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.     

Analysis of probabilistic climate projections: heat wave,overheating and adaptation

Climate change could substantially impact on the performance of buildings in providing thermal comfort to occupants. The recently launched UK climate projections (UKCP09) suggest that all areas of the UK will become warmer in the future with the possibility of more frequent and severe extreme events, such as heat waves. This study, as part of the low carbon futures (LCF) project, explores the consequent risk of overheating and the vulnerability of a building to extreme events. A simple statistical model proposed by the LCF project elsewhere has been employed to emulate the outputs of the dynamic building simulator (ESP-r), which if directly used with the numerous replicated climates available from a probabilistic climate database could be practically challenging. For complex probabilistic climate datasets, we demonstrate the efficiency of the statistical tool in performing a systematic analysis of various aspects of heat waves including: frequency of extreme heat events in changing climate; its impact on overheating issues and effects of specific adaptation techniques applied to offset predicted overheating. We consider a domestic building as a virtual case study. Results are presented relative to a baseline climate (1961–1990) for three future timelines (2030s, 2050s and 2080s) and three emission scenarios (Low, Medium and High).     

Overheating in Scotland: contributing factors in occupied homes

ABSTRACT

There is growing awareness of the overheating risks in new-build properties in the UK. However, this tends to be considered a problem principally for the southern regions in the UK, only becoming a serious issue in the north of England in the medium-term and in the long-term for Scotland. This notion tends to be largely predicated upon climate change predictions, differences in latitude and summer air temperatures. This paper describes the results from Building Performance Evaluation (BPE) studies over a two-year period from 26 occupied new-build homes across Scotland which demonstrated incidences of overheating. Results suggest that low-energy buildings are susceptible to overheating despite northerly latitudes, with 54% of houses studied overheating for more than six months annually, and 27% of homes overheating for less than 10% of the year. Evidence indicated that commonly used prediction tools do not appear to anticipate overheating adequately. This paper maps common overheating causes due to design and the role of occupants, identifying the risks due to the regulatory system, prediction and procurement processes, and design and construction. A common finding was that design and occupancy factors appear to have a greater impact on overheating more than location and climatic factors.     

Low carbon heating and older adults: comfort,cosiness and glow

Policies to decarbonize heat provision involve the diffusion of low carbon thermal technologies (e.g. ground-source heat pumps and wood pellet boilers). In domestic buildings, such efforts presume the compatibility of novel technologies with practices of home-making, in terms of comfort, cosiness and sociability. However, research on engagement with low carbon technologies post-installation is limited, particularly with older adults, a growing social group in an ageing society. This study explores how older adults living with low carbon thermal technologies represent thermal comfort, drawing on in-depth interviews in diverse UK home environments (owner-occupied and rented; extra-care, sheltered and care homes; urban and rural). Findings indicate that cosiness and glow are highly valued by and for older adults, and achieved in diverse ways that may run counter to policy goals. In owner-occupied, rural homes, wood-burning stoves were retained after installation of under-floor heating/heat pumps to provide a visible glow and hospitality to guests. In care homes, fake fireplaces provide cosiness and glow without compromising concerns about risk. The research suggests that presumed emissions savings from the deployment of low carbon heating technologies may be overestimated, as home-making practices lead to the supplementing of these devices to provide comfort, cosiness and sociability.     

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.     

Affordable Housing,Disasters, and Social Equity

Abstract

Problem, research strategy, and findings: The Low-Income Housing Tax Credit (LIHTC) is the most common financing mechanism for subsidized housing production in America. We investigate how and to what extent states are currently using the LIHTC to prepare for and recover from disasters. We systematically code guidelines in the 2017 LIHTC qualified allocation plans from 53 states and territories to identify disaster-related provisions. Twenty-four states and territories include provisions for preparedness or recovery in their allocation plans, of which 13 include only preparedness provisions, 3 include only recovery provisions, and 8 include both types. Preparedness provisions address project design and siting, whereas recovery provisions direct credits to disaster-affected areas or the replacement of damaged units. Using t tests, we compare three sets of states—those without any disaster-related provisions, those with either preparedness or recovery provisions, and those with both types of provisions—across measures of housing cost, demographic composition, disaster exposure, and political ideology. States with higher homeownership rates, lower home values, and lower rents are more likely than other states to have either or both types of provisions. Future research should investigate state adoption of disaster-related LIHTC provisions to better inform affordable housing policy.

Takeaway for practice: State governments could mitigate disaster-related hazards and help speed recovery by including locally relevant preparedness and recovery provisions in their LIHTC allocation plans. These provisions could encourage resilient construction, weigh the social costs and benefits of LIHTC construction in floodplains, or waive program rules to address postdisaster housing shortages.     

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.     

Adaptation to Climate Change

Problem: Even if significant reductions in global greenhouse gas emissions are achieved, some amount of climate change appears to be inevitable. Local, regional, state, and federal planning and regulation should begin to address how to adapt to these changes.

Purpose: This article presents a policy synthesis of adaptation planning issues, using California as a case study. We examine the institutional and regulatory challenges and tradeoffs that climate change poses in six particularly vulnerable areas: water resources, electricity, coastal resources, air quality, public health, and ecosystem resources. We discuss obstacles to adaptation planning and successes overcoming these barriers, and suggest how planning can incorporate adaptation.

Methods: This article presents a policy synthesis of adaptation planning issues, drawing on our recent research on California's experience and related literature. We summarize the results of six studies that draw on quantitative and qualitative information gathered through surveys, interviews, and literature review.

Results and conclusions: Planners should use forward-looking climate data that include higher water and air temperatures, sea-level rise, and increased numbers of extreme events like heat waves, floods, and wildfires when making decisions about future development, infrastructure investments, open-space protection, and disaster preparedness. Climate change will exacerbate conflicts between goals for economic development, habitat protection, and public safety, requiring stronger interagency coordination and new laws and regulations.

Takeaway for practice: Local and regional planners can help society adapt to a changing climate by using the best available science, deciding on goals and early actions, locating relevant partners, identifying and eliminating regulatory barriers, and encouraging the introduction of new state mandates and guidelines.

Research support: Partial support for this research was provided by Pacific Gas and Electric, The Nature Conservancy, and Next 10.     

Combating overheating: mixed-mode conditioning for workplace comfort

ABSTRACT

Using post-occupancy evaluations of seven mixed-mode buildings – three in Australia and four in India – this paper demonstrates that effective mixed-mode conditioning (instead of year-round air-conditioning) can deliver comfortable workspaces. Occupant feedback reinforces strong associations between overheating, thermal comfort, overall comfort and perceived productivity. However, differing levels of thermal acceptability within and between the Australian and Indian contexts are evident. Occupants in the Indian buildings were found to tolerate a wider range of temperatures when compared with Western contexts where lower temperature limits entrench an energy demand through a greater reliance on air-conditioning. The outcomes from the study suggest that the perception of overheating and consequent risk to building performance can be intensified when occupants perceive limited adaptive opportunity or problems are not rectified quickly, whereas perceived control is less important where building systems are user responsive. Occupants in three of the study buildings also perceived higher-than-anticipated comfort which could be attributable to well-liked attributes, such as break-out spaces, daylight and fresh air included in these buildings. The findings challenge designers and clients to develop user-responsive climate interactive workplaces that capitalize on spatial and mixed-mode environmental control to tackle the question of overheating.     

Resilience of naturally ventilated buildings to climate change: Advanced natural ventilation and hospital wards

Naturally ventilated buildings have a key role to play mitigating climate change. The predicted indoor temperatures in spaces with simple single-sided natural ventilation (SNV) are compared with those in spaces conditioned using a form of edge in, edge out advanced natural ventilation (ANV) for various UK locations. A criterion, for use in conjunction with the BSEN15251 adaptive thermal comfort method, is proposed for determining when the risk of overheating, both now and in the future, might be deemed unacceptable. The work is presented in the context building new, and refurbishing existing, healthcare buildings and in particular hospital wards. The spaces conditioned using the ANV strategy were much more resilient to increases in both internal heat gains and climatic warming than spaces with SNV. The ANV strategy used less energy, and emitted less CO₂ than conventional, mechanically ventilated (MV) alternatives. In a warming world, the ‘life-expectancy’ of passively cooled buildings can be substantially influenced by the internal heat gains. Therefore, resilience to climate change, susceptibility to internal heat gains and the impact of future heat waves, should be an integral part of any new building or building refurbishment design process.     

Householders co-managing energy systems: space for collaboration?

ABSTRACT

The potential role of households as ‘co-managers’ of energy in smart grids is widely discussed in the social science literature. Much remains uncertain about the social relations and practices emerging around novel smart grid technologies and their contribution to sustainability. Drawing on 14 ‘show-and-tell’ home tours with householders in a smart grid trial, an analysis is presented of how home energy management (HEM) is performed in everyday life. The focus is on three technologies: monitoring technologies, smart heat pumps and home batteries. How and why householders do (not) engage with energy management during the pilot project is described. When householders participate in HEM practices, they gain energy management understandings and an awareness of smart grid objectives. Since HEM practices are shared between householders and actors from the energy provision system, they display particular ways of distributing responsibilities, power and agency over technologies, experts and householders. The time and space granted to these three smart grid technologies are shown to depend on the trust relationships between householders and the more or less absent providers of technologies and services. These insights emphasize the need to develop smart grid solutions reflexively with respect to the different spaces and practices in households in which they operate.     

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.     

Designing for practice: understanding technology use in rural community-based youth mental health contexts

Abstract

Social and mobile technologies appear to have remarkable scope to improve the access and quality of remote frontline mental health services. However, their potential has not yet been realised, due in part to an insufficient appreciation of remote mental health care settings as contexts for design. This study reports on a participatory design (PD) process involving mental health practitioners and clients, focusing on three participatory future workshops. Visioning, Scenario building and Mock-up phases encouraged participants to explore: (1.) What is needed and possible? (2.) Where would it fit? Who would use it and why? and (3.) How would it look, feel & function? These activities generated a contextualised understanding of frontline mental health service provision, and the possible roles of technology within it. PD methods were effective in a number of respects: defining domain criteria associated with mental health care; supporting community-based youth mental health professionals to articulate the roles of technology in their work; and identifying new opportunities for technologies in this space. Mental health applications can do more than provide a means of self-tracking or serve as a treatment surrogate; rather they can support clients’ autonomy with respect to self-discovery and direction-setting in treatment and recovery.     

Semi-reflecting roller blinds for windows: a performance simulation using real weather data for locations in England,Denmark and Switzerland

This paper assesses the performance, under European weather conditions, of windows fitted with semi-reflecting roller-blinds. The heat balance of a 1 m² window is calculated, using real hourly weather data, for windows facing North, South. East and West in three widely separated locations. Five types of window are considered: single. double and triple glazed, roller-blind permanently down and “managed” roller-blind.

By summing the net heat losses and gains over the local heating seasons. the total losses or gains are obtained for all cases. An attempt is also made to evaluate the summer overheating problem in each case. The managed roller-blind is found to have a performance comparable to that of triple glazing in the heating season and to give substantial reductions in overheating in summer. Maximum acceptable prices for the roller-blinds are estimated from the calculated energy savings and pay-back times assumed for domestic and commercial users.     

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.     

On the influence of building design,occupants and heat waves on comfort and greenhouse gas emissions in naturally ventilated offices. A study based on the EN 15251 adaptive thermal comfort model in Athens,Greece

According to the Intergovernmental Panel on Climate Change the buildings sector has the largest mitigation potential for CO₂ emissions. Especially in office buildings, where internal heat loads and a relatively high occupant density occur at the same time with solar heat gains, overheating has become a common problem. In Europe the adaptive thermal comfort model according to EN 15251 provides a method to evaluate thermal comfort in naturally ventilated buildings. However, especially in the context of the climate change and the occurrence of heat waves within the last decade, the question arises, how thermal comfort can be maintained without additional cooling, especially in warm climates. In this paper a parametric study for a typical cellular naturally ventilated office room has been conducted, using the building simulation software EnergyPlus. It is based on the Mediterranean climate of Athens, Greece. Adaptive thermal comfort is evaluated according to EN 15251. Variations refer to different building design priorities, and they consider the variability of occupant behaviour and internal heat loads by using an ideal and worst case scenario. The influence of heat waves is considered by comparing measured temperatures for an average and an exceptionally hot year within the last decade. Since the use of building controls for shading affects thermal as well as visual comfort, daylighting and view are evaluated as well. Conclusions are drawn regarding the influence and interaction of building design, occupants and heat waves on comfort and greenhouse gas emissions in naturally ventilated offices, and related optimisation potential.     

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.     

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.     

Applying a multi-objective optimization approach for Design of low-emission cost-effective dwellings

Modern buildings and their HVAC systems are required to be not only energy-efficient but also produce fewer economical and environmental impacts while adhering to an ever-increasing demand for better environment. Research shows that building regulations which depend mainly on building envelope requirements do not guarantee the best environmental and economical solutions. In the current study, a modified multi-objective optimization approach based on Genetic Algorithm is proposed and combined with IDA ICE (building performance simulation program). The combination is used to minimize the carbon dioxide equivalent (CO₂-eq) emissions and the investment cost for a two-storey house and its HVAC system. Heating/cooling energy source, heat recovery type, and six building envelope parameters are considered as design variables. The modified optimization approach performed efficiently with the three studied cases, which address different summer overheating levels, and a set of optimal combinations (Pareto front) was achieved for each case. It is concluded that: (1) compared with initial design, 32% less CO₂-eq emissions and 26% lower investment cost solution could be achieved, (2) the type of heating energy source has a marked influence on the optimal solutions, (3) the influence of the external wall, roof, and floor insulation thickness as well as the window U-value on the energy consumption and thermal comfort level can be reduced into an overall building U-value, (4) to avoid much of summer overheating, dwellings which have insufficient natural ventilation measures could require less insulation than the standard (inconsistent with energy saving requirements) and/or additional cost for shading option.     

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.