TEMPERATURES AND HEAT TRANSFER BENEATH A GROUND FLOOR SLAB IN A PASSIVE HOUSE

This paper presents the results of one-year period in situ experiment designed to monitor the temperatures beneath a real ground floor slab in a passive house. Experimental measurements of the subsoil temperatures were performed outside and under the foundation (at various depths and locations) of a timber frame passive house. The results of the experimental measurements of the subsoil temperatures under the foundation of the passive house showed higher temperatures than predicted in standard calculating procedures and moreover they are not included in the calculations at all. This paper also reports the results of the calculation procedures proposed by the standards for slab-on-ground heat transfer. In the following paragraphs, the analytical detailed calculation procedure of CSN EN ISO 13370:2009, the analytical simplified method of CSN EN 12831:2004 and the numerical simulation methods of CSN EN ISO 10211:2009 are described and compared. Different boundary conditions (external design temperatures and external measured temperatures) were used. The ground temperatures were not included in the calculation procedures; only the thermal conductivity of the ground was respected. In particular, a two-dimensional finite element model, was used to simulate the heat transfer beneath a ground floor slab into the soil. The results showed that this model is more suitable tools to predict the thermal performance of the slab-on-ground floor than simplified analytical methods.