Implementing Quality Metrics in Ventilation Projects

Implementing Quality Metrics in Ventilation Projects

By Ruth MacEachern

Product Manager

How to use quality metrics effectively to track and improve ventilation project outcomes.

The key piece of legislation governing ventilation and air flow in domestic dwellings in the UK is Approved Document F, Means of Ventilation. An amendment introduced in June 2022 (2021 Edition) stipulates new requirements regarding design air flow rates and their documentation. Measured in litres per second, the Approved Document specifies air flow rates for various types of ventilation system, and for various rooms within a dwelling. Whole dwelling ventilation rates are also specified based on the number of bedrooms or floor area of a dwelling. 

While maintaining regulatory compliance is certainly a key motivating factor, the ultimate goal in our effort to improve indoor air quality is to ensure the health, comfort and wellbeing of a building’s occupants. Airflow measurements are required to be recorded on the commissioning sheet for submission to building control, however, when it comes to quantifying indoor air quality, Approved Document F offers guidelines rather than stipulating requirements. This is due to the Localism Act of 2011 that allows local authorities to  interpret the Approved Documents on an individual basis, as the minimum standard and provide specialist guidance but then providing an uplift to ensure that standards and best practices are met. These measures are not straightforward, as substantiated by the University of Nottingham’s Benjamin Jones in his round-up of discussions at an Air Infiltration and Ventilation Centre workshop on IAQ: “Indoor air quality is not easy to measure, but metrics must move towards environments that consider occupant health.”

We will now discuss which Indoor Air Quality Metrics can be applied within a ventilation project, and consider the design principles that can be adopted in order to improve the outcome of your ventilation project. 

What are IAQ metrics (Air Quality Metrics)?

A metric is defined as a system or standard of measurement, and so, when we talk about indoor air quality metrics, we are referring to measurements that aim to identify when the quality of indoor air is unacceptable. This assessment should ultimately be based on contaminants' effects on human health and comfort, and so one metric might be to simply ask occupants their opinion regarding the air quality in a building. This may be based on smell, perceived humidity, or the occupants’ general sense of wellbeing in the space. This metric is often referred to as “perceived air quality”. Its usefulness in terms of quality assurance within the context of a ventilation project is naturally limited: whether on account of the subjective nature of human opinion, humans’ inability to smell all harmful contaminants, and people’s propensity to adapt to malodours after a very short time. The fact that it requires subjects to be inhabiting the building of course means that it cannot be used as a quality assurance metric during the planning and realisation of a ventilation installation project. 

There are, however, a number of other metrics that can be measured and the findings applied within the design process for a ventilation project:

• VOC concentration - Volatile organic compounds are a group of chemicals that readily evaporate into the air. They can be emitted from a variety of household products, but also various building materials, and cause a range of symptoms including headaches, dizziness, nausea, irritation of the airways, or in some cases more serious conditions such as cancer. The UK government has published guidance on how to identify and eliminate VOCs from homes, also providing a comprehensive list of VOCs commonly found in domestic dwellings. Measuring VOC levels requires the use of professional devices. 
• Particle measurement – particulate matter refers to a combination of solid and liquid particles such as dust, pollen, ash, dirt, or smoke. Particle measurement is used to determine the size of such airborne particles. PM 10 and PM 2.5 particles measure 10 or 2.5 μm or smaller in diameter, and are therefore inhalable and particularly dangerous to human health. 
• Relative humidity – refers to the level of moisture in a room. High levels of moisture will typically result in mould formation, causing a wide range of respiratory complaints. Relative humidity can be relatively easily measured using a humidity meter or hygrometer. However, rather than stipulating specific limit values, Approved Document F merely states that a properly heated dwelling with typical moisture generation should have no visible mould on the walls and provides a table stating percentage relative indoor air humidity values for various moving average periods, above which it is unlikely that moisture criteria will be met.
• Carbon dioxide and radon levels - carbon dioxide meters and radon detectors will show you whether the levels of these gases have reached a level that could potentially be harmful. This is the only way to be sure that these gases are not having a detrimental impact on the environment or occupant health, as they cannot be detected by human smell, and damage to health is usually gradual.

Some studies have called into question the relevance of some of the quality metrics identified above, for instance regarding VOCs, whereby VOCs are often grouped together producing highly elevated and misleading values, in spite of the fact that there exist more than one million volatile organic compounds (VOCs) with unknown toxicities. Added to this is the fact that many of these contaminants are produced as a result of detrimental practices on the part of the building occupants, such as smoking or the use of aerosols. These reasons perhaps contribute to the fact that UK Building Regulations issue guidelines on the measurement and control of airborne contaminants in new build projects, rather than rigid rules and regulations. However, they can provide an effective means by which to ensure that a chosen ventilation system is appropriately dimensioned and correctly installed. Furthermore, many of the devices used to measure these metrics are simple, handheld units. Consequently, the benefits of quality metrics with regard to ensuring compliance and safeguarding occupant health far outweigh any doubts regarding their effectiveness or relevance.