Modeling and life-cycle cost analysis for secondary HVAC systems

HVAC systems and associated equipment consume a relatively large fraction of total building energy consumption, a significant portion of which is attributed to fan operation. The operation of dampers when installed can cause low energy consumption in supply and/or return fans if they are functioning in proper and optimal manner. In this study, mathematical experessions of individual components of HVAC systems are presented to model secondary HVAC systems based on the knowledge of the underlying physical phenomenon. A life-cycle cost analysis using detailed system modeling and initial and operating costs is applied to evaluate the economic feasibilities of constant air volume (CAV) and variable air volume (VAV) air conditioning systems. Several factors such as the building locations, system characteristics, resistance in the duct and dampers, supply air temperature, damper control, and minimum ventilation requirements are also considered during the evaluations. The results show that the way of the dampers been controlled has a significant effect on fan performance and its energy use. The VAV strategy if properly implemented can provide fan energy saving about 13%. It is found that payback period of VAV is suitable particularly by considering cooling and heating system altogether.