BB101
Under the new BB101, all the ventilation solutions are driven by some clearly defined performance specifications and guidelines that set key criteria in terms of indoor air quality and comfort, covering elements such as carbon dioxide levels, indoor temperature, draughts and potential exposure to airborne pollutants and noise.
As an overview, the new document defines the following statutory requirements
• CO2 levels in natural ventilation systems must not exceed a daily average of 1,500ppm while an average daily CO2level of 1,000ppm must be adhere to by mechanical systems that use fans to drive airflow.
• If these CO2 limits are exceeded, they can only reach 2,000ppm for a maximum of 20 consecutive minutes during a given day.
The document also includes design guidance with respect to occupant comfort, uses the principle of adaptive thermal comfort to measure overheating risk and recommends the use of sensors to monitor post occupation performance.
Energy consumption is a key consideration in building design. The tendency for buildings to become increasingly ‘airtight’ to reduce heating energy consumption and cost, can also have a impact on the ventilation solution.
Manual or automatically operated windows have long been the most common ventilation method in schools, as they’re cost effective and provide adequate ventilation in most, if not all, situations. During summer months they are highly effective, but in cooler winter conditions, windows are often kept closed to retain heat and maintain thermal comfort, which often results in high CO2 levels, indicative of poor indoor air quality.
A series of studies conducted by SE Controls with a number of schools across the country found that even the levels under the previous BB101 were being exceeded consistently, with one classroom exceeding 7,000 ppm for two hours continuously.
Clearly, the revised criteria in the latest BB101 provides a framework in which all of these factors can be addressed and managed in an integrated manner by allowing the best elements of differing technologies to provide an effective solution.
A hybrid solution
Whilst mechanical and hybrid systems provide enough air to meet indoor air quality (IAQ) requirements, they are often insufficient for cooling and have specific maintenance requirements, including filter changes, which can present a potential risk if they are not kept up to date.
On the other hand, windows and louvres, can supply greater airflow to aid summer cooling but, during cold, inclement weather, the airflow can lead to occupant thermal discomfort. Combining the benefits of windows and mechanical/hybrid systems usually provides the optimum ventilation strategy.
A potentially ideal system would consist of a hybrid mixing box for background ventilation during the heating season, ensuring CO2 levels are kept between 1,000 and 1,500ppm, which is combined with windows to provide ventilation and meet mid-season IAQ demands while also preventing overheating in summer.
Natural ventilation using automated windows/vents provide an important connection with nature for building occupants and ensure they can manage their own environment. Automated windows enable accessible controllers to operate high level vents, in line with Building Regulations Part K and they are also a perfect year round solution for sports and assembly halls with high ceilings, as well as for transient spaces – such as communal corridors – where draughts are not an issue.
Although external air and noise pollution can present a challenge in some locations, the scope of BB101 allows ventilation solutions to be designed around the specific needs and environmental conditions around an individual school’s location, which must be considered during the design process.
However, with a number of major car manufacturers already committing to producing only electric vehicles, by 2040 noise and air pollution issues will diminish significantly. So if the aim is to design buildings to last 60 years – we should consider these future scenarios.
The latest BB101 update has been in development and consultation for well over 12 months and will be a comprehensive update to the previous outmoded standards and guidance, allowing the scope for more intelligent and educated solutions for ventilating school buildings leading to improved internal environments.