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This paper outlines the methods and results of a four-year project that measured heat flows through two uninsulated slab-on-ground floors on nominally wet soils. One floor was on peat soil, the other on clay, and water table depths were 0.5 m to 1.0 m through most of the year. Heat fluxes were measured over the whole floor using heat flux transducers (HFT) at the concrete floor surface, and temperatures were measured by thermocouple, continuously for four years. The soil conductivities and soil temperatures were measured daily at 11 positions near one edge of the floors. The R-values of these two floors can be calculated from ASHRAE or CIBSE Handbooks as ~ 1.6 m2 · °C/W and 1.3 m2 · °C/W. The floor R-values were measured, using a cumulative averaging method, to be 2.4 m2 · °C/W and 1.0 m2 · °C/W, respectively, differing by about +50% and -25% from the calculated values. The measurement error is assessed as within ~ ± 7%. The measurements indicate that not only the soil conductivity but also the external wall thickness must be considered when determining floor performance. In the two houses in this project, the calculation errors attributable to not correcting for soil conductivity were ~ +50% and -10%, while those from not correcting for external wall thickness were ~ +10% and +30%. The formulae developed by Delsante (1990) and improved by Davies (1993) best fitted the measurement. Subsidiary data on edge temperature profiles, apparent distribution of R-values over the floor, and the sensitivity to indoor temperature fluctuations are also described. The influence of seasonal and short-term variations of indoor temperature are of practical significance, and the timing of floor heat flux rise and fall raises some questions about the contribution of the floor to overall heat losses.

AUTHOR: Harold A. Trethowen, P.E, Angelo E. Delsante, Ph.D.
CITATION: Thermal Performance of the Exterior Envelopes of Buildings VII
KEYWORDS: December, Florida, 1998
YEAR: 1998