Performance risks of lighting retrofit in Energy Performance Contracting projects

In Energy Performance Contracting (EPC) projects, Energy Service Companies (ESCOs) often provide guarantees on the energy savings of proposed retrofit measures based on a simplified engineering method. In order to assess the risk of saving shortfalls, there is a need to develop an evaluation method based on the probabilistic approach. This study focuses on a proposed probabilistic approach to evaluate the performance risks of common lighting retrofit measures such as replacement of existing lighting, installation of daylight-linked lighting controls and occupancy-based controls. The proposed approach considers the variations in the influential factors affecting energy performance, including daylight availability, occupancy rates, lamp conditions and lighting use patterns. Empirical data is used to develop the probability distribution functions of those influential factors. A hypothetical 40-storey office building with typical design features (such as regularly shaped open plan) in Hong Kong was modeled using EnergyPlus to demonstrate the application of this probabilistic approach. The results indicate that the variations in actual energy savings can be substantial in lighting retrofit projects, ranging from 1,267,000 kWh (43% of pre-retrofit consumption) to 1,927,000 kWh (65% ditto) with 90% statistical significance, posing risk on the achievement of guarantee savings in an EPC project setting.