Experimental, computational and sustainability study of energy-efficient technologies for residential buildings in hot countries

Abstract

Residential buildings account for the highest share of the global final energy use and related carbon dioxide emissions; 22 % and 17 %, respectively while energy for cooling is the fastest growing demand worldwide. Demand for cooling is higher in countries with high ambient temperatures and solar radiation leading to the installation of air-conditioning systems to improve internal thermal comfort. In addition, residential building retrofit has shown high energy savings potential due to the high percentage of existing stock in comparison to new built. This study investigates both the energy and environmental impacts associated with energy use in existing residential buildings in hot countries using two selected case studies. The research involved experimental, computational and sustainability studies of building energy-efficient technologies focussing on external building envelope retrofit and reduction of internal heat gains, and renewable energy production focussing on solar energy systems. Three suitable envelope retrofit strategies were identified through literature review; (a) cool roof paint, (b) roof thermal insulation, and (c) window shading. For the reduction of internal heat gains, household A-rated appliances and energy-efficient lighting were identified as suitable technologies. Literature review also revealed that solar systems are very efficient in locations with high solar radiation, especially if thermal energy is also produced. The study considered Photovoltaic (PV) systems and Photovoltaic Thermal (PVT) systems focussing on the novel High Concentrator Photovoltaic Thermal (HCPV/T) 2000x system which is capable of providing electricity and thermal power with high efficiency. The identified technologies were applied to two case study existing low-rise single-family houses in Portmore, Jamaica and Palermo, Sicily. The experimental study involved monitoring the two case study houses and the HCPV/T system. These were used to calibrate the developed thermal EnergyPlus model used to investigate the houses’ energy consumption and indoor thermal performance. There were also used to develop an analytical model for the HCPVT/T system. The environmental impact analysis was based on Life Cycle Assessment (LCA) methods using SimaPro and the ReCiPe method. The thermal modelling study indicated that the cool roof paint is an attractive low-cost house retrofit solution for energy savings and indoor thermal comfort compared to roof thermal insulation. The cool roof paint and roof thermal insulation show similar energy savings in Jamaica (-189 kWh/m2/year with the cool roof paint and -194 kWh/m2/year with the roof thermal insulation) while a heating penalty was experienced in Sicily. The heating penalty in Sicily results in higher energy savings with roof thermal insulation (influenced by the low U-value of roof thermal insulation); -22 kWh/m2/year for cool roof paint and -30 kWh/m2/year for roof thermal insulation. Results indicate that the studied HCPV/T 2000x system has a high operational efficiency of ~80 % (30 % for electrical efficiency and 50 % for thermal efficiency) compared to PVT (11 % for electrical efficiency and 48 % for thermal) and PV (10 % for electrical efficiency). Therefore, it is the most attractive solar energy system because of its high energy production capability. The annual produced energy by the HCPV/T 2000x system in Sicily (1738 kWh/year and 4125 kWh/year electrical and thermal energy) is higher than the PV (1144 kWh/year electrical energy) and PVT systems (1463 kWh/year and 2695 kWh/year). In Jamaica, the annual produced energy by the HCPV/T 2000x system (1111 kWh/year and 2662 kWh/year electrical and thermal energy) is higher than PV (1100 kWh/year electrical energy) and PVT (814 kWh/year and 1980 kWh/year). The sustainability study critically assessed the environmental impacts of the cool paint and the HCPV/T 2000x system in both case-study locations. It was found that the environmental impacts of cool roof paint are lower than thermal insulation; for example, the Global Warming Potential (GWP) of cool roof paint were 4 – 7-fold lower than thermal insulation materials. The environmental impact (which includes GWP) of the HCPV/T 2000x are lower than fuel-based Combined Heat and Power and non-RES systems; for example, the GWP of the HCPV/T 2000x system was up to 4-fold lower than coal and natural gas systems. Based on these findings it is concluded that the potential of operational energy use reduction and the whole life environmental impact of renovation components should both be considered to ensure the least impacting solution for building renovation.