Converting Efficiencies for Residential and Commercial Water Heaters

Residential Unshared Water Heaters

If you are modeling a water heater in Residential Unshared Water Heaters and the efficiency is given in COP, you can convert this to EF the following way:

If the water heater is tankless, then use the COP as the EF directly. 

If there's a tank, then take the EF determined above and derate it by a factor between 0.8 & 0.85 as described in our Conditioning Equipment help (which assumes a boiler but the same logic applies for a heat pump; screenshot below).

For indirect (AKA combo, side arm tank) water heaters, we recommend calculating EF by dividing the AFUE of the boiler by 100 and multiplying by a factor between 0.8 and 0.85 depending on tank size and insulation. Conservatively, we advise using 0.8, but for a low volume (<= 30 gallons) or super-insulated (>= R-20) tank, use 0.85.

Commercial Water Heaters

To model a commercial hot water heater in Ekotrope Commercial Water Heaters, the unit's Energy Factor must be used and can be calculated using the Commercial DHW EF Converter spreadsheet attached below. Should you need to convert from UEF to EF, you can use the attached converter as well.

**Please note that as of August 2021, Ekotrope supports the modeling of Commercial Water Heaters, so this workaround may not be necessary.

**Please note that Ekotrope does not currently support modeling shared/commercial heat pump water heaters directly. To model these types of units, please refer to this article on how to model shared heat pump water heaters.