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Calculation of relative humidity and temperature in an early stage of the design process is important to avoid moisture damages in wooden walls. Previous studies show that a sufficient air flow in the air gap behind the façade panel is important to ensure a moisture safe construction. This study investigates if blind WUFI 5.0 calculations with a varied air flow in the air gap behind the façade give a better correlation to measured values compared to calculations with a constant air flow. Calculations for two cases are compared to measured values in single family house. The results show that calculations with a wind dependent air flow does not necessary give better correlation to measured values compared to calculations with a constant air flow. However, the calculated values are confirmed with measured values during the warm period and there are deviations in the outer part of the wall during the cold period. Variations in measured values at the same depth in different places in the studied wall are larger compared to differences between calculated values with or without a wind dependent air flow in the façade air gap.

Ventilation of Danish and many other European dwellings has in the past mainly been achieved by natural ventilation or mechanical exhaust systems. Requirements for energy efficiency is changing this picture and mechanical ventilation with balanced exhaust and supply, efficient heat recovery and efficient fans is becoming the standard solution. The building regulation requirement for air change in dwellings is often a constant value that has been chosen to avoid moisture related problems in the indoor environment. This required air change is sometimes sufficient, sometimes too low and sometimes too high. Too low ventilation rate results in poor air quality for the occupants and moisture risk. Too high ventilation rate results in unnecessary energy consumption. This paper presents results from a study where demand controlled ventilation was installed in an existing single family house. In the studied house two control strategies were tested. A simple strategy where all sensors and controls were located in the air handling unit and only the speed of the fans can be controlled, and a complex strategy where sensors were placed in each room and where individual control of air flow in each room was possible. The results showed that the ventilation rate in periods can be reduced significantly without significant increase in moisture or CO2-concentration.