Life cycle assessment of a CAV, a VAV, and an ACB system in a modern Swedish office building

Sammanfattning: Energy use in buildings contributes significantly to the global energy demand and environmental impacts. Among all building services, heating, ventilation, and air conditioning (HVAC) systems consume the most energy. HVAC systems are as well one of the largest consumers of natural resources and materials in the building sector. Studies have shown that the manufacturing and operation of HVAC systems have a significant impact on the environment. With a constant growing awareness towards thermal comfort and energy use, the question remains, which HVAC system has a better environmental performance. This thesis presents a comparison between the life cycle impacts of three different HVAC systems — constant-air volume, variable-air volume, and active climate beam systems — designed for a Swedish modern office building. The system boundary of the life cycle assessment was set to be cradle-to-grave with options, over a 20-year period. SimaPro software was used for the life cycle assessment (LCA) of the systems. The CML IA (baseline) method was used for the life cycle impact assessment and the results were weighted based on the shadow cost Dutch method. Initially, a base case scenario was set for all three HVAC systems, using Copper material for the hydronic system and using Swedish electricity mix. Varying the material used for the hydronic system and the electricity type, a parametric study was then conducted comparing the environmental impacts of the systems. The results of the Base case scenario showed that, from a life cycle perspective, the ACB and VAV systems have similar environmental performance. During the life cycle of the CAV and VAV systems, the operational phase showed to have the highest environmental impact. Whereas, for the life cycle of the ACB system, the manufacturing phase exhibited the highest environmental impact. The biggest reduction in environmental impacts was observed when PVC pipes were used instead of copper pipes, in the ACB system. A slight reduction was seen when 100 % renewable-based electricity was used by the systems instead of the Swedish electricity mix. Under all case-scenarios, the CAV system showed to have the highest environmental impacts. Further research regarding the impacts of the maintenance phase and life span of the systems would be relevant for the comparison of life cycle impacts of the systems.