Photo: Sami Heiskanen

General ventilation guideline to harmonise best practices in municipalities

Indoor air experts in the largest municipalities in Finland have drafted a general ventilation guideline for public service buildings. The goal is to improve the quality of indoor air and develop and establish harmonised methods based on research data.

Helsinki is part of the network of experts responsible for the drafting of the general guideline. The guideline is a recommendation, which means that each municipality can decide how they want to observe it.

In Helsinki, the plan is to present the guideline to the Urban Environment Committee and comply with it. In practice, this means that ventilation systems will be monitored and adjusted more actively in schools and daycare centres, for example. Overall, the guideline will not cause any significant changes to the methods of the City of Helsinki.

Adjusting ventilation systems is important

The City of Helsinki owns approximately one thousand service buildings. Their age, purpose of use, condition and technical systems vary greatly.

The core objective of the new instructions is to have the ventilation in each building operate in the best way possible in the revailing conditions. Air flow must be adjusted so that the pressure difference between indoor and outdoor air is as small as possible. This prevents harmful substances from entering the indoor air.

The guideline also points out that the temperature of inlet air should be two degrees lower than the target temperature of indoor air in order for inlet air to mix with indoor air more efficiently.

Thus far, the air flows of ventilation systems have not been measured and adjusted methodically in Helsinki each time after cleaning the system. This means that following this guideline will improve the current situation. Adjusting air flow is also important after sealing repairs have been performed on buildings.

Turning the ventilation on at the right time

In 2018, Helsinki City Council discussed a proposal (in Finnish) aimed at running ventilation in schools and daycare centres 24 hours a day. In its general ventilation guideline, Kuntien sisäilmaverkosto (the inter-municipal indoor air network) states that if the ventilation system functions well and is efficient, it is only necessary to run it when the building is in use.

In order to flush out any impurities from respirable air, the guideline recommends that daily ventilation be started two hours before the users of the building enter it. Ventilation should be kept running for 1–2 hours after the users have left the building.

“This is what we have been doing in Helsinki for at least 25 years now. Adapting the use of ventilation to the hours of use of the building generates significant savings in energy consumption and reduces the carbon footprint of buildings. However, the city will never compromise on ventilation for the sake of savings; the primary goal is always to ensure healthy respirable air,” says Sari Hildén, Built Property Manager.

Constant ventilation is needed in some buildings

Some buildings need continual ventilation at all times. If the building has water damage or microbial contamination, ventilation should be kept running at all times, as long as the supply or exhaust air flows have first been measured and balanced, if necessary.

When a building suffers from water damage or microbial contamination, the task of indoor air experts is to assess the effect of the ventilation system on the situation and decide on the best operating times for ventilation. This is the current procedure in Helsinki.

In addition to this, the network of experts recommends that ventilation be kept running continuously in newly-completed buildings for one year in order to flush any of the emissions from new materials out of the indoor air. This, too, has been standard operating procedure in Helsinki for years now.

The inter-municipal indoor air network is growing

The inter-municipal indoor air network was in charge of preparations for the general ventilation guideline. It is a network of experts established in 2018 to promote better indoor air quality in municipal buildings. The network looks for solutions and operating models to prevent and overcome issues with indoor air quality.

Founding members of the inter-municipal indoor air network include Helsinki, Espoo and Vantaa. New additions to the network include Lahti, Jyväskylä, Turku, Oulu, Tampere, Kuopio and Sisäilmayhdistys ry (the indoor air association). This year, Porvoo also joined the network.

Experts from Sisäilmayhdistys ry, other municipalities, research institutes, universities and consulting companies from the field of indoor air also participated in drafting the general ventilation guideline.

The guideline was published on 14 March 2019 in connection with the ‘Hyvä Sisäilma’ (good indoor air) recommendation by Sisäilmayhdistys.

Additional information (in Finnish):

Kuntien sisäilmaverkosto: palvelurakennusten ilmanvaihdon yleisohje ja perustelumuistio