Work Package Three: Monitoring and modelling of PD housing
Research Questions
What are the exposure levels to excess heat/cold and indoor air pollutants of populations living in PD housing?
How do these levels compare against exposure levels experienced across the English housing stock?
What retrofit strategies need to be implemented to improve indoor environmental conditions in PD housing, now and in the future?
Approach
By employing a quantitative approach combining indoor environment monitoring and modelling, this WP will be closely linked to WP2 and will further quantify current and future potentially harmful thermal and/or air pollutant exposures in PD housing.
Sampling and data collection
WP3 will carry out detailed indoor hygrothermal and air quality monitoring in a sub-sample of the homes participating in the WP3 interviews over at least a one-year period (to capture at least one heating / cooling season). Participants will be approached following a positive response in the WP2 recruitment invitation about their willingness to participate in a more detailed follow-up monitoring study. The target sample size is 50 dwellings across England. This sample size was determined so as to balance the cost and time requirements for intensive monitoring and characterisation (varying building construction age, building type, tenure type, household socioeconomic characteristics and occupancy patterns, multiple thermal indicators and air pollutants, personal indoor-outdoor exposures etc.) with statistical power and precision. Selection of homes for monitoring will be informed by our own initial draft typology of PD homes, understanding typical conversions it is leading to. Figure 1, at the end of this document, gives an initial illustration of this and would be further refined through WP2 results and engagement with planning documents and data from previous research on design of PD homes (Clifford et al 2018 and 2020). It is worth noting that although WP4 will generate valuable data to characterise indoor thermal conditions and air quality in the participating dwellings, the sample is not intended to be representative of the entire PD housing stock in the UK. National representation will be achieved through the subsequent development and application of dynamic thermal models to provide small-area quantification of exposures and health impacts of PD housing across the UK.
Detailed hygrothermal and indoor air quality monitoring will be carried out in all 50 homes by monitoring dry bulb temperature, relative humidity, particulate matter (PM10, PM2.5, PM1), NO2, CO and CO2 continuously at 5-minute sampling intervals in the main living area, using an integrated, extensively evaluated indoor environment monitoring solution, Eltek AQ210, (Eltek, 2021). The Eltek AQ210 uses an optical particle counter sensor for PM (Plantower PM5003), electrode gas sensors for NO2 and CO (Alphasense A43F and A4F), an E+E EE895 sensor for CO2, and SHT85 sensor for temperature and relative humidity. The sensors have been evaluated in a large range of academic studies (Crilley et al., 2018; Feenstra et al., 2019; Sousan et al., 2016), and the units have been used in previous studies by the applicants (Stamp et al., 2020). The unit can also send and receive data via GPRS. Dry bulb temperature, relative humidity and CO2 levels will also be monitored in the main sleeping area of each home at 5-minute intervals using HOBO data loggers (Onset, 2021). Due to local urban climate modification, for example the presence of the Urban Heat Island, climate data collected from weather stations may not adequately describe external environmental conditions in close proximity to a dwelling (Mavrogianni et al. 2011). Therefore, external dry bulb temperature and relative humidity will be monitored by HOBO data loggers with radiation shields in outdoor locations in close proximity to the monitored homes. Specific Volatile Organic Compounds (VOCs) will be monitored in the main living area over 1-week periods in two seasons by passive monitors (thermal desorption tubes) and analysed by gas chromatography-mass spectrometry (Stamp et al., 2020). VOCs to be monitored include: benzene, toluene, naphthalene, a-pinene, d-limonene, trichloroethylene (T3CE), tetrachloroethylene (T4CE), styrene, ethylbenzene, m-xylenes, p-xylenes, o-xylenes, 1,2,4-and 1,3,5-trimethylbenzeneand formaldehyde (captured by passive DNPH badge). Appropriate validation of the equipment will be conducted.
Analysis of WP3 environmental assessments will help develop a refined typology of PD housing (archetype), including building geometry, construction and conversion type/age, building fabric characteristics (with a focus on thermal efficiency of the building envelope), but also and occupant characteristics, including tenure type and household socioeconomic characteristics. Modelling of indoor environmental conditions in these typologies will be performed using EnergyPlus, a comprehensive, open access and widely tested tool that addresses, in an integrated manner, indoor environmental quality (air pollutant concentrations and temperatures) and building the energy demand of buildings (US DoE, 2021). EnergyPlus has been previously used to dynamically simulate indoor (inter-zonal) airflows, indoor-outdoor air exchange, indoor air pollutant concentrations, the hygrothermal indoor environment and indoor-outdoor pollutant ratios of dwellings in the UK housing stock in the context of the NIHR HPRU project (Symonds et al., 2016; Taylor et al., 2016). For individual dwellings, EnergyPlus estimates indoor concentrations for a range of air pollutants (including PM2.5, NO2, VOCs such as formaldehyde) based on setting-specific input parameters, including outdoor air pollutant concentrations, indoor emission rates and schedules, and deposition rates/velocities obtained from the literature and as used in previous work by the applicants (Taylor et al., 2014a, 2014b). To account for differences in behaviour across occupant groups, including target groups of young children, older people, and other vulnerable population segments, WP3 will draw on the findings of the WP2 survey results and interviews to develop detailed indoor time-activity occupant profiles as inputs into EnergyPlus. A wide range of home retrofit scenarios will be tested, including energy efficiency, passive cooling, and indoor air quality improvement strategies, building on existing detailed retrofit scenarios developed in the HPRU and NERC ClimaCare projects (Oikonomou et al., 2020; Symonds et al., 2016; Taylor et al., 2016). Simulations will be carried out for the current and future climate, using UK Climate Change Projections (UKCP09) data (Eames et al, 2011) to quantify the effect of these strategies on indoor environmental exposures and associated health impacts. This will be accompanied by a cost benefit and technical feasibility analysis of these measures with inputs from construction industry stakeholders.
Analysis
Taking into consideration that the cost of monitoring a control housing sample to the same level of detail would be prohibitive, this study will make efficient use of existing resources from past, large scale housing surveys: statistical analysis of WP3 monitored data from a range of PD housing will be used to benchmark, following weather correction, their current thermal performance against that of a nationally representative English housing stock sample through comparisons against monitored indoor air temperature data of 823 homes in the English Housing Survey Energy Follow-Up Survey (EHS EFUS), previously analysed by the applicants (Symonds et al., 2017). Modelling results will also be compared against monitored indoor air quality data in 80 newly built homes (AECOM 2019). Monitored data from WP4 will also be used to calibrate the dynamic thermal and air quality models of varying PD housing typologies. Descriptive and inferential statistical analysis of monitoring and modelling results will identify the most effective remedial retrofit strategies to be implemented to improve create a robust evidence base of current and future indoor thermal comfort heat, cold and air quality pollutant exposures in PD housing now and in the future, under the current and future climate and evaluate the effectiveness of potential remedial retrofit strategies.