Public Health England estimates that air pollution is responsible for between 28,000 and 36,000 deaths a year, costing the healthcare sector £20bn annually. Combined with the increasing requirements for air-tightness in architectural design, it’s clear that a whole-building approach to HVAC is needed.
Shockingly, we spend around 90% of our time indoors. With this in mind, it’s crucial that building occupants have access to a healthy, clean and pleasant internal environment - free from pollutants, allergens, odours and water vapour. There are numerous factors that contribute to the creation of a comfortable internal environment, including lighting, humidity, cleanliness, temperature and fresh air. Ensuring that all these factors are considered within the building design, with a suitable level of control also enabled, is key.
In many ways, effective ventilation is the cornerstone of achieving this well-balanced internal environment. Put simply, ventilation works by removing stale indoor air and replacing it with ‘fresh’ outdoor air. It also helps to extract water vapour, airborne pollutants and odours and control humidity.
Although opening a window may, on the surface, appear to be an equivalent solution, it is not always possible – particularly in modern high-rise buildings – and actually, it can do more harm than good, allowing polluted air from outside to enter the internal space.
If a ventilation system is to succeed in its role of improving indoor environment quality, it must be designed to provide both sufficient fresh air supply and extraction. Only then can it minimise moisture build-up, deal with bio-effluents (body odour) and keep exposure to NO2, CO and VOCs to a minimum.
When approaching a system design that takes all of the above factors into account, it is important to refer to the relevant building regulations. In the UK, ventilation design is controlled by the Building Regulations Approved Document Part F, which sets out the criteria for both homes and ‘non-domestic’ buildings – primarily offices. Building ventilation also has to comply with a number of British Standards, covering energy performance, filters and maintenance.
As part of a wider HVAC system, ventilation must comply with Approved Document Part B (fire safety), Part C (site preparation and resistance to contaminants and moisture), Part E (resistance to the passage of sound), Part L (conservation of fuel and power), Part J (combustion appliances and fuel storage systems) and Part P (electrical safety).
Fortunately, there is also a wide range of ventilation guidance available, published by industry bodies including the CIBSE and the Building Research Establishment.
Of course, no building is the same and so it stands to reason that different buildings will require different levels of ventilation, and for different reasons, depending on its function. For example, when designing a ventilation system for a domestic house, the required ventilation rates are dependent on the number of bedrooms, from 13 l/s for a one-bedroom home to 29 l/s for a five-bedroom property.
In comparison, the total air supply and extraction rates for office ventilation (assuming there are no significant pollutant sources) is generally 10 l/s per person. Intermittent extract ventilation will also be required for specific areas, including toilets, showers, printing or photocopying rooms and kitchen areas.
When designing ventilation for healthcare environments, such as hospitals, it is important to also refer to Approved Document Part F: Health Technical Memorandum 03-01, published by the Department of Health. Of course, some healthcare environments, such as operating theatres, critical care areas and isolation units, will have additional ventilation requirements, in order to prevent the spread of infection.
As well as the design and placement of the ventilation units inside a building, it is also important to carefully consider the placement of ventilation intakes and exhaust outlets outside. If placed incorrectly, they could negatively impact the performance of the ventilation system and the indoor environment quality, with the potential for pollutants to enter the interior space.
Ventilation intakes must be placed as far away as possible from the main sources of local outside air pollution, such as road traffic. For HVAC systems, this typically means on the roof of the building, unless there are higher-level pollution sources. Alternatively, air intakes can be installed on walls, in courtyards and in atria.
It is equally important to avoid cross-contamination from boiler flues. Exhaust stacks should also be placed as far away as possible from the ventilation intakes, preferably at a higher level, and also downwind. They should not discharge into courtyards or other enclosed spaces and it is recommended that they discharge vertically, to avoid downwash.
With ventilation having such an active and crucial role to play in delivering a pleasant, clean and healthy internal environment for occupants to enjoy, designing the system correctly and in accordance with the relevant Building Regulations and industry guidance is essential. Effective filtration measures and a regular programme of servicing and maintenance are also important to ensure the system continues to perform as intended.