Controlled Environment Horticulture Prescriptive Requirements for Space Conditioning Systems
Measure Overview
This proposed measure would establish mandatory sizing requirements and controls requirements for space conditioning systems providing heating, cooling, and dehumidification to support plant growth in Controlled Environment Horticulture (CEH) spaces and would prescriptively require these systems meet key functional and performance metrics.
These requirements would only apply to space conditioning systems serving CEH spaces with lighting power density (LPD) greater than 30 watts (W) per canopy square foot in indoor (skylight ratio below 50%) CEH facilities with at least of 5000 ft2 of plant canopy. Facilities subject to these proposed prescriptive requirements would also have the option to comply via the performance pathway via a new indoor CEH prototype and modeling capabilities being introduced to the California Building Energy Code Compliance (CBECC) software.
These proposed requirements recognize that functions of cooling and dehumidification 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. The proposed code changes would require the applicant to define a primary space conditioning system providing cooling, dehumidification, and reheat. The prescriptive requirements would require the primary system to have a variable sensible heat ratio (SHR), to be capable of modulating the amount of dehumidification process heat recovered between ten percent and 90 percent, and to be sized to meet at least [TBD 70 percent] of the peak combined sensible and latent load. The primary system could be an integrated direct expansion (DX) system, a desiccant-based system, or a heat recovery chiller system.
This prescriptive requirement would be used to set an energy budget for compliance via the performance pathway, where applicants could comply by modeling an alternative system.
The mandatory sizing requirement would require the submission of calculated sensible and latent loads and sizing calculations for space conditioning systems serving spaces with LPD above 30 W per canopy square foot.
In addition to the primary space conditioning system, the proposed requirements would allow the use of supplemental equipment to meet sensible or latent loads exceeding the primary system’s capacity.
Mandatory requirements would require the installation of a central control system for the primary space conditioning system, with additional controls integrating any supplemental equipment with the primary system.
Mandatory requirements for the primary system would require that it be controlled to do the following:
- Modulate sensible heat ratio (SHR) in response to room conditions and temperature and humidity setpoints;
- Modulate reheat to reject or recover dehumidification process heat, as needed to meet supply air setpoints; and
- Limit the use of primary heating (i.e. resistance, furnace, or boiler) heat to periods when the use of recovered process heat cannot meet supply air setpoints.
Controls for supplemental unitary dehumidification equipment without variable SHR or heat rejection capability would be required to do the following:
- Integrate and stage supplemental equipment with primary system to meet temperature and humidity setpoints;
- Stage unitary dehumidifiers in response to humidity sensors (including those that measure relative humidity, dewpoint, or wet bulb);
- Only activate dehumidification equipment when either all waste heat can be used in the space or the primary system cannot satisfy 100 percent of cooling, heating, and dehumidification loads.
The requirements would be the same for all 16 California Climate Zones. The proposed requirements would apply to new construction, additions, and major alterations. Replacing a single piece of equipment in a larger system would not trigger the requirements (minimum threshold to be defined prior to publication of the Final CASE Report).
This code change proposal would also review and reconsider requirements from the general non-residential space conditioning code, such as outdoor air ventilation requirements, that may negatively impact plant growth or efficiency.
Title 24, Part 6 does not currently include prescriptive measures for CEH spaces, and CBECC does not currently include an indoor CEH prototype. To provide facility designers with flexibility in equipment selection, CBECC would need to be updated for use in demonstrating compliance using the performance approach.
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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, prescriptive, performance | Add new feature | 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 horticultural lighting and space conditioning systems make up about 80 percent of energy consumption, split roughly evenly between them. Each of these two end-uses provides significant opportunities for savings. Until this code cycle, CEH lighting has been 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 EUI of 760kBtu/sf/year.
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 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, which lead to highly variable room sensible heat ratio (SHR). Sizing methods, design approaches, and equipment requirements are vastly different from those for spaces designed primarily for human occupancy—and equipment designed to maintain human comfort is poorly suited to the unique conditions found in CEH process spaces.
Over the past decade there have been significant advances in the development of variable capacity, fully integrated space conditioning systems suitable for high latent loads, and capable of quickly adjusting to highly variable loads, offering better environmental control and far more efficient operation than fixed-capacity, “decoupled” systems. Unfortunately, many designers continue to use inefficient fully decoupled equipment in the design of new facilities, even though much more efficient, better performing, integrated equipment is now available from multiple manufacturers and has been recommended for energy efficiency and more precise environmental control in industry best-practices guides for several years.
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 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 energy used by more efficient integrated HVAC/dehumidification (HVAC/D) systems is approximately 40 percent less than energy use by a 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 recent comparative study2, facilities using these systems can produce more grams of dried product per square foot and per kWh, improving both space and energy resource efficiency.
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.