Paper Conference

ASHRAE & IBPSA-USA SimBuild 2016: Building Performance Modeling Conference


The Impacts of HVAC Downsizing on Thermal Comfort Hours and Energy Consumption

Elvin Ruya, Godfried Augenbroe
Georgia Institute of Technology, Atlanta, GA

Abstract: In current practice, HVAC designers oversize systems in order to provide the theoretical benefit of perfect occupant comfort in the consideration of all possible extreme conditions. Routine use of the autosize option of simulation tools and the assigned or implied safety factors leads to the potential oversizing that have been reported in literature. Even though the most important mandate is to reduce the risk of uncomfortable hours, current design methods and simulation tools offer only a limited way to do this. Indeed, unwanted outcomes can result from uncertainty in the parameters of the building energy model that is used. How to overcome the negative effects of oversized HVAC systems in terms of energy use, equipment life, maintenance and financial penalties by rightsizing strategies with various perspectives has been subject of previous studies. This study focuses on an incremental downsizing approach backed up by an uncertainty analysis. A system consisting of packaged heat pump units in commercial buildings is used to demonstrate the approach. Even though a heat pump unit has both heating and cooling coils, only the capacity of cooling coils is analyzed in this paper. Acceptable risk magnitudes in terms of unmet hours, impact of modeler's ignorance, and energy & cost savings as the result of downsizing are investigated. The proposed method opens the door to selecting the appropriate system size with more flexibility and confidence in cases where comfort criteria can be relaxed.
Pages: 165 - 172