Controlled Environment Horticulture: Space Conditioning Systems for Indoor CEH
Measure Overview
This proposed measure would establish mandatory sizing, functional, equipment, and controls requirements for space conditioning systems that provide heating, cooling, and dehumidification to support plant growth in indoor CEH spaces. This proposal establishes mandatory requirements only and does not introduce prescriptive or performance compliance pathways.
These requirements apply where a space conditioning systems serves 5,000 square feet or more of plant canopy area[1], with horticultural lighting power density greater than 30 W per square foot of plant canopy area. These thresholds are intended to target high-intensity indoor cultivation applications, which are predominantly associated with cannabis production in California.
These proposed requirements recognize that functions of HVAC and dehumidification (HVAC/D)equipment are highly interactive and must be considered together as a part of a space conditioning system that manages both temperature and humidity in CEH spaces, and that the purpose of these systems is to support an agricultural process. The proposal would revise the definition of “directly conditioned space” to exclude CEH spaces, develop a new definition for “indoor CEH spaces”, and unify both HVAC and dehumidification requirements for CEH spaces in the process loads section of the energy code.
The proposal distinguishes between federally regulated consumer dehumidifiers and commercial dehumidifiers used in CEH applications. Consumer dehumidifiers remain subject to federal appliance standards under 10 CFR Part 430, while the proposal establishes separate qualification, testing, and certification requirements for commercial dehumidifiers used to comply with CEH requirements in California.
Because commercial dehumidifiers used in CEH are not addressed by the same regulatory framework as consumer dehumidifiers, the proposal includes a new Nonresidential Appendix establishing qualification requirements, a California-specific test procedure derived from the federal dehumidifier test procedure, and product certification to the California Energy Commission.
For covered space, the requirements would require the applicant to identify whether the primary space conditioning system is (1) an integrated HVAC/D system capable of providing cooling, dehumidification, and reheat within a unified system; or (2) a coordinated system using separate commercial dehumidifiers and commercial HVAC equipment. The proposal would establish mandatory requirements that apply to both system types, as well as mandatory requirements that are specific to each unique system type.
Integrated HVAC/D systems would be required to provide a primary system sized to meet at least 80 percent of the design peak sensible and latent loads, to be capable of modulating sensible heat ratio, recovered heat used for reheat, heat rejected outside the space, and supply fan speed in response to measured space conditions and temperature and humidity setpoints. The remaining load not served by the primary system could be met by fixed-capacity equipment.
For covered high-intensity CEH spaces, systems using separate dehumidification and HVAC components would be required to use qualifying commercial dehumidifiers and qualifying commercial HVAC equipment, together with integrated temperature and humidity controls. In effect, consumer dehumidifiers would no longer be an allowable compliance option for these covered spaces.
Because integrated system requirements are based on a functional description of range of required sensible heat ratios, range of heat recovery modulation and minimum combined cooling and dehumidification size to design capacity, a variety of primary systems could comply with the requirements such as an integrated direct expansion (DX) system, a desiccant-based system, or a heat recovery chiller system.
The proposal would require design heating, cooling, and dehumidification loads to be calculated according to a new Nonresidential Appendix and documented in construction documents for covered indoor CEH spaces. The HVAC/D systems shall be sized to meet both sensible and latent loads for representative early-, mid-, and late-stage grow cycle conditions, including both lights-on and lights-off operation. The proposal would require that all covered space conditioning systems include integrated control systems that coordinate temperature and humidity control based on measurements within the plant canopy. These controls would be required to automatically stage and modulate all space conditioning equipment, including cooling, dehumidification, heat recovery, heat rejection, supplemental heating, and airflow, to maintain temperature and humidity setpoints.
Systems using integrated HVAC/D equipment would be required to include controls capable of modulating sensible heat ratio, heat recovery, heat rejection, and airflow in response to measured space conditions and temperature and humidity setpoints. If no supplemental equipment is used, the equipment may be provided with controls that meet the requirements.
Systems using commercial dehumidifiers in combination with separate HVAC equipment would be required to centrally coordinate and sequence all equipment to meet temperature and humidity setpoints. Dehumidification equipment without modulating heat recovery and rejection would need to be automatically staged based on dehumidification load and limited to operation under specified conditions.
Control system functionality would be verified through acceptance testing performed by a field technician.
The requirements would apply in all 16 California Climate Zones to new construction, additions, and major alterations. Replacing a single component of a larger system would not trigger the requirements. Covered alterations would include those projects that increase plant canopy area by at least 5000 square feet, replace greater than 50 percent of the total capacity of heating, ventilation, air conditioning, cooling, and dehumidification systems serving at least 5000 square feet of plant canopy area in indoor growing spaces, or increase the lighting power density to more than 30 W per square foot of canopy area.
A prescriptive and performance compliance framework was evaluated during measure development, including the use of a detailed EnergyPlus-based prototype to support a potential performance pathway. However, due to the current absence of an approved and standardized compliance modeling approach for indoor CEH space conditioning systems within the Title 24 compliance software environment, a performance compliance pathway is not included in this code cycle.
To ensure enforceability and timely implementation, the proposal focuses on mandatory requirements that establish minimum system functionality, sizing, and control performance. Development of a performance compliance pathway may be considered in future code cycles as modeling approaches and compliance tools for CEH applications mature.
This proposal would also revise outdoor air ventilation requirements for CO2 enriched CEH spaces. Ventilating these spaces may negatively impact plant growth or efficiency. The California Fire Code has requirements for CO2 monitoring, alarm response, and purge ventilation for these spaces, so this is not required in Title 24, Part 6.
[1] Plant Canopy Area is the aggregate horizontal surface area occupied by actively growing vegetation within a cultivation facility. It is measured by the boundaries of the specific grow trays/benches utilized, excluding non-productive spaces such as aisles, walkways, ancillary equipment zones, and structural columns.
The following table summarizes the scope of the proposed code change. Note that this proposal includes acceptance testing performed by a field technician. Because the field technician is typically a member if the installation team, this acceptance testing is not considered “third party verification.”
Provide Feedback
This measure page will be updated as the 2028 code cycle progresses. For questions or suggestions, email [email protected]. Please include the measure name in the subject line.
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 | no updates | No changes to third party verification |
Justification for Proposed Change
CEH facilities, particularly indoor facilities with high lighting power density, are among the most energy-intensive buildings in California. In these facilities, the lighting and space conditioning systems make up about 80 percent of energy consumption, split roughly evenly between the two systems. Each of these two end-uses provides significant opportunities for savings. Until this code cycle, CEH lighting was the primary focus of Title 24, Part 6, leaving significant opportunity for code to regulate CEH space conditioning systems and achieve deep statewide savings. For indoor cannabis facilities, flower rooms contribute roughly 86 percent of facility energy use. A field study of flower rooms in two California CEH facility found an average Energy Use Intensity (EUI) of 760 kBtu/yr per ft2 (Stober & Weitze, 2024).
Since large-scale indoor farming is relatively new, driven primarily by legalization of cannabis in California, CEH facility designers initially had little choice but to repurpose conventional HVAC equipment and consumer dehumidifiers to manage sensible and latent loads in indoor farms. However, space conditioning systems designed to support plant growth need to adapt to highly variable latent and sensible loads (room SHR), which can most effectively be conditioned by HVAC and dehumidification systems with variable equipment SHR[1] (sensible heat ratio). Controls, sizing methods, design approaches, and equipment requirements are vastly different from those for spaces designed primarily for human occupancy, and off-the-shelf equipment designed to maintain human comfort is poorly suited to the unique conditions found in CEH process spaces. (A CEH process space is any room or area where the primary function is the cultivation of plants, and the environmental conditions are controlled for the plant-growing process, not for human comfort.)
Over the past decade, industry has significantly advanced the development of high-capacity, efficient commercial dehumidifiers, plant canopy sensors, and controls that can integrate HVAC and dehumidification equipment, as well as variable capacity, fully integrated space conditioning systems. Integrated systems that are suitable for high latent loads, and capable of quickly adjusting to highly variable loads, which offer better environmental control and more efficient operation than most fixed-capacity fully decoupled[2] systems. However, decoupled systems that use high-efficiency equipment and a central control system that stages and modulates equipment based on readings from humidity and temperature sensors co-located in the canopy can also operate efficiently. Unfortunately, many designers continue to use inefficient fully decoupled equipment in the design of new facilities, even though much more efficient, better performing equipment and controls are now available from multiple manufacturers and have been recommended for energy efficiency and more precise environmental control in industry best practices guides for several years (Resource Innovation Institute, 2022; Harris Design Studio, 2022).
The market’s failure to broadly adopt this more efficient space conditioning equipment presents an excellent opportunity for the energy code to develop new efficiency requirements for CEH facilities.
The proposal would improve performance for both integrated and coordinated decoupled system configurations by establishing enforceable requirements for sizing, controls, and equipment qualification, while also addressing a regulatory gap for commercial dehumidifiers commonly used in CEH facilities. The proposal also creates a state qualification pathway for commercial dehumidifiers used in CEH applications, where the existing federal consumer-dehumidifier framework does not adequately address the equipment commonly used in these spaces.
The opportunity for energy savings is very high because energy intensity of indoor farms is very high, market adoption of efficient space conditioning systems is relatively low, and the current energy code language does not address CEH HVAC systems or the interaction between HVAC and dehumidification systems. Statewide CASE Team energy modeling of HVAC and dehumidification systems indicate that annual energy used by more efficient integrated HVAC/dehumidification (HVAC/D) systems is approximately 25 percent less than energy use by a fully decoupled, code-minimum HVAC and dehumidification system, consistent with measured and modeled data.
Furthermore, the more precise temperature and humidity control provided by variable-capacity integrated systems can increase crop yields, reduce mold risk, and help avoid crop loss. As demonstrated in a Statewide CASE Team review of recent unpublished data from 10 flower rooms and 42 grow cycles, facilities using these systems can produce more dried product per square foot and per kWh, improving both space and energy resource efficiency. Note that this study was a parallel comparison across different facilities, not a before/after upgrade.
[1] Room SHR refers to the ratio of sensible to total (both latent and sensible) heat in the space, while Equipment SHR refers to the ratio of sensible cooling capacity to total cooling capacity of the cooling/dehumidification equipment (prior to reheat).
[2] Background section provides relevant definitions.
Relevant Documents
CASE Reports
Round Two Utility-Sponsored Stakeholder Meeting Materials
Round One Utility-Sponsored Stakeholder Meeting Materials
-
Use the form above to provide feedback on this measure.
Give Us Your Feedback
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.