The Role of Ventilation in Achieving Indoor Air Quality Standards

The Role of Ventilation in Achieving Indoor Air Quality Standards

By Ruth MacEachern

Product Manager

As we continue our detailed look at indoor air quality standards, we will now focus on the role of ventilation in achieving indoor air quality. In this article we will first consider the principles of ventilation. We will then summarise the different types of ventilation system, considering the benefits and potential drawbacks of various systems.

Ventilation and indoor air quality – the key principles of ventilation

A report drawn up by the Canadian Centre for Occupational Health and Safety, but one that is also relevant both to the UK and to residential properties, highlights four purposes of ventilation:

1. Provide a continuous supply of fresh outside air.
2. Remove or dilute airborne contaminants.
3. Reduce potential fire or explosion hazards.
4. Maintain temperature and humidity at comfortable levels.

Often an afterthought when designing a building, ventilation plays a key role in ensuring that a building provides a safe and pleasant home for its occupants. With government regulations imposing increasingly strict requirements on ventilation, air flow, and air quality, careful advance planning of building ventilation is now more important than ever.

How ventilation works – 2 operating principles

Ventilation systems work according to 2 main operating principles…

• Circulation - if air is allowed to remain still for a prolonged period, it begins to separate into layers; a process known as stratification. This can affect the temperature and composition of the air and can cause shortages of critical gases such as oxygen. By ensuring a continuous flow of air from one room to another, an effective ventilation system can prevent this phenomenon, while also avoiding the build-up of bacteria and allergens.
• Air exchange – while similar to the principle of air circulation, air exchange involves the introduction or fresh external or filtered air. The air flow generated moves the air within the indoor space in the same way as circulation, but also enables the cleaning of the exchanged air and the regulation of the air temperature and humidity at the point of exchange.

Different types of ventilation system – benefits and drawbacks

Whole-House Systems

As the name perhaps suggests, whole-house systems require significant advance planning and should ideally be installed during construction, rather than being retrofitted at a later date. Here we will highlight three such systems…

1. PIV (Positive Input Ventilation) – this popular low-energy ventilation solution can be retrofitted without major renovation work. A single unit, often installed in the loft, draws in fresh air via a system of ducts. This air is passed through a filter in the unit before being fed throughout the home. The drawback here is that the ventilation is not as effective as other whole-house systems and there is no option to control the temperature of the filtered air.
2. MEV (Mechanical Extract Ventilation) – this system requires significant advance planning (duct routing, dimensioning of the system) and cannot be so readily retrofitted. It offers an effective solution that can be fitted and then forgotten about, with no need for monitoring or the adjustment of settings. One concern when replacing stale indoor air with air from outside is heat loss. For a detailed look at heat loss as a result of ventilation, consult our article.
3. MVHR (Mechanical Ventilation with Heat Recovery) – this system replaces the extracted air with heated and filtered outside air, thus offsetting home heating costs and improving indoor air quality at the same time. These systems can be adjusted and configured to suit the conditions in and around the building. They require that the home be made as airtight as possible, thereby also reducing the ingress of noise and pollution, and avoiding unnecessary thermal emissions. One potential drawback of ventilation systems that run continuously is that of running costs. With an MVHR system, the heat recovery compensates for this potential drawback. An article discussing the running costs of ventilation systems is available here.

Targeted Systems

There are a number of inexpensive and easily installed solutions that provide targeted ventilations in rooms with high levels of humidity or high occupancy levels. These include extractor fans and oven hoods, window trickle vents, and through-wall vents. While these offer the ability to target specific rooms while keeping financial outlay to a minimum, they are naturally much less efficient with regard to improving overall air quality within a building and are also susceptible to heat loss. Information on extractor fans and vents can be found in our article on ventilating rooms without windows.

New government targets and regulations governing air flow and indoor air quality in new dwellings mean that ventilation is a subject that house builders and developers simply must get to grips with. If you require further information regarding which solution would best suit your construction project, or how to ensure compliance with regulations, consult our online articles or feel free to contact our team of experts.