Variable Capacity Heat Pump Modeling

Variable Capacity Heat Pump Modeling

• Q: What changed for variable capacity heat pump (VCHP) modeling in CBECC?

  • A: CBECC and approved third-party residential compliance software use a new method for modeling single-speed and variable-speed unitary air conditioners (AC) and heat pumps (HP). This update introduces physics-based modeling for variable-speed heat pumps (VCHP), improving accuracy over the previous compliance option credit.

• Q: Is the VCHP Performance Compliance Option credit still available?

  • A: No, the VCHP Performance Compliance Option credit is not usable for 2025 compliance. The compliance option was introduced because we could not model these systems in CBECC and CBECC-Res. With the introduction of the physics-based model we no longer have this limitation and the compliance credit is no longer needed.

• Q: What is the basis for the new modeling method?

  • A: The new modeling method is based on RESNET Publication-003: Guidelines for Simulating Unitary Air-conditioning and Air-source Heat Pump Equipment

• Q: What system types are affected by this change?

  • A: The new modeling method applies to all single and variable speed residential and multifamily unitary air conditioners and air-source heat pumps.

• Q: Why is my compliance going down when I switch my heat pump from single to variable speed? I thought variable speed heat pumps performed better than single speed equipment.

  • A: To get accurate results from the new model you must enter real (or close to real) rating data. By this, if you enter SEER2 and EER2 ratings based on a single speed cut sheet and then switch the 'Speed' input to 'Variable' you will not get accurate results. To compare variable to single speed performance you need to use SEER2 and EER2 ratings applicable to the type of equipment you're modeling.

• Q: Do any of the VCHP Performance Compliance Option requirements still apply to ducted and ductless VCHP systems?

  • A: No, the requirements of the VCHP Performance Compliance Option available in 2022 Energy Code software no longer apply to VCHP systems modeled with the new method available in 2025 Energy Code software. Requirements such as certification to the CEC of low-static ducts, non-continuous fan operation, and other requirements of the previous compliance option are no longer applicable to the new modeling method.