文章目录
- The 2022 code adds prescriptive requirements for exhaust air heat recovery based on climate zone, percent of outdoor air, and annual operating hours (Tables 140.4-J and 140.4-K). It also adds a dedicated DOAS prescriptive path (§140.4(p)). A key interaction: a cooling system combined with a DOAS that includes exhaust-air heat recovery is exempt from the economizer requirement below 54,000 BTU/h, whereas a standalone unit needs an economizer above 33,000 BTU/h. Element Title 24 2022 provision DOAS exhaust-air heat recovery Prescriptive design path added (§140.4(p)) Economizer relief DOAS + recovery allowed < 54,000 BTU/h without economizer Exhaust recovery tables 140.4-J (by climate zone / % OA), 140.4-K (by operating hours) Filtration MERV 13 minimum on mechanical ventilation supply (§120.1(c)1)
- For balanced-ventilation multifamily dwelling units in Climate Zones 1–2 and 11–16, the code prescribes a heat or energy recovery ventilator with a minimum sensible heat recovery effectiveness of 67% at design conditions. Fan efficacy limits are strict: Unitary ERV/HRV: fan efficacy ≤ 0.6 W/cfm (a mandatory 1.0 W/cfm floor applies in all climate zones). Central ERV/HRV (multi-unit): ≤ 1.2 W/cfm, and a bypass function is required so intake air can bypass the core like an economizer.
- The 2022 code strengthens the push from gas to heat pumps (§140.4(a)2) and targets net-zero-energy commercial buildings by 2030. Recovery is the demand-reduction step that makes an all-electric, heat-pump strategy affordable. For the cross-jurisdiction picture, see the building code heat recovery mandate comparison, and for the federal floor see ASHRAE 90.1-2022 (50% minimum). California's 67% sensible floor for multifamily is notably higher than the federal 50% enthalpy floor.
- Specify the core and verify pressure drop inside the AHU selection calculation. Pair a non-rotating membrane core where cross-contamination control matters; otherwise a wheel clears the 67% threshold comfortably — but watch frost, per energy recovery wheel troubleshooting.
California Title 24, Part 6 (the Building Energy Efficiency Standards) is the most aggressive state energy code in the U.S., and its 2022 edition — effective 1 January 2023, with a July 2024 Supplement — puts heat recovery at the center of both nonresidential and multifamily compliance. This article distills the recovery provisions that trigger HRV/ERV specification in California.
The 2022 code adds prescriptive requirements for exhaust air heat recovery based on climate zone, percent of outdoor air, and annual operating hours (Tables 140.4-J and 140.4-K). It also adds a dedicated DOAS prescriptive path (§140.4(p)). A key interaction: a cooling system combined with a DOAS that includes exhaust-air heat recovery is exempt from the economizer requirement below 54,000 BTU/h, whereas a standalone unit needs an economizer above 33,000 BTU/h.
| Element | Title 24 2022 provision |
|---|---|
| DOAS exhaust-air heat recovery | Prescriptive design path added (§140.4(p)) |
| Economizer relief | DOAS + recovery allowed < 54,000 BTU/h without economizer |
| Exhaust recovery tables | 140.4-J (by climate zone / % OA), 140.4-K (by operating hours) |
| Filtration | MERV 13 minimum on mechanical ventilation supply (§120.1(c)1) |
For balanced-ventilation multifamily dwelling units in Climate Zones 1–2 and 11–16, the code prescribes a heat or energy recovery ventilator with a minimum sensible heat recovery effectiveness of 67% at design conditions. Fan efficacy limits are strict:
- Unitary ERV/HRV: fan efficacy ≤ 0.6 W/cfm (a mandatory 1.0 W/cfm floor applies in all climate zones).
- Central ERV/HRV (multi-unit): ≤ 1.2 W/cfm, and a bypass function is required so intake air can bypass the core like an economizer.
The 2022 code strengthens the push from gas to heat pumps (§140.4(a)2) and targets net-zero-energy commercial buildings by 2030. Recovery is the demand-reduction step that makes an all-electric, heat-pump strategy affordable. For the cross-jurisdiction picture, see the building code heat recovery mandate comparison, and for the federal floor see ASHRAE 90.1-2022 (50% minimum). California's 67% sensible floor for multifamily is notably higher than the federal 50% enthalpy floor.
Specify the core and verify pressure drop inside the AHU selection calculation. Pair a non-rotating membrane core where cross-contamination control matters; otherwise a wheel clears the 67% threshold comfortably — but watch frost, per energy recovery wheel troubleshooting.