Energy efficiency retrofits of tertiary education buildings: An investigation of case studies in New South Wales

Abstract

Improving the energy efficiency of existing building stock has been acknowledged as one of the most critical environmental challenges facing the building industry. However, the efficacy of such retrofits in improving energy efficiency has not been comprehensively explored. Existing tertiary education buildings have been particularly underserved by previous research in this area. Previous methods for evaluating the impact of retrofits, for the most part, measured the differences between annual energy consumption immediately before and after the retrofit. Monitoring energy consumption in previous case studies has generally been limited to the initial 12 -18 months post-retrofit. The longer-term impact of energy efficiency retrofits on energy trends has not been adequately examined. This renders most reported figures on the impact of retrofit on energy consumption unreliable, or limited at best, as they fail to allow enough time for retrofitted systems to reach their peak efficiency. The lack of long-term monitoring in the post-retrofit period may have been due to perceived difficulties in keeping track of the many variables in a particular building, both building-related and occupant-related, for extended periods. The lack of sub-metering in many buildings added another layer of complexity in determining retrofit impact, as it restricted assessment to only a broad energy trend analysis, rather than a precise measurement. In addition, there were insufficient suitable energy-use-intensity (EUI) benchmarks against which to assess energy consumption, given each building’s unique mix of space use. A total of 12 case studies from 4 tertiary education institutions in New South Wales were investigated in this study. The retrofit scope predominately involved works in HVAC (heating and cooling) and lighting, the two leading areas of energy use in an average university building. Most of the retrofit cases involved both active and passive systems, with active systems being the majority of the work scope. A preliminary building space audit was carried out for each case study to establish the size and percentage of spaces allocated to each use. Each space category was allocated with a low and a high EUI benchmark, amalgamated from existing literature. This range was then weighted according to the percentage of space use to form a customised EUI range for each building. The pre- and post-retrofit EUIs of the building were then measured against 4 the benchmarks to indicate their relative performance. The result of the preliminary audit established a broad metric of each building’s general energy performance, given its space composition. The data analysis component of this study consists of two parts: an energy trend analysis and a multivariate regression analysis. The energy trend analysis offers a broad view of energy variations against seven energy-related parameters: energy cost, campus-wide consumption, mean external temperature, heating degree days, cooling degree days, total degree days and daylight hours. The multivariate regression analysis is a comprehensive assessment of variations in the regression relationship between energy and following five parameters: mean external temperature, heating degree days, cooling degree days, total degree days and daylight hours. The combination of these two analyses offered detailed insight into the behaviour of the retrofitted systems and their interaction with external environmental variables. The results suggest that although energy usage seemed to have decreased in most cases, there were many issues that eroded the gains in energy efficiency over the long term. This brought to light the many complex and sometimes conflicting interests involved in retrofitting. There were significant gaps between the case study EUIs and the current industry benchmarks that are considered best practice for existing tertiary education buildings. The results from investigating the EUI benchmarks in turn raised questions about the feasibility of some current standards and suggest the need for a set of achievable benchmarks in current retrofit practice. Buildings in the tertiary education sector are some of the most varied and complex of all existing building stock. As the case studies in this thesis were considered to be a subset of commercial buildings, this research and its findings contribute to our understanding of energy efficiency not just in tertiary education buildings, but also in commercial buildings and the built environment at large.