Summary and conclusions, Miljøstyrelsen

Natural Ventilation in School Building

Summary and conclusions

The aim of the project presented in this report is to construct a public building with low environmental impact, based on ecological materials and optimised indoor climate.

By choosing ecological indoor environment-friendly materials, a substantial obstacle to the application of the natural ventilation principle was eliminated: The emission of gases from building materials and furniture.

As a pilot project including new features, among others an advanced natural ventilation principle, the use of maintenance reducing ecological materials, constructions and furniture, it was accepted that the costs might exceed the costs normally accepted for traditional buildings, because the overall economic requirements, including expenses for maintenance and running, are expected to be lower.

Materials and indoor climate

One of the major barriers to thorough analyses and choice of ecological materials is the lack of documentation and classification of the ecological products. Alternative materials are to a great extent targeted towards private households. Thus, the lack of documentation of strength, the demand for an up-to-date building process with time limits and guarantees, contributed to the rejection of materials and constructions - as was for example the case with unburned clay tiles.

By regarding the whole building as a contributing element in the realisation of the optimal indoor environment, additional requirements were made, which caused further restrictions of possible solutions.

One example of these considerations is the accumulation of heat and vapour: Because of the function of the building in the optimisation of the indoor climate and the accumulation of heat and vapour, a heavy brick building was chosen, and not a wooden building: and red tiles with documented low energy use in production were used.

To minimise the release of dust from materials, maintenance of diffusion openness, light open premises and reduced maintenance, indoor surfaces had to be treated. In the end, diffusion-open ecological materials are not easy to maintain, and therefore it was decided to treat wall surfaces up to the height of reach of children with cleaning and maintenance friendly paints, while wall sections above that height were treated with diffusion- open paint.

Natural ventilation and indoor climate

The use of indoor environment-friendly and ecological building materials opened up the possibility of natural ventilation.

The disadvantages of natural ventilation are unstable rates of air exchange, and, during the winter, draft and heat loss.

By using emission-free materials the air exchange rate requirements were considered less important, and it was therefore possible to establish a natural ventilation principle allowing for a good indoor climate.

It was decided to use the principle of seasonally adapted ventilation., aiming to keep RH percentages between 40 and 60%. In winter the cold air can cause very low RH percentages indoors. In classrooms RH percentages of 10 - 15 % have been recorded at indoor temperatures of 24 - 25 degree Celsius.

By using the seasonally adapted ventilation principle, the air exchange is reduced, thus maintaining the RH at the level intended, and, thus, improving the indoor climate reducing the loss of heat.

The solution to the problems of draft during the winter was found by leading the fresh air through a "ventilation basement", where the air is preheated by the higher temperature of the surrounding grounds.

In classrooms the problem can be too high temperatures during the summer. In other schools it is necessary to ventilate the buildings by night by mechanical ventilation systems, in order to reduce the high indoor temperatures reached during the day. Temperatures above 24 degrees Celsius reduce the learning capacity of the children and may also cause physical nuisances.

In the natural ventilation principle of Sdr Vang School, the ventilation basement is used for cooling the fresh air in summer.

Thus, the seasonally adapted natural ventilation principle developed, serves to aims: To preheat the fresh air in the winter and to cool the fresh air in the summer.

In this building, the ventilation is controlled by the users (except CMS-control in bad weather and outside school opening hours). Each classroom is fitted with control panels, allowing control of individual dampers in the stacks.

If needed, the air exchange can be supplemented by opening of doors and windows in the classrooms, and by windows placed high up on the walls of common areas.

Ecological building, indoor climate and users

A substantial element in the project was the involvement of the users, opening up ideas and solutions that could be used in every day life, improve the users’ consciousness of the building ("make it theirs"), and create the basis for behaviour that goes along with a naturally ventilated ecological building.

For instance the users must change footwear when entering the building, in order to minimise cleaning and reduce the amount of dust.

As opposed to mechanically ventilated buildings, the users in the Sdr. Vang project are strongly involved in establishing a comfortable indoor climate for themselves, and they are able to regulate ventilation air by regulating the dampers in the stacks.

The great user involvement in the control and use of their building has given them a much greater feeling of ownership to the building, which in the end is expected to be reflected in much less vandalism.

Naturally ventilated, ecological building and economic aspects

On the basis of the experiences from the Sdr. Vang project, it is expected that in the future, similar buildings can be built largely at the same m²-prices as traditional buildings.

In the light of the user involvement, the natural ventilation principle, the long life span and the minimised maintenance costs, the annual maintenance and running expenses are expected to be substantially reduced. The estimated costs of energy and water is, thus DKK 43,000 (approx. Euro 5,760), corresponding to about 40% of the costs of traditional buildings of the same surface area of 875 m².

The value of a good working climate, user responsibility and minimisation of allergens, cannot be capitalised, but will be important elements in future projects based on the experience gained in this project.