Calculating average plan depth for HQM Temperature Tool - KBCN0891
The average plan depth is calculated by measuring, for each room, the distance from the window nearest to the centre of the room. Then calculate the total distance for all rooms and divide this by the number of rooms. The following should also be taken into account:
- If the room is a straightforward parallelogram, the ‘centre’ of the room can be considered the midpoint between a line perpendicular to the midpoint of the external wall with the window and the opposite wall.
- If the room is more complicated, a point marked visually (by eye) is acceptable where the plans are provided as evidence.
- Alternatively, the centroid of the floor plan polygon can be calculated mathematically if the calculations are also submitted.
- Only the window nearest to the centre is considered, for each wall.
- Roof lights should not considered.
There is an element of discretion in terms of calculating this and common sense should be applied to ensure that room depth is being calculated correctly, keeping in mind that this aspect is about determining the rooms ability to circulate air as part of managing high temperatures.
Generally speaking, the average plan depth only becomes an issue for homes with relatively deep rooms and it does not tend to be a problem in the majority of cases, for the purposes of the HQM temperature tool.
The HQM temperature outputs help to determine homes that are less likely to be at risk of overheating in summer months. It is not a design tool and efforts should be applied to reduce risk wherever possible (e.g. appropriate use of ventilation and thermal modelling).
Thermal model sampling - KBCN1015
Thermal modelling, in accordance with CIBSE AM11, does not need to be carried out for each individual home, where the thermal modeller uses their professional judgement to ensure that an appropriate sampling approach is adopted, in line with section 3.1 of CIBSE TM59 and the following considerations:
- All house types are adequately sampled
- The homes and situations most at risk of overheating are modelled (i.e. the worst case scenarios)
- There is no risk of overheating in the homes not modelled
The modeller needs to provide evidence and justifications that demonstrate how the samples have been determined, with their justifications, in line with the above.
A house type should include homes that are identical in specification, design and location (end/ mid-terrace, ground or mid/ top floor).
