Floors F- factor to Uvalue for equest input

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Dear equest users,
I am using equest for LEED projects.
In table 5.5-1of ASHRAE 90.1-2010 the F factor is given for floors.

How can F- factor be used in order to get Uvalue, which is needed in equest
for floors?

Thank you

Konstantina Kalliakoudi
Mechanical Engineer ?.Sc.

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You can search the archives for the thread titled ?Slab on Grade Floor Heat Loss? but here is how I personally handle F-factor to U-factor conversions:

In the past I?ve done a conversion of F-factor (perimeter based) slab-on-grade heat loss to U-factor (area) and input that in on a zone-by-zone basis if I really wanted to nail down SOG heat loss.

Example- Space is 20? x 30?, but the exposed perimeter is only two of the faces (20? + 30?). Let?s say it is uninsulated SOG.

F-factor from 90.1: F = 0.73 Btu/(hr*ft*F)

Perimeter based heat loss: 0.73 Btu/(hr*ft*F) * 50 ft = 36.5 BTU/(hr *F)

Then we can back-calculate the U-factor to assume for the whole floor to equate to that heat loss: 36.5 BTU/(hr *F) = 600 SF * X BTU/(hr*SF*F) -> U = 0.0608 BTU/(hr*SF*F)

You can create a custom floor construction for each space to provide the U-factor to produce equivalent heat loss that the F-factor calcs are telling you lose. For purely core zones (no exposed perimeter), I guess the F-factor calcs are telling us were not really losing heat through that slab (doesn?t? seem right, but it probably is relatively small) .

Nathan Miller, PE, LEED AP BD+C ? Mechanical Engineer/Senior Energy Analyst
RUSHING | O 206-285-7100 | C 207-650-3942

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You can also use the approach in Ashrae Fundamentals Chap 18, p. 39, or from Ashrae 90.1-2010 Appendix C (C.6.10.1).

Shaun Martin LEED-AP, BEMP


Shaun Martin Consulting

ph. 604-789-1095

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