Residential HVAC Performance

Proposal Description

The Residential HVAC Performance CASE Report documents a set of proposals designed to ensure that Residential HVAC systems perform efficiently and effectively, providing comfort and protecting the condition of the equipment, in the following areas:

• Design (Sizing, Equipment Selection, and Ducts/Diffusers): The requirements proposed include requiring that load calculations be completed in more situations, and that their results be documented and submitted, while they do provide an allowance to use simplified calculations in some cases. They require that duct and diffuser designs be submitted with building plans. After load calculations are completed, they provide different limits on the system capacity than currently recommended nationwide, to reflect California climates—primarily not allowing undersized heat pumps that would require supplementary heating to meet capacity and not allowing oversized cooling systems when ducts are not correspondingly sized.
• Supplementary Heating Control: The supplemental heating measure requires installation of controls that lock out the operation of gas or electric supplementary heating when temperatures are not severe and limit the capacity of electric resistance strip heating to the minimum needed for emergency or defrost operation. Because the configuration of this control is so challenging and so critical, installer verification is proposed to be required.
• Defrost: This measure would require that, when present, the manufacturer’s defrost delay timer be set to a moderate value of no less than 90 minutes to extend the amount of time between defrost cycles. This would reduce energy use by heat pumps by reducing the frequency of defrost cycles and the length of time the unit spends in defrost mode. The proposed control requirement would prevent excessive winter morning peak demand, as well as improve comfort and reduce wear and tear on a system and improve system life, by reducing the frequency of defrost operation.  Installer verification of the setting of this control is proposed to be required.
• Thermostat/Crankcase Heating: This mandatory space conditioning control measure requires installation of an Occupant Controlled Smart Thermostat to reduce energy use and implement demand response. Alternatively, the installer can choose a system that has no crankcase heating (CCH), or one that has a CCH with better controls. These “better controls” can include a 71°F lockout of the CCH, differential temperature control, or self-regulating control; in all these cases the CCH would have to also be disabled when the compressor is operating.
• Refrigerant Charge Verification: The proposed measure would require verification in more climate zones, but just for heat pumps. It retains existing methods (except the Fault Indicator Display method, which is proposed to be retired) but adds rigor to the weigh-in method.
• Variable Capacity and Zonally Controlled Systems: The proposed measure would require a change in the way that fan efficacy is measured during field verification and clarifies how system air flow is defined in zoned systems. It also proposes modifying the way that variable capacity systems are modeled in vented attics.

Relevant Documents

CASE Report

• Final CASE Report – Residential HVAC Performance (UPDATE: CASE Report was revised November 2023)
• Draft CASE Report – Residential HVAC Performance

Round One Utility-Sponsored Stakeholder Meeting Materials

• Stakeholder Meetings Introduction
• Residential HVAC Performance – Proposal Summary
• Residential HVAC Performance – Presentation (Jan. 24, 2023)
• January 24, 2023 Meeting Notes