Comparison of three HVAC systems in an office building from a life cycle perspective

Abstract

This study aims to explore the life cycle environmental impacts of typical heating ventilation and air condition (HVAC) systems including variable air volume (VAV) system, chilled beam system and underfloor air distribution (UAD) system through a case study based on an RMIT office building. Life cycle assessment (LCA) is employed to evaluate the environmental impacts associated with different life cycle phases of HVAC systems. Using carbon emissions as the environmental indicator, ranges of impact for each HVAC system in different life cycle stages are calculated and compared based on the information uncovered in the literature review and relevant LCA inventory database. The system designs on case study are outlined based on the characteristics of a case building. The building was originally equipped with VAV system and was then designed with the chilled beam system and UAD system for comparison purposes. The lists of materials and products used in these three HVAC systems are illustrated, forming the basis of the life cycle assessment. Inventory analyses diagrams have been established based on the activities of HVAC systems in four life cycle stages: manufacturing, construction, operation & maintenance, and demolition. Calculation methods for carbon emissions are established. In particular, inventory data have been developed for manufacturing of HVAC products as well as transportation. We found that the environmental impacts between these three HVAC systems are found to be of different magnitude in different life cycle phase. For instance, the embodied energy of UAD system is the lowest in manufacture stage while that of the chilled beam system is the highest. However, chilled beam system has much more energy saving potential than the other two air conditioning systems in operation stage, and also from a life cycle perspective, the chilled beam system has the lowest environmental impact over a 50 year time frame, and VAV system has the highest environmental impact among the three HVAC systems compared.