An example using Equations 5 and 6 to determine the monthly mains temperature profile for Chicago, Illinois, is shown in Figure 15.
BA - Monthly Mains Water Temperature and DHW Usage Using TMY2 data for CHICAGO, IL
Temperature (°F) & Gallons/day
80 70 60 50
40 30 20 10 0
T ambient T mains DHW gal/day
Figure 15. Mains temperature profile for Chicago
Hot water distribution system design can have a significant impact on wait times for hot water, interior heat gains from pipes, and total water heating energy. NREL and Davis Energy Group (DEG) analyzed a wide range of distribution system types, and developed a set of equations to assist with the calculation of whole-house energy savings for improved distribution systems. The basic characteristics of the Benchmark distribution system are summarized in Table 13. Treatment of other distribution system types is discussed in the “Modeling the Prototype” section of this report.
Table 13. Benchmark Hot Water Distribution System Characteristics
Branching Configu Material Pipe insulation
Trunk and Branch Copper None
Pipe lengths and diameters
Based on 2010 ft2 prototype house layout developed by DEG for CEC (DEG 2006)
Number of bathrooms Recirculation loop
Inside conditioned space
The daily internal heat gain caused by the Benchmark distribution system shall be calculated using Equation 7. The heat gain shall be applied using the combined hourly DHW profile in Figure 14.