A PROBABILISTIC RISK ASSESSMENT OF RETROFIT STRATEGIES TO CREATE A NET-ZERO-ENERGY DISTRICT – CASE STUDY: NATIONAL UNIVERSITY OF SINGAPORE, SCHOOL OF DESIGN & ENVIRONMENT

Abstract

This paper focuses on the existence of the Performance Gap – a gap between predicted and actual energy performance of retrofitted buildings, as a common occurrence that plagues green building retrofit projects today and therefore acts as a barrier against widespread green retrofitting on existing buildings. Performance gaps are mainly attributed from uncertainties within building retrofit plans. To aid decision makers with potential reduction of this gap, a simulated-based probabilistic risk assessment method is proposed as a viable methodology to assess uncertainty risk in green building retrofit projects. To assess the viability of a Net-Zero-Energy District (“NZED”) in a tropical climate, a retrofit plan to create a NZED with clusters of buildings is developed in this study, to turn existing buildings into energy-efficient buildings. For use as a case study to be retrofitted into a NZED, educational buildings at National University of Singapore – School of Design & Environment (“SDE”) 1 to 4, has been selected. However, since SDE 4 is already an established Net-Zero-Energy Building, only SDE 1 to 3 as old existing buildings, will be retrofitted. In the final simulation after retrofitting SDE1-3, the overall annual simulated results of the NZED put together (SDE1-4) observed an annual Net Site Energy (“NSE”) surplus of 129,945.84 kWh (3.8%) of electricity, on top of achieving Net-Zero-Energy status. Thereon, to evaluate the uncertainty risks associated with the retrofit plans, the above proposed risk assessment method is conducted. The results of the study indicate that the simulated annual NSE follows a Beta probability distribution with a mean annual NSE value of 142,768.04 kWh and a standard deviation of 88,438.51 kWh. In comparison to the annual NSE value of SDE1-3 (post retrofit) of -26,585.6 kWh, there is a performance gap of 169,353.64 kWh. Following that, according to the cumulative percentage graph of the same output, it is found that the probability of the retrofit intervention achieving a netzero or plus-energy outcome is lower than 2.5%.