The following three criteria, taken together, are used to assess the risk of overheating of buildings in the UK and Europe. A room or building that fails any two of the three criteria is classed as overheating.
1.The first criterion sets a limit for the number of hours that the operative temperature can exceed the threshold comfort temperature (upper limit of the range of comfort temperature) by 1°K or more during the occupied hours of a typical non-heating season (1st May to 30th September).
2.The second criterion deals with the severity of overheating within any one day, which can be as important as its frequency, the level of which is a function of both temperature rise and its duration. This criterion sets a daily limit for acceptability.
3.The third criterion sets an absolute maximum daily temperature for a room, beyond which the level of overheating is unacceptable.
Further information on these criteria can be found in TM52 – 2013, section 6.1.2.
Hours of exceedence
The number of hours during which ΔT is greater than or equal to one degree (°K) during the period May to September inclusive shall not be more than 3% of occupied hours. ΔT is defined as operative temperature less the maximum acceptable temperature. ΔT is rounded to the nearest whole degree.
Please note:
If data is not available for the whole period (or if occupancy is only for a part of the period) then 3% of available hours should be used. It may be seen that educational NCM occupancy profiles are inappropriate due to prolonged unoccupied periods in these profiles. The user should assess the appropriate profiles for their models.
Daily weighted exceedence
To allow for the severity of overheating, the weighted exceedence shall be less than or equal to 6 in any one day.
Upper limit temperature
To set an absolute maximum value for the indoor operative temperature the value of Δ T shall not exceed 4 °K.
