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Starting already 1950 i.e. for more than 60 years back in time – we have been using a probably quite unique quality assurance system in Sweden covering all aspects of building and installation technologies. Practically all buildings and their installations are performed according to the quality requirements in the AMA specification guidelines (General Material and Workmanship Specifications). The AMA requirements are made valid when they are referred to in the contract between the owner and the contractor.
The HVAC-part of AMA included requirements for tight ventilation ductwork systems already in the early sixties. Sweden has thus a long and unbroken tradition of demanding tightness of ventilation ductwork. During this long period, since 1966, the AMA tightness requirements have been raised in tact with technology improvements and increased energy costs.
But requirements and demands can be worthless unless they are controlled. The AMA requirements thus also include demands for tightness testing of the ductwork. The result of the tightness test has to be reported on standard protocol forms signed by the testing contractor.
And this has been shown to be very effective in raising the quality of ductwork. As e.g. shown in two EU-projects this long time focus on ductwork quality in Sweden has resulted in very low air leakage in normal Swedish duct installations.
And there are several reasons that justify the requirements for tight duct installations:
- Many studies have identified defective ventilation systems and insufficient airflows as a main reason for occurrence of sick buildings - the supply air needed to assure a good air quality should thus reach the areas where it is needed and not disappear along its transport through the building.
- The supply air flow has to cover the sum of total nominal air flow and the leak flow. With leaky ductwork this will lead to a considerable and costly increase of the needed fan power.
- Duct leaks can result in disturbing noise.
- When leaky supply and extract air ducts are installed above a false ceiling part of the air will take the simplest way, from the supply duct direct to the extract duct without bothering to pass through the connected rooms.
Swedish industries, building owners and authorities work together with the object to increase the quality of ventilation systems. Parallel with the voluntary AMA demands (i.e. voluntary until the contract has been signed) Swedish authorities 1991 thus started a compulsory system for ventilation control (OVK) in Sweden with aim to control and improve the function of ventilation installations. According to the ordinance (1991:1273) a control of the ventilation in most types of buildings has to be made before the installations are taken into operation and then regularly at recurrent inspections.