22 May 2008

HVAC OPTIONS FOR LOW ENERGY RESIDENTIAL BUILDINGS


Data now available from prototype low energy residences confirm that peak
heating and cooling loads can be reduced by factors of 3 to 5, using currently available
technologies. This work explores the range of candidate HVAC systems capable of dealing
with such fundamentally different load profiles as 8°C balance points, spatially non-uniform
loads, and non-negligible thermal capacitance. This paper quantifies peak heating and
cooling load reductions in a North American climate, investigates the necessity of ductwork,
and examines the role of thermal mass effects in low energy residences.
Results reveal surprisingly small differences in overall efficiency among well-designed
centralized (ducted) and decentralized vapor-compression heat pump systems employing
either mechanical or desiccant dehumidification. Centralized systems offer opportunities for
integration of domestic hot water heating, and some types of decentralized systems offer the
long-term possibility of being integrated into wall panels or other structural elements.
Decentralized system options included DX and secondary loops. Since energy efficiencies
are comparable, system selection is therefore likely to be driven by such factors as initial
costs, complexity and reliability.