Building Bulletin 101 ‘BB101 Guidelines for ventilation, thermal comfort and indoor air quality in schools – your technical questions answered
As the amended Building Bulletin 101 ‘BB101 Guidelines for ventilation, thermal comfort and indoor air quality in schools regulation’ reaches its final stage, Jaga has provided insights into the new regulations for education design consultants. As a follow up to this, Jaga has also provided responses to the frequently asked technical questions on what the amended regulations mean for the heating and ventilation of schools.
In the new regulations, why are CO2 levels now measured at specific heights in a classroom?
It is critical that CO2 levels are measured at the point at which most people will be breathing in the air. It has been recommended that design consultants place sensors at seating height, which is 1.1 metres for primary school pupils and 1.4 metres for secondary school pupils. If consultants are unsure during the design stage whether the school will be used as a primary or secondary school, it is best to position the sensors at 1.1 metres because CO2 is heavier than ambient air. It is critical that sensors are positioned in the correct place to ensure that pupils are working in an environment with good Indoor Air Quality (IAQ).
What is the motivation behind keeping the surface underfloor temperature below 26 degrees in a classroom?
If the surface temperature of the classroom floor is higher than 26 degrees and a teacher is stood on this floor for an average of seven hours each day, it can lead to discomfort in the ankles and feet. In the guidance document it recommends that the overall user comfort is heightened wherever possible to improve the health and wellbeing of teachers. Supplementary heating systems are recommended to keep the room temperature at a comfortable level.
Does the amended BB101 guidance document define the ventilation recommendations for breakout and communal school areas?
In the amended document, there is minimal information on the exact requirements for breakout spaces versus the information for classrooms. What it does highlight is that the quality of the air shouldn’t be defined by the level of CO2, temperature and classroom occupancy. Instead, it recommends that the air quality in breakout spaces is measured by looking at the air volume per cubic metre for the space.
Is the prescribed external CO2 concentration of 380 parts per million (ppm) used in a school regardless of its location, or does this vary?
In the document it only lists the one concentration of 380ppm, however this is something which we think could have been developed further in the document. Schools located in rural areas would be expected to have a considerably lower level of CO2 than those located in urban areas. Although higher external CO2 levels will not necessarily effect the internal CO2 concentration limit, it will mean that the ventilation system will have to work harder to bring in more air.
Can occupancy heat gains be used to offset ventilation heat losses in winter?
The heating of incoming air is something which must be considered in a school environment. If a demand controlled ventilation (DCV) strategy isn’t used, then a minimum of three litres per second, per occupant would need to be included into the heat load calculation. However, if a demand (DCV) strategy is used then this requirement is waived, as it is assumed that the ventilation won’t be running until the room is already up to temperature and occupied. This means that the designer will only need to take into consideration the fabric loss, not the ventilation loss. This could result in a reduced operating cost of the heating system and a reduced capital cost as the heating system doesn’t need to be sized quite as large.