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Introduction
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
supporting the growth of bacteria, viruses, fungi (moulds, molds)
and mites. According to ASHRAE Transaction Human Exposure to
Humidity in Occupied Buildings and the 2011 ASHRAE Application
Handbook humidity less than 30% or more than 60% can introduce
higher multiple microbial risk factors. As noted in the EPA
Indoor Air Plus program, "You have to control humidity to below
60% RH."
Clearly you can see that various risk occur
through the relative humidity range but the optimum zone with
the least risk occurs between 30% and 60%. According to the 2011
handbook this illustration describes, "Optimum Humidity Range
for Human Comfort and Health". Within this controlled humidity
range
properly designed and controlled
radiant cooling system can easily operate without
condensation.
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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Update: An excellent discussion on humidity and
microbial was recently authored by Stephanie H. Taylor, M.D. who
states, "The movement and infectivity of bacterial, viral, and
fungal organisms vary with the RH of the air…" This is supported
by Dr. R.L. Dimmick from the Naval Biological laboratory, Univ.
CA, Berkeley who stated, “Moisture content may, indeed, be the
most important environmental factor influencing the survival of
airborne microbes.” Taylor goes on to state, “Maintaining the
relative humidity of hospital indoor air between 40% and 60% can
significantly decrease healthcare associated infections.” As we
have noted repeatedly humidity must be controlled and 60% as an
upper limit serves the physicians and the occupants and the
engineer.
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