Energy-cost relationship of high-rise office buildings in Hong Kong from the life cycle perspective

Abstract

It has been realised that the energy and costs of buildings relate with, and impact on, each other through the building’s life cycle. However, scant research investigated how the buildings’ energy relates to their cost performance. This research aims to examine the energy-cost relationship (ECR) of high-rise office buildings from the life cycle perspective. This research has been carried out through the combination of a critical literature review, desk studies of four overseas buildings projects, in-depth case studies with ten high-rise office buildings in Hong Kong (HK), and one case-based modelling and optimisation. Statistical analysis and modelling were used in this research. The first round literature review aimed to develop the theoretical model of the influencing parameters of the ECR of buildings from the life cycle perspective drawing on the Political, Economic, Socio-cultural, Technological, Environmental and Legal (PESTEL) analytical framework. This model was validated through desk studies, of which data validation was conducted with the information providers of the four case projects through a questionnaire survey. The second round literature review aimed to develop the life cycle energy assessment (LCEA) and life cycle cost assessment (LCCA) models of office buildings. The ten in-depth case studies aimed to evaluate the life cycle energy (LCE) of high-rise office buildings. For ensuring data validity and reliability, in-depth case studies engaged various data collection methods including desk study of documents of the case buildings, site visits to the case buildings, and face-to-face interviews with three contractors and seven material suppliers in HK. One case-based modelling and optimisation aimed to investigate the sensitivity of operational energy and cost performance using variance-based global sensitivity analysis, and the operational energy and cost relationship (OECR) of high-rise office buildings from the life cycle perspective. The energy simulation model of this case building was validated using audited energy use data. Face-to-face interviews with 42 product agencies from 30 companies were employed to collect product information and its procurement cost for modelling and optimisation. The developed models and research results were validated through a questionnaire survey with five experts including government officials, researchers and consultants. This research concludes as follows: (1) important influencing parameters of building’s ECR reside in internal project designs and external environments, and the ECR can be attributed to the synergy of simultaneous and unilateral effects of the identified parameters; (2) operational energy (78-89%) should be prioritised in energy conservation of high-rise office buildings over embodied energy (11-22%); (3) lighting, heating, ventilation, and air conditioning (HVAC) system and glass should be paid more attention to reducing operational energy, of which optimising lighting energy use is identified as the most economical solution; (4) a U-curve relationship exists between operational energy saving and initial investment cost and a significant linear correlation exists between operational energy saving and net present value (NPV) while optimising operational energy of high-rise office buildings. This research contributes a novel systemic perspective on the research of life cycle assessment of building energy and economics. The findings should inform building developers and designers of the relationship between energy and economics and support their decision-making in optimising operational energy of high-rise office buildings in an economically attractive way.