TM59 Design Methodology for the Assessment of Overheating Risk
in Homes
Dr Anastasia Mylona, CIBSE Research Manager
London Climate Change Partnership - Heat Risk in London Group
September 19, 2017
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Overheating in homes
Zero Carbon Hub
report published
• Overheating identified as an issue
2015
• Multiple studies calling for a consistent
methodology
Article by Liza Young
CIBSE Journal August 2014
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Why is overheating a problem now?
• Climate Change
• Urban Heat Island Effect
• Smaller homes
• Larger windows for maximum daylight
• Air tightness for winter energy efficiency
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Design aspects that contribute to overheating risk
• Single aspect flats
• Large areas of glazing
• Limited ventilation
• Restricted openings
• Urban homes - noise and/or air
pollution limiting natural
ventilation
• Community heating
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What is overheating?
• No one definition fits all
• Comfort is subjective
• Depends on both environmental
and human factors
• Duration/ timing of high
temperatures is important
• Very high temperatures > 35°C
lead to Heat stress
• High bedrooms temperatures
(>26°C) can impair sleep Image from ZCH Overheating in
homes - Where to Start - An
introduction for planners, designers
and property owners, 2013
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CIBSE TM59
• Provides a consistent design methodology
for the assessment of overheating risk in
homes
• Based on the use of dynamic thermal
modelling
• Based on current knowledge and
resources but simplified
• Key aim is to highlight designs that are of
high risk of overheating
Available for free:
http://cibse.org/knowledge/knowledge-
items/detail?id=a0q0O00000CQ83EQAT
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Definition of overheating - Based on Guide A and TM52
Criterion 1: For living rooms, kitchens and bedrooms: 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. (CIBSE TM52 Hours of exceedance)
Criterion 2: For bedrooms only: the operative temperature from 10pm
to 7am shall not exceed 26°C for more than 1% of annual hours (33
hours)
Bedrooms must pass both requirements
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Standardised internal gains and occupancy profiles
• 24/7 occupancy of bedrooms (worst case)
• Daytime (10am-10pm) occupancy of living rooms and kitchens
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Weather file to be used
Minimum requirement
• DSY1
• Nearest location
• 2020s
• High emissions,
• 50th %ile
Recommendation to also test designs under DSY2/3 or
2050s/2080s data for risk assessment purposes
but not required in order to pass
Recommendation to run for DSY2/3 or 2050/2080s data but not required to pass
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Blinds to be included only if part of the design
• If blinds form part of the mitigation strategy then these must be included in
the base build
• Results without blinds must be included in the report
• Blinds should not interfere with the ventilation capacity of open windows, or
if they do, this reduction in their capacity for natural ventilation should be
taken into account in the design
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Other key considerations
Opening of windows for natural ventilation
• Taking into account any security, noise or air quality issue
• Windows considered open only when rooms are occupied, unless secure
openings are provided
Vulnerable residents
• Care homes and accommodation for vulnerable occupants should
assume Type I occupancy (see CIBSE TM52 for description)
Community heating
• Heat losses from pipework should be included
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Thank you for listening
amylona@cibse.org
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