Solar Water Heating Performance: Use of Energy Factors

Secondary Author(s)

Merrigan, Timothy; Tiedemann, Thomas; Block, David

Report Number





Solar Thermal


The goal of increasing solar energy installations is widely accepted by all. The Florida Solar Energy Center (FSEC) concluded that the goal of increasing solar hot water system installations in Florida could be greatly enhanced by concentrating its efforts on new construction through simplification of the residential building energy code. Since implementation in 1980, the Florida Energy Efficiency Code for Building Construction has required a calculation procedure that assigns multipliers to residential water heating systems. The multiplier for every water heating system type except solar is based on the system's rated efficiency at standard conditions and is a one- or two-step process. Solar water heating system multipliers were not based on standard conditions and required an eight-step selection process. For these reasons, FSEC initiated a program to simplify the specification of solar water heaters in new home construction to a two-step code process. The process used is to rate solar water heating performance by the use of energy factors -- the same efficiency rating used for electric, gas and heat pump water heaters. This process was adopted for the 1993 Energy Code by the Florida Department of Community Affairs during 1992. This paper presents the methodology used to determine these energy factors for more than 275 solar hot water systems currently approved by the Florida Solar Energy Center for use in the State.

Date Published



Solar Thermal

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