Greenhouse cooling and where it fits in your operation

Greenhouse Management: When a grower is in the facility planning phase, how should they be evaluating whether they will need active vs. passive greenhouse ventilation, or are most operations using a mixture of both?

Keith Bemerer: This really boils down to economics. Active ventilation is a proven method to reduce temperature and humidity and allow for air exchanges via natural vents (roof, sidewall, etc.); passive ventilation allows this by using fans, shutters and evaporative cooling. With active ventilation, you’re operating manually or with a motor periodically; passive ventilation requires electricity and costs more to run at all times to keep things cool. So the economic factor kicks in for deciding what a grower can afford to do.

GM: Should growers be setting up their cooling capabilities at higher capacities than they would otherwise need, so that they are ensured they will have the requisite amount of cooling in case of extreme weather events (i.e., a warming climate)? 

KB: This boils down to static pressure (i.e., resistance of airflow). If you have static pressure that is too high, you’ll either cause a vacuum effect or not enough air movement, and the system can work too hard, burning out the motors. This needs to be thought of like your HVAC system in your home: if the filter is clogged, air cannot move through the house and the system fails. The same concept applies with a greenhouse. It’s better not to oversize the cooling capabilities for the volume of air that needs to be moving through the structure, or restrict it too much. It’s not unheard of, however, to have a mixture of active and passive cooling to maximize climate control.

GM: Where do you find the inflection point of retrofitting an older structure with cooling technologies vs. just starting over and building a completely new facility? I understand there are cost concerns with retrofitting that might be alleviated by just building a new facility from scratch?

KB: The age of the structure plays a significant factor when it comes to retrofitting. Many older structures built in the '80s and earlier may have not been designed for the cooling loads that customers are now seeking. Retrofitting may end up costing more in the long run than starting a new facility. However, it’s all about what’s grown in the greenhouse! You may find that some greenhouses hold much more relative humidity than newer, taller structures. That may work for propagation facilities, but not for finished crops. Also, many manufacturers may not keep older extrusions to retrofit for active ventilation, and gables and sidewalls may not be able to support the required sizes for passive ventilation.

GM: What are some of the newer cooling technologies that the top-end growers are looking at/interested in? 

KB: We’re seeing a lot of changes in the controls aspect of greenhouses. Many growers want real-time control, with the ability to implement control from several devices (computers, cell phones, tablets, etc.). This is becoming more prevalent. In the next few years, we may start seeing easier ways to set limits on active vent machines, DC motor technology (versus AC), and more items running with variable frequency drives (VFDs) to keep energy costs down. This will be a game-changer in the future with passive ventilation systems.

GM: How important is it to make sure (before purchasing) that cooling and ventilation technologies (that are able) can interface with the greenhouse climate control system? 

KB: It’s very important. Before making large cooling and ventilation system purchases, if you have an existing greenhouse climate control system, you’ll need to determine if expansions and controllers can be added. Many CCS companies have newer systems and have discontinued older-style systems, and parts and add-ons are not possible. This should be your first question before starting a retrofit or new build, to make sure you will not run into problems later. We’re seeing a lot of growers having outdated systems, and finding out upgrading to a new system is much more than they’re willing to spend.

GM: How is supply currently in the cooling/HVAC world when it comes to greenhouse solutions? Are lead times increasing on new builds due to not being able to get products as quickly as in the past? How much lead time is that adding to new build projects?

KB: As with the rest of the industry, supply is inconsistent because of the COVID-19 pandemic. Steel and aluminum are the primary reasons; but with chip and motor technologies being harder to get, it’s affecting the supply chain as well. We’re seeing estimates of 12 to more than 16 weeks sometimes for materials (it had been four to six weeks in the past). Long gone are the days of ordering June 1 for an August or September install. Being proactive, asking about timelines and understanding that shipping may be past your window of install will all help you to get moving on your installation and arrival of goods.

Ensure that you have the right cooling system by partnering with controlled environment agriculture technology experts. You can leverage their deep soil-to-market experience. You’ll recognize them because the right partner for your commercial greenhouse will have succeeded at every aspect — design, installation, integration, operations, maintenance and expansion — over and over again.

Keith Bemerer has worked for Prospiant for the past eight years. He earned a bachelor’s degree in crop science from The Ohio State University. He specializes in floriculture crops and greenhouse businesses.