Cooling and Dehumidification for Indoor Farming

Controlled-environment agriculture needs constant management of sensible heat from lighting and latent moisture from crop transpiration, making cooling and dehumidification main contributors to facility electricity use. This project assessed alternative methods for independently managing these loads in a container-based indoor lettuce farm, including rotary desiccant dehumidification, indirect evaporative cooling (IEC), and integrated hybrid configurations, relative to conventional vapor-compression air conditioning. Container-scale experimentations were performed under partial- and full-plant conditions to evaluate environmental control, electrical energy use, sensible and latent loads, moisture removal, and water recovery. Trial data were also used to calibrate and validate component-based TRNSYS models, which were applied to 8,760-hour simulations for San Francisco, Sacramento, and Long Beach, California. Experimental load separation showed that approximately 22 percent of the LED-associated thermal load was latent and 78 percent was sensible. The rotary desiccant system offered dedicated moisture removal, however, introduced about 0.110 kW of adsorption-related sensible heat. Combining IEC lowered this sensible penalty to about 0.089 kW, a 19 percent reduction. The validated baseline model reproduced cumulative cooling energy within 2.18 percent. Annual simulations showed that closed-loop IEC achieved significantly better than open-loop operation, but its energy benefit remained climate dependent: annual conditioning electricity increased by 9.6 percent in San Francisco and 5.6 percent in Sacramento and decreased by 0.6 percent in Long Beach. Rotary-desiccant-containing configurations generally increased annual electricity use at the evaluated container scale, although integrated closed-loop operation recovered approximately 10,325–12,490 kg of water annually. The results show that separating sensible and latent conditioning can improve control flexibility and water recovery, but energy benefits depend strongly on climate, equipment sizing, airflow configuration, and latent-load intensity. Closed-loop IEC warrants targeted optimization and demonstration rather than broad deployment as a universally energy-saving technology.