What are the DOE Hot Water Load Patterns used in the OG-300 Puerto Rico Supplement and ENERGY STAR certifications?

Hot water load patterns are used to indicate the size, timing and flowrate of hot water draws from the solar water heating system during a 24-hour time period.  Different building types, occupancies, local practices and the time of year all impact the amount of hot water drawn from a domestic water heater.  SRCC’s OG-300 program, which started in the US, utilizes a 64.3 gallon per day hot water draw pattern with two peaks, one in the morning and one in the evening.  The 64.3 gallon per day value was established by the U.S. Department of Energy for water heater testing prior to 2015. 

Recognizing that there are significant differences in the hot water drawn in various cases, the DOE created four different hot water draw patterns that were implemented in 2015.  These are labeled “Very Small Usage”, “Low Usage”, “Medium Usage”, and “High Usage” and represent different types of domestic hot water use.  The hot water draw patterns differ in both the total volume, and in the timing, flow rate and number of hot water draws, as summarized below.