Moisture conditions and energy consumption in heated crawl spaces in cold climates

A crawl space foundation is widely used in buildings and detached houses in northern countries. The relative humidity (RH) of the air in crawl spaces is the most critical factor of the mould growth in the structures of a crawl space. The objective of the study was to find out whether heating is a feasible alternative for crawl space moisture control with reasonably low energy consumption. The effects of summer heating in an outdoor air-ventilated crawl space with different ground covers and air change rates were simulated in this study. The simulations were carried out for an apartment building and a detached house. The effects of the control strategy, heating capacity, air change rate and ground covers on the energy consumption were studied. Mould growth index was used as performance criteria for acceptable conditions in the crawl space. To assess the sensitivity of the main simulation parameters a differential sensitivity analysis (DSA) was used. In the parametric simulations, the used ground covers were lightweight expanded clay aggregate (LWA), crushed stone (CS) and PVC. The control of heating was based on RH controller with the set point between 70 and 80% and a heater with heat output from 2.5 to 10 W/m2 of crawl space area. It was shown that a thick layer of LWA prevents mould growth even without heating, but the layer with heating still provides lower RH An alternative method for moisture control is to use a ground cover without thermal insulation and heating of the crawl space. This method proved to be a good alternative to control mould growth. The specific energy consumption for heating of the crawl space was roughly the same order of magnitude in the studied apartment building and detached house. Annual specific energy consumption was generally low, within the range of 1.4– 3.6 kWh/m2 of the crawl space area in most of studied cases. The energy consumption rose considerably when a lower set point value of RH was used, consequently the time when the heating is on was the highest when the set point value was lowest. With heating, it was possible to prevent any mould growth, i.e. to keep mould growth index equal to zero.