Comfort level measurement in Hannover

Comfort measurements were made in 32 apartments. Twelve of them had been refurbished to a higher level of energy efficiency (with Passive House components). The following parameters were measured: air and radiation temperature, vertical temperature distance, radiation temperature asymmetry between interior und exterior walls, air humidity, air velocity and turbulence, and CO₂ concentrations in the indoor air and surface temperatures at the coldest point of the exterior walls.

The evaluation of thermal comfort was based on DIN EN ISO 7730. This standard describes a procedure to determine the PMV and PPD indices: the Predicted Mean Vote of thermal comfort and the Predicted Percentage Dissatisfied. (rated over a large group)  The results show that all apartments lie within the PMV limits of category B, a medium expectation value.

The analysis verified that the operative temperature, radiation temperature asymmetry, vertical temperature difference and measured air velocity are within the comfort limits for all apartments.

Relative humidity is important for people's health and the comfort. Mite infestation and the danger of mould are especially important factors, and these are strongly influenced by high interior humidity values. A critical situation can be recognised by measuring surface temperatures at the coldest point together with the room temperature and indoor air humidity.

In some apartments (11% of the total) the admissible surface temperature of external walls fell below the critical limit over a long period. One of the reasons for this critical situation can be thermal bridges, which are difficult to avoid in retrofitting and can lead to low temperatures on the indoor surfaces of external walls.

Another reason may be lower ventilation frequency by apartment residents. In line with results from other projects, our results show that user behaviour strongly influences indoor air humidity. With regular ‘shock ventilation' (brief but thorough airing of rooms), low humidities can be achieved even in apartments without a mechanical ventilation system. However, tenants who go out to work often cannot meet these demands.

In the buildings retrofitted with Passive House components (including ventilation systems) only one apartment reached a critical point over a long period, the reason being that the ventilation system was not in use.

The CO₂ concentration in a room is a good indicator of ‘fresh' air. It is a recognised fact that there are fewer complaints about tiredness, lack of concentration etc in well ventilated rooms with a low CO₂ concentration. The collected data on CO₂ concentrations exhibit very clear diurnal variations. Through the presence of people the CO₂ concentration in a room increases; it rapidly decreases with ventilation. If a room is not ventilated after the person has left the room, the CO₂ concentration only decreases slowly through exfiltration. Nevertheless, a quantitative statement on this connection was not possible (but is plausible) as the presence of people could not be verified.

EN 13779 sets limits for CO₂ concentration at 1.400 ppm for medium indoor air quality. The average CO₂ concentration in the apartments (which was not exceeded for 90% of the measurement time) was approx. 1.600 ppm for the apartments retrofitted to EnEV new build standard. For apartments retrofitted with Passive House components and a ventilation system (when in use) the average value was approximately 1.300 ppm.

As a result, the evaluation shows that all apartments complied with the set comfort limits. In some apartments, however, increased indoor air humidities and higher CO₂ concentrations were measured.