Measure Overview
This measure seeks to establish mandatory and prescriptive requirements for smart DOAS in non-residential new construction and additions and alterations, aligning with national best practices.
The measure package consists of four sub-measures that would apply to Section 120.1(d) and Section 140.4(p) as described below.
The proposal would add the following mandatory requirements:
- Require all DOAS systems to include an air valve with Air Flow Measurement System (AFMS) per thermal zone to modulate and/or shut off flow at each thermal zone required to have DCV or occupied standby, while still maintaining required ventilation to all zones served by the system.
- Clarify where Occupied Standby is currently required in Section 120.1(d)5A.
The following prescriptive requirements are proposed:
- Require VFD fan instead of 3-Speed fan to facilitate variable flow control in addition to system balancing.
- Revise the Supply Air Temperature (SAT) from current 60°F to a lower temperature, e.g., 55°F to save energy. The measure applies to DOAS with cooling, heating (direct and or heat recovery) and ventilation, which serves multiple zones. This aligns with ASHRAE TC 1.4’s current DOAS RP-1865.
These measures are applicable to new construction, additions, and alterations (system replacements and new installations only) in climate zones where proven cost-effective.
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This measure page will be updated as the 2028 code cycle progresses. For questions or suggestions, submit feedback to [email protected]. Please include the measure name in the subject line.
View the Energy Commission's proceedings and available proposed code language by visiting their CEC 2028 Proceedings Website page.
Scope of Proposed Code Change
| Building Type(s) | Construction Type(s) | Type of Change | Updates to Compliance Software | Third Party Verification |
| Nonresidential | New construction, additions, alterations | Mandatory, prescriptive | Update existing feature, Add new feature | No changes to third party verification |
Justification for Proposed Change
A DOAS is an energy-efficient HVAC system that maintains indoor air quality by bringing fresh air into interior spaces and handling ventilation independently from heating or cooling. Unlike typical rooftop units that mix large portions of return air with outdoor air, it brings in a dedicated supply of fresh outdoor air, dehumidifies it, conditions it, and then delivers at the right temperature and humidity to occupied spaces, decoupling the latent loads from sensible loads.
Smart DOAS incorporates into existing acceptance testing and automatically complies with both the demand control ventilation (DCV) and energy recovery requirements. It uses Variable Frequency Drive (VFD) fans to precisely match ventilation demand, and leverages energy recovery ventilators to precondition the incoming air – reducing cooling and heating loads.
This proposal seeks mandatory requirements to include air valves for all DOAS systems. Some DOAS designs do not have outlets for each thermal zone, just one outlet for several thermal zones. This does not meet the T24 ventilation requirements. Adding air valve not only complies with Occupied Standby but also saves energy and improves IAQ by dynamically ventilating the zones as needed.
The proposal also seeks to clarify the code language in section 120.1(d). This will expand the occupied standby control requirements to non-mandated zones when they are scheduled to be occupied but unoccupied.
Space decoupled ventilation systems (e.g., DOAS) serving spaces required to have occupant sensing ventilation controls shall include modulating pressure independent air valves or other means of modulating outside air at all space conditioning zones. This shall be done to disable ventilation to unoccupied zones while maintaining measured outside air ventilation rates to occupied zones within 10% of the design minimum outside air ventilation rate per 120.1(f)2 and shall include demand ventilation controls for high-density spaces per 120.1.(d)3.
Both these sub measures offer the potential for significant energy savings.
The sub-measure 3 of “Expand Variable Speed DOAS” is a prescriptive measure that proposes to replace the current 3-speed fan requirement with a Variable Frequency Drive (VFD) to provide more precise ventilation and airflow management. This will reduce energy consumption and fine-tune the total airflow based on the individual zone requirement, which may consequently result in cooling and heating savings.
Requiring the DOAS system to be a variable air volume (VAV) could reduce energy consumption, in addition to providing system balancing and reducing stress on motors and other components during startup and operation.
The sub-measure 4 proposes to reduce the DOAS supply air temperature (SAT) from current 60⁰F under heating or heat recovery mode to 55°F when most zones require cooling. This will result in energy savings as allowing warmer air to enter the space will increase the energy for the space cooling equipment. The current 60°F was based on ASHRAE 90.1 Section 6.5.2.6, which was arbitrarily chosen. ASHRAE TC1.4 has completed a research project (DOAS RP-1865: Optimizing Supply Air Temperature Control for Dedicated Outdoor Air Systems) on revising the SAT. Tentatively, the CASE team proposes 55°F to estimate the preliminary analysis. The final proposal will be revised based on the outcome of the RP-1985 voting.
The proposed recommendations will reduce the fan energy at part load, improve indoor air quality, eliminate or reduce recooling energy of warm ventilation air when the majority of the zones call for cooling, and reduce ventilation system cooling and heating energy for all zones.
Relevant Documents
Round One Utility-Sponsored Stakeholder Meeting Materials
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The Statewide CASE Team values input from all stakeholders engaged in the Title 24, Part 6 code change process. We encourage the open exchange of code change comments and concerns.