Evaluation of variable volume and temperature HVAC system for commercial and residential buildings

The variable volume and temperature (VVT) system meet energy efficiency constraints during peak and partial load conditions while maintaining thermal comfort requirements. Although there are numerous alternatives available for changeover from an existing inefficient constant-air-volume system, the VVT system is of particular interest due to the favorable economics and minimal time requirements for installation. The objectives of this paper are (1) the presentation of simulation results for constant-air-volume, variable-air-volume, and VVT systems; and (2) the comparison of annual energy consumption and economic selection factors for these systems. A typical three-story office building and a typical residential building, located in Des Moines, Iowa, were examined. The results show that the VVT system should be considered during the design stages for new projects and as a replacement in retrofit projects. For a commercial office building, the payback period for retrofit from a constant-air-volume system to the VVT system is estimated at 3-4 yr. For a residential building, capital-cost-recovery periods of 6 mo for retrofit and 18 mo for a new installation of the VVT system are predicted.