Building Bulletin 101 v1 (August 2018) (Guidelines on ventilation, thermal comfort and indoor air quality in schools) came into force on 23rd August 2018. Here are the main updates that M & E designers need to take account of:
The 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.
The 3 overheating criteria continue as defined by TM52 (The limits of thermal comfort). However, the focus is now on Criterion 1 (Duration): This states that there should not be more than 40 hours during the period between May 1st-September 30thwhen 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 to be assessed, but the results are 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 F7 standard when it comes to polluted areas. When the air is not polluted M5 single filtration as a minimum is required. As far as the cleanliness of natural ventilation systems is concerned, BB101 is silent.
To help you analyse and assimilate the issues raised by BB101 (2018), SAV have summarised the most significant points for inclusion in their current AirMaster CPD. CPDs are usually arranged during lunchtimes at whatever venue is convenient to the client / consultant parties. If this would be of interest now or at some time in the future, please provide us with contact details on the form below and we’ll work something out.