rescues heer is a easy way to get the idea across put a lower water temp fixed mixer in place of the one they have,go away and tell them to give you a call in a few days,then you can explain the profundities of comfort and explain the advantages in modulating mixes,variable speeds,out door reset,all kinds of modern wonders:)p.s no zone vlve or no check in circ pump that tends to bounce things around even worse.another way is to place a temp gauge in the supply line...that gives the ho something to do:)and may give you a really good idea of what is actually happening and when... the end game is you being able to prove to them when you are finished the number of variables you have changed for the better....Hey! they will probably tell You!:)