3280 -- Equipment Sizing Procedures for Combination SpaceoHeating/Water-Heating Systems PDF

The last several years have seen a rapid growth in the installation of combination space-heating~water-heating systems that use conventional resiclential gas-fired, storages.type water heaters as the sole source of heat. These installations have been made primarily in multifamily apartments, where space-heating requirements are relatively low and floor space is at a premium, but use of the concept is growing in single-family residences as well. An unresolved issue regarding these systems is the absence of a generally accepted procedure for sizing system components for simultaneously meeting the peak space-heating and water-heating demands. Varying procedures have been proposed by equipment manufacturers and gas utilities, but the technical basis for these procedures has not always been evident. This paper reviews sizing methods currently in use. A more rigorous sizing method is developed for personal computer use. A simplified approach and a rule-of-thumb guideline are also developed and shown to be reasonably consistent with the more detailed calculation procedure. These new approaches to sizing, which are recommended for future use, are then compared to methods currently being used.