Investigation of EPC, Ventilation, and Indoor Temperatures
Aside from energy matters, the investigation gave insights in several other aspects that are linked with indoor climate and how well laws are followed. In terms of law, every multifamily building in Sweden should have:
• A valid EPC certificate that shows the performance of the building and has suggestions on how this can be improved. The performance is usually based on energy bills and an audit. All buildings should have the certificate since 2011.
• A valid certificate from a mandatory ventilation inspection (OVK) where ventilation flows and function is checked. The law was enforced in 1992 after that a large investigation of the building stock showed that residences in general had too small ventilation rates, thereby creating a poor indoor air quality.
• Building codes have for decades stated that residences must be ventilated with fresh air corresponding to at least 0.5 ACH.
According to the top left display in Fig. 8.3, one of the 11 buildings does not have a valid EPC. Moreover, only five buildings have approved OVK. This may have consequences for ventilation statistics.
Fig. 8.3 Top left: number of approved EPC and OVK certificates for the 11 buildings. Top right: indoor temperatures measured for 2 weeks in an apartment of each building. Bottom left: measured air change rates per hour (ACH) in each apartment. Bottom right: measured air tightness—the unit is the air flow (liter per second) through the envelope area at 50 Pa pressure difference
Assessment of ventilation, temperature, and air tightness results in Fig. 8.3
• Ventilation rates are often too low in apartments, on an average 0.41 ACH.
• Mean indoor temperatures are within authority (Public Health Agency) recommended ranges (20-24 °C) (2005) but can for various buildings be reduced since the mean value for all is 22.3 °C. A comment on building 10—the tenant was visiting the hospital for a longer period and lowered the indoor temperature when away.
• Air tightness of envelopes is dependent on construction type, with wood/timber frames being most leaky. As a reference value, older building codes had requirements on maximum 0.8 l/(s m2). Buildings with masonry or concrete frames (0.8 l/(s m2)) are more airtight than buildings with timer or wood frames (1.9 l/ (s m2)). However, there is no clear correspondence between ventilation rates and envelope air tightness in Fig. 8.3.