Model Code for the Control of Residential HVAC Distribution System Leakage and HVAC-Induced Building Leakage

Abstract

Modifications to local and state codes are seen as an appropriate strategy for the prevention of residential air distribution system leakage and its impacts. A model code element has been developed to assist this strategy. Recent field studies of Florida residences by Cummings, Tooley and Moyer have revealed a mean leakage of 11 percent for the air distribution systems of central, fan-force heating and air conditioning systems. Such leakage may cause an estimated 20 percent increase in energy consumption for air conditioning, as well as a 50 percent increase in peak cooling load and an 80 percent increase in peak heating load. In addition, building air leakage may be expected to be several times greater when duct leakage is present or when avenues of air egress from closeable rooms are absent. The model duct construction element presented here contains all of the standards, definitions and code language needed to replace the current duct construction element of the local or state code. The content of this paper was used as a principal source for language adopted for the 1991 Florida Energy Efficiency Code For Building Construction. Addressed are the most appropriate standards required for the closure and sealing of metal duct, rigid fibrous glass duct, and nonmetallic flexible duct. Also addressed are (1) detailed requirements for the sealing of mechanical closets when they function as plenum chambers, (2) detailed requirements for the sealing of enclosed support platforms or air handlers and furnaces when they function as return duct, (3) detailed requirements for the sealing of uninhabitable cavities of the building structure, when they function as duct, and (4) detailed requirements for the egress of air from enclosed rooms which receive supply air. Where necessary, commentary is provided to explain the options available for implementing the model code provision as well as its ramifications. All provisions of this model code are compatible with the requirements, standards and guidelines contained in related documents published by the following organizations: the Southern Building Code Congress International, Inc., the Sheet Metal and Air Conditioning Contractors National Association, the American Society of Heating, Refrigerating and Air conditioning Engineers, Underwriters Laboratories, Inc., the Air Conditioning Contractors Of America, the Thermal Insulation Manufacturers Association, the National Fire Protection Association, and the Gypsum Association.