Multifamily Indoor Air Quality

Measure Description

This report provides proposed updates to Title 24, Part 6 for three submeasures related to ventilation in multifamily dwelling units. Submeasure A would require heat or energy recovery in multifamily units for whole dwelling unit ventilation in select climate zones and primarily provides energy benefits. Submeasure B addresses kitchen ventilation to reduce pollution from cooking and kitchen appliances, and primarily provides IAQ benefits. The requirements are structured by dwelling unit size; while the scope of this Final CASE Report is only multifamily buildings, the Statewide CASE Team recommends that similar requirements be made for single family multifamily units. Submeasure C addresses sealing of central ventilation ducts in multifamily buildings; it primarily provides IAQ benefits, but also results in statewide energy savings. While all relate to dwelling unit ventilation, each is a stand-alone measure and discussed separately in this report. 

Energy or Heat Recovery Ventilator (ERV or HRV)

This proposed measure builds on existing language in the 2019 Title 24, Part 6 Standards that require that all new construction multifamily units either provide balanced ventilation or demonstrate “compartmentalization”—i.e., demonstrate through a blower door test that leakage of the dwelling unit envelope area does not exceed a certain value. For projects following the balanced ventilation path, the proposed requirement for the 2022 Title 24, Part 6 code cycle adds HRV or ERV as a prescriptive requirement in California Climate Zones 1-2 and 11-16. This proposal aligns with a measure in American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) Standard 90.1 (added to the 2019 version) that will require an HRV or ERV for high-rise (buildings with four occupiable floors or higher) multifamily dwelling units of new construction in all climate zones except ASHRAE—International Energy Conservation Code (IECC) 3C (mild, marine climate zone), which generally maps to California Climate Zones 3 through 6. The proposed prescriptive requirement specifies the following, to be verified by the building inspector: 

1. Unitary equipment (one ERV or HRV serving each dwelling unit) must have a sensible heat recovery efficiency of at least 67 percent, and fan efficacy ≤ 0.6 W/ cubic feet per minute (cfm);  
2. Central equipment (one ERV or HRV serving multiple dwelling units) must have a sensible heat recover effectiveness1 of at least 67 percent, minimum fan efficacy as required in Section 140.4, and include a bypass function whereby the intake air bypasses the heat exchanger and the equipment functions similar to an economizer. 

These requirements would be assumed for the standard design in the performance path in Climate Zones 1, 2, and 11-16. In addition, the proposal adds a mandatory measure for fan efficacy of 1.0 W/cfm for unitary ERVs/HRVs for all climate zones. Projects using central ERVs/HRVs in climate zones not regulated under the proposed requirement would continue to comply with applicable requirements in Title 24, Part 6 Section 140.4. 

Kitchen Exhaust Minimum Capture

California’s 2019 Title 24, Part 6 Standards require that dwelling units meet all requirements of ASHRAE Standard 62.2, except where specified. The proposed changes are new requirements for range hoods to better ensure that a kitchen exhaust system can adequately remove cooking-related pollution. Specifically, the proposal builds upon recent research from Lawrence Berkeley National Laboratory (LBNL) that estimated the minimum range hood capture efficiency needed to maintain fine particulate matter (PM2.5, for all ranges) and to maintain nitrogen dioxide (NO2, for natural gas-fueled ranges) at acceptable levels specified, depending on the size of the dwelling unit. Both pollutants have been linked to numerous health problems. While a requirement based exclusively on capture efficiency would be the most direct approach to address IAQ, manufacturers have not yet published the capture efficiency of their equipment, so there is little market data regarding capture efficiency of available products. LBNL research and research conducted for this Final CASE Report have found a direct relationship between airflow and capture efficiency (i.e., a higher airflow generally results in a higher capture efficiency). As additional background, manufacturers are moving toward increasing the static pressure requirements during testing through industry stakeholder groups and through a working group formed by the ASHRAE 62.2 committee. The proposed requirement avoids retesting of range hoods should manufacturer testing requirements change. Consequently, the proposal requires that all multifamily dwelling units have an exhaust system in the kitchen that meets one of the following compliance pathways: 

1. A vented range hood with a minimum capture efficiency shown in Table 1, using ASTM Standard E3087-18 at nominal installed airflow (defined in HVI Publication 920), or 
2. A vented range hood with a minimum airflow shown in Table 1, at 0.1 inches water column (w.c.) (25 Pascals [Pa]), or  
3. A vented downdraft kitchen exhaust fan with a minimum airflow of 300 cfm at 0.1 inches w.c. (25 Pa) or higher, or 
4. A continuous exhaust system with a minimum airflow equal to five kitchen air changes per hour at 50 Pa for enclosed kitchens only (an enclosed kitchen is defined as a kitchen whose permanent openings to interior adjacent spaces do not exceed a total 60 square feet (ft2) [6 square meters]). 

Table 1. Minimum Range Hood Capture Efficiency (CE) or Airflow Requirements by Dwelling Unit Floor Area and Range Fuel, For Demand-Controlled Range Hoods 

Pathway 1 is new and pathway 2 is a modification to the existing standard. Pathways 3 and 4 are kitchen exhaust requirements under ASHRAE Standard 62.2 and adopted under California’s 2019 Title 24, Part 6 Standards. California’s 2019 Title 24, Part 6 Standards added one amendment to ASHRAE Standard 62.2, allowing sound to be rated at working speed, as defined by HVI Publication 916.2 The proposed requirement maintains these existing requirements. Capture efficiency and airflow would be determined in a laboratory and published by manufacturers, as is currently done for sound ratings. 

Central Ventilation Duct Sealing

This proposal defines a “central ventilation duct” (also referred to as a “central ventilation shaft”) as ductwork that serves multiple dwelling units and provides dwelling unit ventilation supply or exhaust air. 2019 Title 24, Part 6 Standards include a requirement that central ventilation systems be balanced, to ensure that each dwelling unit receives the required ventilation rate. The proposed measure builds on this requirement by requiring that project teams seal central ventilation duct systems that provide continuous ventilation airflows or that serve as part of dwelling units’ balanced ventilation system. The proposed measure requires field verification of shaft leakage using a fan pressurization test to ensure that leakage does not exceed 10 percent of the central (e.g., rooftop) fan airflow rate at 50 Pa (0.2 inches w.c.) for central ventilation duct serving more than six dwelling units, and does not exceed 6 percent of the central fan airflow rate at 25 Pa (0.1 inches w.c.) for central ventilation duct serving six or fewer dwelling units. The lower test pressure for ducts serving fewer units aligns with current low-rise duct testing requirements, and ducts serving fewer units typically have a lower static pressure. 

This measure provides cost-effective energy savings through reduced fan energy and reduced loss of conditioned air. In addition, central ventilation shaft sealing provides IAQ benefits by improving the reliability of supply and exhaust rates, and reducing the leakage of exhausted air, which can include various pollutants such as PM2.5, NO2, volatile organic compounds (VOCs), and relative humidity (which can cause mold) into other interior spaces, including other dwelling units.  

Relevant Documents

Measure proposals, supporting documents, and other outside references will be made public as they become available.

• 2019 New and Revised Multifamily Prototypes

Reports

• CASE Study Results Report – Multifamily Indoor Air Quality
• Final CASE Report- Multifamily Indoor Air Quality
• Draft CASE Report – Multifamily Indoor Air Quality

Round Two Utility-Sponsored Stakeholder Meeting Materials

• Presentation – March 25 – Multifamily HVAC and Envelope
• Notes – March 25 – Multifamily HVAC and Envelope
• Kitchen Range Hood Capture Submeasure Summary
• HRV ERV Submeasure Summary
• Central Ventilation Duct Sealing Submeasure Summary

Round One Utility-Sponsored Stakeholder Meeting Materials

• Presentation – Aug. 22 – Multifamily HVAC and Envelope Utility-Sponsored Stakeholder Meeting
• Notes – Aug. 22 – Multifamily HVAC Envelope Utility-Sponsored Stakeholder Meeting

Submeasure Summaries

• Reduce Infiltration Submeasure Summary
• Central Ventilation Shaft Sealing Submeasure Summary
• Heat or Energy Recovery Ventilation in Select Climate Zones Submeasure Summary
• Kitchen Range Hood Capture Efficiency Submeasure Summary