Investigation of a model for the ventilation of suspended floors

Abstract

International Standard ISO 13370 “Thermal performance of buildings — Heat transfer via the ground — Calculation methods” provides a method to calculate the R-value of a suspended floor. The method is a modification of a methodology first published in the CIBSE Environmental Design Guide A -1998. The thermal network that forms the basis of the CIBSE calculation includes radiative transfer between the suspended platform and the ground, conductive components and a sub-floor ventilation component. In the ISO 13370 methodology the surface resistance (the inverse of the combined convective and radiative co-efficient) is used as a proxy for the more explicit calculation (as is done in most building heat transfer calculations). This paper deals with the ventilation component of the ISO 13370 calculations. This component would seem to have its origins in an infiltration model developed during the late 1970s and early 1980s by Max Sherman and others at LBL. It is a singlezone model that incorporates both stack and wind induced effects. This paper investigates whether this model can in fact be applied to sub-floors and shows how an “exact” formulation may be derived from first principles.