Online educational resource on achieving indoor environmental quality with radiant based HVAC systems
Not for profit educational resource on indoor environmental quality.
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Fundamentals of indoor environmental quality / thermal comfort and air quality solutions using radiant based HVAC

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."

Figure 1 Moisture content of wood in equilibrium with stated temperatures and relative humidity

Figure 2. Change in width and thickness as a result in changes to in-service moisture content.



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


See also:

Radiant Cooling - Part I, Fundamentals
Radiant Cooling Systems: Calculation Example
Tres Bien for Large Scale Radiant Cooling
Radiant Cooling for Sceptics: How to do radiant cooling in high humidity geographies
Radiant based HVAC systems - bibliography / resources
Radiant Cooling Systems: Condensation Concerns Part 1 of 6, Preservation of Materials
Radiant Cooling Systems: Condensation Concerns Part 2 of 6, Microbial
Radiant Cooling Systems: Condensation Concerns Part 3 of 6, Hydrolysis
Radiant Cooling Systems: Condensation Concerns Part 4 of 6, Dimensional Stability of Hygroscopic Materials
Radiant Cooling Systems: Condensation Concerns Part 5 of 6, Respiratory Discomfort
Radiant Cooling Systems: Condensation Concerns Part 6 of 6, Thermal Comfort



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