Payback period based prioritization of building retrofit technologies: an innovative use of critical path method

Most metropolitan office buildings in Australia were built in 1980s and have out of date building services, consuming high level of energy and water as compared to new built green buildings. With a wide range of retrofit technologies/ options available in the market, building asset managers often find it difficult to develop a retrofit plan and select appropriate technologies. This paper categorized the retrofit technologies into three stages (passive control, active control and substitution control), and then proposed an innovative prioritization model using the concept of critical path method to design sequential implementation of sustainable retrofit technologies based on payback period. A few new concepts such as Add-on Effect and Drag-on Effect were introduced to measure the impact of a selected technology on the payback period of a chain of retrofit technologies. An empirical case was used to demonstrate the application of the model. The prioritization model supplemented with other tools such as GreenStar rating and risk management will guide building managers to develop a more effective building retrofit plan.