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### Decision Logic for Supplementary Electric Resistance Heating

Using ResStock 2.2.4, OpenStudio 2.9.0, EnergyPlus 9.2

For the heat pump measures provided in the ResStock project, what is the decision logic for determining when to use the supplementary heater? Is it dependent on heat load? Is it dependent on temperature?

I ask this because I'm trying to model a dual-fuel ASHP/MSHP, but with a propane furnace as the supplementary heater versus an electric resistance. Because ResStock does not currently have that as a measure, a workaround for me is to just take the heating output from the heating & supplementary coils and convert it to an equivalent amount of propane needed to burn to meet that output. (i.e. HEATING COIL HEATING ENERGY)

However, I'd like to use the propane furnace only when the ASHP/MSHP falls below a certain efficiency, say for example, an instantaneous COP of 1. I determine the instantaneous COP by dividing the HEATING COIL HEATING ENERGY (RES ASHP HTG COIL) [J] by HEATING COIL ELECTRIC ENERGY (RES ASHP HTG COIL) [J]. So this begs the question: how does the ASHP/MSHP measure in ResStock choose when to start using the supplementary heater?

### Decision Logic for Supplementary Electric Resistance Heating

Using ResStock 2.2.4, OpenStudio 2.9.0, EnergyPlus 9.2

For the heat pump measures provided in the ResStock project, what is the decision logic for determining when to use the supplementary heater? Is it dependent on heat load? Is it dependent on temperature?

I ask this because I'm trying to model a dual-fuel ASHP/MSHP, but with a propane furnace as the supplementary heater versus an electric resistance. Because ResStock does not currently have that as a measure, a workaround for me is to just take the heating output from the heating & supplementary coils and convert it to an equivalent amount of propane needed to burn to meet that output. (i.e. HEATING COIL HEATING ENERGY)

However, I'd like to use the propane furnace only when the ASHP/MSHP falls below a certain efficiency, say for example, an instantaneous COP of 1. I determine the instantaneous COP by dividing the HEATING COIL HEATING ENERGY (RES ASHP HTG COIL) [J] by HEATING COIL ELECTRIC ENERGY (RES ASHP HTG COIL) [J]. So this begs the question: how does the ASHP/MSHP measure in ResStock choose when to start using the supplementary heater?