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Hea 04 Thermal comfort

Number of credits available	Minimum standards
3	No

Aim

To ensure that appropriate thermal comfort levels are achieved through design, and controls are selected to maintain a thermally comfortable environment for occupants within the building.

Assessment criteria

The following is required to demonstrate compliance:

One credit - Thermal modelling

Thermal modelling has been carried out using software in accordance with CIBSE AM111CIBSE Applications Manual AM11 Building energy and environmental modelling, CIBSE, 1998 Building Energy and Environmental Modelling.
The software used to carry out the simulation at the detailed design stage provides full dynamic thermal analysis. For smaller and more basic building designs with less complex heating or cooling systems, an alternative less complex means of analysis may be appropriate (such methodologies must still be in accordance with CIBSE AM11).
The modelling demonstrates that:
1. For air conditioned buildings, summer and winter operative temperature ranges in occupied spaces are in accordance with the criteria set out in CIBSE Guide A Environmental design2CIBSE Guide A Environmental Design,8th Edition, CIBSE, 2015, Table 1.5; or other appropriate industry standard (where this sets a higher or more appropriate requirement/level for the building type).
2. For naturally ventilated/free running buildings:
  1. Winter operative temperature ranges in occupied spaces are in accordance with the criteria set out in CIBSE Guide A Environmental design, Table 1.5; or other appropriate industry standard (where this sets a higher or more appropriate requirement/level for the building type).
  2. The building is designed to limit the risk of overheating, in accordance with the adaptive comfort methodology outlined in CIBSE TM52: The limits of thermal comfort: avoiding overheating in European buildings3CIBSE TM52 The limits of thermal comfort: Avoiding overheating in European buildings, 2013.
For air conditioned buildings, the PMV (predicted mean vote) and PPD (predicted percentage of dissatisfied) indices based on the above modelling are reported via the BREEAM assessment scoring and reporting tool.

One credit - Adaptability - for a projected climate change scenario

Criteria 1 to 4 are achieved.
The thermal modelling demonstrates that the relevant requirements set out in criterion 3 are achieved for a projected climate change environment (see Hea 04 Thermal comfort).
Where thermal comfort criteria are not met for the projected climate change environment, the project team demonstrates how the building has been adapted, or designed to be easily adapted in future using passive design solutions in order to subsequently meet the requirements under criterion 6.
For air conditioned buildings, the PMV and PPD indices based on the above modelling are reported via the BREEAM assessment scoring and reporting tool.

One credit - Thermal zoning and controls

Criteria 1 to 4 are achieved.
The thermal modelling analysis (undertaken for compliance with criteria 1 to 4) has informed the temperature control strategy for the building and its users.
The strategy for proposed heating/cooling system(s) demonstrates that it has addressed the following:
1. Zones within the building and how the building services could efficiently and appropriately heat or cool these areas. For example consider the different requirements for the central core of a building compared with the external perimeter adjacent to the windows.
2. The degree of occupant control required for these zones, based on discussions with the end user (or alternatively building type or use specific design guidance, case studies, feedback) considers:
  1. User knowledge of building services
  2. Occupancy type, patterns and room functions (and therefore appropriate level of control required)
  3. How the user is likely to operate or interact with the system(s), e.g. are they likely to open windows, access thermostatic radiator valves (TRV) on radiators, change air-conditioning settings etc.
  4. The user expectations (this may differ in the summer and winter) and degree of individual control (i.e. obtaining the balance between occupant preferences, for example some occupants like fresh air and others dislike draughts).
3. How the proposed systems will interact with each other (where there is more than one system) and how this may affect the thermal comfort of the building occupants.
4. The need or otherwise for an accessible building user actuated manual override for any automatic systems.

Checklists and tables

None.

Compliance notes

Ref	Terms	Description
Shell and core
CN1	Applicable assessment criteria	Thermal modelling, criteria 1 to 4 Option 1: Shell only: This issue is not applicable. Option 2: Shell and core: All criteria relevant to the building type and function apply. Adaptability - for projected climate changes, criteria 5 to 8 Option 1 - Shell only: These criteria are not applicable. Option 2 - Shell and core: All criteria relevant to the building type and function apply. Thermal zoning and controls criteria 9 to 11 Both options: These criteria are not applicable. Refer to Appendix D – BREEAM UK New Construction and Shell and Core Project Assessments for a more detailed description of the above shell and core assessment options.
CN1.1	Thermal model - thermal modelling See criteria 1 to 4.	Option 2 - Shell and core Where assumptions are required for the purpose of the thermal model, these must be reasonable and represent typical use patterns and loads given the parameters and function of the building. Note that thermal modelling may need to be completed on the basis of a typical notional layout.
CN1.2	Thermal model - adaptability See criteria 5 to 8.	Option 2 - Shell and core Where assumptions are required for the purpose of the thermal model, these must be reasonable and represent typical use patterns and loads given the parameters and function of the building. Note that thermal modelling may need to be completed on the basis of a typical notional layout.
Simple buildings
CN2	Applicable assessment criteria	All criteria relevant to the building type and function apply.
CN2.1	Dynamic thermal modelling	For simple building assessments, dynamic thermal modelling is not a requirement to achieve the credits but may be preferable as it can provide more accurate analysis results. Note that assessment criterion 2 already clarifies use of an alternative less complex means of modelling, which must be in accordance with CIBSE AM11.
General
CN3	Typical occupancy/use patterns	If it is not possible to confirm the number of building occupants using the building, e.g. speculative developments (or shell and core), then the default occupancy rates given in CIBSE Guide A can be used to determine a default number of users. Where the typical use patterns are also unknown, the table given in Tra 01 Public transport accessibility can be used to determine the typical opening hours of different building types. The design team need to justify/validate the occupancy number and use patterns applied in the thermal model.
CN3.1	Appropriate industry standard See criterion 3.	BREEAM has not attempted to list all appropriate industry standards. Any recognised collaborative industry or sector best practice standard or guidance that sets thermal performance levels, in terms of thermal comfort and design temperature can be considered an appropriate industry standard for the purposes of this BREEAM issue. CIBSE Guide A (table 1.5) includes recommended summer and winter comfort criteria (temperature ranges) for a number of specific building applications. See also the relevant compliance notes below for industry standards deemed appropriate by BREEAM for schools and healthcare buildings.
CN3.2	Buildings with less complex heating/cooling systems See criterion 11.	For buildings with less complex heating/cooling systems the thermal comfort strategy need only comply with criteria 11a and 11b. Compliance can be demonstrated where zoning allows separate occupant control (within the occupied space) of each perimeter area (i.e. within 7m of each external wall) and the central zone (i.e. over 7m from the external walls). For example, adequate TRVs (thermostatic radiator valves) placed in zones around the building perimeter, and the provision of local occupant controls to internal areas, such as fan coil units. Note: The distance requirement for smaller buildings is approximate; however, the assessor must use sound judgement considering fully the aims of this issue, before accepting solutions that do not strictly meet the above criteria. Examples of potentially compliant heating control measures can be found in Technology Guide CTG065 Heating control4CTG065 Technology Guide, Heating control: maximising comfort, minimising energy consumption, The Carbon Trust, 2011.
Building type specific
CN4	Industrial Industrial unit with no office space	Where an industrial unit contains no office space and only an operational or storage area, this BREEAM issue does not apply.
CN4.1	Education (schools only): Appropriate industry standards and criteria for schools, See criterion 3.	An appropriate industry standard for schools is Building Bulletin 101, Ventilation of school buildings (April 2014). For schools with a straightforward servicing strategy, ClassCool is considered a suitable alternative to an AM11 full dynamic model.
CN4.2	Healthcare: Appropriate industry standards and criteria See criterion 3.	The appropriate industry standard for healthcare is Health Technical Memorandum 03-01 Specialised ventilation for healthcare premises. Thermal comfort levels in patient and clinical areas must be in accordance with the temperature ranges set out in HTM 03-01, Appendix 2. Furthermore, internal summer temperatures must not exceed 28ºC dry bulb for more than 50 hours per year (as defined in HTM 03-01, paragraph 2.15). Other occupied spaces not covered in HTM03-01 Appendix 2 should be in accordance with CIBSE Guide A Environmental Design.
CN4.3	Education and prisons Occupant controls See criterion 11.	In this issue, occupant controls are intended to be for staff use only.

Methodology

None.

Evidence

Criteria	Interim design stage	Final post construction stage
All	One or more of the appropriate evidence types listed in The BREEAM evidential requirements section can be used to demonstrate compliance with these criteria.
10, 11, 12	Thermal comfort study	Refer to generic evidence requirement above

Relevant definitions

ClassCool

A tool developed by the Department for Children, Schools and Families (DCSF, formerly DfES) which provides a simplified method of assessing the extent of classroom overheating. ClassCool may not be appropriate for other spaces, such as libraries and halls, and other means of assessing overheating will be required:www.teachernet.gov.uk.

Clinical areas

Refer to BREEAM issue Hea 01 Visual comfort

Occupied space

Refer to Hea 01 Visual comfort, however for the purpose of BREEAM issue Hea 04 the definition excludes the following;

Atria or concourses
Entrance halls or reception areas
Ancillary space e.g. circulation areas, storerooms and plant rooms.

Passive design

Passive design uses layout, fabric and form to reduce or remove mechanical cooling, heating, ventilation and lighting demand. Examples of passive design include optimising spatial planning and orientation to control solar gains and maximise daylighting, manipulating the building form and fabric to facilitate natural ventilation strategies and making effective use of thermal mass to help reduce peak internal temperatures.

Patient areas

Refer to BREEAM issue Hea 01 Visual comfort.

Predicted mean vote (PMV)

The PMV is an index that predicts the mean votes of a large group of persons on the seven-point thermal sensation scale based on the heat balance of the human body. Thermal balance is obtained when the internal heat production in the body is equal to the loss of heat to the environment. See 'Other Information' for the seven-point thermal sensation scale.

Predicted percentage dissatisfied (PPD)

The PPD is an index that establishes a quantitative prediction of the percentage of thermally dissatisfied people who feel too cool or too warm. For the purposes of ISO 7730, thermally dissatisfied people are those who will feel hot, warm, cool or cold. See the seven-point thermal sensation scale in Other information.

Projected climate change environment

Dynamic thermal simulation software packages currently provide the facility for building designs to be assessed under external climatic conditions specific to geographic location. Industry standard weather data for the UK is available in the form of Test Reference Years (TRYs) and Design Summer Years (DSYs) provided by CIBSE.
This weather data enables thermal analysis of building designs under current climatic conditions, yet no account is taken of the projected variations in weather data that will occur during the building's life cycle as a result of climate change. The following probabilistic DSY weather data files should be used to establish the projected climate change environment against which the design is evaluated:

Free Running Buildings

Time period: 2050s
Emissions scenario: Medium (A1B)

Mechanically Ventilated or Mixed Mode Buildings

Time period: 2030s
Emissions scenario: Medium (A1B).

The above weather files represent the minimum requirements to perform thermal modelling under a climate change scenario and subsequently demonstrate compliance. Where design teams feel that added consideration of building occupant risk/sensitivity to overheating is necessary, weather files can be used that exceed the minimum requirements outlined above. The time periods indicated above have been selected to represent the building services life cycle likely to be present in each building services strategy type. A shorter time period is chosen for mechanically ventilated/mixed mode building types due to consideration of mechanical servicing equipment life span (before major upgrade or replacement is required), and to avoid over-specification of plant which could lead to inefficient operation.

Separate occupant control

Responsive heating or cooling controls for a particular area/zone of the building that can be accessed and operated by the individual(s) occupying that area or zone. Such controls will be located within, or within the vicinity of, the zone or area they control.

Thermal comfort

In British Standard BS EN ISO 7730:2005: Ergonomics of the thermal environment. Analytical determination and interpretation of thermal comfort, thermal comfort is defined using the calculation of PMV and PPD indices and local thermal comfort criteria and is ‘that condition of mind which expresses satisfaction with the thermal environment.’ The term ‘thermal comfort’ describes a person’s psychological state of mind and is usually referred to in terms of whether someone is feeling too hot or too cold. Thermal comfort is difficult to define because it needs to account for a range of environmental and personal factors in order to establish what makes people feel comfortable. HSE considers 80% of occupants as a reasonable limit for the minimum number of people who should be thermally comfortable in an environment. The purpose of this issue is to encourage appropriate and robust consideration of thermal comfort issues and specification of appropriate occupant controls to ensure both maximum flexibility of the space and thermal comfort for the majority of building occupants.

Thermal dynamic analysis

Thermal comfort analysis tools can be subdivided into a number of methods of increasing complexity. The most complex of these and the one that provides greatest confidence in results is the full dynamic model. This type of model enables annual heating or cooling loads, overheating risks and control strategies to be assessed.

Other information

CIBSE Guide A and BS EN ISO 7730:2005

The assessment criteria for this issue require compliance with the operative room temperature ranges set out in CIBSE Guide A, Table 1.5.

The operative room temperature ranges provided in CIBSE Guide A have been derived in accordance with the heat balance model for thermal comfort (predicted mean vote (PMV) and predicted percentage dissatisfied (PPD)) as detailed in BS EN ISO7730.

The CIBSE Guide A operative temperature ranges correspond to a PMV of +/- 0.25 which sits between the Category A and Category B requirements listed in Annex A, Table A.1 of EN ISO 7730. Compliance with the CIBSE Guide A criteria will therefore effectively also demonstrate compliance with the Category B requirements set out in EN ISO 7730.

Projected climate change weather data

A range of alternative probabilistic weather files produced in accordance with the UK climate impacts programme (UKCIP) 2009 projections have been produced to be compatible with simulation software packages. These weather files provide the opportunity to evaluate the impact of varying climate change scenarios building design performance throughout its life cycle. Projected climate change weather files are currently available in TRYs and DSYs and according to three projected time periods; 2030s, 2050s and 2080s, and for each period, two 'emissions scenarios' are available; Medium Emissions (A1B) and High Emissions (A1F1).

The PROMETHEUS project at Exeter University has produced a number of future weather files specific to different locations across the UK, created using the UKCP09 weather generator. Weather files produced under the PROMETHEUS project are available at the following location:

http://emps.exeter.ac.uk/research/energy-environment/cee/research/prometheus/downloads/