ML-11-014 -- Development of a Design Procedure for Radiant Heating in Slab-on-Grade Floors in a Cold Climate PDF

A two-dimensional steady-state numerical model was developed for in-floor-heated slab-on-grade foundations. The model allows for various placements of insulation, including bottom, edge (both outside and inside the footing), and skirt. The model was validated by comparing results with previous numerical and experimental results. Comparisons were also made with the design procedure recommended by ASHRAE Handbook—Systems and Equipment (ASHRAE 2008) for calculating panel surface temperature, heating tube outer wall temperature, downward and edge heat losses, and heating tube water average temperature for in-floor-heated slab-on-grade floors. These comparisons suggested that improvements could be made to the ASHRAE procedure. In the present work, a new design procedure has been developed for calculating heating tube outer wall temperature, downward and edge heat losses, and heating tube water average temperature for a concrete slab with vertically centered heating tubes. This new design procedure is based on the numerical results of the two-dimensional model and is valid for outdoor air temperatures ranging from –20°C to 0°C (-4°F to 32°F), heating tube center-to-center spacing ranging from 100 to 360 mm (3.94 to 11.81 in.), heating tube outside diameters ranging from 16 to 29 mm (0.63 to 1.14 in.), concrete thickness above the heating tube ranging from 40 to 100 mm (1.57 to 3.94 in.), concrete thermal conductivity ranging from 0.7 to 1.4 W/m·K (0.40 to 0.81 Btu/h·ft·°F), and soil thermal conductivity ranging from 0.6 to 1.8 W/m·K (0.35 to 1.04 Btu/h·ft·°F). This design procedure can be applied to both uninsulated slabs and slabs with insulation placements suitable for cold climates, including bottom insulation, external edge insulation, and skirt insulation.