Evaluating Overheating Risk and Mitigation Strategies ...

Evaluating Overheating Risk and Mitigation Strategies in Low Energy Houses in the UK: Two Sheffield Case Studies CIBSE ASHRAE Technical Symposium, Loughborough, UK 5-6 April 2017 The authors:

AZLIZAWATI IBRAHIM

DR SOFIE PELSMAKERS

MSC, BARCH, BSC, [email protected], [email protected] (Corresponding author)

PHD, MSC, MRES, PGDIP, RIBA, ARB [email protected]

XI CHEN MSC, BA, [email protected]

DR CHENGZHI PENG BARCH, DIPLA, MSC, PHD [email protected]

School of Architecture, The University of Sheffield

Introduction

Housing sector

Committee on Climate Change, 2014

CIBSE ASHRAE Technical Symposium, Loughborough, UK 5-6 April 2017

This paper presenting methods of studying overheating risks by using two real case studies, rather than evaluating the exact building performance of the specific designs.


Predicting Overheating Risks for Low Energy House case studies in Sheffield:

1

Case Study : A retrofit project in Sheffield: Knowle House

2

Case Study : A new-build project in Sheffield: Archer Lane


Predicting Overheating Risks for Low Energy House Case studies in Sheffield Case Study 1: A retrofit project in Sheffield: Knowle House

Location

Retrofit strategies Energy software

• The project is a retrofitted detached house in the South-west of Sheffield • The main design strategy was retrofitting to Zero Carbon standard to meet Fabric Efficiency Standards of 10%.

summer heat protection is necessary. Overheating risk exceed comfort limit >10%.

summer heat protection is necessary. Operative temperatures exceeded 1% of the annual occupied hours in both bedrooms and living rooms.

summer heat protection is necessary. Operative temperatures far exceeded 1% of the annual occupied hours in both bedrooms and living rooms.


Overheating metrics – which one is useful? PHPP and CIBSE Guide A (2006) are measuring overheating risks which expressed through different ways (PHPP is using total time of the year and CIBSE Guide A is using the annual occupied hours) and internal maximum temperature for comfort. Thus, depending on the overheating studies that most suited to the research, both overheating thresholds are useful.


Overheating mitigation strategies in low energy houses are needed now and in the future predicted climate. For case study 1, • all mitigation strategies tested were applied to the Passivhaus retrofitted case study to investigate the efficacy of measures in the worst case scenario. • Six main strategies and two combination strategies were used to evaluate the most appropriate overheating mitigation measures CIBSE ASHRAE Technical Symposium, Loughborough, UK 5-6 April 2017

For case study 2, • two approaches to reducing overheating were tested (window specification and external shading), in response to the excessive solar gain highlighted by the models

Overheating Mitigation Strategies Case Study 1 (Knowle House, Sheffield) – Single mitigation strategies (2050s High Emission)

Results

Overheating Mitigation Strategies Case Study 1 (Knowle House, Sheffield) – Single mitigation strategies (2080s High Emission)

Results

Overheating Mitigation Strategies Case Study 1 (Knowle House, Sheffield) – Single mitigation strategies

In both 2050s and 2080s, the most effective single overheating

mitigation strategies suggested is reducing glazing g-value (from 0.62 to 0.3) in Sheffield, followed by internal light coloured internal shading and permanent external shading.

Results

Overheating Mitigation Strategies Case Study 2 (Archer Lane, Sheffield) – Single mitigation strategies and a combination strategies (2050s and 2080s High Emission Scenario)

Results

Overheating Mitigation Strategies Case Study 2 (Archer Lane, Sheffield) – single mitigation strategies

In both 2050s and 2080s, the most effective single overheating

mitigation strategies suggested is adding external adjustable blinds, followed by reducing glazing g-value.

Results

Most effective (Case 1)

Results

Overheating mitigation strategies

Least effective (Case 1)

Modelling Software Differences PHPP (Passivhaus Planning Package)

ENVI-met and DesignBuilder

Energy performance

• PHPP is very good and reliable software for modelling the energy performance.

Overheating frequency

• PHPP can predict Overheating frequency

• ENVI-MET can be used as a future microclimates simulation tool. • DesignBuilder is a powerful and reliable modelling tool on building performance simulation. • The DB simulation does not show the overheating frequencies • Not tested for different indoor temperature values

Summer internal temperature

• The maximum temperature for summer thermal comfort can be predefined by changing the indoor temperature summer temperature. • In PHPP, only one indoor temperature can be simulated in one simulation file and it will assume all areas having the same temperature. This method was used to test OF CIBSE Guide A overheating metric.

Reflections

Modelling Software Differences PHPP (Passivhaus Planning Package)

ENVI-met and DesignBuilder

Prediction of internal temperature

• PHPP could not predict the internal temperature.

Prediction of location of OH

• PHPP could not predict the location/where overheating will occur within a dwelling.

• The DB simulation results can predict the indoor temperatures and for how long the temperature exceeds thermal comfort level. • DB simulation can predict the exact heat gain and air temperature of individual room.

• PHPP can produce faster simulation result even for the whole year simulation

• DB require more time to do a whole year simulation

Time

Reflections

Conclusion 1. Low energy housing standards

such as the

Passivhaus standard lead to significantly reduced space heating demands in the two studied Sheffield case study dwellings. As predicted by models, a higher overheating frequency would occur over time due to a changing climate

2.

As long as appropriate overheating mitigation

strategies were applied, such low energy housing standards are beneficial in both the current and predicted future UK climate, leading to reduced winter energy use (and associated carbon emissions reductions) and enhanced winter occupant thermal comfort.

3.

According to both case studies, summer

overheating mitigation measures were necessary in the current and future projected climate in Sheffield CIBSE ASHRAE Technical Symposium, Loughborough, UK 5-6 April 2017

4. The most effective single overheating mitigation strategies suggested are reduction of glazing g-values, temporary internal shading and permanent external shading.

5. Single mitigation measures alone were less robust than multiple strategies; the most optimal mitigation strategy was a combination glazing g-values, appropriately designed external shading devices, and good ventilation

overheating of reduced internal or night-time

It should be noted that this study is based on modeling and assumes certain user interactions, which may not occur in reality and further research is required.

Acknowledgement

Many thanks to: The case studies’ architects and house owners

Thank you

Presented by: Dr Sofie Pelsmakers In collaboration with Azlizawati Ibrahim, Xi Chen and Chengzhi Peng School of Architecture, The University of Sheffield