Radiant Infloor Thermostat #FAIL: How Not to be Comfortable


This weekend through a series of unfortunate events my radiant in floor system briefly went offline and the results play right into some recent comments on LinkedIn.

Robert Bean recently shared the DOE Building America findings that declared an air temperature of 70 +/- two degrees is a benchmark for thermal comfort. Quoting Robert;

…..would like to know how the researchers came to the conclusion that 70F +/-2F air temperature is a proxy for a thermal comfort band when the ASHRAE/ISO thermal comfort band defines it differently.

In my own home I am using a radiant smart control in combination with a standard dual sensing thermostat that controls my system which reports data to a cloud server every few seconds. This has enabled me to capture an anomaly in my radiant infloor heating system and share it.

The graph below shows the recent air temperature in my radiant zone and as you can see it is a very constant 72.01 degree fluctuating at most .5 of a degree. I meet the guidelines for the DOE Building America standards for thermal comfort.

air temperature

The issue the above graph does not show you is that during almost the entire time shown my radiant in-floor system was actually offline due to a pump issue..

The graphs below further demonstrate what happened. The first graph shows my cold supply / return water temperatures, the second graph shows my stable and constant air temperature. ( Note: The ‘spiking’ in air temperature is only because my smart control I built measures air temperature down to 2 decimals. The actual variation is less than .5 degrees. )

The last part of my graph shows system delta T and the BTU output flat lined since the system was offline. The very end of the graphs is where I got my tools out and fixed the problem.

radiant control

Moral of the story?

The factors that contribute to ‘thermal comfort’ are many and air temperature alone does not provide ‘thermal comfort’. Further more +/- 2 degrees as illustrated above is a very poor benchmark of thermal comfort.

The secondary message of this post is if you are controlling a radiant infloor system with an air sensing thermostat alone you are without question completely missing out on the true comfort and value that  a radiant system gives you.


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