Location, Location, location – where to put the dew point sensors? So here
we may hear a lot about classical physics and the ideal gas laws, in
particular, Avogadro's Law and Fick’s Laws of Diffusion. Without going
deeper into this, these laws tell us that 1) humidity seeks equilibrium and
does not need the actual movement of in order to equalized across an area,
and 2) that, as counterintuitive as it may seem, a volume of air is lighter
when it has a higher humidity, and therefore rises. Don’t worry about which
law wins. In a cooler part of an enclosed space, RH will be higher because
the air can hold less moisture, in a warmer area the air can hold more water,
so the RH is lower. Neither have anything to do with the dew point unless
the actual (absolute) humidity changes.
Don’t worry about it or let the experts confuse you. Just locate the dew
point sensors in the area served by the radiant cooling surface, and
generally as near as practical to the surface that you are protecting from a
dew point issue. We are only concerned about the dew point and not RH in
this regard.
For most users, one or two dew point sensors, more or less central to the
area, based on common sense, per floor, is all that’s needed. If you use
radiant from the ceiling you can put the sensors higher on the wall, for floor
radiant it really does not matter.
One note –if you have a persistent source of new absolute humidity, like a
leaky pipe, fix it.
Another note – if you have a high cathedral type ceiling, this is a good
location to pull in air for your dehumidifier,
Dew Point Sensors
Proper Location
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