Modelling and analysis of daylighting relative to energy consumption of a heritage category A3 building under Energy Zone 4 in South Africa
Overen, Ochuko Kelvin
Restriction of participating buildings in the recently promulgated energy performance certificate (EPC) regulations to buildings completed after 1999 might have a negative impact on intended outcomes considering that a significant number of public-use buildings in the country were completed before 1999. Arising from this concern, this study evaluates daylighting interventions for a heritage instruction-cum-office building with the objective of reducing overall energy-use intensity (EUI), related operational energy cost and CO2 emissions. A quantitative study approach based on experimental and simulation research tools was employed on Livingstone Hall (University of Fort Hare, Alice campus in Eastern Cape) as the case study building. Through measurements and simulation, indoor daylighting levels were evaluated against the 300 lux threshold (recommended workplace illuminance levels in South Africa). The data indicate that on typical clear sky days in summer and winter, average daylight illuminance for 50% of the six sample spaces was below 300 lux, while for typical cloudy-sky days in both seasons, daylight illuminance for all the spaces was below 300 lux. This implies that, for cloudy-sky days in both seasons, daylight cannot fully replace electric lighting for office and academic tasks in the building. Based on simulation results, for a typical summer clear-sky day, the average daylight illuminance in spaces 41, 43, 49, 11, 15 and 22 was up to 2 000 lux, while average daylighting in the same spaces on a typical winter clear-sky day was relatively lower. In addition, the annual “as-is” cumulative energy-use of the building was 49.02 MWh, and overall EUI was 31 kWh/m2/yr. The annual operational energy cost of the building was R67 108.50, while receptacle equipment (devices such as computers and other appliances connected to sockets) energy cost was R32 702.14 and the energy cost of electric lighting was R20 091.86. Cumulatively, the annual CO2 emission of the building was 25 440 kg (averaging 2 120 kg /month). Automated on/off and continuous dimming (smooth decrease of electric lighting capacity with ambient illuminance at a pre-set light level) daylight interventions were considered in the study. Continuous dimming intervention shows the best reduction in annual lighting energy-use by 64% and overall annual energy-use by 20%, while overall EUI reduced by 19%. The resultant overall energy cost saving was R12 420.73 while mitigated CO2 emission was 4 839 kg per annum.
A research report submitted in partial fulfilment of the requirement for the degree of Master of Urban Studies in Sustainable and Energy Efficient Cities to the Faculty of Engineering and Built Environment, School of Architecture and Planning, University of the Witwatersrand, Johannesburg, 2022