The energy and environmental specialist company Cenergia has in March 2003, in co­operation with the companies Borry Henriksen ApS and the architects Thure Nielsen & Rubow, built a small 32 m2 mobile low-energy wood house with paper granulate insulation from the company Ecofiber and with a 80-85% efficient heat recovery unit from EcoVent.

A new thing is that the wood construction system has been constructed in a way to make the house completely airtight and without cold bridges. Monitoring tests of air leaks of the house have shown the leaks to be so small that they nearly cannot be measured by Cenergia’s "blower door test” equipment. Besides a thermo photography shows that there is in fact no cold bridges at all.

For the first time in Denmark there has, in connection with this project, been used a structural principle introducing a wood concrete plate / rabbet unit with a diffusion open membrane which according to Borry Henriksen makes the construction completely secure as to humidity. Built-in humidity sensors has been used to substantiate this. The paper granulate insulation of the house has been incorporated as to set the wall insulation in contact with the roof insulation, this has been done due to the settling of the insulation granulate.

The test house was built at the Ganlose Sawmill near Copenhagen where they also manufacture weekend cottages.

For the test house there has been used an improved level of insulation even comparing with the new EU-Energy Performance Directive for Buildings, EPD which is expected to be introduced in Denmark in 2005/2006, with an improvement in the level of insulation of approx. 33% as compared to the insulation level of today. Further energy windows, from the companies Velfac and Velux, have been used, and as regards ventilation a high — efficient heat recovery ventilation (HRV) unit with a width of 20 cm only, was placed in a partition wall. The electricity consumption of the HRV unit is very low with only 20-30 W, compared to building regulation demands of maximum 87 W.

The heat recovery ventilation unit requires only short channel elements in order to take air in and out of the house as well as a short air intake channel in the house. Thus the installation price of the heat recovery ventilation unit can be kept at a low level, and at the same time a balanced ventilation can be obtained with a good indoor climate.

On the metallic roof facing south PV modules are installed. This system has been developed by the Finnish manufacturer Rannilla, in such a way that the intake air is directed into a gap under the total roof so a solar heating of the ventilation air is possible. At the same time the idea is that the PV modules (about 13 m2) produce electricity which on a yearly basis makes the house CO2 neutral as regards heating and ventilation.

With the chosen level of insulation and other qualities mentioned the low-energy wooden house can simulate the function of a somewhat larger house according to the "house without heating system” concept which has been used with considerable success for example in Gothenburg in Sweden.

This means that we do not require a usual heating system but require only a very small heating supplement to the house via the ventilation air (max. 900 W for a 100 m2 housing unit). This can for example be achieved by help of a small “mikro” heat pump which together with a solar DHW system can supply the domestic hot water.

Testing of a heat pump solution for the house will be completed during 2004.