Estimated Weekly Domestic Hot Water (DHW) Usage


5 Person Household


If you plan to use a solar thermal system to heat domestic hot water, an estimation of the building's consumption must be made in order to properly size the system. Some analysis has been done to help predict how much a 5 person household will use.

Summary

Common uses Number of people (person) Number of cycles (cycles/person/week) Total cycles (cycles/week) Hot water (liters/cycle) Total hot water (liters/week) Average hot water (liters/day) Total energy (kWh/week) Average energy (kWh/day)
Dishwasher 5.0 1.4 7.0 30.4 212.7 30.4 8.9 1.3
Clothes washer 5.0 1.0 5.0 14.6 73.2 10.5 3.1 0.4
Shower 5.0 7.0 35.0 84.7 2,964.4 423.5 124.2 17.7
Miscellaneous 5.0 7.0 35.0 0.8 28.2 4.0 1.2 0.2
Total 3,278.5 468.4 137.4 19.6

Temperature Conditions

Description Value Units
Cold water from the utility grid 12.8 °C
Hot water from the domestic hot water tank 49.0 °C
Temperature difference 36.2 °C


Calculation notes:
  • Shower flow rate equal to 7 liters/minute for 15 minutes
  • Dishwasher based on Whirlpool large capacity model DU850SWP
  • Clothes washer based on Whirlpool super capacity model WTW5100S
  • Miscellaneous uses might include hand washing, coffee or tea making, cooking, etc.
  • Liters/cycle indicates amount of hot water used from the domestic hot water tank
  • Total mixed temperature water used (not shown) may be more than hot water used
  • Temperature of cold water from the utility grid and hot water from the DHW tank may vary based on climate and season
For a list of common DHW tank manufactures, please see the Solar Energy Links page.

Domestic hot water consumption will vary based on many variables (number of occupants, habits of those occupants, climate, appliances, etc.). In order to more accurately predict domestic hot water production, you will need tweak this estimation for your conditions. A spreadsheet is available in several file formats to assist you.

Printable PDF File
Editable OpenOffice Calc Spreadsheet

Please Contact Me if you have any questions or improvement suggestions related to this estimation.





©2007 - Andy Schroder