Are Boiler Efficiencies in EnergyPlus Based on LHV or GCV?

boiler+condensing-boiler+lhv+hhv

asked 2025-09-17 17:23:53 -0500

Behnam
63 ●2 ●3

Hi there,

I hope you are pretty well.

In the EnergyPlus Engineering Reference (Boilers section), the definition of boiler efficiency and fuel input does not explicitly state whether the calculations are performed on a Lower Heating Value (LHV / NCV) or a Gross/High Heating Value (GCV / HHV) basis.

When we specify the “Nominal Thermal Efficiency” for a Boiler:HotWater object, does EnergyPlus interpret this efficiency relative to LHV or GCV?

Is there an internal assumption in the code that all fuel energy content is on an LHV basis, or does EnergyPlus simply use the efficiency as entered by the user, without any conversion?

For example, if a boiler manufacturer lists efficiency as 90% LHV, and I input 0.90 as the nominal efficiency, am I being consistent with EnergyPlus’s internal treatment?

Finally, is there any official documentation or source code comment that clarifies whether EnergyPlus internally assumes one convention or leaves it to the user to maintain consistency with their fuel data?

I am asking because in Ireland gas billing is on a GCV basis, while much equipment performance data is provided on an LHV basis. To align EnergyPlus simulations with actual operating cost and billing data, I need to know which convention EnergyPlus assumes.

Thanks a myriad, Behnam

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answered 2025-09-17 18:31:26 -0500

shorowit

12750 ●226 ●9 https://www.nrel.gov/b...

There is description in the EnergyPlus Input/Output Reference for the Nominal Thermal Efficiency field here:

This required numeric field contains the heating efficiency (as a fraction) of the boiler’s burner. This is the efficiency relative to the higher heating value (HHV) of fuel at a part load ratio of 1.0. Manufacturers typically specify the efficiency of a boiler using the higher heating value of the fuel. For the rare occurrences when a manufacturers (or particular data set) thermal efficiency is based on the lower heating value (LHV) of the fuel, multiply the thermal efficiency by the lower-to-higher heating value ratio. For example, assume a fuel’s lower and higher heating values are approximately 45,450 and 50,000 kJ/kg, respectively. For a manufacturers thermal efficiency rating of 0.90 (based on the LHV), the nominal thermal efficiency entered here is 0.82 (i.e. 0.9 multiplied by 45,450/50,000). Note that a nominal efficiency greater than 1.0 is allowed for special applications, but will generate a warning.