THE IMPACTS OF HVAC DOWNSIZING ON THERMAL COMFORT HOURS AND ENERGY CONSUMPTION
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.
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