Dr Martin Fletcher

Shared ground loops (SGLs) combine shared ground heat exchangers with distributed heat pumps across multiple properties and may offer a route to decarbonise heating where individual heat pumps or heat networks are not feasible. SGLs can be installed in homes and buildings with limited outside space for a heat pump or insufficient demand density to support a heat network. To make the most of potential opportunities, greater awareness of factors shaping UK deployment is needed. Through a mixed-methods approach combining rapid evidence assessment, case studies and policy mapping, this study finds SGLs mostly limited to deployment by social landlords and in new build settings, with wider use impacted by high capital costs, policy gaps around mid-scale solutions, market concentration around a single supplier, and the need for business models applicable to mixed-tenure settings. SGLs are particularly suitable for dwellings in higher density areas outside of government-designated Heat Network Zones, where it is expected that large heat networks will deliver the lowest-cost route to decarbonising heat. We suggest policy and practice recommendations intended to create conditions for wider deployment. At a national policymaker level, SGL suitability for mid-scale, medium-density settings and support for a flexible energy system should be more clearly recognised, especially in areas outside Heat Network Zones. At the individual company level, deployment would be supported through development of utility-style business models and installation approaches by infrastructure developers which can offer SGLs to households of a range of tenure types.

Exercise is a significant contributor to health and wellbeing and many activities rely on a dedicated indoor facility to take place. Substantial resource is used to condition indoor sport facilities despite there being limited understanding of what constitutes thermal comfort during exercise. Conventional metrics to evaluate thermal comfort are derived from sedentary or near-sedentary individuals, prompting investigation into the fundamental notions of comfort during exercise. Whilst insightful, prior research on this topic has predominantly occurred in laboratory settings that lack experiential realism. Thermal surveys to explore occupant sensation, comfort, preference, acceptability, tolerance, and environmental perception were undertaken in a naturally ventilated multi-purpose indoor sports hall in the UK over a 24-month period. Environmental conditions were monitored at 4 locations in the hall, with the sample encompassing low (<3 MET), medium (3-5 MET) and high (>5 MET) activity intensities. The study highlights the complexity of monitoring large open indoor spaces, particularly direct measurement of radiant effects at the centre of the space. Using non-parametric methods, data were analysed to evaluate thermal judgements and their implications for space conditioning. Comfort was observed across a broad range of environmental air temperatures (13-24°C), with discomfort increasing as thermal sensation became more intense. Exercising individuals exhibited a drift in thermal neutrality, with a preference for a warmer personal thermal sensation corresponding to +0.7 scale points on the thermal sensation scale. This did not apply to environmental air temperature, where preference was for thermally neutral conditions (i.e. neither cool nor warm). This suggests that the commonly used 7-point thermal sensation scale is not an appropriate proxy for satisfaction with environmental conditions for exercising individuals. Metabolic rate was significant in the perception of thermal sensation during exercise (rs = .337, p < .001), with environmental conditions observed to have less impact. Environmental air temperature was, however, a critical factor for the acceptance (rs = -.269, p = .002) and tolerance (rs = .283, p = .001) of overall thermal state, declining where environmental conditions exceeded 24°C and highlighting the significance of appropriate sport facility conditioning strategies.

The development of mathematical models that can reliably simulate the energy performance of a whole building or a building component with minimal discrepancy between the real and simulated data is a major aim of Building Physics science. In order to create models that accurately represent real physical phenomena it is necessity to perform tests on buildings and building components, producing real data that can be used to adjust and validate these models. If these tests are not undertaken correctly, incorrect data sets, insufficient data sets or excessively complex and expensive experiments may be performed. Thus, depending on the aim and the accuracy needed for the mathematical models, the test environment and test set up must be chosen correctly. This problem has been studied inside Subtask 2 of the Annex58 “Reliable building energy performance characterisation based on full scale dynamic measurements”. The aim was to come to a roadmap on how to measure the actual thermal performance of building components and whole buildings. This means under realistic boundary conditions (field exposure or artificial climate) and taking into account workmanship. Since there are many established methods and different Standards for different measurement purposes, the solution has been to organize the existing methods (both Standards and widely used non-Standard testing methods) into a decision tree. This decision tree begins with the question “What do you want to characterize?” and determines the context, environment, experimental design and analysis method being used by the user, terminating in a document reference. In a very simple format, following the decision tree and having a clear idea of what you need to characterize or model, you will reach an end branch of the decision tree where a testing Standard or testing method will be defined. The objective of this paper is to present the decision tree, its logic and the way it should be used.

This report summarizes the activities that were carried out in the framework of Subtask 2 of IEA Annex 58. Subtask 2 dealt with the challenge of optimizing full scale dynamic testing. The aim was to arrive at a roadmap presenting the user with reliable methods used to measure the actual thermal performance of building components and whole buildings. The roadmap (using a decision tree logic) is aimed at multiple audiences from both academic and industry backgrounds. The present report focuses on the development of the Decision Tree and how it changed throughout the course of Annex 58, giving an overview of the presented work.

The Passive House (PH) Standard is a voluntary building energy performance standard focused upon reducing space heating demand to a very low level and therefore considered a viable climate change mitigation technology. Besides comfort and energy requirements, the PH standard also defines criteria with respect to ventilation. However, the question remains, how well do PH dwellings perform when they are occupied? Does the PH approach provide good indoor air quality (IAQ) for its occupants and how does IAQ compare to non-PH homes, in particular, naturally ventilated homes? Additionally, can PH certification improve the quality of installed ventilation systems? This paper summarizes indoor air quality relevant aspects of the PH standard and presents results from measurements examining in-use IAQ in more than 600 PH or PH-like, newly built or retrofitted dwellings. The results reveal that pollutant and carbon dioxide concentration are generally lower compared to naturally ventilated homes, presumably due to the requirement to install a balanced Mechanical Ventilation with Heat Recovery (MVHR) system. Results also suggest that the quality assurance measures of PH certification are capable of improving ventilation and IAQ performance. However, the lack of cooking fume capture requirements in the PH standard, in combination with efforts to avoid energy losses associated with a possible extraction kitchen hood, may lead to elevated particulate matter concentration in PHs. Future research on cooking induced IAQ impairment is encouraged to assess the effectiveness of recently published PH-specific recommendations. Future efforts in empirical IAQ research should also address the lack of high quality IAQ measurement data and the standardisation of IAQ assessment methods and protocols.

Within the UK there has been skepticism about whether Passivhaus buildings can offer high standards of comfort and occupant satisfaction. A survey has been undertaken in order to develop a better understanding as to whether or not this skepticism is warranted. The project examined suggests that homes built to the Passivhaus Standard can address many of the concerns that have been raised, however, issues such as overheating risk may require even closer examination during the design process.

The development of mathematical models that can reliably simulate the energy performance of a whole building or a building component with minimal discrepancy between the real and simulated data is a major aim of Building Physics science. In order to create models that accurately represent real physical phenomena it is necessity to perform tests on buildings and building components, producing real data that can be used to adjust and validate these models. If these tests are not undertaken correctly, incorrect data sets, insufficient data sets or excessively complex and expensive experiments may be performed. Thus, depending on the aim and the accuracy needed for the mathematical models, the test environment and test set up must be chosen correctly. This problem has been studied inside Subtask 2 of the Annex58 “Reliable building energy performance characterisation based on full scale dynamic measurements”. The aim was to come to a roadmap on how to measure the actual thermal performance of building components and whole buildings. This means under realistic boundary conditions (field exposure or artificial climate) and taking into account workmanship. Since there are many established methods and different Standards for different measurement purposes, the solution has been to organize the existing methods (both Standards and widely used non-Standard testing methods) into a decision tree. This decision tree begins with the question “What do you want to characterize?” and determines the context, environment, experimental design and analysis method being used by the user, terminating in a document reference. In a very simple format, following the decision tree and having a clear idea of what you need to characterize or model, you will reach an end branch of the decision tree where a testing Standard or testing method will be defined. The objective of this paper is to present the decision tree, its logic and the way it should be used.

Retrofitting projects can have multiple socio-environmental benefits, improving the energy efficiency of buildings, reduce environmental impacts, extending the life of buildings, promoting renewable energy use, and improving occupant comfort, health and wellbeing. Additionally, they can have economic benefits such as lowering energy bills and creating skilled jobs. However, measuring the benefits from retrofits can be challenging. This study employs the Build Upon 2 (BU2) toolkit to evaluate the economic benefits of five case study, area-based, domestic retrofit projects managed by a local authority in the North of England between 2022 and 2024. Stakeholders such as project managers, contractors, and quantity surveyors were interviewed to explore how data on economic benefits of retrofit projects can be captured and assessed using the BU2 tool. The analysis revealed a complexity of challenges in acquiring data on the financial details of the project and fuel bill savings. Recommendations to improve processes include a top-down approach to data collection and streamlining of the data collection and evaluation process.

Urban green spaces are acknowledged as a vital component in a healthy city, providing a wealth of benefits. Urban green infrastructure (UGI) can help to moderate the intensity of the Urban heat Island (UHI), there is however a lack of high temporal and spatial ground-level data that quantifies the impact of UGI on air temperature and human comfort within UHI areas, and particularly for cities in temperate marine climates, which are not comprehensively understood. This paper therefore uses data from a high-resolution monitoring campaign in the UK city of Leeds to describe the diurnal characteristics of air temperature in grey and green spaces between May and August 2021. Average UHI intensity during this period was 0.9 °K, with a summer maximum of 3.1 °K occurring in late evening. Although there is variation across the monitoring sites, green space was on average 0.7 °K cooler than the grey spaces during the summer months, and up to 2.6 °K cooler on some of the hottest days. Air temperature in urban woods was up to 4.0 °K cooler on the hottest days. These measured data demonstrate the influence of UGI on air temperature in UHI areas, and quantify the impact of different types of UGI, identifying the UGI types that are most effective at regulating higher summertime air temperature. Results presented here provide valuable quantitative data that can support the protection and expansion of urban green space as part of policy development and urban planning in practice.

Whilst it is broadly understood that urban green infrastructure (UGI) helps to mitigate against the urban heat island (UHI) effect, there remains a relatively small body of measured data that quantify the impact of UGI on urban temperatures. This paper presents interim results from a long-term monitoring campaign in the city of Leeds, UK. A network of air temperature sensors housed in Stevenson shields were deployed across Leeds in the summer of 2019. Initially, a total of 17 sensors were included in this network: 10 in grey (man-made built-up areas) urban spaces, 5 in UGI, and 2 sensors at rural reference sites. The data set reported in this paper covers the period July 2019 to November 2020 at an hourly resolution. Results characterise the urban heat island intensity (UHII) and the differences between air temperatures in the urban grey and green spaces. There are both diurnal and distinct seasonal differences in the hourly temperature data. The average UHII during this period was 1.8 °C, with a summer peak of 4.9 °C occurring in late evening. Within the UHI during summer months, the green space was on average 0.5 °C cooler than the grey spaces and up to 2.8 °C cooler on the hottest days. These measured data quantify the local cooling effects of the green space, which is useful at both a macro city-scale and micro citizen-scale. Results of this nature are useful in building a quantitative evidence base that supports the retention and introduction of urban green infrastructure.

Evaluating the performance of domestic retrofits is essential in appraising their success and identifying if they improved the lives of occupants. In the UK, billions of pounds are invested annually in retrofits through policy funding, however, current building regulations do not mandate evaluation, and monitoring requirements are poorly defined. Without agreed standardised protocols or tools, retrofit evaluations remain inconsistent and incomparable, providing little assurance to occupants, landlords, installers, or the government. Post-occupancy evaluation (POE) is a common and well-established form of building performance evaluation (BPE) used in retrofit evaluations; however, it faces challenges in multi-dwelling retrofit schemes. This research evaluated the effectiveness of occupancy evaluation surveys in five domestic retrofit projects overseen by a local authority in Northern England between 2022 and 2024. Phase one implemented a retrofit survey taken from the UKGBCs BuildUpon2 Framework. In phases two and three, iterative improvements were made to the survey based on feedback from occupants and surveyors from the previous phases. Five key barriers were identified: resources, technical challenges, surveyor engagement, trust, and accessibility. Addressing these challenges increased the survey response rate from 25% to 98%. The refinements significantly improved the quality and usefulness of the data collected, offering valuable insights for designing robust, easily implementable occupant surveys.

This report presents the findings from part of the Peacock and Verity SHEEPISH Development Stage project, which is funded by the North East and Yorkshire Net Zero Hub’s Energy Project Enabling Fund. The SHEEPISH project aims to develop 15 Silver Street, Masham, North Yorkshire, using bioconstruction materials, particularly sheep’s wool insulation (SWI), become a SWI training site for installers across Yorkshire and the North East, and create a stakeholder cooperative into a robust circular SWI supply chain. Leeds Sustainability Institute has been appointed by Peacock and Verity to consult with stakeholders to find out whether there is support for a Yorkshire-based SWI supply chain, advise on how the performance of SWI at 15 Silver Street could be monitored over time, and perform hygrothermal simulations of building elements at 15 Silver Street to assess whether there are any moisture risks associated with using SWI. Twelve stakeholder interviews were conducted in February 2024 with participants from four stakeholder groups: Yorkshire sheep farmers; general contractors; private and social housing clients; and both SWI suppliers and wool merchants. Participants talked about their current beliefs about SWI, barriers to its use, the potential of developing a Yorkshire SWI market and rationale behind it. Cost was perceived to be the main barrier to increasing use of SWI. Farmers were willing to supply their fleeces if it were financially advantageous to do so, but despite the cost of raw wool making up a fraction of overall manufacturing costs, SWI suppliers and wool merchants thought there would be little opportunity to pay farmers more for their fleeces. There is already a SWI manufacturer based in Yorkshire but for a collaboration to develop, demand for Yorkshire SWI would need to grow. This could be stimulated by promoting the low-carbon, safer-to-install and breathable credentials of SWI to a potential Yorkshire client base, such as private homeowners, prestige commercial organisations, and those with historic assets or a sustainable ethos. Literature on SWI indicates favourable performance for improving air quality, controlling moisture levels and reducing sound transmission. However, most of this data comes from laboratory testing which does not replicate the reality of a product's performance within a construction, highlighting the value of capturing in situ performance data at 15 Silver Street. A range of monitoring options, together with practical considerations, are discussed. We recommend monitoring SWI moisture levels over an extended period and measuring air quality during SWI and conventional insulation installation periods for comparison. Moisture behaviour and breathability of SWI is often considered to be a benefit; however, natural materials can be more vulnerable to decay due to moisture accumulation over time. Hygrothermal simulation models the movement of heat and moisture through materials in a representation of a building element, such as a wall or roof, in response to internal and external climate conditions. Hygrothermal simulation models were used to assess the risk of moisture accumulation over time in selected external elements at 15 Silver Street following a retrofit. Modelling was carried out using the WUFI Pro version 6.7 software for four external wall build ups and three roof build ups, where each case was simulated for a virtual 3 and 10- year period. Overall, hygrothermal simulation indicates that the proposed build ups, including those using SWI, have low moisture risk. In each of the cases modelled, total water content declined over the simulation period or reached an equilibrium state that indicates a low risk of water accumulation in the building fabric. Therefore, the use of SWI appears to be as safe as the wood fibre insulation also specified in the design at 15 Silver Street.

Energy used for space heating accounts for the majority of anthropogenic greenhouse gas emissions from the built environment in the UK. As the fabric performance of new build dwellings improves, as part of the UK’s response to reducing national CO2 emissions, the potential for excessive overheating also increases. This can be particularly pertinent in very airtight low-energy dwellings with high levels of insulation and low overall heat loss, such as Passivhaus dwellings. The work described in this paper uses calibrated dynamic thermal simulation models of an as-built Certified Passivhaus dwelling to evaluate the potential for natural ventilation to avoid excessive summertime overheating. The fabric performance of the Passivhaus model was calibrated against whole dwelling heat loss coefficient measurements derived from coheating tests. Model accuracy was further refined by comparing predicted internal summer temperatures against in-use monitoring data from the actual dwelling. The calibrated model has been used to evaluate the impact that user-controlled natural ventilation can have on regulating internal summer temperatures. Thermal performance has been examined using simulation weather files for existing climatic conditions and for predicted future climate scenarios. The extent of overheating has been quantified using absolute and adaptive comfort metrics, which exceed the relatively restricted measures used for regulatory compliance of dwellings in the UK. The results suggest that extended periods of window opening can help to avoid overheating in this type of low-energy dwelling and that this is true under both existing and future climatic conditions.

Energy used for space heating accounts for the majority of anthropogenic greenhouse gas emissions from the built environment in the UK. As the fabric performance of new build dwellings improves, as part of the UK’s response to reducing national CO2 emissions, the potential for excessive overheating also increases. This can be particularly pertinent in very airtight low-energy dwellings with high levels of insulation and low overall heat loss, such as Passivhaus dwellings. The work described in this paper uses calibrated dynamic thermal simulation models of an as-built Certified Passivhaus dwelling to evaluate the potential for natural ventilation to avoid excessive summertime overheating. The fabric performance of the Passivhaus model was calibrated against whole dwelling heat loss coefficient measurements derived from coheating tests. Model accuracy was further refined by comparing predicted internal summer temperatures against in-use monitoring data from the actual dwelling. The calibrated model has been used to evaluate the impact that user-controlled natural ventilation can have on regulating internal summer temperatures. Thermal performance has been examined using simulation weather files for existing climatic conditions and for predicted future climate scenarios. The extent of overheating has been quantified using absolute and adaptive comfort metrics, which exceed the relatively restricted measures used for regulatory compliance of dwellings in the UK. The results suggest that extended periods of window opening can help to avoid overheating in this type of low-energy dwelling and that this is true under both existing and future climatic conditions.

This paper presents the methodology, along with some of the initial findings and observations from tests performed on two dwellings, of differing construction and form, in which a coheating test was performed using the dwelling's central heating system; this method is referred to as integrated coheating. Data obtained during the integrated coheating tests using a dwelling's heating system have been compared with data obtained during electric coheating of the same dwelling. In one instance, integrated coheating test data from one dwelling was compared to a similar adjoining control dwelling that was simultaneously subject to an electric coheating test. The results show a good agreement between the heat loss coefficients (HLC) obtained using a dwelling's own heating system and those obtained through electrical coheating. Initial analysis suggests the HLC estimate obtained from integrated coheating is likely to be more representative of how a dwelling performs in-use. The findings question the appropriateness of comparing current steady-state HLC predictions to those derived from in-use monitoring data. Integrated coheating has the potential to provide a more cost-effective and informative indication of whole house heat loss than electric coheating, as it enables in situ quantification of both fabric and heating system performance.

Urban heat islands are having a detrimental impact on the health and wellbeing of inhabitants in major cities. The impact of global warming is affecting all, but groups, including infants, the elderly and those with poor health are vulnerable and fatalities during hot weather are increasing. High temperatures adversely affect all ages, reducing the ability to function, live and work comfortably and effectively. The planning and design of buildings and their surrounding infrastructure, especially the green assets (trees, plants and vegetation) can reduce the impact of urban heat islands. The problem and challenges of Urban Heat Island are described in this chapter as well as recent research which proposes to capture climate data and the impact of green infrastructure asset and thereby providing guidance for those designing and planning urban developments.

The York Passivhaus is a 3-bed home in York, North Yorkshire, that achieved Passivhaus certification on completion in 2015. The project aim is to evaluate the building fabric and system performance of the home seven years post-completion against design targets and initial performance tests. Areas of interest are energy consumption, ventilation and air quality, thermal comfort, airtightness and building fabric. Looking at these in turn, fuel bills were used to explore how gas and electricity consumption had changed since occupation in 2016. Gas use was higher during the first year postcompletion in 2016 but has steadily declined since. Electricity use has remained relatively constant. The annual energy consumption in 2023 was 2467kWh for gas (20kWh/m2/year) and 1652kWh (13kWh/m2/year) for electricity, which is between 60 and 74 per cent less for gas and between 9 and 39 per cent less for electricity than the average UK house. The mechanical ventilation heat recovery (MVHR) system was not balanced when flow rate test results were compared against commissioning figures, as extract air flow rates were higher than intake air flow rates. This meant that the system no longer satisfied Passivhaus requirements. Air quality was monitored inside and outside of the home over 12 months. For CO2, a high level of IAQ was recorded, with an average of less than 872 ppm. CO2 levels dropped when the MVHR filters were changed coupled with the onset of warmer weather. Higher noise levels associated with the MVHR system ceased following a service. Higher levels of particulate matter (PM) were recorded at the front of the house, close to a car parking area. Three peak periods were examined to see how particulates generated externally or internally rose and fell over time. Spikes in internal PM levels were generally due to cooking or use of the woodburning stove and dissipated quickly. Elevated PM level patterns recorded outside were often mirrored inside but at a much lower level. Twenty internal sensors monitored temperature and humidity levels. Temperatures remained constant above 15°C throughout winter with all sensors staying within a 3-4°C range, indicating a low level of thermal variation across the home. However, internal temperatures were quite low – usually under 20°C, despite the space heating system defaulting to set points of 24°C during the day and 15°C at night during the winter months. This suggests that the space heating system was undersized for the current occupancy level, as design calculations were based on higher occupancy assumptions. It was assumed at the design stage that the wood-burning stove would meet 30 per cent of the home’s heating demand when during the monitoring period it was rarely used. During warmer weather, higher temperatures were recorded across the two southwest facing first-floor bedrooms. There was no evidence of overheating when the home was occupied during warmer weather. In general, the house is still extremely airtight with a mean permeability of 0.86 m3/(h.m2) @50Pa. However, this is a significant increase in air leakage in relative (rather than absolute) terms since certification was carried out in October 2015, where a mean permeability of 0.39m3/(h.m2) @ 50Pa was recorded. The little air leakage detected appears to come from window seals at casements, the boiler flue, plus some air movement behind plasterboard in the upstairs rooflights, and at wall-to-ceiling, or wall-to wall-junctions. The air leakage area has increased only slightly – from around 73cm2 to 104cm2. Therefore, after seven years the home now satisfies EnerPHit rather than Passivhaus airtightness requirements. A QUB test was used to measure fabric performance. First, a design-stage heat transfer coefficient (HTC) for the home was calculated, which was 69.5 W/K and then tested against. Three tests were done in the summer/autumn of 2022 and two in the winter of 2023. The average measurement was 76.3 W/K. This is a low HTC but 10 % greater than the designstage performance calculation. Overall, as a seven-year-old Passivhaus, the home’s performance is still exceptional compared to current-day new-build homes. Some performance aspects have deteriorated since completion, such as the airtightness and MVHR performance, which could be associated with wear and tear. It is not possible to compare changes to air quality, thermal comfort and HTC, as they were not monitored post-completion. The only area of note is thermal comfort in winter depending on the temperature sought by occupants, as the space heating system is not designed for the current occupancy level and could be considered on the cool side of comfortable.

Environmental conditions in buildings are linked to the physical and mental wellbeing of occupants. Thus, it follows that the internal environment affects human performance and user experience during sport and activity. There are several indices that are used to evaluate occupant thermal comfort, the Predicted Mean Vote (PMV) index being the metric most commonly used. PMV is designed to evaluate comfort for sedentary occupants with low metabolic rates; however, PMV has also been used to evaluate comfort for individuals engaged in high metabolic rate activities, such as those common in sport facilities. This paper investigates the implication of using PMV to evaluate thermal comfort in sport facilities using empirical data recorded over 24 months in a multi-purpose sports hall in the North of England. Data are used to develop and propose methodological modifications to improve the standard PMV model prediction to account for occupants having higher metabolic rates. The paper evaluates the use of metabolic rate data from different sources including the Compendium of Physical Activities and quantifies the impact that the metabolic weighting approach has on predicted comfort. Finally, a novel method is proposed to modify PMV for use where occupants have high metabolic rates. Despite the improvements made, the findings suggest that even a modified PMV may not be able to accurately evaluate the thermal comfort of people engaged in non-sedentary activity, recommending that use of the PMV index is restricted to activities with metabolic rates <2 MET.

Improving the energy efficiency of the UK housing stock is important both to meet carbon emission reduction targets and to reduce fuel poverty. For this reason, domestic properties are frequently retrofitted with energy saving measures. This study looks at how the energy consumption, thermal properties and internal temperature of 14 dwellings change as a result of a solid wall insulation (SWI) retrofit. A decrease in heat transfer coefficient of 11+6−7% was calculated for 2 dwellings, which is slightly lower than the previously modelled value of 18%. However, many houses displayed evidence that the full benefit of SWI was not being realised as, for example, energy savings were offset with increases in internal temperature. Future retrofit schemes should therefore consider supplementing the changes in fabric with increased guidance for the occupant.

Global concern around energy use and anthropogenic climate change have resulted in an increased effort to reduce the energy demand and CO2 emissions attributable to buildings. This has led to the development of a number of low energy building standards, one of which is the internationally recognised Passivhaus Standard. The Passivhaus Standard aims to reduce the space heating energy demand of a building by adopting a ‘fabric first’ approach, thus ensuring the thermal envelope is highly insulated and airtight whilst also maximising passive solar heat gains. However, adopting such an approach does present a risk of overheating; a situation that is of particular concern when the occupants have additional healthcare requirements. This study uses 21 months of in-use monitored data to consider the overheating risk in a UK Passivhaus dwelling with vulnerable occupants using both static and adaptive thermal comfort assessment methods. The analysis of the data suggests the occurrence of substantial overheating according to PHPP, CIBSE Guide A and CIBSE TM52 criteria. The analysis was then expanded to consider a novel composite method to overcome the limitations of existing approaches, allowing overheating to be assessed during non-typical periods i.e. the heating season. This revealed apparent overheating during colder months, in addition to substantial night-time overheating. This has implications for the thermal comfort assessment of low energy dwellings and the design and operation of Passivhaus buildings, particularly those with vulnerable occupants.

Dr Fiona Fylan

This book tackles the challenges posed by accelerating urbanization, and demystifies Social Sustainability, the least understood of all the different areas of sustainable development.

Heat exchange between chilled food storage and conditioned spaces in large food retail stores is not currently required as part of design stage regulatory compliance energy performance models. Existing work has identified that this exchange has a significant impact on store energy demand and subsequently leads to unrealistic assessment of building performance. Research presented in this article uses whole building dynamic thermal simulation models that are calibrated against real store performance data, quantifying the impact of the refrigeration driven heat exchange. Proxy refrigerated units are used to simulate the impact of these units for the sales floor areas. A methodology is presented that allows these models to be simplified with the aim of calculating a realistic process heat exchange for refrigeration and including this in thermal simulation models; a protocol for the measurement of chilled sales areas and their inclusion in the building models is also proposed. It is intended that this modelling approach and the calculated process heat exchange inputs can be used to improve the dynamic thermal simulation of large food retail stores, reduce gaps between predicted and actual performance and provide more representative inputs for design stage and regulatory compliance energy calculations.

There remains a significant number of occupied and uninsulated solid wall dwellings in the UK. Deep retrofit is often required for these buildings to become energy efficient but it is difficult to determine how these buildings will respond to retrofit without a detailed understanding of their fabric thermal performance Greater certainty can however be achieved by combining theoretical models and practical field tests, prior to the design of retrofit programmes. This type of approach can then be used to inform and optimize the design of retrofit interventions. This paper presents results from a series of in situ fabric performance tests undertaken on two no-fines concrete, conjoined dwellings pre- and post-retrofit and demonstrates how empirical data can be used to inform and calibrate the thermal performance of dynamic simulation models (DSMs). This is a particularly pragmatic calibration method as it eliminates the need for actual weather data, which is expensive and prohibitive to collect and collate. The DSM inputs and outputs were compared with those obtained from Standard Assessment Procedure (SAP) calculations. The results illustrate how the fabric performance of no-fines concrete can vary between similar house types within the same development. This research also validates the effectiveness of the calibration methodology that uses the whole house Heat Transfer Coefficient (HTC) as the qualifying metric. Furthermore, results also emphasize the importance of appropriately characterizing the physical properties of existing buildings before designing retrofit strategies. This paper contributes to the growing knowledge base concerned with the energy performance gap. In this instance, SAP predicts higher absolute savings then measured in situ which is problematic when assessing the financial viability of retrofits.

The whole-life sustainability of a building should be underpinned with a demonstration of functional value and an awareness of the direct environmental impact. While a great deal of energy and resources are consumed in the construction of buildings, this is marginal when compared to the operation costs and associated energy used during a building's life cycle. Many reports identify the build costs and associated resources to be less than 1 % of the whole-life operation costs. The exact energy use of a building can vary widely, depending on the use, energy efficiency of the building and occupant behaviour; thus, a greater deal of attention should be given to understanding the energy used in buildings and how energy efficient operation is achieved.

To meet targets on fuel poverty, energy efficiency and carbon emissions existing homes need to be more energy efficient. We report the results of a participatory action research project to explore the challenges associated with energy efficiency retrofit programmes and ways to better implement future schemes. Six focus groups were held with 48 participants from a range of energy efficiency roles. Data were analysed thematically using the research question “What are the challenges presented by implementing energy efficiency retrofit programmes”. We identified four themes in the data: Funding mechanisms; Predicting performance; Installation; and People. Challenges include funding mechanisms for retrofit programmes resulting in insufficient time to plan, publicise, implement and evaluate a scheme and insufficient flexibility to specify the most appropriate intervention for individual homes. Site workers sometimes need to adapt retrofit designs because of insufficient detail from the designer and can equate quality of installation with quality of finish. Landlords and occupier behaviour can impact on the programme's success and there is a need for greater information on benefits for landlords and for energy behaviour change interventions run alongside retrofit programmes for occupiers. There is a need for outcome evaluations of retrofit schemes with the results shared with stakeholders.

Retrofitting solid walled homes is one of the greatest challenges for the UK in achieving its net zero ambitions. Solid walled homes have unique features, that require special consideration. They are among the least efficient in the UK, and their occupants are more likely to be in fuel poverty. They are also at elevated risk of surface condensation, excessive cold in winter and overheating in summer. Retrofitting these homes is a cornerstone of UK policy to tackle fuel poverty and to facilitate the delivery of decarbonised electrified heat into homes. However, installing solid wall insulation is costly and poses more risks of unintended consequences than any other retrofit. Previous projects investigating solid wall insulation have identified major failures when retrofits are installed in a ‘piecemeal’ way i.e., they did not consider how the retrofit measure affects risks of damp, inadequate ventilation, and overheating in homes. This led to the adoption of the whole house approach in new technical standards for retrofit installers (PAS 20351) to ensure that all risks of retrofit measures were always considered, even if only one measure was being installed at a time. Industry is beginning to adapt to these standards, but more research is needed to explore the benefits of adopting the whole house approach, and more guidance is needed to support retrofits in solid walled homes. Insights from this project explain how solid walled homes can be retrofitted more safely and effectively.

The DEEP case study retrofits provide compelling evidence on how a whole house approach to retrofit can reduce heat loss, surface condensation risk and overheating risks in solid walled homes. From the data collected, specific guidance is produced outlining how to install retrofits in solid walled homes more safely and effectively. Recommendations are provided on how to make measurements and modelling predictions of the technical performance of retrofits more accurate. The findings can inform evidence-led decisions at multiple levels to ensure retrofits in solid walled homes are safe and effective.

17BG was one of fifteen case study homes retrofitted in the DEEP project. The case studies were used to identify the performance of, and risks associated with, retrofitting solid walled homes. The data from the case studies was also used to evaluate the accuracy of modelled predictions around retrofit performance and risk.

56TR is one of fifteen homes being retrofitted in the DEEP project. The case studies are being used to identify the performance of, and risks associated with, retrofitting solid walled homes as well as to evaluate the accuracy of retrofit models.

01BA is one of fourteen case study homes retrofitted in the DEEP project. The case studies identify the performance of, and risks associated with, retrofitting solid walled homes. A retrofit was undertaken in stages, reflecting a piecemeal approach to retrofit, followed by undertaking activities that would be required for a whole house approach as a final stage. The data from the case studies is also being used to evaluate modelled predictions of retrofit performance and risk.

55AD and 57AD, are a pair of identical semi-detached homes, and are two of fourteen DEEP case study homes in which the comparison between a whole house and piecemeal approach to retrofit was evaluated.

00CS is one of fifteen case study homes retrofitted in the DEEP project. The case studies were used to identify the performance of, and risks associated with, retrofitting solid walled homes. The data from the case studies was used to evaluate the accuracy of modelled predictions around retrofit performance and risk.

04KG is one of fourteen case study homes being retrofitted in the DEEP project. The case studies are being used to understand the performance of, and risks associated with, retrofitting solid walled homes. The data from the case studies is also being used to evaluate modelled predictions of retrofit performance and risk.

52NP and 54NP are two of fourteen case study homes retrofitted in the DEEP project. The case studies were used to identify the performance of, and risks associated with, retrofitting solid walled homes. The data from the case studies were also used to evaluate modelled predictions of retrofit performance and risk.

This report describes the common data collection and analysis methods used in the DEEP retrofit case studies. These are generically described to avoid repetition in the individual case study reports.

Thermal and hygrothermal simulations are undertaken to estimate energy performance, condensation risks, the potential for moisture accumulation, and timber rot. These simulations use default book values to estimate the material properties of solid brick walls. This report investigates the variability of brick properties found in solid walled homes in the UK and compares these to the default book values. It also explores how varying material property inputs in models affects thermal performance and moisture risk in solid walled homes.

Surveys and air tests were performed at 160 solid and cavity walled homes in Northern England, which had a mix of insulated and uninsulated walls. Blower door tests and Pulse tests were compared and used to quantify the airtightness of the homes. An evaluation of how building characteristics affected the results was performed, and common leakage pathways were identified. Data was also collected on the condition of the homes, potential barriers to external wall insulation (EWI) retrofit, as well as perceptions of occupants.

19BA is a mid-terraced pre 1900 solid walled home where airtightness improvements and room-in-roof retrofits have been installed. Building performance testing has been undertaken to collect data on the performance and risks of these improvements, and to evaluate the accuracy of modelled predictions on the retrofit performance and risk.

07LT and 09LT are two of fourteen case study homes retrofitted in the DEEP project. The case studies have been used to identify the performance of, and risks associated with, retrofitting solid walled homes. The data have also been used to evaluate the accuracy of the modelled predictions of the retrofit performance and risk.

08OL is one of fourteen case study homes being retrofitted in the DEEP project. The case studies are used to identify the performance of, and risks associated with, retrofitting homes without conventional cavities. The data from the case studies are used to evaluate the accuracy of modelled predictions of retrofit performance and risk.

27BG is one of fourteen solid walled DEEP case study homes. In this home building performance tests were undertaken to investigate the success and risk of retrofitting suspended timber floors and how the results compare to predictions.

Leeds was designated a core city for trialling the Government’s Green Deal domestic energy efficiency policy. Leeds Beckett University undertook a monitoring and testing program on 65 dwellings to investigate the effectiveness of the insulation measures installed and to understand any underperformance. This report outlines the findings from a series of investigations including; surveys, air tightness tests, co heating tests, in situ U-value tests, hygrothermal and thermal bridging modelling, in use monitoring and occupant interviews. The surveys revealed that the ‘whole house approach’ to retrofit was, more often, missing, and quality assurance around insulation detailing was regularly absent, leading to avoidable errors and potentially embedding problems in the installations. Furthermore, moisture issues were, in the majority of instances, over-looked or made worse despite over half the sample having some form of damp. Despite this, energy savings were observed and the appearance of the dwellings were improved, thus apparent satisfaction was generally high, even though the installs were imperfect and moisture problems were introduced. Hygrothermal modelling of IWI cases suggests that thermal bridging at party walls can increase by more than 60% and that there could be potential for rot to embedded timbers. Insulation was recorded to reduce background ventilation of the dwellings by around 25% (a factor unaccounted for in government energy models), although some dwellings were still left with air tightness levels worse than modern day UK Building Regulations limits and replacing wet plaster with IWI was seen to undermine the performance of the insulation. The heat loss coefficient of three homes were tested and showed improvements of 25% and 56% for full retrofits with IWI, and 8% for a party wall retrofit; ¾ of these savings were achieved by fabric improvements and the final quarter from incidentally making dwellings more air tight. The before and after in use monitoring suggested the average savings in energy consumption from all retrofit types (EWI, IWI or other) were between 20% and 29%, although small sampling periods limits the certainty of the results. More reliably it was observed that comfort conditions improved; before the retrofit, 14 of the homes were experiencing discomfort from cold; the retrofit brought on average 2 /3 of uncomfortable homes into more reasonable comfort bands. Nearly all of the occupants had positive experiences, although no householders had to pay for the retrofit, reporting being warmer, bringing unused rooms back into operation and feeling more pride in their homes and communities. A variety of perceptions and behaviours were observed around set point temperatures, use of heating controls and motivations for using energy, all of which contribute to make a complex policy landscape. There is huge potential for domestic retrofit and although this research suggests the current

Wakefield & District Housing (WDH) commissioned the Leeds Sustainability Institute (LSI) at Leeds Beckett University to undertake pressurisation tests and thermographic surveys on 20 semi-detached dwellings (of which only 19 granted researchers access), these were;  14 British Iron Steel Federation (BISF) homes with external wall insulation (EWI)  1 BISF without EWI  2 solid brick properties with EWI  2 solid brick properties without EWI The aim was to identify the influence of EWI on the air tightness of the buildings. The results showed that there was no noticeable improvement in the airtightness of dwellings that had EWI compared to those without EWI in either BISF or solid‐walled dwellings. A larger sample size of BISF homes without EWI and both solid‐walled properties with and without EWI would be needed to assess if this finding was statistically significant. CO2 decay analysis was used in an attempt to validate the blower door results however the results were inconclusive due to a low sample size and an uncontrolled conditions due to occupant activity. Improving airtightness is not the main function of EWI and this has been sustained by our findings. The results confirm that the fabric performance benefit of EWI is restricted almost exclusively to improving wall U‐values, i.e. reducing heat loss through the fabric, not affecting heat loss through uncontrolled ventilation in the dwellings.

Thermal performance is often assumed to be constant over the service life of insulation. The aim of this project was to establish the existing evidence on the impact of retrofit degradation over time, and what it means for insulation performance. This report summarises current understanding, classifying key mechanisms for degradation and makes recommendations for how to address identified knowledge gaps.

The benefits and risks associated with installing internal wall insulation (IWI) and thin internal wall insulation (TIWI) retrofits into solid wall homes are researched and evaluated for BEIS. In order to deliver this, a holistic approach was adopted and the project was split into four main sections, each of which has an accompanying Annex to this summary report: Annex A: Review of existing literature as well as primary investigations using house surveys, householder questionnaires and installer focus groups into the sociotechnical barriers to IWI and TIWI. Annex B: Technical evaluation of the performance of IWI and six novel TIWI retrofits installed in field trial solid wall Test Houses using before and after building performance evaluations. Annex C: Modelling of the impact on annual energy consumption, EPC rating, overheating risk, condensation risk and moisture accumulation made by IWI and TIWI retrofits in a range of UK house archetypes. Annex D: Laboratory testing of test walls using hygrothermal chambers to quantify the change in moisture and thermal performance of solid brick walls when they are insulated with IWI and TIWI to determine how weather