Gamla gymnasiet i Karlstad

History

In the middle of the 1700s there were only a few high schools in Sweden. In the Karlstad diocese there was an elementary school with education for high school proficiency. The school was made of timber and when it burned down in 1752 the church decided to construct a new high school with an observatory on the roof.

The assignment was given to architect Carl Hårleman. He died in 1753 but left behind his signed drawings. When the construction of the building started, his colleague and successor, architect and director Carl Johan Cronstedt had revised and adapted the drawings.

In 1754, construction of the high school was started. The building was completed in 1759. Architect Johan Eberhard Carlberg was responsible for the construction together with senior master, Johan Fryxell. Carlberg is named as the architect that designed Karlstad High School. The special stepped gables are attributed to him. The building has been a state-owned listed building since 1935.

Renovation

The building has been renovated and altered on several occasions due to wear and tear, neglected maintenance and poor masonry.

All major changes to the building were carried out before it was listed as a state-owned historic building. The most recent renovation was carried out in 2005_2006.

Ventilation before the renovation

The building was stack ventilated. The exhaust air rose out via tiled stoves with the help of temperature differences, the stack effect. Replacement air, (outdoor air), was drawn in through leakage between window frames and window casements. However, the ventilation did not function. The brick flues had not been cleaned and had cracks due to settlement damage. Some parts of the flues had disintegrated

Conditions for a renovation of the ventilation system

The building was constructed using the building techniques of the period, with thick stone and brick external walls and with large ceiling heights, which provide good conditions for stack ventilation during the part of the year when the outdoor air is cooler than the indoor air.

During the summer months the stack effect decreases and with that, the exhaust air. The intention was to create a ventilation system that could function year-round. The attic and cellar have always been storage areas and would remain so, and therefore did not require extra ventilation and cooling, which would otherwise be necessary in order to have workplaces there.

Conservation principles

As a listed building, it is required that all walls remain intact. This means that new installations can not be hidden in the walls. The technical additions must then be designed so that the rooms retain their architectural character.

SFV´s cultural heritage unit proposed, at a very early stage in the design process, that the building´s original exhaust air flues should be restored. This, together with the engaged ventilation consultant proposing an automatic window opening system, made the conservation principles quite simple. The only internal ventilation additions were the motors controlling the automatic opening of certain window casements and the visible electrical and computer connections to these. The location of the motors, was an aesthetic conservation issue.

The fact that this automatic window opening system actually was able to be used was due to the window casements having been replaced in the 1920s with connected casements, which were suitable for this solution. If the casements had been original from the 1700s things would have been different. 18th century casements can be very fragile and are not suited for this motorized window opening system.

Ventilation after the renovation

The natural ventilation system has been retained and developed. Air still comes in via gaps in the windows but certain rooms on the second floor have an automatic window opening system.

Exhaust air still rises thermally through the old brick flues. Propeller fans were installed in the flues and are turned on when the stack effect ceases during the warm part of the year. In this way the building has a functioning exhaust air system year-round.

Intake air

Replacement air is drawn in via gaps between the upper part of the window-casement and the window-frame, where there are no draught strips.

Exhaust air

All exhaust air flues were made of brick (in chimney stacks) and in a very poor condition before th renovation. During the survey it was discovered that the flues had very restricted cross sectional areas.This meant that they could not provide the required air exchange for a good indoor climate.

Since the brick flues were to be used for exhaust air they had to be renovated. It was possible to seal some flues with plaster. Other brick flues had partially disintegrated and were too costly to rebuild. Therefore flexible flue liners were inserted, even though this results in a reduced cross sectional area.

Initially, many exhaust air flues served more than just one room; sometimes rooms on other floors. This problem was unable to be solved and instead, attempts were made to minimize the number of shared flues and also ensure that no rooms on different floors were served by the same flue. Fire compartmentalizing in accordance with today´s requirements could not be achieved and the entire building is one fire compartment.

Axial fans (propeller fans) are installed on top of the chimneys. The fans ensure that the building has a background ventilation during the warmer part of the year (March through September), when the stack effect ceases. The fans are turned off in winter. They provide virtually no resistance when turned off and therefore, do not counteract the stack effect.

The original exhaust air grilles have been kept to the extent possible but new ones were manufactured. Behind these grilles control valves are mounted. They are adjusted to provide the correct exhaust air flow since one fan serves all the flues in each chimney.

Since the exhaust air flues only provide background ventilation, the exhaust air in certain rooms must be increased by cross-ventilation via an automatic window opening system.

Intake and exhaust air via automatic window opening systems

In some parts of the building the possible rate of exhaust air via flues can not provide the acquired air exchange for the operation being carried out there.To compensate for this an automatic window opening system has been installed. For every set of windows, one of the uppe casements is equipped with a motor-controlled arm that can automatically open the window casement as much as is needed.

The opening of the windows _ how much and how long _ is governed by carbon dioxide meters that are placed in various zones in the building and also by the weather station on the roof. It has a meter for wind direction, wind velocity,rain and indoor and outdoor temperature. During the summer,cross-ventilation is done at night by the automatic window opening system for cooling the fabric of the building prior to the forthcoming, warm working days.

Experiences

The National Property Board Sweden had an interest in testing an automatic window opening system and the decision to do so has been very successful.

The property´s tenants are satisfied with the ventilation. The air is perceived as pleasant. The tenants have no problem adapting to the building´s conditions. In those rooms with automatic window opening, everyone knows to use paperweights for their papers due to the cross-ventilation.

During the warm summer weeks, extra ventilation at night cools the building. This, in combination with the building´s very thick external walls, has helped to maintain a satisfactory indoor temperature even during extremely hot summers. The thick brick walls assist night-time cooling, which evens out the daytime temperature.

The purpose of the renovation of the building was to retain the original ventilation system and complement it with new technology _ an automatic window opening system _ which is not at variance with the conservation of the building. Consequently, for aesthetic reasons, external air is drawn in through natural gaps. No draught strips are used between the upper part of the window-casement and the window-frame.