Thermal comfort: winter in a passive house

Thermal comfort: Three key criteria

Thermal comfort is a feeling of well-being of the body in relation to the indoor thermal environment. The level of thermal comfort varies according to three main criteria: the ambient temperature, the level of humidity and the presence of air streams. The Passivhaus standard considers that the average temperature in winter should be 20ºC, the humidity level should be between 35 and 55% and air leaks should be reduced to a minimum.

Thermal comfort and passive construction

In order to achieve these criteria for an optimal thermal comfort, passive constructions comply with the following principles:

• An excellent insulation of the outside envelope of the building to eliminate thermal bridges, which are conducive to mold.
• Windows with excellent thermal performance.
• An airtight envelope to avoid humidity and heat loss.
• A mechanical ventilation with heat recovery.

In addition to these basic principles, passive construction shares the principles of bioclimatic construction, which takes into account environmental factors: orientation of the house to take advantage of solar gains and avoid cold winds, favouring south-facing glazing, favouring vegetation with deciduous tree for better sunshine exposure,…

Heat in a passive house

To be certified Passivhaus, a building must have a heating requirement less than or equal to 15 kWh/m² per year (i.e. 4 to 10 times less than for a traditional house).

In traditional buildings, the large temperature difference between the walls and the windows systematically implies the installation of a heater under the window for better thermal comfort. By favouring high-performance thermal insulation and the installation of high-performance windows, passive buildings considerably reduce the need for heating. 

Within a passive housing located in a country with a Mediterranean climate such as Portugal, the heat distribution by dual flow ventilation, the heat provided by internal gains (human heat, cooking, domestic appliances) and solar gains generally compensate for heat loss.

Note that depending on the climate, when temperatures are very low or when the house is unoccupied for a long period of time, these heat gains may not be sufficient. In this case, it is possible, for example, to couple the mechanical ventilation to a heating battery powered by a heat pump.

One of the advantages of passive construction is the stability of thermal comfort in summer and winter.