Building Services Engineering Research & Technology

The new CIBSE design summer years (DSYs) for London Weather Centre, Heathrow and Gatwick in London are now available for three baseline years: 1976, 1989 and 2003. This study tested how these different design summer years impacted the assessment of overheating in a naturally ventilated office in London. Two office designs were tested, an uninsulated and one retrofitted with insulation and night cooling. The choice of baseline year impacted the level of overheating for both the uninsulated and retrofitted models. Tested in the more severe years, 1976 and 2003, the offices experienced the highest levels of overheating. When an office was retrofitted and night cooled, the choice of location had more of animpact on overheating due to the urban heat island effect. London Weather Centre and Heathrow experienced higher levels of overheating than Gatwick. The study highlights the need for designers to carefully consider how the differences between the weather files will impact their overheating assessment depending on their buildings’ fabric and ventilation design.

Practical application : This study provides initial testing of the how the new CIBSE design summer years impact overheating within a naturally ventilated office in London. Initial analysis of the weather files highlights the differences between locations and baseline years. These differences are then shown to have an impact on overheating depending on the building fabric and ventilation strategy. The results highlight how important it is that practitioners understand how both the weather variables and building and ventilation design will impact the predicted levels of overheating.

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 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.

The Low Carbon Futures tool provides a probabilistic assessment of future overheating risks and cooling demands for domestic and nondomestic buildings in the UK. The approach adopted for the development of the Low Carbon Futures tool includes academic rigour within the development of the calculation engine, and also practitioner feedback throughout the process. This paper discusses the journey of the tool from modelling and simulation to the practitioner engagement, which took place by means of a questionnaire, focus groups and interviews with building design professionals aimed at understanding how the issue of overheating in buildings is being addressed. Throughout these events, the synergies between designing for low-carbon targets and designing for a future climate were explored. A final dissemination event was held to identify output styles that could be generated by the Low Carbon Futures tool that would be more practical and useful for specific client types. The workshop discussions serve to shape the outputs from the tool, and the feedback gathered will be used to inform a number of output styles, based on client type.

Practical application : This paper outlines the development of the Low Carbon Futures tool for analysing overheating risks in buildings and discusses the practitioner feedback obtained from industry professionals on the use and applicability of the tool, in a final event hosted by the Low Carbon Futures research team in London. This event confirmed that practitioners need to be comfortable with the layout and format of the output in order to communicate its meaning and possible implications to a range of clients. A balanced output is required, which conveys some of the complexity of the underlying analysis, but which is easily understood and conveyed to a potentially lay audience.

This paper investigates the risk of projected post-2050s overheating in existing, retrofitted and new-build dwellings in the United Kingdom. As shown in the previous research, passive measures may not be sufficient in mitigating overheating risk. Therefore, mechanical cooling technologies that may be deployed to ‘adapt’ to a warming climate are tested for energy and CO₂ implications. For retrofits, heating demand is projected to remain dominant, whereas in post-2016 new-build, greater cooling system efficiency will be important. Thermal mass is shown to reduce future cooling load. The heat recovery element of mechanical ventilation with heat recovery may be rendered unnecessary in super-efficient homes. Ceiling fans coupled with natural ventilation may be sufficient in providing thermal comfort in the north of England. Ultimately, not planning for future overheating and cooling systems could create a new performance gap in design, construction and occupant behaviour.

Practical application : Overheating, already experienced in dwellings throughout the United Kingdom and projected to increase in occurrence, should be considered in all new design and retrofit. Dwellings designed to meet thermal comfort performance targets may be at risk of non-compliance as a result of a warming climate. Furthermore, dwellings designed to meet energy performance targets may be at risk of non-compliance as a result of potential need for cooling systems. The findings have implications for policy-making in relation to decarbonisation of the electricity grid, implementation of the Green Deal and upgrading building regulations to future-proof new and existing housing against a warming climate.

Major energy efficiency refurbishment of the UK housing stock is needed to help attain emission reduction targets of greenhouse gases. Such measures typically entail some planned or incidental reduction of uncontrolled ventilation in dwellings. This paper examines the trade-offs for health and sustainability objectives of typical retrofit refurbishments in UK homes. While reducing ventilation can help protect against the ingress of harmful pollutants from the outdoor air, our results demonstrate that reducing permeability to low levels, without additional purpose-provided ventilation, is likely to lead to substantial increases in pollutants derived from indoor sources, including indoor-generated particles, radon and environmental tobacco smoke. The monetised equivalent cost of the health dis-benefits associated with these exposures may exceed the potential benefits of reducing energy costs and greenhouse gas emissions.

Practical application : Reducing uncontrolled ventilation of dwellings helps to improve energy efficiency and can protect against the ingress of pollutants from the outdoor environment. However, simulation studies suggest that at high degrees of airtightness (very low permeability) there is a potentially steep rise in pollutants of indoor origin, whose adverse effects on health may outweigh the benefits of reduced energy use, lower CO₂ emissions and protection against outdoor pollution. Though the optimal permeability level for a given dwelling will vary with local circumstances, considerations of health protection suggest the need to avoid reducing permeability to low levels.

High temperatures, an extremely polluted ambient environment, alongside disparities in housing quality and household energy use, indicate overheating risk and poor indoor air quality in Delhi dwellings. In this study, we explore a range of interventions to reduce adverse temperature exposure and improve indoor air quality, focusing on PM_2.5, for exemplar base case households developed to cover the range of settlements types found in Delhi. Interventions are modelled using dynamic thermal simulation, and include a range of modifications to dwelling operation and building fabric, as well as additional building components. A weighted multi-objective assessment considering annual energy use, intervention cost, and a health metric encompassing heat, cold and PM_2.5 exposure, is employed to score the suitability of strategies for each settlement type. The most effective strategy is found to be a combination of changes in building fabric with evaporative cooling and cooking ventilation in all archetypes. The results demonstrate how a weighted multi-objective assessment is effective in selecting strategies for settlement types with differing priorities.

Practical application : Current dwellings in Delhi risk significant energy consumption or provide inadequate indoor environmental quality. This work presents the performance of potential interventions, by considering multiple criteria, which could be deployed in Delhi households to provide low-energy healthy homes.

The late 1970s design for the Rosie Maternity Hospital on the Addenbrookes campus in Cambridge is a recurring type across the UK National Health Service, a framed three-storey courtyard configuration in brick masonry. It was selected as a case study project for the ‘Design and Delivery of Robust Hospitals in a Changing Climate’ project, pursuing the methodology developed for that research. Temperature data were collected in representative spaces within the hospital, over a two-year period. These revealed overheating in mild conditions relative to an observed 24℃ threshold for sleep but concealed within the customary 28℃ threshold marking the upper limit of acceptable conditions. The building was modelled using current climate data to predict 2010 conditions. The model was then calibrated against the observed 2010 data and used to predict the likely internal temperatures in current and 2030s. The results indicated an increase in peak temperatures. Four adaptive intervention schemes were subsequently developed: an ‘enlightened’ industry standard ‘Passivhaus’-type option providing superinsulation, sealed glazing and heat recovery; a lower technology-based scheme promoting natural cross-ventilation by providing greater opening glazing area, opening up the plan, sunshading and additional insulation; an enhanced natural ventilation scheme glazing over the courtyards to provide supply air winter gardens, and an advanced natural ventilation option pursuing passive downdraught cooling. All four schemes were modelled using the projected current and 2030s weather data and their performance was compared. The schemes were fully costed to yield relative ‘value for money’ guidance to National Health Service Trusts.

Practical application: The Heat wave Plan for England 2014 warns National Health Service (NHS) organisations of the risks to patients, particularly the very young, the elderly and the seriously ill, from extreme summer heat events.¹ The Chief Medical Officer in her introduction challenges each NHS locality to plan well in advance of hot spells, as appropriate. This paper describes the likely extent of overheating risk and a series of potential adaptation plans for a recurring NHS hospital building type. As a consequence, estates and facilities decision makers in NHS organisations and Public Health England officers charged with the mitigation of risk resulting from overheating of wards and clinical spaces will benefit directly in their necessary decision making from the findings. Policy makers in the Department of Health and policy advisors in the NHS Sustainable Development Unit and the Climate Change Committee Adaptation Sub-Committee will benefit from the evidence presented in advising the NHS and Department of Health.

Indoor temperature and air quality in dwellings are closely coupled. Differences between the indoor temperature and the temperature outside and in adjoining zones can influence airflow due to the stack effect, whilst changes in ventilation can cause changes in indoor pollution and temperature. This paper demonstrates the relationship between an indoor air pollutant, PM_2.5, and temperature in UK domestic building archetypes using the dynamic thermal and contaminant modelling capabilities of EnergyPlus 8.0 under various UK Climate Projections 2009 (UKCP09) scenarios (current, current ‘hot’, 2050 High Emissions and 2050 High Emissions ‘hot’), with both internal and external PM_2.5 sources. Results indicate that flats have 0.7–0.8 times as much outdoor PM_2.5 infiltrating indoors compared to detached dwellings, but 1.8–2.8 times more PM_2.5 from indoor sources. During hot periods, temperature-dependent window opening increases exposure to outdoor PM_2.5, meaning that as temperatures rises, dwelling occupants will become exposed to relatively higher levels of outdoor PM_2.5 and lower levels of indoor PM_2.5 due to the need to increase dwelling ventilation. The practical implications for government and designers and possible policy implications of this research are discussed.

Practical applications : This paper demonstrates how an increase in summertime ventilation is necessary in UK homes to reduce overheating risks due to climate change and energy-efficient building retrofits. This, in turn, will lead to a change in the profile of indoor air pollution exposure, with greater exposure to pollution from outdoor sources and reduced exposure to pollution from indoor sources. Roof insulation and trickle vents reduce overheating risk, whilst increased use of mechanical ventilation heat recovery systems in the UK is encouraged, as it offers the co-benefits of cooling through increased ventilation, energy recovery and the potential to reduce indoor pollution levels.