September 13, 2019 | Nancy Kellogg
Denver’s cannabis growing facilities (which are mostly indoor grows) account for about 4% of Denver’s total electricity consumption, while producing over 50% of the state’s supply of marijuana. Indoor grows are fairly energy intensive, consuming about ten times as much energy per square foot as a typical Denver office building. There are also many cost-effective opportunities to improve energy productivity (grams of product per unit of energy consumption) including more efficient lighting, cooling, and dehumidification. Utility or state/local technical assistance and incentive programs for cannabis growers can be very helpful. In addition, building code requirements can set a baseline for reasonable energy efficiency practices for new grows and renovations/additions to existing grows.
The Denver Building Code committee recently approved two new sets of requirements for indoor ag/cannabis facilities, affecting lighting and dehumidification. The Denver City Council still has to officially approve them, likely in the next few months, but the language of the requirements will not change. SWEEP proposed both code amendments and led efforts to gather enough industry support to gain the Code Committee’s approval.
The first requirement is for lighting in new grow facilities, or additions/expansions to existing facilities (existing plant growth areas are not affected). Overall, lighting accounts for about 55% of total energy consumption for a typical indoor grow. The most efficient lighting technologies for cannabis (and other indoor ag) are LED and double-ended high-pressure sodium (DE HPS) lighting. The latter type is widely accepted within the cannabis industry for use in flower rooms, which require the most intense lighting and consume the most energy, followed by the vegetative rooms.
The accepted metric for the efficiency of horticulture lighting is “photosynthetic photon efficacy” (PPE), measured in units of micromoles per joule (µmoles/J). Because many cannabis growers prefer high-pressure sodium lighting (standard or double-ended) and are still somewhat wary of using LEDs for their flower rooms, SWEEP proposed setting the PPE requirements at a level which would allow the use of DE HPS lighting as well as LEDs. DE HPS fixtures are about 30% more efficient than standard HPS fixtures, and are only slightly less efficient than LEDs, based on PPE.
The level chosen in the new code requirements, 1.6 µmoles/J for lighting fixtures, is achievable by many of the more efficient DE HPS fixtures (at least 15 products are currently available, based on test results available from the Design Lights Consortium). The Denver requirements for minimum PPE will apply to 80% of the lighting watts in the plant growth areas of a new facility (or addition/expansion). This will allow flexibility for Denver growers to use less efficient and less expensive lighting for the clone/seedling areas, for example, with only a minor penalty in overall energy efficiency.
The new requirements will result in significant energy savings. Compared to the standard practices for cannabis grows, the new minimum efficacy requirements will result in about 30% energy savings for flower rooms, and up to 50% energy savings for vegetative rooms, per gram of product.
The second new code requirement applies to dehumidification and cooling systems. Dehumidification and cooling account for about 35% of total energy consumption for indoor cannabis grow facilities. The new Denver code requires indoor ag/cannabis facilities to install stand-alone dehumidifiers that meet a minimum efficiency level of 1.9 liters per kWh. This requirement nearly meets the Energy Star level of efficiency and ensures that only the most efficient dehumidifiers will be employed. Most cannabis grow facilities already use dehumidifiers. However, an inefficient practice that is sometimes still used, which the code would not allow, is to rely solely on standard rooftop air-conditioning (AC) units to provide the facility’s dehumidification needs. During lights-off periods, when there is no sensible cooling load from the lights but while plants are still transpiring, the rooftop AC units overcool the space in order to dehumidify. And in the process, standard AC units (those without heat recovery or hot gas reheat capability) waste a lot of energy reheating the space using electric resistance or natural gas heating. Compared to this practice, the code requirements would reduce the energy consumed for dehumidification by 25-30%.
In addition to strong technical assistance and incentive programs targeting cannabis/indoor agriculture, SWEEP recommends that state or local governments adopt these energy efficiency requirements to achieve energy savings in the cannabis sector.