Clancy MEP Specialists Advise ESFA on BB101 2018

Article posted on: 30th March 2019

Experts at Clancy Consulting have found, following considerable analysis, that Hybrid ventilation manufacturers have not been able to demonstrate compliance with BB101 2018 under cold weather conditions.

BB101 is referred to under Building Regulations Part F as the method of demonstrating compliance for schools.

BB101 has various criteria that must be met, the main ones of concern during the winter period being:-

  • Minimising drafts at head height
  • Maintaining an average CO2 during the day of <1000 ppm
  • Maintaining a peak CO2 during the day of <1500 ppm for 20 min max

Brian Whitehead, Divisional Director at Clancy Consulting, explains, “The issue we have found is, that for unheated units during low external temperatures, to minimise draughts the external air must be mixed with a higher quantity of room air.

As the fans can only deliver a fixed amount of air, as the ratio of room air increases the CO2 limits are exceeded.

Manufacturers have been providing various solutions, but all seem to entail including breaks/lunch purge periods or clarifying which days of the weather file the assessment is based.

“These clarifications to some extent are non-compliant with BB101 2018 and as such do not potentially meet Building Regulations Part F.”

Manufacturers have been talking direct to the ESFA relating to how BB101 is applied, however this to date has not been backed up by any definitive Guidelines from the ESFA.

Following discussions led by Clancy Consulting with the ESFA, it has been agreed that the following protocols should be adopted when evaluating Hybrid Ventilation systems.

  • Modelling should be undertaken using the standard hours defined in Clause 8.1 of BB101
  • Wintertime modelling should be undertaken using the latest TRY weather file (2016)
  • Weather data should be considered for all days, if the coldest days falls notionally on a Saturday or Sunday these should be treated as a normal school day
  • When the external temperature during the occupied period (ie between 9.00 to 16.00 hours) falls below -1 oC then CO2 requirements may be relaxed.
  • Relaxed CO2 requirements should be <1500 ppm average during the occupied period with a max 20 min peak of no more than 2000 ppm.
  • Draught criteria in Table 7-4 should not be amended
  • Heat losses for the spaces shall be considered based against the CIBSE steady state conditions (external temperature as applicable to the local area)


For further information, please contact Brian via email

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