Welcome BB101 (2016)
Published: 02 June, 2016
Major changes in the legislation for ventilating schools are imminent. Gary Morgan of Eco-Airvent helps readers update their understanding.
With the final consultations now completed, the long-awaited BB101 2016 ‘Guidelines on ventilation, thermal comfort and indoor air quality in schools’ will soon be with us, so what will change?
BB101 (2016) gives a detailed holistic approach to the internal environment in schools with a greater emphasis on energy efficiency. It) will be the benchmark for at least the next five years.
Working in tandem with BB93 ‘Acoustic design of schools- performance standards (2015)’, which outlines regulations relating to acoustic requirements for ventilation, it’s the largest fundamental change in schools ventilation legislation in 10 years. While not being too prescriptive, to allow designers to use innovative energy-saving solutions, it does offer a better framework to steer sensible choices for building-services equipment.
All ventilation systems must have the capability to operate in all reasonable UK weather conditions — including high winds and rain! Final ventilation designs will depend on the following main factors.
• Building location
• Type of construction
• Levels of noise ingress
• Local air quality/levels of pollution
• Amount of glazing/solar gains
• Patterns/types of use.
Life-cycle costs should be calculated so the long-term overall running and maintenance costs of any ventilation system are known.
Summer over heating is a major factor in school design, and reference to CIBSE TM57 is advised to correctly model schools.
Where possible, good natural cross ventilation combined with a night cooling strategy is recommended, especially where appropriate building thermal mass is present, to maintain acceptable internal room temperatures during the summer months.
Natural ventilation from high-level windows in atria or roof vents combined with lower level windows and/or wall mounted louvres with dampers should be considered.
Consideration must now be given to ‘air quality’ and meeting ‘National air quality standards’ as a direct result of the alarming report from the Royal College of Physicians ‘Every breathe we take: the lifelong impact of air pollution’ (February 2016).
Designers planning to build schools in air-quality-management areas or low-emission zones will have to give careful thought to internal pollution and how it can be maintained at acceptable levels.
Air filtration is the most cost effective solution currently available to reduce harmful particulates entering the building. Full mechanical-heat-recovery ventilation would need to be employed if air filtration is used while still aiming to achieve BB101’s low energy requirements for ventilation equipment. Areas with high air pollution from traffic may want to consider local road closures or diversions adjacent to school so other forms of unfiltered air ventilation, including natural ventilation, can be used.
Where mechanical heat recovery is to be used, the thermal-efficiency requirement needs to satisfy a minimum air-supply temperature differential of not more than 5 K lower than room design temperature in UK winter conditions. Designs using higher thermally efficient heat recovery units to further reduce energy consumption in winter often incur little additional capital cost.
Recognition is given that space-heating costs can be reduced by the correct design and installation of complementary low-energy ventilation solutions. Building tightness has also been recognised as an important energy-reduction factor in Part L, so most notional buildings are now designed at far lower air-permeability levels than the maximum allowable.
Ventilation represents a significant part of the of the total space-heating load, particularly in new-build schools with low fabric heat losses. Heating incoming air can represent 20 to 50% of a building’s thermal load, so it should be reduced as far as practically possible. Outside air entering the building in the winter above the minimum ventilation requirement to achieve good air quality represents wasted energy.
Using internal heat gains and existing space-heating load to temper incoming air to the minimum air temperature via a ‘mixing box’ is widely advocated for new-build schools; however careful design is needed to ensure satisfactory results are achieved.
Beware of claims of ‘heat recovery’ from some less well informed quarters as this type of system usually lacks a heat-recovery function — room air is mixed with fresh outside air via fans. BB101 (2016) recognises that mixing outside air with internal warm air in the winter is far better suited to highly insulated new schools than refurbishment schools that have generally higher fabric heat losses.
Refurbishments using mixing-box systems will often have substantial additional energy use for electric/gas heater batteries as the ‘balance point’ for the building’s external temperature can be as high as 15°C to maintain classroom comfort temperatures in the winter. BB101 (2016) states, ‘After refurbishment the criteria should not be worse than before refurbishment in any aspect affecting thermal comfort.’
Minimum energy usage levels are set for ventilation systems using the ‘Non domestic building services compliance guide’ for installed performance specific fan power (SFP, expressed as W/l/s).Experience shows that by using well designed ventilation equipment, these energy levels can be considerably improved to achieve SBEM compliance for the building as a whole — often reducing overall capital and running costs.
Trying to scrape through compliance is a risky strategy because if actual overall energy use for the building does not meet with design compliance levels then additional costly remedial works will normally be required.
In a recent example, a new-build school failed to meet its design air-tightness target.Fortunately , better performing ultra-low-energy heat-recovery units with an installed performance specific fan power of 0.7 W/l/s had been selected against the design level of 1.6 W/l/s — allowing the school to comply with the building’s energy regulations without additional air-tightness repairs.
Gary Morgan is director of Eco-Airvent. He is a member of the advisory board to the Education Funding Agency for BB101.