"Many growers spend a lot of time thinking and worrying about the topic of tier spacing. In vertical farming, you have a distance between your grow tray and the bottom of your grow lights, which is called tier height or tier spacing. After over 3,000 rooms that Pipp has designed and installed, we've learned some of the best practices and what challenges growers run into in terms of height," says Anders Peterson of Pipp Horticulture in the latest Cultivation Elevated podcast, hosted together with Michael Willamson. 
The Pipp Horticulture team at GreenTech Amsterdam: Anders Peterson, Craig Umans, Lisa LaFemina, Michael Williamson and Del Rockwell
Higher electricity costs
According to Anders, the company sees quite a wide variation of tier spacing in the industry. "Many growers that are new to multi-tier cultivation are worried about plant stretch and their plants growing into the lights. A byproduct of that is that they often request a very tall tier spacing to give themselves some buffer. I would consider tall spacing to be anything over 6.5 feet," Anders says. "I've even seen 8-foot spacing."
Yet what are the pros and cons of having such tall tier spacing? Anders explains that the main challenge is lighting and airflow efficiency. "When you're plants are young and you've moved them into veg, let's say they're about 18-24 inches tall. With an 8-foot tier spacing, you still have 6 feet of distance between the top of your plants and your lights. That means your lights need to penetrate 6 feet and your air flow system needs to be able to supply the appropriate air velocity 6 feet below the duct work, all along the length of the row. Can it be done? Absolutely. Is it the most efficient way of doing it? Not in my opinion," Anders says.
For example, as markets get more competitive, it's not optimal to have to run your lights at 100% in the first few weeks, Anders says. "Yet this would be necessary to achieve your target PPFD because of the distance, which means you're now running more electricity. So you're having to operate at a higher electricity cost with this taller tier spacing. The same goes for your air flow system. You could have achieved the same parameters with a shorter tier height and less electricity."
Ceiling height
Another thing to consider is ceiling height. "Oftentimes, when we see 7 or 8 foot tier heights, the top of the racking system is extremely close to the ceiling," Anders says.
"I think people get enamored with the idea of fitting as much canopy as possible into the space," Michael says. "Typically, when we get drawings at Pipp, we don't get the mechanical drawing. We normally get a bird's eye view architectural drawing. So the grower will often say: I've got an 18-foot ceiling, so I want 16-foot tall racks. While that may look good on paper, where do the sprinklers go, or the ducting, or do you have air handlers hanging down?"
On top of that, a 'buffer space' needs to be taken into consideration. "You want an environmental bubble above your canopy. Some breathing room to get the humidity and treated air up off your crop." Indeed, Anders says that's one of the cons of pinning the racks as close to the ceiling as possible. "There's nowhere for the heat to rise. If you over-maximize your space, there are negative repercussions in terms of environmental control."
Short spacing
While tall tier spacing comes with challenges, so does tier spacing that is too short. "If you have around 4-4,5 feet of tier spacing, you have to be concerned about plant stretch and growing into the lights. So your cultivation schedule needs to be very dialed in and exact," Anders says. "With such short tier heights, there's way less wiggle room."
Michael adds that substrate type then plays a crucial role too. "You want the substrate to be low and wide, because every inch matters in that scenario. Another thing to think about: if your spacing is low, there's a restriction on the diversity of genetics you can grow."
According to both Anders and Michael, a tier spacing of around 5,5-6 feet from tray to light is their ideal height for growers.
Click here to listen to the full podcast episode.
For more information:
Pipp Horticulture
[email protected]
www.pipphorticulture.com
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