Exploring thermal insulation and energy use in low-income households on the South African Highveld

Abstract

A significant proportion of households in South Africa are classified as low-income households and often reside in dwellings that are inadequately insulated which threaten indoor thermal environments for occupants. This study was conducted in three low-income settlements on the South African Highveld namely: KwaDela, Jouberton, and KwaZamokuhle-settlements known to have a high proportion of poorly insulated residential dwellings. The purpose of this study was to explore the link between thermal insulation, indoor thermal environments and domestic energy use in low-income households. Indoor and ambient temperature monitoring were done over winter and summer seasons using Thermochron iButton loggers while aerial thermography was done in winter using a FLIR Vue Pro R. Questionnaires were used to gather data to explore the link between thermal insulation and domestic energy use. In winter, the study found that the majority of sampled dwellings’ average indoor temperatures fell below 18 °C, the WHO indoor minimum temperature guideline. In some instances, however, day time winter indoor temperatures also dropped below 18 °C, although this was less frequent. Also, during summer season median indoor temperatures regularly exceeded the WHO indoor maximum temperature guideline of 24 °C for both the living room and bedrooms. Furthermore, in winter, the study established that ambient temperatures influence indoor temperatures moreso, at night time showing a night time positive Pearson r which ranged from r=0.39 (KwaDela), r=0.77 (Jouberton 2016) to r=0.91 (Jouberton 2017) in bedrooms and living rooms respectively, and was always stronger than day time. Besides during winter, in KwaZamokuhle, non-insulated dwellings showed the most significant association between ambient and indoor temperatures during day time (r = 0.68) while partially insulated dwellings showed a moderate relationship of r = 0.40, while insulated dwellings yielded r = 0.29. In summer, non-insulated dwellings showed the most significant relationship between ambient and indoor temperatures during night time as well (r = 0.61) with partially insulated dwellings showing a weak link during night time (r = -0.25), while insulated dwellings yielded almost no link. Furthermore, the study also established that thermal variability between dwellings with different levels of insulation was observable through aerial TIR with non-insulated dwellings exhibiting significant variability and were distinguishable from partially and fully insulated dwellings. Further analysis of aerial thermal infrared (TIR) imagery also showed that non-insulated dwellings had higher temperature variability than partially or fully insulated dwellings. Findings from the study additionally indicated that the difference between TIR imagery obtained during midnight and TIR imagery gathered during the early evening were the most feasible way of identifying non-insulated dwellings with the study estimating that 18% and 10% of 3555 dwellings in the settlement had a very high and high probability, respectively, of being non-insulated. On domestic energy use, some link between thermal insulation status of dwellings and domestic energy use was established with more energy consumption for space heating in non-insulated dwellings compared to partially or fully insulated dwellings in winter. Furthermore, the study ascertained that low-income households rely on a mixture of energy carriers to meet their domestic needs including electricity, LPG, coal, and wood. This affirms that the insulation status of dwellings has a definite effect on the indoor thermal environments experienced by low-income households and stresses the importance of adequate thermal insulation materials for low-income residential dwellings. The low-quality thermal insulation in low-income residential dwellings means that these households are often exposed to extreme indoor temperatures for prolonged periods. Such exposure could lead to physical health-related ailments that are either directly associated with heat or cold exposure, or indirectly associated with the air pollution that results from indoor burning (for space heating). To improve indoor thermal environments of low-income households thermal insulation retrofits can be used for existing housing stock.