TRV - What is the likelyhood of...

ChasMan

I have been studying up on what is involved in adding a radiant floor to an existing home with Hydronic baseboard.. One of the main issues seems to be the need for a TRV. If I were to shoot say 180 degree water at this beast, what is the possibility it will come out the other end and into the floor? Is it possible for it to fail open?

Brad White_9

TRV failure

is something I have never seen. Not to say it will not happen. What could happen is a leak of the thermally expansive fluid, more likely if a capillary is involved. If so, it would fail open. It is thermal expansion of the fluid or wax that compresses the valve piston spring.

That said, let's think about what the worst thing is that would happen. The piping would see whatever the hottest water would be available from your boiler.

Check the rating of your PEX. It is rated like all piping systems and materials at a certain pressure AND temperature. PEX can handle 180 degrees (the brand I have can) and at more pressure than my system will ever see. It will soften and will expand more of course.

I see this as low possibility of failure and of not much consequence if it does. If you do have concerns you could do any number of the following:

1) Install a second TRV in series with the first, with a different (higher) setpoint which would take over for the first if that failed. Would add pressure drop to your circuit for the life of the system, but it is one idea. You would never know if the second valve failed, or the first for that matter unless you checked.

2) Install a high limit strap-on or immersion well sensor downstream of the mixing point. If the limit is exceeded it shuts off the circulator. May even send an alarm/LED that it did so. (It is only money.)

Anyway, a couple of thoughts.

Brad

ChasMan

Thanks for the information. I like the idea of a safety for that due to the high cost of flooring replacement and my lack of trust for plumbing parts in general :-)

jerry scharf_3

I don't think you want a TRV

Chasman,

You've got 180F water coming from the boiler. Whether the valve opens a little or a lot, that's still too hot to be shoving into the floor circuits. You need to mix boiler water with recirculated radiant loop water to get the desired water temperature for the floor. You will have terrible heat distribution and could damage the floors.

Taco makes a nice simple unit call a Radiant Mixing Block (RMB.) The nice thing about this is all the controls and pumps are already done, you just hook up the ins and out, Tstat and outdoor reset thermistor and you're done. There are other ways to do this as well.

jerry

Brad White_9

You know, Jerry is right

Call me 'stuck on stupid', but I focused on the TRV issue as if that was a foregone direction. Shame on me. And I addressed the Climate Panel potential issues with 180 degree water (I have that below tile and have taken 180 on occasion during initial shake-down), but if wood flooring, especially if put down in a more humid environment, could be a disaster with cupping and splitting. Good call.

Jerry is right, the Taco RMB is an excellent and cost-effective choice among other means and methods. You are by no means limited to using a TRV, (poor man's control, albeit effective when the limitations are known.)

ChasMan

Thanks for the information! Looks like lots of interesting devices are available to do this.