F-Factor Calculation - ASHRAE 90.1-2007 Table A6.3

Does anyone know what the two different columns for unheated and heated slabs represent in Table A6.3 ? Why are there different F-Factors for the same horizontal insulation distance and the same R-value? The example below that is highlighted is that if I have a slab with 12 inches of R-5 horizontal insulation is the F-Factor 0.72 or 0.61?

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TaylorRoberts

asked 2015-03-12 15:30:43 -0500

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__AmirRoth__

updated 2017-05-08 15:59:02 -0500

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Does anyone know the basis of this table?

Joe Huang (2015-03-13 09:27:18 -0500) edit

These values come from work David Baylon and Mike Kennedy did for the state of Washington. See this publication for more background.

Neal Kruis (2015-03-13 15:07:22 -0500) edit

Hhhmmm. That's interesting. These numbers are somewhat lower than those in my 1988 paper. I guess I'll have to read the Baylon paper to find out how he and Mike got the F-Factors. I just did a regression of the fluxes to the Inside-Outside Air Temp Difference, so the F-Factors can vary depending on location.

Joe Huang (2015-03-13 18:49:39 -0500) edit