Mean radiant temperature

Online educational resource on achieving indoor environmental quality with radiant based HVAC systems
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facts and myths on radiant barrier


Mean Radiant Temperature (MRT) - Part III
Copyright (c) 2011, Robert Bean, R.E.T., P.L.(Eng.) and

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Mean Radiant Temperature (MRT) - Part I: Introduction/theory
Mean Radiant Temperature (MRT) - Part II: Application of theory
Mean Radiant Temperature (MRT) - Part III: Spreadsheet tool for thermal bridging
Mean Radiant Temperature (MRT) - Part IV: Project examples & ASHRAE research
Mean Radiant Temperature (MRT) - Part V: Calculation example (REHVA GB #7)

Download the spreadsheet. Join our linked In group and request the password.

This beta version spreadsheet can be used to calculate the area weighted thermal performance of a wood frame wall based on the percentage of studs and window area in relationship to the total insulated wall area. You can see from the graph that as the framing factor increases and/or window area increases the actual wall R -value rating goes down.

Message: A R-20 wall is only a R-20 Wall if there are no studs and no windows. As soon as you add the framing and windows that R-20 wall is no longer an R-20 wall - duh!

Final note: Even if you account for thermal bridging to obtain the adjusted "real" R value, it still is only an estimate because the enclosure and its R-values are also affected by air flow, temperature, density, moisture content and homogenous characteristics of the material.

See overview of housing performance categories in North America.

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