Hea 04 - Thermal comfort

Acceptable deviations – ISO 7730:2005 category B - KBCN1714

Acceptable deviations from category II thermal modelling criteria can be made in accordance with CEN 16798-2:2019 Anne E, only when the thermal comfort assessment uses CEN 16798 to demonstrate compliance. Where this is the case, up to a 6% deviation based on yearly occupied hours can be accepted when demonstrating compliance.  ^{Note: this KBCN no longer allows the deviations to be used for ISO 7730:2005. However, for assessments where the assessor has advised the project team based on the original KBCN, prior to this update, this will be honoured if you provide evidence of this in your assessment. KBCN wording 16 Jan 2025 - 10 Jul 2025: ~ Acceptable deviations from the ISO 7730:2005 category B criteria thermal modelling criteria can be made in accordance with CEN 16798-2:2019 Annex E. Up to a 6 % deviation based on yearly occupied hours can be accepted when demonstrating compliance ~}

10 Jul 2025 - KBCN updated following further review of relevant standards

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Adaptability for a projected climate change scenario – Winter conditions - KBCN1715

Where future climate change scenario projections in winter indicates a higher temperature and, therefore, more thermally comfortable climate compared to the current winter temperatures, it can be assumed that the winter conditions within the climate change scenario are met based on the thermal modelling of current winter conditions. Justification must be provided for each project confirming that the future winter conditions will be met with the current heating system. In a warming climate the heating system needs to be sized for the beginning of its lifespan, whereas the cooling systems need to be sized for the end of their life span (Ref: CIBSE TM55: 2014)

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Air-conditioned spaces - KBCN00035

Air-conditioned spaces are assessed to ensure appropriate thermal comfort levels are achieved. Cooling capacity should be sufficient to comply with the requirements of CIBSE Guide A, however providing sufficient space to install additional capacity to meet the requirements at a later date in line with projected climate change scenarios is also acceptable. In addition, if it can be demonstrated that the air-conditioning system can achieve the thermal comfort criteria in accordance with CIBSE Guide A, Table 1.5, thermal modelling does not need to be carried out. The “time out of range” (TOR) metric should be reported as 0%.  

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Assessing thermal comfort – Residential buildings - KBCN1408

CIBSE TM59 can be used to demonstrate compliance with the thermal comfort requirements for residential buildings, instead of ISO 7730:2005. This is to recognise the most up to date methodology relating to the assessment of homes.

26 Jan 2025 - Updated to apply to multi-residential buildings (long-term stay) and scheme applicability extended to account for this.

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Definition of concourse - KBCN0386

A concourse is an open area within or in front of a public building which is used primarily for circulation, short term waiting, or incidental interaction, analogous to the concourse of a train station. It should not be considered occupied space.  

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Future thermal comfort – mechanical ventilation, mixed mode and limited comfort cooling - KBCN1877

Where a building or space incorporates mechanical ventilation systems, including mixed-mode strategies, the selection of future weather files for thermal comfort assessment should be based on the expected service life of the systems installed. This includes systems providing mechanical ventilation, with or without limited comfort cooling, and mixed-mode spaces where natural ventilation is supplemented by mechanical systems within the same space. For the purposes of this guidance, ‘mechanical ventilation with limited comfort cooling’ refers to systems that may provide some degree of cooling or air tempering but are not designed to fully maintain internal conditions to defined air-conditioned setpoints throughout occupied hours. Although these systems do not provide full air conditioning, their presence influences internal environmental conditions and overheating risk. As their performance is dependent on mechanical components with defined service lifespans, the future thermal comfort assessment should be aligned with the expected lifespan of these systems (typically 15 years), rather than the overall building lifespan.  For schemes where free‑running buildings are assessed using a longer lifespan for future climate scenarios, a shorter system lifespan should be used where mechanical systems are present

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Natural ventilation – use of CIBSE TM52 - KBCN0935

For a naturally ventilated building, it is acceptable for the thermal comfort limits and calculation methodology in CIBSE TM52: The Limits of Thermal Comfort: Avoiding Overheating in European Buildings to be used in place of ISO 7730:2005. BREEAM recognises that adaptive comfort models can provide more appropriate thermal comfort limits for naturally ventilated buildings.

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Occupant control – BMS and degree of control - KBCN0175

A Building Management System controlled set point with local override controls limited to a set range would satisfy the occupant control requirement so long as the temperature range available to building users is confirmed as appropriate for the building type and user profile.

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Occupant control – spaces requiring user controls - KBCN0170

This guidance is intended to clarify the types of area for which user controls are required or would be considered beneficial. Zoning is required in all areas of the asset where specified in the assessment criteria. Please refer to the specific requirements of the applicable BREEAM standard to interpret this guidance appropriately. User controls required Spaces where users are expected to have independent control over their environment.

• Owned spaces: small rooms for a few people. For instance, cellular offices, owned spaces in residential assets.
• Temporarily owned spaces: where occupants expect to operate the environmental controls while they are there. For instance, meeting rooms and hotel bedrooms.
• Shared spaces. For instance, multi-occupied areas such as open-plan offices or workshops.

User controls not required Spaces where users are not expected to have independent control over their environment.

• Managed spaces: where environmental control is expected to be centrally managed. For instance, atria, circulation areas, concourses, entrance halls, function halls, restaurants, libraries, and shops.
• Occasionally visited spaces. For instance, storerooms, bookstacks in libraries, aisles of warehouses, toilets.

14-Dec-2022 - KBCN applicability updated to include BIU. Wording clarified, and amended for compatibility with BIU criteria.

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PMV and PPD reporting for mixed mode ventilation buildings - KBCN0632

When assessing buildings where both naturally ventilated and air conditioned spaces are included, reporting the PMV and PPD indices is required.

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Reporting PPD and PMV Figures - KBCN0867

The PMV (Predicted Mean Vote) and PPD (Predicted Percentage Dissatisfied) values need to be entered into the scoring & reporting tool for data recording purposes. The thermal modelling specialist should be able to provide values for both the PMV and PPD for the asset. The values to report are the observed range of values for PMV and PPD:

• Across all occupied areas and,
• Across all expected occupied hours.

If the software or calculation method used does not generate these PMV / PPD metrics, they do not have to be provided. [accordion] [accordion_block title="Example"] An asset has the following thermal comfort ranges across its occupied spaces:

• PMV ranges from -0.3 to +0.2. Enter '-0.3 to +0.2' into the relevant field.
• PPD ranges from 3% to 10%. Enter '3% to 10%' into the relevant field.

[/accordion_block] [/accordion]

15.09.22 Wording and example clarified.

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User controls – Thermal comfort - KBCN1813

The requirement for user controls does not mandate a specific type of control; e.g. local manual adjustment. Where control is provided indirectly, e.g. via BMS or central management, the assessor must demonstrate that this approach meets the intent of the user comfort and accessibility criteria and is informed by end-user discussions or relevant design guidance. Please refer to KBCN0170 for clarification of the types of space requiring user controls.

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