TM52 - Low Energy Consultancy talk overheating analysis | Low Energy Consultancy

TM52 - Low Energy Consultancy talk overheating analysis

We are currently experiencing a heat wave in the UK. Low Energy Consultancy discuss the benefits of TM52 when analysing overheating in construction.

Construction standards have vastly improved in the last decade. The refinement and imposing of tighter compliance through Building Regulations Part L has seen greater efficiency in fabric performance.

The resulting reduction in use of energy is a positive outcome. However, on the flip side, cases of room/dwelling and landlord corridor overheat have increased. Although pupil comfort in schools was addressed under BB101, there is now a wider reaching issue for commercial and domestic situations. As consultants we have found that the best measure for comfort compliance is the CIBSE technical memorandum TM52.

The main purpose of TM52 overheating is to carry out thermal comfort analysis within residential and non-residential buildings. The analysis is carried out for every occupied zone within the building to test if the room temperature is under a comfortable range or if it is overheating. Analysis looks at the occupancy period (on an hourly basis) during the summer period.

There are three criteria for TM52 overheating analysis. Each occupied zone within the dwelling must pass at least two of the three criteria. The room’s operative and maximum temperature plays an important role in overheating analysis.

For example, a bedroom has a normal operating temperature of 20°C (CIBSE Guide A) which means its maximum temperature can be calculated by the following formula:

Tmax = 0.33 Trm + 21.8 (° C) = 6.6 + 21.8 = 28.4 °C

The three criteria of TM52 analysis for a bedroom can be described as: 

  1. The bedroom temperature must not be exceeding the temperature 27.9°C for 3% of the occupied period.
  2. The bedroom temperature should not be exceeding 22.9°C any time during the daily occupancy hours.
  3. The bedroom temperature should not be exceeding 24.9°C any time during the daily occupancy hours.

Overheating analysis is carried out using dynamic simulation software IES, which gives the opportunity to look at real situations on an hourly basis from May till September (summer period).

Internal temperatures are assigned on the zonal level by using the ‘Building Template Manager’ option in the IES software. Internal heat gain is an important element for overheating analysis. Before starting the overheating analysis simulation option in IES software, the heat gains must be correctly assigned within the space, for example, in bedrooms the main heat gains are produced by people, lighting and equipment. A normal infiltration rate of 0.25 is introduced for such types of zones.

Another important aspect is building construction, specifically the fabric makeup and U-values, glazing U-values and g-values. Bedroom occupancy profiles are introduced to make analysis more accurate and realistic. All the values of heat gains and infiltration are taken as per CIBSE guidance and the client’s demands.

If the bedroom does not comply with the overheating criteria, improvement measures can be introduced to overcome the overheating issue, for example window openings and auxiliary ventilation as per the client’s advice. Recommendations are also included in reports for clients, explaining the best possible options for them.

The same method is applicable to any other zones of a building for example living room, kitchen, offices and laboratories.