The latest draft version of the new BB101 (Guidelines on ventilation, thermal comfort and indoor air quality in schools) was issued in January 2017. It is understood that at least minor comments have been received back by the Education Funding Authority, but no further revision or final draft have been received so far.
New BB101 is much more open-minded about the use of hybrid methods of ventilation. It describes numerous approaches to combining elements of mechanical and natural ventilation in differing proportions according to circumstances. Hybrid methods recognise the advantage of natural ventilation in providing increased air flows during summer time operation, whereas mechanical methods are valued for their contribution in controlling wintertime draught. For example, it is now possible to have mechanical ventilation providing the main fresh air requirement, supplemented by openable windows.
Figure 1: Types of ventilation system
Guidelines for CO2 and VOCs
The goal posts for Indoor Air Quality (IAQ) are now given in terms of average CO2 values in classrooms during the occupied period, defined as between 9 am and 4 pm. This means that periods of low occupancy can be taken into account (i.e. breaks and lunch time periods), as well as those of full occupancy during normal class time. The 2006 approach based on personal requirements (e.g. 5 and 8 l/sec/person) is now shown in Annex A, for information purposes only. The distinction between ventilation methods is still retained; natural ventilation must be kept under 1,500 ppm average, whereas mechanical is held to 1,000 ppm for the occupied period. For accurate sizing of equipment, it is now possible to establish the classroom timetable and then use CO2 concentration analysis to optimise the selection of unit size best able to meet the average CO2 threshold.
Figure 2: Typical changes in CO2 levels with demand controlled
room-based mechanical ventilation systems. Graph provided by SAV AirMaster.
Volatile Organic Compounds (VOCs) receive considerable attention, as their consequences to health can be severe. The main recommendation from BB101 is to reduce contamination at source by the appropriate specification of fabric materials.
The control of draught now receives considerably more attention than was the case in 2006. Draught is unwanted local cooling. In BB101 it is quantified by the temperature difference ΔT between the air already in and the air arriving at the occupied zone at the centre of a classroom. For standard classrooms, this ΔT is not to exceed 2 or 3° for mechanical systems, but is allowed to reach 5° for natural ventilation. Future field experience will tell whether these limits are sufficient to curtail complaints of discomfort due to winter draught, which are all too common in UK classrooms.
Overheating criteria in BB101 have been subject to change through the various document revisions since 2015. Although the 3 main criteria remain as defined in TM52 (The limits of thermal comfort), the focus is now solely on Duration – Criterion1: That there should not be more than 40 hours during the period between May 1st-September 30th when the temperature reaches 1° above the allowable maximum. Full occupancy is to be assumed through the holiday period. The other 2 Criteria (to do with Severity and Upper Temperature Limit) are also required, but for information purposes only.
Specialist guidance is given for the ventilation of laboratories, sports halls, ICT suites and school kitchens.
Filtration is now discussed in considerable detail, in recognition of the fact that the UK suffers from high levels of air particulates and gaseous pollutants. It is clear that designers of mechanical systems should consider air filtration to at least F7 standard. The comment is made that even M5 filters would not make the supply air into buildings clean enough to breathe, without risk to health. As far as the cleanliness of natural ventilation systems is concerned, BB101 is silent.
To help you prepare for the reissue of BB101, these issues and their implications are included in the current AirMaster CPD offered by SAV. CPDs are usually arranged during lunchtimes at whatever venue is convenient to the client / consultant parties. If this would be of interest at some time in the future, please provide us with contact details on the form below and we’ll work something out.