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One of the myths perpetuated with radiant cooling
systems is condensation risk on the cooling surface. This would
be a real risk if there was no moisture control. Without
moisture control numerous risk factors develop such as
invoking respiratory discomfort. There is extensive
medical and comfort research showing the effects of high and
low humidity on respirator discomfort, an example illustrated by
Figure 1. You can clearly see from this one sample study for the
least amount of people dissatisfied (PD) at 10%, a corresponding
space condition exists for 20% to 60% relative humidity for a
temperature range between 68°F(20°C)
and 78°F(26°C).
You can also see the increase in discomfort due to increase in
relative humidity at a given air temperature. For example at 72°F(22°C)
there is a 10% increase in people dissatisfied going from
approximately 40% RH to 65% RH; and a further 10%
dissatisfaction going from 65% RH to 80% RH. Not covered here
but also of great importance is the effect that high and low
humidity has on the eyes, mucous membranes and skin. Also to be
considered is the effect of high and low humidity on the
perceived indoor air quality.
There is an exhaustive supply of research
addressing this topic and readers are encouraged to seek out
these documents for detailed study. For our purposes here, it is
enough to say once again moisture must be controlled in
habitable spaces
which ultimately enables the successful use of radiant cooling.
This content is a key component from our course,
"Integrated HVAC Engineering: Mastering Comfort, Health,
and Efficiency."
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References:
1.
Jørn Toftum, Anette S. Jørgensen, P.O.
Fanger, Upper limits of air humidity for preventing warm
respiratory discomfort, Energy and Buildings, Volume 28, Issue
1, August 1998, Pages 15-23
2. Jørn Toftum, Anette S. Jørgensen,
P.O. Fanger, Upper limits for indoor air humidity to avoid
uncomfortably humid skin Energy and Buildings, Volume 28, Issue
1, August 1998, Pages 1-13
3. Fang L, Clausen G, Fanger PO. Impact of temperature and
humidity on the perception of indoor air quality. Indoor Air
1998;8:80–90.
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