How are the OG-300 performance ratings calculated?

ICC-SRCC calculates all performance ratings for solar water heaters in the OG-300 certification program using performance data for each component, modeled using proprietary software in the TRNSYS platform.  The programs use weather data files for that best represent median weather conditions during one year in a specific geographic location.  This is combined with local water supply temperatures, standardized system characteristics, and a hot water draw pattern to obtain performance results that permit relative comparison between systems on a consistent basis.  The models are run over one full year using time steps of five minutes or less and averaged to provide annual average ratings.  Performance is reported using the solar fraction metric.  This is the ratio of the added energy in the hot water delivered to the plumbing system that came from solar energy, averaged over one year for that location.

The OG-300 ratings cannot specify exactly how much energy will be collected for a given project in each location due to installation, hot water use, actual weather and other variations.  But they can provide a useful relative comparison between different geographic locations and between different types of systems.

For the Puerto Rico Supplement, this modeling is done five times for each location – once using SRCC’s standard 64.3 gallon per day hot water draw pattern and the other four using hot water draw patterns set by the DOE.