Overheating in vulnerable and non-vulnerable households

ABSTRACT

As the 2003 European heatwave demonstrated, overheating in homes can cause wide-scale fatalities. With temperatures and heatwave frequency predicted to increase due to climate change, such events can be expected to become more common. Thus, investigating the risk of overheating in buildings is key to understanding the scale of the problem and in designing solutions. Most work on this topic has been theoretical and based on lightweight dwellings that might be expected to overheat. By contrast, this study collects temperature and air quality data over two years for vulnerable and non-vulnerable UK homes where overheating would not be expected to be common. Overheating was found to occur, particularly and disproportionately in households with vulnerable occupants. As the summers in question were not extreme and contained no prolonged heatwaves, this is a significant and worrying finding. The vulnerable homes were also found to have worse indoor air quality. This suggests that some of the problem might be solved by enhancing indoor ventilation. The collected thermal comfort survey data were also validated against the European adaptive model. Results suggest that the model underestimates discomfort in warm conditions, having implications for both vulnerable and non-vulnerable homes.     

Meta-analysis of indoor temperatures in new-build housing

ABSTRACT

Despite growing concerns about overheating, a lack of evidence exists on the scale of the problem, particularly in contemporary UK housing. This paper presents the results of a meta-analysis of indoor temperatures in selected low-energy housing. Temperature data recorded at five-minute intervals in 60 dwellings across 19 demonstration projects (2012–14) were collated and analysed to investigate the prevalence of overheating. Findings evidence high summertime temperatures, with 27% of living rooms exceeding 28°C during August. Based on the Chartered Institution of Building Services Engineers (CIBSE) threshold of 5% annual occupied hours > 25°C, 57% of bedrooms and 75% of living rooms were classified as having overheated. Overall, 30% of living rooms exceeded the adaptive comfort threshold of > 3% occupied hours ΔT?≥?1?K. The results suggest a fundamental relationship between ventilation and indoor temperatures. The higher minimum and average summertime temperatures observed in mechanical ventilation with heat recovery (MVHR) homes (p?<?0.05) and lower temperature range (p?<?0.001) suggest the need for greater attention to adequate summertime ventilation provision in airtight homes. The results demonstrate a high prevalence of overheating in exemplary housing, indicating the need for greater efforts to ensure the effective implementation of strategies to minimize overheating and improve ventilation in low-energy homes.     

Overheating in care settings: magnitude,causes, preparedness and remedies

ABSTRACT

Research in UK and elsewhere has highlighted that older people are particularly vulnerable to negative health effects of overheating. This paper examines the magnitude, causes, preparedness and remedies for addressing the risk of summertime overheating in four case study residential care and extra-care settings across the UK, spanning different building types, construction and age. An interdisciplinary approach is adopted, drawing from building science and social science methods, including temperature monitoring, building surveys, and interviews with design and management teams. The findings suggest that overheating is a current and prevalent risk in the case study schemes, yet currently little awareness or preparedness exists to implement suitable and long-term adaptation strategies (e.g., external shading). There was a perception from designers to managers, that cold represents a bigger threat to older occupants’ health than excessive heat. A lack of effective heat management was found across the case studies that included unwanted heat gains from the heating system, confusion in terms of responsibilities to manage indoor temperatures, and conflicts between window opening and occupant safety. Given that care settings should provide protection against risks from cold and hot weather, design, management and care practices need to become better focused towards this goal.     

Functional recovery of a resilient hospital type

Four adaptation options for ‘Nightingale’-type hospital ward buildings devised with practising clinicians are presented and evaluated. The adaptations recover functionality in an archaic ward configuration by delivering care to current UK National Health Service (NHS) models whilst preserving resilience to summer overheating. The investigation builds on recent work that demonstrates the significant resilience to heatwaves enjoyed by such traditionally constructed communal dormitories, the dominant UK hospital type between the late 1850s and 1939. Nightingale wards are potentially well-ventilated naturally, with good dilution of airborne pathogens. Although condemned as outdated by health ministers in recent years, many remain in use. As financial retrenchment suggests economical, creative refurbishment of hospitals will be required rather than new-build and replacement, the authors argue for health estates’ strategies that place value on resilience in a changing climate. Proposed adaptation options are investigated to assess resulting internal airflows and patient exposure to airborne pathogens. Options are costed and payback periods calculated to the standard public sector methodology. The proposed adaptations save time and cost over new-build equivalents. Selection of the most appropriate option is dependent on the characteristics of the patient cohort and care required.     

Exposure duration in overheating assessments: a retrofit modelling study

ABSTRACT

A new indicator of overheating risk is introduced that more comprehensively represents heat stress and the way thermal environment is experienced. This indicator is compared with the industry standard overheating assessment approach (CIBSE TM52). This is demonstrated using an energy retrofit simulation case study of a typical London, UK terraced dwelling under different climate scenarios. Overheating was evaluated first according to TM52, then via an assessment of continuously overheated intervals (COIs) that account for the duration where adaptive limits are continuously exceeded. Results for the case study show that, first, extent of overheating can vary greatly based on climate uncertainties. Second, insulation retrofit only contributes to substantial overheating when the space lacks proper ventilation or protection from solar radiation. Nevertheless, overheating cannot be avoided completely under future climate scenarios even with appropriate passive cooling. More importantly, the results show that overheated hours tend to occur consecutively. This implies that violations of TM52 criterion 1 (which currently applies only at the seasonal scale) can occur at the monthly/weekly resolutions. This ‘buried’ information can be revealed via the COI approach to more comprehensively capture how an overheating situation unfolds in a manner more relevant to heat stress and occupants’ thermal experience.     

Development of an England-wide indoor overheating and air pollution model using artificial neural networks

With the UK climate projected to warm in future decades, there is an increased research focus on the risks of indoor overheating. Energy-efficient building adaptations may modify a buildings risk of overheating and the infiltration of air pollution from outdoor sources. This paper presents the development of a national model of indoor overheating and air pollution, capable of modelling the existing and future building stocks, along with changes to the climate, outdoor air pollution levels, and occupant behaviour. The model presented is based on a large number of EnergyPlus simulations run in parallel. A metamodelling approach is used to create a model that estimates the indoor overheating and air pollution risks for the English housing stock. The performance of neural networks (NNs) is compared to a support vector regression (SVR) algorithm when forming the metamodel. NNs are shown to give almost a 50% better overall performance than SVR.     

Overheating in retrofitted flats: occupant practices,learning and interventions

ABSTRACT

The overheating risk in flats (apartments) retrofitted to energy-efficient standards has been identified by previous studies as one that is particularly high. With climate change and rising mean temperatures this is a growing concern. There is a need to understand the kinds of practices, learning and interventions adopted by the occupants of individual homes to try to reduce overheating, as this area is poorly understood and under-researched. This case study focuses on the impact of different home-use practices in relation to the severity of overheating in 18 flats in one tower block in northern England. Internal temperatures monitored in comparable flats show that the percentage of time spent above the expected category II threshold of thermal comfort according to BS EN 15251 can differ by over 70%. Extensive monitoring, covering a full year, including two summer periods, has identified emergent changes in heatwave practices linked with increased home-use skills and understanding among the research participants. Close analysis of design intentions versus reality has identified key physical barriers and social learning opportunities for appropriate adaptation in relation to heatwaves. Recommendations for designers and policy-makers are highlighted in relation to these factors.     

Bridging the domestic building fabric performance gap

It is recognized that there is often a discrepancy between the measured fabric thermal performance of dwellings as built and the predicted performance of the same dwellings and that the magnitude of this difference in performance can be quite large. This paper presents the results of a number of in-depth building fabric thermal performance tests undertaken on three case study dwellings located on two separate Passivhaus developments in the UK: one masonry cavity and the other two timber-frame. The results from the tests revealed that all the case study dwellings performed very close to that predicted. This is in contrast with other work that has been undertaken regarding the performance of the building fabric, which indicates that a very wide range of performance exists in new-build dwellings in the UK, and that the difference between the measured and predicted fabric performance can be greater than 100%. Despite the small non-random size of the sample, the results suggest that careful design coupled with the implementation of appropriate quality control systems, such as those required to attain Passivhaus Certification, may be conducive to delivering dwellings that begin to ‘bridge the gap’ between measured and predicted fabric performance.     

Inhabitant actions and summer overheating risk in London dwellings

ABSTRACT

An indoor overheating assessment study of 101 London dwellings during summer 2009 is presented. The study included building surveys, indoor dry bulb temperature monitoring and a questionnaire survey on occupant behaviour, including the operation of passive and active ventilation, cooling and shading systems. A theoretical London housing stock comprising 3456 combinations of building geometry, orientations, urban patterns, fabric retrofit and external weather was simulated using the EnergyPlus thermal modelling software. A statistical meta-model of EnergyPlus was then built by regressing the independent variables (simulation input) against the dependent variables (overheating risk). The monitoring and questionnaire data were analysed to explore the relationship between self-reported behaviour and overheating, and to test the meta-model. The monitoring data indicated that London homes and, in particular, bedrooms are already at risk of overheating during hot spells under the current climate. Around 70% of respondents tended to open only one or no windows at night mainly due to security reasons. An improvement in the coefficient of determination (R²) values between measured temperature and meta-model predictions was obtained only for those dwellings where occupants reported actions that were in line with the modelling assumptions, thus highlighting the importance of occupant behaviour for overheating.     

Quantifying the extent of space shortages: English dwellings

Lack of internal space is a problem in UK homes, and is often linked to a lack of space standards for housing in the UK. Although previous studies have examined new-build housing, this paper uses a new method to study 16 000 dwellings in the English Housing Survey (EHS) 2010 to examine existing housing and compare them with a modern space standard in an attempt to quantify the extent and magnitude of the problem. Dwellings in the survey were compared against a slightly modified version of the London Housing Design Guide 2010 internal space standard. It was found that between 21% and 55% of dwellings failed to meet the standard; and that flats and small terraced houses were most commonly below the standard. Dwellings were also frequently found to be under-occupied in comparison with the number of bedrooms. This research hypothesized that this was a result of the lack of space. To illustrate the use of this new analysis method, a recent change to the Housing Benefit system (colloquially known as the ‘Bedroom Tax’) has been considered. Households receiving Housing Benefit were more likely to be undersized, suggesting that the policy to withdraw housing benefits from these households may be misguided.     

Assessing impacts of summertime overheating: some adaptation strategies

The UK is predicted to experience warmer summers in the future, but the domestic building stock in England was not designed to cope with this change. The Standard Assessment Procedure (SAP) 2009 is used to assess the current state of the English building stock in terms of its vulnerability to overheating. The English Housing Survey 2009 provided data for 16 150 dwellings which are weighted to represent the housing stock. SAP predicts 82% of dwellings are currently at ‘slight’ risk of overheating and 41% at medium to high risk. If summer temperatures become 1.4°C warmer, then 99% of properties are predicted to have a medium to high risk of overheating. Several potential adaptations to the housing stock were considered to reduce overheating. Although ventilation strategies had the largest positive effect, the use of solar shading and shutters which allow secure ventilation could reduce vulnerability to overheating in the current climate. In a warmer climate, although some dwellings would still be at slight risk, the results suggest that solar shading strategies could reduce the percentage of those at medium to high risk to 6%. Future energy efficiency programmes will need to include adaptation measures to prevent overheating.     

Climate change future proofing of buildings—Generation and assessment of building simulation weather files

Simulation packages for predicting building performance in terms of energy and comfort are becoming increasingly important in the planning process. However, current industry standard weather files for building simulation are not suited to the assessment of the potential impacts of a changing climate, in particular summer overheating risks. In addition, no bespoke climate change weather files are readily available that can be loaded directly into environmental simulation software. This paper describes the integration of future UK climate scenarios into the widely used Typical Meteorological Year (TMY2) and EnergyPlus/ESP-r Weather (EPW) file formats and demonstrates the importance of climate change analysis through a case study example. The ‘morphing’ methodology published by the Chartered Institution of Building Services Engineers (CIBSE) is utilised as a baseline for transforming current CIBSE Test Reference Years (TRY) and Design Summer Years (DSY) into climate change weather years. A tool is presented that allows generation of TMY2/EPW files from this ‘morphed’ data and addresses the requirements related to solar irradiation, temperature, humidity and daylighting beyond the parameters provided by CIBSE weather years. Simulations of a case study building highlight the potential impact of climate change on future summer overheating hours inside naturally ventilated buildings.     

Case study of zero energy house design in UK

Possible solutions for zero energy building design in UK are discussed in this paper. Simulation software (EnergyPlus and TRNSYS 16) are employed in this study, where EnergyPlus simulations are applied to enable facade design studies considering building materials, window sizes and orientations and TRNSYS is used for the investigation of the feasibility of zero energy houses with renewable electricity, solar hot water system and energy efficient heating systems under Cardiff weather conditions. Various design methods are compared and optimal design strategies for typical homes and energy systems are provided.     

Thermal zoning and interzonal airflow in the design and simulation of solar houses: a sensitivity analysis

Many assumptions must be made about thermal zoning and interzonal airflow for modelling the performance of buildings. This is particularly important for solar homes, which are subjected to high levels of periodic solar heat gains in certain zones. The way in which these passive solar heat gains are distributed to other zones of a building has a significant effect on predicted energy performance, thermal comfort and optimal design selection. This article presents a comprehensive sensitivity analysis that quantifies the effect of thermal zoning and interzonal airflow on building performance, optimal south-facing glazing area, and thermal comfort. The effect of controlled shades to control unwanted solar gains is also explored. Results show that passive solar buildings, in particular, can benefit from increased air circulation with a forced air system because it allows solar gains to be redistributed and thus reduces direct gain zone overheating and total energy consumption.     

Modelling the carbon-saving performance of domestic ground-source heat pumps

A ground-source heat pump (GSHP) model is formulated and used to estimate the potential of a domestic GSHP as a carbon-saving technology (compared to a conventional gas boiler) with actual thermal data for a dwelling in the UK. The model shows good agreement with current sizing guidelines but shows possible barriers to the carbon-savings (and running cost savings) of GSHPs. This includes an analysis of output temperatures, system sizes and grid CO₂ intensity. The model suggests that GSHPs should be aimed towards a new-build market (rather than retrofit) due to the likely reliance on high surface area/low temperature distribution systems. Also, grid CO₂ intensity needs to be better understood when estimating the electrical consumption CO₂ emissions of GSHPs, both for current and future scenarios.     

Probabilistic climate projections with dynamic building simulation: Predicting overheating in dwellings

This study, as part of the Low Carbon Futures project, proposes a methodology to incorporate probabilistic climate projections into dynamic building simulation analyses of overheating in dwellings. Using a large climate projection database, suitable building software and statistical techniques (focussing on principal component analysis), output is presented that demonstrates the future overheating risk of a building in the form of a probability curve. Such output could be used by building engineers and architects to design a building to an acceptable future overheating risk level, i.e. providing evidence that the building, with specific adaptation measures to prevent overheating, should achieve thermal comfort for the majority of future climate projections. This methodology is overviewed and the use of the algorithm proposed in relation to existing building practices. While the methodology is being applied to a range of buildings and scenarios, this study concentrates on night-time overheating in UK dwellings with simple and achievable adaptation measures investigated.     

Development of an adaptive window-opening algorithm to predict the thermal comfort,energy use and overheating in buildings

This investigation of the window-opening data from extensive field surveys in UK office buildings demonstrates: (1) how people control the indoor environment by opening windows; (2) the cooling potential of opening windows; and (3) the use of an ‘adaptive algorithm’ for predicting window-opening behaviour for thermal simulation in ESP-r. It was found that when the window was open the mean indoor and outdoor temperatures were higher than when closed, but it was shown that nonetheless there was a useful cooling effect from opening a window. The adaptive algorithm for window-opening behaviour was then used in thermal simulation studies for some typical office designs. The thermal simulation results were in general agreement with the findings of the field surveys. The adaptive algorithm is shown to provide insights not available using non adaptive simulation methods and can assist in achieving more comfortable, lower energy buildings while avoiding overheating.     

Beyond design review: collaborating to create well-designed places in Scotland

ABSTRACT

This practice paper reflects on the national design advice service in Scotland that has been operated by Architecture & Design Scotland (A&DS) since 2005. Placed in the context of research on design review practice, the paper describes how design review in Scotland has evolved from a traditional panel model operating alongside a range of training and skills development functions into a more holistic and dynamic design advice service. The paper argues that the evolution of design review in Scotland signifies an innovative shift away from the often combative setting of a design panel, where the force of an argument frequently wins the day, towards a more measured, iterative and collaborative process of nurturing and enabling well-designed buildings and places.     

Do housing costs impact on poverty in rural areas?

Abstract

This research examines evidence for whether housing costs are more likely to be associated with poverty in rural than in urban Scotland. It reports the results from probit modelling of British Household Panel Survey data from 1999 to 2008. Empirical work is set in the context of understandings of factors associated with poverty, defined on an income basis, and specific features associated with rural locations. Attention is drawn to the way in which rurality is defined and that definition operationalized. The finding from the multivariate analysis is that a household’s housing costs do not appear to have a different association with its propensity to experience poverty in rural as opposed to urban Scotland. The paper sets out conclusions in the recognition of possible limitations and identifies ways in which the evidence can be extended.