Alex Summerfield

Solid-wall U-values: heat flux measurements compared with standard assumptions

The assumed U-values of solid walls represent a significant source of uncertainty when estimating the energy performance of dwellings. The typical U-value for UK solid walls used for stock-level energy demand estimates and energy certification is 2.1 Wm−2 K−1. A re-analysis (based on 40 brick solid walls and 18 stone walls) using a lumped thermal mass and inverse parameter estimation technique gives a mean value of 1.3 ± 0.4 Wm−2 K−1 for both solid wall types. Among the many implications for policy, this suggests that standard UK solid-wall U-values may be inappropriate for energy certification or for evaluating the investment economics of solid-wall insulation. For stock-level energy modelling, changing the assumed U-value for solid walls reduces the estimated mean annual space heating demand by 16%, and causes a proportion of the stock to change Energy Performance Certification (EPC) band. The analysis shows that the diversity of energy use in domestic buildings may be as much influenced by heterogeneity in the physical characteristics of individual building components as it is by variation in occupant behaviour. Policy assessment and guidance material needs to acknowledge and account for this variation in physical building characteristics through regular grounding in empirical field data.

Challenges and future directions for energy and buildings research

Introduction In 2007 Building Research & Information published a special issue on the challenges posed by climate change for the building stock. Its focus was well-timed in addressing technical strategies and government policy options for reducing carbon emissions. In the wake of the Stern Review (Stern, 2007) and then again with the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) (Metz et al., 2007), considerable international impetus existed for governments to move from broad carbon reduction targets to specific sectoral contributions to reduce energy demand, for instance by increasing the performance of new and refurbished construction via building regulations. Lowe’s (2007a) editorial in that special issue highlighted the need to consider energy supply and demand for the building stock as a system, and specifically the implications of decarbonizing the electricity supply in step with addressing energy demand in terms of the interactions influencing the choice and staging of options available to policy-makers.

Uptake of energy efficiency interventions in English dwellings

Little detailed evidence has previously been available regarding the uptake rate or prevalence of energy efficiency interventions among specific household groups. This study uses the Home Energy Efficiency Database (HEED) to investigate both the combination of measures that have been installed, and in which dwellings, according to key neighbourhood socio-demographic variables, including income and tenure. Analysis of 2000–07 data indicates that approximately 40% (9.3 million) dwellings in England had approximately 23.7 million efficiency measures installed, with an average of 2.5 measures per dwelling. Building fabric-related measures were the most frequent (e.g. cavity wall insulation, loft insulation and glazing) with an average of 2.1 million installed each year. Dwellings with the highest number of fabric interventions (the top 20%) were more likely to be found in areas with low income, with more owner-occupied dwellings, experiencing lower winter temperatures, having a lower proportion of flats, and having a slightly higher proportion of older adults and children. Energy efficiency installations have tended to occur among specific types of households or parts of the building stock. These findings have implications for the design of future government programmes for targeting energy efficiency measures to specific household groups or dwelling types.

Historic Variations in Winter Indoor Domestic Temperatures and Potential Implications for Body Weight Gain

It has been argued that the amount of time spent by humans in thermoneutral environments has increased in recent decades. This paper examines evidence of historic changes in winter domestic temperatures in industrialised countries. Future trajectories for indoor thermal comfort are also explored. Whilst methodological differences across studies make it difficult to compare data and accurately estimate the absolute size of historic changes in indoor domestic temperatures, data analysis does suggest an upward trend, particularly in bedrooms. The variations in indoor winter residential temperatures might have been further exacerbated in some countries by a temporary drop in demand temperatures due to the 1970s energy crisis, as well as by recent changes in the building stock. In the United Kingdom, for example, spot measurement data indicate that an increase of up to 1.3°C per decade in mean dwelling winter indoor temperatures may have occurred from 1978 to 1996. The findings of this review paper are also discussed in the context of their significance for human health and well-being. In particular, historic indoor domestic temperature trends are discussed in conjunction with evidence on the links between low ambient temperatures, body energy expenditure and weight gain.

Is CO2 a good proxy for indoor air quality in classrooms? Part 1: The interrelationships between thermal conditions, CO2 levels, ventilation rates and selected indoor pollutants

Current indoor air quality (IAQ) guidelines in school buildings are framed around thermal conditions, carbon dioxide (CO2) levels and corresponding ventilation rates without considering specific indoor pollution levels. Drawing on detailed monitoring data from a sample of 18 classrooms from six London schools, the aim of this paper is to highlight behavioural and environmental factors that affect pollution levels in classrooms, and evaluate the adequacy of CO2 as an overall predictor for IAQ using multilevel modelling. Together with elimination of indoor emission sources, keeping the temperatures below 26℃, and preferably below 22℃ depending on season, may limit total volatile organic compounds below thresholds associated with sensory irritations. The models suggested that after removing dust reservoirs from the classrooms, lowering average indoor CO2 levels below 1000 ppm by increasing ventilation rates can limit indoor airborne particulate matter concentrations below recommended annual WHO 2010 guidelines. Uncontrolled infiltration rates may increase indoor NO2 levels and microbial counts of fungal and bacterial groups, whose presence is associated with wet and moist materials. Overall, indoor CO2 levels were a useful proxy for indoor investigations as they can prevent overheating, dilute pollutants with indoor sources and purge concentrations of airborne particles; however, they were a poor predictor of traffic related pollutants. Practical implications of the findings on the UK policy and building design industry are discussed. Practical application : Driven by the growing population, and many years of intensive use, the UK building stock is in need of rapid expanding, extensive refurbishment and maintenance. However, local authorities lack the money for comprehensive and specialist renovations. The recommendations presented in this paper take into account specific needs and possibilities, and target building designers, engineers and occupants involved with daily operation and management of school buildings. Timely control of ventilation and heating systems, informed selection of construction materials, interior finishing and elimination of indoor sources may improve IAQ of school classrooms.

The shape of warmth: temperature profiles in living rooms

The most commonly used family of models in representing the UK building stock, BREDEM (the Building Research Establishment Domestic Energy Models), assume that all homes exhibit the same heating pattern and hence can be expected to have similar temperature profiles over the course of a day. The presented research shows that homes differ significantly in their respective temperature profile over the course of the day. A cluster analysis performed on temperature data from 275 living rooms in English homes over three winter months resulted in four different clusters of temperature profiles. The clusters differ significantly in their shape, as revealed by visual inspection, and supported by significant differences in minimum and maximum temperatures and temperature variability across the day. About 40% of homes showed a bimodal temperature pattern as assumed under BREDEM. However, the remaining 60% showed very different profiles. These findings challenge the assumption that one standard pattern fits all homes. Different temperature demand profiles have important implications for future peak power demands, particularly if domestic space heating is switched to electricity. It is also helpful for relating occupant demographics to appropriate forms of fabric retrofit.

Is CO2 a good proxy for indoor air quality in classrooms? Part 2: Health outcomes and perceived indoor air quality in relation to classroom exposure and building characteristics

The aim of this paper is to investigate whether keeping indoor thermal conditions and carbon dioxide (CO2) levels within the current guideline values can provide a healthy and comfortable school environment. The study was organised as a longitudinal investigation over an academic year using a cohort of 376 students aged 9 to 11 (response rate: 87%) attending 15 classrooms in five London primary schools. The prevalence of asthmatic symptoms and asthma attacks was significantly higher among children attending urban schools (10.2%) than suburban schools (1.5%), and was significantly related to exposure to higher nitrogen dioxide (NO2) concentrations (odds ratio: 1.11, 95% confidence interval: 1.00–1.19). Self-reported dermal, mucosal, respiratory and general symptoms were 18.5%, 60.7%, 28.2% and 43.6% respectively in the heating season, and decreased in the non-heating season. Infiltration rates were negatively associated with prevalence and incidence of all sick building syndrome symptoms. Exposure to traffic-related pollutants, such NO2, ozone (O3) and tetrachloroethylene (T4CE), associated with mucosal symptoms, also increased dissatisfaction with indoor air quality (IAQ) and, therefore, perceived IAQ might be a first indication of exposure. Among targeted microbial counts, only Trichoderma viride remained significant predictors of satisfaction with IAQ even at low concentrations. The study provides evidence that simultaneous provision for limiting indoor CO2 levels and thermal conditions below current guidelines (e.g. below 1000 ppm and 26℃ or 22℃ depending on season) may improve perceived IAQ. This paper stresses the need to go beyond current regulations to investigate concentrations of specific pollutants to ensure a healthy school environment, and closes with a section on the practical implications on the UK policy and the building design industry. Practical application : The findings highlight the role and responsibility of stakeholders, from regulators to designers and school authorities, to account for the external environment and take the steps needed to ensure that schools provide a healthy indoor environment for their students. The recommendations focus on the need to decrease outdoor pollution levels in the school vicinity, thus improving health of the students and reducing the prevalence of respiratory illness. Building designers and engineers shall adopt an integrated approach for the simultaneous provision of adequate thermal conditions and IAQ in classrooms.

A Victorian school and a low carbon designed school: comparison of indoor air quality, energy performance, and student health

This paper compares energy and ventilation performance, and levels of pollutants in six school classrooms and associates them to asthmatic and Sick Building Syndrome (SBS) symptoms and the perceived indoor air quality (IAQ) of students. Self-reported data on subjective perception of air quality and health responses were gathered with a standardised questionnaire completed by 151 school children (Response Rate (RR):86%) attending two schools in the Greater London Area: a contemporary suburban low carbon school building and an urban, high thermal mass school built in the 19th century. Temperature, particulate matter (PM), nitrogen dioxide (NO2), ozone (O3), and volatile organic compounds (VOCs) concentrations were monitored in three classrooms and one outdoor site in each school for 5 consecutive days during the heating seasons. Biological parameters were determined in settled dust and analysed with molecular methods. Overall, asthma prevalence in the school environment was associated with exposure to higher NO2 levels (odds ratio (OR): 1.1, 95% confidence interval (CI): 1.0–1.2). Exposure to PM in all classrooms was high and was associated with increased mucosal symptoms (OR: 1.4, 95% CI: 1.1–1.9) and eczema (OR: 1.3, 95% CI: 1.0–1.6) prevalence. Higher indoor CO2 levels were associated with general symptoms (OR: 1.1, 95% CI: 1.0–1.2). Increased dissatisfaction with IAQ was associated with higher temperatures and exposure to higher NO2, CO2, fungal, cat allergens, and VOC levels (limonene and formaldehyde). Direct access to the playground without buffer zone and user behavioural patterns may affect energy consumption. Findings suggest that increased ventilation rates may mitigate overheating, alleviate SBS symptoms, and improve satisfaction with IAQ.

Application of a Monte Carlo model to predict space heating energy use of Belgrade's housing stock

Detailed domestic stock energy models can be used to help formulate optimum energy reduction strategies. However, there will always be considerable uncertainty related to their predictions due to the complexity of the housing stock and the many assumptions required to implement the models. This paper presents a simple Monte Carlo (MC) model that can be easily extended and/or transformed in relation to data available for investigating and quantifying uncertainties in both the housing stock models predictions and scenario assumptions. While 90% of the MC model predictions fell within a range which is ±19% the mean value, 50% of them were within ±8% of the mean. The findings suggest that the uncertainties associated with the model predictions and scenario assumptions need to be acknowledged fully and – where possible – quantified as even fairly small variability in the influential variables may result in rather large uncertainty in the aggregated models prediction.

Indoor air quality in London schools. Part 1: ‘performance in use’

This study aims to assess the adequacy of current guidelines, framed around thermal comfort, estimated ventilation rates, and CO2 levels, for the provision of indoor air quality (IAQ) in school classrooms. It draws on detailed monitoring data from a sample of 18 classrooms from 6 London schools. Overheating during the non-heating season was identified in eight south-, south-east-, and east-facing classrooms in two Victorian and two contemporary schools. Four classrooms in these contemporary schools also failed to keep average indoor CO2 levels below 1500 ppm in the non-heating season. During the heating season, eight classrooms exceeded the daily average indoor CO2 levels. Mean indoor particulate matter (PM)10 and PM2.5 levels recorded in all classrooms in both seasons were higher than 20 and 10 μg/m3, respectively, indicating that school exposure during an academic year may exceed annual recommended WHO [2006. Air Quality Guidelines: Global Update 2005: Particulate Matter, Ozone, Nitrogen Dioxide, and Sulfur Dioxide. Copenhagen: WHO Regional Office for Europe; 2010. WHO Guidelines for Indoor Air Quality: Selected Pollutants. Copenhagen: WHO Regional Office for Europe.] guideline values in all classrooms. In both seasons, all classrooms were found to have indoor total volatile organic compounds levels (median: 269 ppb and interquartile range: 64–408 ppb) above guideline thresholds (130 ppb) associated with sensory irritations. Identification of specific volatile organic compounds indicated the presence of strong indoor sources including furniture, cleaning products, and teaching materials. Findings suggest that these school classrooms often have poor IAQ due to a combination of sub-optimal building operation and management practices. Furthermore, while CO2 and ventilation rates are a useful tool for IAQ assessment, findings indicate that consideration of specific pollutants is necessary to ensure a healthy indoor environment.