F-Factor for slabs with both vertical and horizontal insulation

savecancel

F-Factors are tricky because there is no referenced definition or methodology that others can use to generate them. I am considering putting together an ASHRAE Research Topic Acceptance Request (RTAR) to better define the ASHRAE 90.1 requirements for foundation insulation.

In the meantime, it might be possible to generate F-Factors using Kiva. You would have to simulate your foundation and fitting a line using the following equation:

$$F = \frac{\dot{Q}}{P \cdot (T_i - T_g)}$$

where

• $P$ is the perimeter of your foundation,
• $T_i$ is the interior temperature, and
• $T_g$ is the ground temperature as defined by the ground temperatures 0.5 meters below the surface (included in EPW file headers)

Short of doing some kind of numerical calculation, it is not possible to generate new F-Factors.

Disclosure: I develop Kiva