Predicted vs. Actual Energy Performance of Non-Domestic Buildings

Abstract

With the increasing demand for more energy efficient buildings, the construction industry is\nfaced with the challenge to ensure that the energy efficiency predicted during the design is\nrealised once a building is in use. There is, however, significant evidence to suggest that\nbuildings are not performing as well as expected and initiatives such as PROBE and\nCarbonBuzz aim to illustrate the extent of this so called "Performance Gap". This paper\ndiscusses the underlying causes of discrepancies between detailed energy modelling predictions\nand in-use performance of occupied buildings (after the twelve month liability period). Many\nof the causal factors relate to the use of unrealistic input parameters regarding occupancy\nbehaviour and facilities management in building energy models. In turn, this is associated with\nthe lack of feedback to designers once a building has been constructed and occupied.\nThis paper aims to demonstrate how knowledge acquired from Post-Occupancy Evaluation\n(POE) can be used to produce more accurate energy performance models. A case study focused\nspecifically on lighting, small power and catering equipment in a high density office building is\npresented. Results show that by combining monitored data with predictive energy modelling, it\nwas possible to increase the accuracy of the model to within 3% of actual electricity\nconsumption values. Future work will seek to use detailed POE data to develop a set of\nevidence based benchmarks for energy consumption in office buildings. It is envisioned that\nthese benchmarks will inform designers on the impact of occupancy and management on the\nactual energy consumption of buildings. Moreover, it should enable the use of more realistic\ninput parameters in energy models, bringing the predicted figures closer to reality.