Monday, 14 November 2011

CEPHEUS – measurement results from more than 100 dwelling units in passive houses

An EU demonstration project was carried out called CEPHEUS (Cost Efficient Passive Houses as European Standards).14 passive houses with 221 dwellings were built at different sites, with different planners and users and using different construction methods. 11 of these dwellings were assessed in the CEPHEUS project.

All projects showed exceptional low space heating consumption up to 80% less than houses complying with local legal standards valid in 1999. The aim of the CEPHEUS project was to keep the total primary energy requirement for space heating, domestic hot water and household appliances below 120kWh(m2a).

Passive houses offer a cost efficient way of reducing the energy demand of new houses by optimising the efficiency of the building envelope, windows, ventilation system but the heating load cannot exceed 10W/m2 or 0.6ac/h. This is achieved by using modern technologies and designs.
Passive houses rely on superinsulation where U-values usually range between 0.1-0.15W/(m2K). High efficiency heat recovery systems are needed to bring the space heating requirement below 15 kWh/(m2k).

Solar gains are an important source of heating for passive houses. Suitable glazing needs to be selected to minimise heat losses and southward orientation is preferable. Thermal bridges need to be eliminated and windows and frames must have U-value of less than 0.8W/(m2K).

The results presented by CEPHEUS may show some inaccuracies as many dwellings were unoccupied during the measurement stage and continuous measurements over a long period of time are not available for some of these.

The CEPHEUS project measured 11 properties in its study. It determined that for 9 of the 11 projects had air leakage rates between 0.3-0.6h-1.Remedial works could be carried out on the houses that exceeded the limit of 0.6 air changes per hour. Below a video explaining air tightness can be seen.

Space heating consumption varied significantly and this was attributed to different construction types and occupancy levels in the buildings. Given the reduced space heating consumption of passive houses the share of electricity consumption can be higher. The installation of energy efficient appliances is essential and in Hannover an incentive was put in place where buyers were entitled to €2000 rebate if their annual demand was less than 18kWh(m2a).

In all CEPHEUS buildings the mean indoor temperature was above 200C. The mean indoor temperature was below this in some unoccupied dwellings. User comfort is key, and comfortable indoor temperatures are achieved in both summer and winter. CEPHEUS found that users can attain comfortable room temperatures in summer and winter through appropriate ventilation management. Occupancy ratios and shading elements are important during the summer however these are secondary to ventilation behaviour. The cost of heat saved in these projects was 6.2cent/kWh.

CEPHEUS has tested and proven the viability of the passive house concept at the European level. The project demonstrated the functional viability of the passive house concept on all sites, the actual achievement of the space heat savings target, practical implementation of passive houses in a broad variety of building styles and constructions, project-level economic  viability and a high degree of satisfaction of building occupants.

Passive house technology has triggered a fresh burst of innovation in the construction industry and CEPHEUS has made available all experience gained and the key planning tools for the passive house concept.

1 comment:

  1. Interesting article John. The reduction of 80% in space heating requirements is amazing. But I do agree with you that some of the figures found in test like those complete by CEPHEUS are often very impressive and sometimes to impressive. Similar to what Henrik had written in his blog about the concrete build homes, clearly there is some bias in the findings.

    But with that said I would still assume that passive houses would have great energy efficiencies.