Hydronic in floor heat

[nizak]

I have a customer who wants some wall thermostats installed. The type of heat being controlled is boiler heated water thru PVC tubing.

He commented that I could place the stats wherever I thought they would be the most effective.

He said that there wasn't any type of sensor installed prior to the concrete pour.

Will a stat without a sensing probe in the slab effectively control the temperature?

Not familiar with this type of work.

Thanks

 

[mbrooke]

In floor tubes must be kept from going above a specific temperature and this (in my experience) is done via 3 way temperature regulating valves independent of the thermostat.

 

[mbrooke]

This:

3-Way Mixing Valve Applications
Three-way valves are used to mix heating water to a desired temperature. The hot water from the boiler is blended with the correct proportion of cooler water returning from the system to maintain the target temperature as the HWR Platinum control resets the hot water temperature based on outside temperature.

http://www.heat-timer.com/2-way-and-3-way/



Of note the above company is typically used for commercial / apartment buildings and paired with an electronic temp controller, but the same concept should work for resi. I believe Honeywell makes a valve without the separate electronic control while still being able to regulate temps. In your case the thermostat will simply open and close a 24 volt zone valve.


Edit, Honeywell's version:


https://forwardthinking.honeywell.com/new/63-9379.pdf

 

[Dennis Alwon]

The hydronic heat is used to heat the room as well as the floor so the t-stat will sense the room temp and should work fine

 

[Sierrasparky]

We usually use TACO zone controller and 24v contacts to Thermostat. There will be a Auqu Stat too

 

[__dan]

I have a customer who wants some wall thermostats installed. The type of heat being controlled is boiler heated water thru PVC tubing.

He commented that I could place the stats wherever I thought they would be the most effective.

He said that there wasn't any type of sensor installed prior to the concrete pour.

Will a stat without a sensing probe in the slab effectively control the temperature?

Not familiar with this type of work.

Thanks

Hot Water Reset

https://en.wikipedia.org/wiki/Hot_water_reset

Infloor heat in the slab, you are in contact with the radiator at all times. Most common complaint is it is too hot, even with fixed temp mixing valves.

A reset control measures the outside air temp and sets the distribution system mixed water temp linearly with OAT. The infloor loop water temp would vary in the range ~ 90 to 130 F with the reset system while the room stat only calls the circ or zone valve (on/off).

Depends on the boiler. Modern condensing modulating fire gas boilers have hot water reset controls built in. Old style non condensing boilers run at 180 F on the boiler aquastat and would have to have the reset control added on the secondary distribution loop to vary the distribution loop temp with OAT. Necessary and expensive to add if it's not there now.

A standard boiler I would set up for primary secondary pumping with a Tekmar 361 to reset the secondary loop temp. This by itself can run in auto with almost nothing for room stat control.

http://tekmarcontrols.com/products/hvac-systems/361.html

You can mix with either a three way valve or variable speed injection pump

http://tekmarcontrols.com/support/tekmarglossary/33-support/glossary/193-variable-speed-output.html

If he's running straight boiler temp water to the in slab radiant loop, that would sound like trouble. If the boiler water is already mixed down to the distribution loop temp using OAT reset, that's about 90% of the work necessary, and any room stat calling the circ or zone valve will do. Tekmat makes combined space and slab temp sensing stats, but without OAT reset of the loop water temp the job could prove unsatisfactory.

http://tekmarcontrols.com/support/tekmarglossary/33-support/glossary/84-outdoor-reset.html

http://tekmarcontrols.com/solutions/browsesolutions/radiant.html