Recently it has been pointed out that there is a wide range of problems with the indoor climate in low-energy housing. People experience that their houses are too cold in the winter and cannot be heated due to undersized heating systems. At the same time the houses often get too hot in the summer due to uncontrollable and inconveniently large energy supplements through the south-facing windows.

Aside from the lack of common engineering sense, often the reason is that the buildings are built on the basis of energy and indoor climate calculations where the house is considered as one large zone. In that way the calculations cannot show that it gets too hot in rooms with the south-facing windows and too cold in north-facing rooms where the radiators are not big enough. Furthermore, the calculations are often made in the simplified calculation programme Be10 (the former B06), which is inappropriate as it is an energy rating tool and not a design tool.

The approach from low-energy office buildings can with advantage be transferred to residential housing, as office buildings do not seem to have the same problems. Far more detailed calculations of the indoor climate are often carried out at the planning and designing of office buildings and this is an important condition for achieving good indoor climate.

Documentation of the thermal indoor climate of low-energy housing
The problems in low-energy housing could probably have been avoided if instead the calculations had been divided into more zones according to window orientation and room function, and if more appropriate programmes for the indoor climate assessment had been used. In the light of the recorded indoor climate problems in low-energy housing, the last revision of the building regulations has stipulated requirements for a more detailed documentation of the thermal indoor climate of the low-energy housing.

In connection with design and planning of office buildings it is quite normal to carry out more detailed calculations of the indoor climate. Typically, it is chosen to calculate specific rooms with different function and window orientation to be able to get a picture of the expected indoor climate in the completed building. This is not to say that indoor climate problems do not occur in low-energy office buildings, and it should be noted that there are no major indoor climate surveys of low-energy office buildings in the same way as it is the case for low-energy housing.

Office buildings with great indoor climate
Company House III (COM III) was built near Kolding in 2008 and is an office building of approx. 5,000 m². From the start of the construction focus was brought on building low-energy offices in the highest indoor climate quality. The building was built by NCC Property Development with C. F. Møller as architect, ALECTIA as consulting engineer and NCC Construction as contractor. ALECTIA moved in as tenants in COM III in 2008 and after some initial challenges with the ventilation system the indoor climate has been very good, and since then there have been no complaints from the users.  

The objective of the COM III building was to obtain the then low-energy class 2 and a thermal and atmospheric indoor climate in class 1. In connection with the building works the density of the building envelope was measured with a “blower-door” test, and the specific ventilation unit power consumption for air conveyance (SEL) was measured in order to find the maximum air volume of the building. It appeared that both ratios were significantly lower than assumed in the planning, which was a result of the great focus from all parties on building in low-energy standard. As regards the calculations, COM III complies with the energy frame for low-energy class 1, and in that way indoor climate class 1.

The relation between the calculated and the actual energy consumption
One thing is the calculation based on energy key figures measured under ideal conditions, various standard assumptions and empirical figures. Another thing is the actual measured energy consumption, which is dependent on general execution, specific weather conditions and, not least, user behaviour. ALECTIA has therefore procured the measured energy consumption of the building from 2010 and compared it to the calculated energy need.

The total energy consumption measured for COM III is 7 % higher than the calculated energy consumption when it is adjusted according to weather conditions, etc., and this must be described as a satisfactory result. It should be noted that there is a substantial deviation on the individual energy items, and therefore the overall result largely reflects the fact that what is lost on the roundabouts is gained on the swings.