Predicted vs. actual energy performance of non-domestic buildings: Using post-occupancy evaluation data to reduce the performance gap

Abstract

With the increasing demand for more energy efficient buildings, the construction industry is faced with the challenge to ensure that the energy performance predicted during the design stage is achieved once a building is in use. There is, however, significant evidence to suggest that buildings are not performing as well as expected and initiatives such as PROBE and CarbonBuzz aim to illustrate the extent of this so called 'performance gap'. This paper discusses the underlying causes of discrepancies between energy modelling predictions and in-use performance of occupied buildings (after the twelve month liability period). Many of the causal factors relate to the use of unrealistic input parameters regarding occupancy behaviour and facilities management in building energy models. In turn, this is associated with the lack of feedback to designers once a building has been constructed and occupied.The paper aims to demonstrate how knowledge acquired from Post-Occupancy Evaluation (POE) can be used to produce more accurate energy performance models. A case study focused specifically on lighting, small power and catering equipment in a high density office building is analysed and presented. Results show that by combining monitoring data with predictive energy modelling, it was possible to increase the accuracy of the model to within 3% of actual electricity consumption values. Future work will seek to use detailed POE data to develop a set of evidence based benchmarks for energy consumption in office buildings. It is envisioned that these benchmarks will inform designers on the impact of occupancy and management on the actual energy consumption of buildings. Moreover, it should enable the use of more realistic input parameters in energy models, bringing the predicted figures closer to reality.

Energy-related standards and UK speculative office development

“…EPC ratings, Part L compliance and the dark art of modelling A 'performance gap' has been identified between EPC ratings and real-world energy consumption data (Better Buildings Partnership, 2012;Cohen & Bordass, 2015;Menezes et al, 2012). This is ascribed to the behaviour of building occupants, and a 'perception gap' in which calculations do not refer to all the energy a building uses.…”

“…This is not to deny the existence or importance of the 'performance gap' (Fedoruk et al, 2015) as an explanation of how energy performance can fail to manifest. It is clearly important that many energy demanding processes are unregulated, and that the ways in which tenants occupy buildings can be responsible for much energy use (Arup, 2013;Fedoruk et al, 2015;Menezes, Cripps, Bouchlaghem, & Buswell, 2012). Instead it is important to push similar enquiries into the design processes.…”

The potential for energy reduction in UK commercial offices through effective management and behaviour change

“…Junnila (2007) notes that the existing literature on energy efficiency in office buildings does not provide good data for estimating energy reduction potential through occupant behaviour change. Furthermore as discussed by Menezes, Cripps, Bouchlaghem and Buswell (2012) this lack of understanding of unregulated energy use can be identified as a contributory factor to the 'performance gap' between predicted/design and actual/in-use energy performance. In UK office spaces this performance gap has in some cases resulted in in-use carbon emissions 2-3 times that of the original design estimate (Bordass, Cohen & Field, 2004).…”

Power-use profile analysis of non-domestic consumers for electricity tariff switching

“…For example, using six non-domestic buildings, Masoso and Grobler (2010) showed that more than half of the energy demand occurred outside of working hours. As part of postoccupancy evaluation studies, Menezes et al (2012) derived profiles from monitoring lighting and small power loads, while electrical load profiles due to airconditioning for offices and hotels in Hong Kong have been examined by Qi et al (2012). A useful literature review of measuring electrical loads in non-domestic buildings is presented by Kamilaris et al (2014).…”