HWS Calculation Details:

The calculations on the HWS page are briefly summarized:

1) Electricity Usage: measured watt hours of electrical heating and pumping and controls

2) Natural Gas Usage: measured cubic feet of natural gas for appropriate systems

3) Energy Output: Measured energy during hot water draws: (Toutlet - Tinlet) * Gallons * 8.33

4) Total Daily Gallons: Measured total hot water draws over the 24 hour period

5) Daily Efficiencies: Total Hot Water Energy Output / Electricity and Natural gas Energy Content (This is the system COP) - Where: Energy Content = 3413 Btu/ kWh and 1020 Btu/cubic foot of natural gas

6) Weather conditions: Measured test building and outdoor temperature and measured solar irradiance at collector tilt (W/m2)