Dual Fuel Heat Pumps

[William E. Beaver]

I don’t see a way to enter data for a dual fuel heat pump, one that uses a gas furnace with an electric heat pump. I see quite a bit of that in this mixed-humid climate. Thanks.

[Gamaliel Lodge]

Hi William.

Dual fuel heat pumps are modeled as two separate systems in OptiMiser. You model the furnace and heat pump components as separate systems that each handle a portion of the annual load. You can estimate the split yourself or have OptiMiser do it using the Advanced heat pump model. The Advanced model will also estimate the actual HSPF for the heat pump using the dual fuel configuration.

1. Specify the two systems in the main interface, assigning the load in any way you want
   • Make sure the total load assigned to the two systems is the load that will be met by the combined dual fuel system
   • If you are using an existing fuel fired system as backup, then be sure to set the improved system to No Improvement
   • Use COP and EER units for the heat pump efficiency, if you have those value. Otherwise, use HSPF and SEER
2. Click the Advanced button to open the popup
3. Change Model Setup to Live, unless you need to use the advanced model for multiple heat pumps
4. Set the Backup control to the correct heating system and specify the Heating Threshold temperature at which the backup will switch on
5. Click the Copy Result and Close Window button and OpitMiser the correct % Load for the heat pump and backup systems

Note: If you need to use the advanced model for more than one heat pump, then set Model Setup to “Calculator”. When you do this, then OptiMiser will copy the calculated annual efficiency values back into the main interface, rather than connecting the advanced model directly to the main energy model. If you do this, then it is very important to complete all other aspects of the building model first to ensure that the advanced heat pump model is working with correct hourly loads.

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