Five major end uses are identified for DHW: showers, baths, sinks, dishwasher, and clothes washer. If a clothes washer is not provided by the builder, the Benchmark clothes washer shall be included in both the Benchmark and Prototype models, except in the case of multi-family housing with a common laundry room. The average daily water consumption by end use is shown in Table 10. For showers, baths, and sinks, the specified volume is the combined hot and cold water. This allows hot water use to fluctuate depending on the cold water (mains) temperature.3 Hot water usage values for the clothes washer and dishwasher were estimated based on several scientific references studied by NREL. For showers, baths, and sinks, the water usage is based on the average of three DHW studies (Burch and Salasovich 2002, Christensen et al. 2000, and CEC 2002). The relationship between the number of bedrooms and hot water usage was derived from the 1997 Residential Energy Consumption Study (RECS) (DOE 1999). This relationship also applies to machine energy for certain appliances, which will be discussed later in this report. Latent and sensible heat gains were estimated based on guidance from the American Society for Testing and Materials (ASTM) Manual on Moisture Control in Buildings (ASTM 1994). The water usage equation for a common laundry room stems from the National Research Center’s study of laundry use in multi-family housing (NRC 2002). The equation for the office/public sink is based on engineering judgment.
7.5 + 2.5 × Nbr gal/day (Hot Only)
2.47 gal/day/housing unit (Hot Only) 2.5 + 0.833 × Nbr gal/day (Hot Only)
14.0 + 4.67 × Nbr gal/day (Hot + Cold)
741 + 247 × Nbr Btu/day
703 + 235 × Nbr Btu/day (0.70 + 0.23 × Nbr pints/day)
3.5 + 1.17 × Nbr gal/day (Hot + Cold)
185 + 62 × Nbr Btu/day
12.5 + 4.16 × Nbr gal/day (Hot + Cold)
310 + 103 × Nbr Btu/day
140 + 47 × Nbr Btu/day (0.14 + 0.05 × Nbr pints/day) 0.314 × Nunits Btu/day (3.14 × 10-4 × Nunits pints/day)
Office/ Public Sink
0.028 × Nunits gal/day (Hot + Cold)
0.69 × Nunits Btu/day
Table 10. Domestic Hot Water Consumption by End Use
Water Usage End-Use Sensible Heat Water Gain Temperature
Latent Heat Gain
Hourly hot water use profiles for individual hot water end uses are shown in Figure 6 to Figure 13. For software tools that do not accept this level of detail, the combined hourly hot water
, “Appliances and
Sensible and latent heat gains from appliances are included
Miscellaneous Electric Loads.” ** Negligible compared to showers and sinks.
in the section titled
3 The clothes washer in the Prototype may also consume a variable amount of hot water depending on mains temperature if it uses a thermostatic control valve to adjust the proportion of hot and cold water necessary to maintain a certain wash temperature. However, the Benchmark clothes washer does not have this feature.