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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
the dimensional instability of hygroscopic materials. From
the Wood Handbook published by Forest Products Laboratory (U.S.
Department of Agriculture/Forest Services), you can clearly see in Figure 1 that
the moisture content in wood is a function of the relative
humidity. From Figure 2 you can see the ideal "in service"
moisture content is between 6% and 14% as provided by the Canada
Mortgage and Housing Corporation, Wood Frame Envelopes Best
Practice Guide. The ideal in-service range corresponds to
relative humidity's between 40%+/-10% and 60%+/-10%
at temperatures typical for space heating and cooling. When
hygroscopic materials such as wood are operated in an
uncontrolled environment their moisture content can fluctuate
leading to shrinking and swelling which results in dimensions
instability.
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.
Forest Products Laboratory. Wood handbook - Wood as an
engineering material. General Technical Report FPL-GTR-190.
Madison, WI: U.S. Department of Agriculture, Forest Service,
Forest Products Laboratory: 508 p. 2010
2.
Wood-Frame Envelopes, Best Practice Guide - Building
Technology, Canadian Wood Council, Canada Mortgage and
Housing Corporation, 1999 |
