A Horizontal Air Flow (HAF) fan in a Cloud CO Farms greenhouse.
Photo by Jermaine Amado

The quality of greenhouse- grown cannabis has everything to do with the climate control technology employed in the greenhouse. A facility properly designed and outfitted with efficient HVAC systems will create a better environment to help you consistently produce a connoisseur-grade product. Here are a few elements greenhouse growers can incorporate to improve their climate control.

1. Evaporative Cooling.

These systems include a cooling pad made of a porous material that has water flowing through it, keeping it saturated, on one end wall of the greenhouse. At the opposite end wall of the greenhouse is a large extraction fan that creates negative pressure within the structure, pulling exterior air through the cooling pad, moving it along the length of the facility and back out the other end. As the warm outside air passes through the cooling pad and evaporates the water within it, the air drops in temperature and cools the climate in the greenhouse.

2. Shade Cloth.

One of the least expensive ways to keep your greenhouse cool is the use of shade cloth. On a sunny day, a 25-percent shade cloth will help keep temperatures down while still allowing more PAR (photosynthetically active radiation) to reach your plants than an artificial light source can produce. Using reflective shade cloth will maximize the cooling effect inside your greenhouse.

3. Under-Bench Heating.

Running thin piping underneath your benching that circulates water heated by a boiler is an effective way of heating your greenhouse. Under-bench heating is very efficient because the hot water flowing through the pipes causes the ambient temperature to rise where it is most needed: among the plants and their delicate root zones.

4. Forced-Air Heating.

Though under bench heating may be sufficient in moderate climates, many growers will also need to utilize forced-air heating to keep their greenhouses warm in winter months. Forced-air heaters typically burn natural gas or propane, and use one or more fans to propel the heat they generate throughout the greenhouse.

5. Horizontal Air Flow (HAF) Fans.

With greenhouses that measure well over 100 feet in length, it can be challenging to maintain a consistent climate from one end of the facility to the other. Stationary HAF fans simply move air from the intake end of your greenhouse to the exhaust end. Utilizing multiple HAF fans along the length of your greenhouse will help keep temperature levels optimal for every plant.

Jeremy Raab is a professional cannabis grower, researcher and consultant. He is the director of production at CFH, Ltd. His areas of focus include lighting, environmental control, nutrient profiles and fertigation methods, growing substrates, plant manipulation and canopy management, plant populations and integrated pest management.