“As lights come on, your HVAC systems also turn on to try and lower the radiant heat from the grow lights. This battle can be expensive,” says Nick Earls, cannabis specialist for Wadsworth Control Systems, a provider of greenhouse automation systems.
The Cannabis Conservancy, for example, specializes in making cultivation facilities more energy efficient and has developed standards for sustainable cultivation, as well as its own sustainability certification, according to Jacob Policzer, the company’s director of science and strategy.
1. Audit energy usage.
The essential first step to reducing electricity usage is measuring a facility’s actual usage, Policzer says. Cultivators can use smart meters to measure their baseline energy usage and determine where and how to make improvements.
Growers should perform an energy audit of their operation, which can be done using simple calculations, Policzer says.
With lighting, for example, cultivators can multiply the wattage of their lights by how many hours a day they are used. This figure can then be deducted from the energy bill, and the amount left is generally how much the HVAC system and environmental controls cost to operate, he says.
2. Calculate PPFD and DLI.
Once cultivators know how much energy they are using, they can take a deeper dive into optimizing their lighting, including the photosynthetic photon flux density (PPFD) and daily light integral (DLI). PPFD measures the number of photons in the visible light spectrum that fall on the plants per second, while DLI measures the amount of light the plants receive in a day.
“By calculating what your target DLI is or should be—which, I would say, on average, is about 35 moles per square meter per day—you can start to mess around with the amount of lighting hours your plant needs,” Policzer says.
And if you’ve been giving your plants more light than necessary, you can reduce the amount of time the lights are on and thus reduce your electricity usage.
“You can start to see, oh, well, we’re doing 18 hours a day of lighting and the plants are getting this amount in the day. Maybe we can go down to 17 hours or go down to 16 hours,” Policzer says. “As long as you don’t pass the threshold for photo period where the light’s going to cause flower when you’re trying to keep it in veg, you can start to reduce your energy consumption that way.”
Greenhouse growers can use DLI and PPFD readings to know if supplemental lighting is needed, he adds.
3. Know your VPD.
In addition to PPFD and DLI, growers should measure and understand their vapor pressure deficit (VPD), which indicates the evaporation potential of water into the air. VPD is essentially the difference between relative humidity and air temperature, and can be used to find the optimum climate for plants to photosynthesize efficiently, Policzer says.
“You can use that to determine your set points on what you want your air to be and what you want your humidity to be to essentially reflect the outside conditions,” he says. “If you’re in the summer, you try to run your facility a bit hotter, whereas in the winter you can run your facility a little cooler, so you’re working more with nature rather than against it. It will put less stress on your machines [and] your equipment.”
4. Have an integrated climate control system.
A climate control system is really the brains of the operation, Policzer says, and with so many integrated systems on the market, it is important for cultivators to do their research and choose the one that is best for their grow.
“I highly recommend environmental controls that can control all your equipment in your grow,” Earls says. “Some grows will have multiple separate controls [for HVAC, lighting, CO2 and irrigation], which aren’t speaking with each other. … So, when you are injecting CO2 based on PPM, you might also have your exhaust fan on due to cooling. Now you are wasting CO2.”
Roof vents are another problem area when operated with a separate control, Earls adds. If a facility’s roof vents operate with a wax piston, the wax expands when warm to open the vent, but if the heater turns on because it is too cold, then the heat may rise and unnecessarily open the roof vent. “You are now wasting utilities as the heater runs all night with the vents open.”
5. Use equipment with variable settings.
“Equipment that has multiple stages—multiple settings— [allows you to] go with a lower setting first and then ramp it up, rather than just having on and off,” he says. “It just gives you more control, and a lot of that can be controlled through the voltage of these machines. That works for dimmable LEDs [and] exhaust fans like ventilation and circulation fans. … That’s a way of saving a bit of money, just having more control of your system, and then having a climate control controller that will integrate all of those things, so they’re not competing against each other.”
“I also recommend multi-output or variable speed equipment,” Earls adds. “This reduces your amp draw, which saves you on power consumption. It also prevents plant shock by not going from off to an immediate high setting.”
6. Stagger equipment.
To further reduce the chance of energy peaks, cultivators should stagger when different pieces of equipment turn on. When trying to control a facility’s temperature, for example, start by turning on fans and exhaust, which use less energy than the HVAC system. Then, if the desired results aren’t achieved, one air conditioning unit can be turned on at a time until the optimum temperature is reached. This way, the facility is only using as much power necessary.
“If you turn on all, say, six units all at once, you’re going to cool it down really quickly and they’re going to turn off, but you just peaked your energy bill, … and that’s going to affect your total bill at the end of the month,” Policzer says.
Lights can also be staggered to help control energy spikes, he adds. For example, rather than having one big flower room where all the lighting turns on at the same time, lights can turn on in 15-minute increments, so they are not all running at the same time.
“You can also do four smaller grow rooms or two grow rooms where they’re on four-hour opposite intervals,” Policzer says. “So, instead of having 100 lights turn on at the same time, you have 50 lights turn on, and when those turn off, you have the other 50 lights turn on, so you’re lowering your peak demand.”
To calculate peak demand charges, the utility company takes a facility’s energy peaks—or its highest energy demand—for a given month and multiplies the peaks by a higher rate to calculate that portion of the bill, Policzer says.
For example, if one month’s peak is 25 kilowatts, but the facility ran at an average of 15 kilowatts, that peak rate of 25 kilowatts will be multiplied by how many hours were used to calculate peak demand charges.
“If you can lower it, you’ll have your 100,000 hours multiplied by your 15-kilowatt charge,” Policzer says. “And the higher your peak is, the more expensive it is. … Essentially, by changing your peak, you could be saving yourself tens of thousands of dollars.”
7. Choose efficient fans.
“And all that means is … the motor is super-efficient, so it’s using less watts to power a larger fan, but it’s still giving you the power, the CFMs—cubic feet per minute—[and] the air changes that you need,” he says.
8. Use proper insulation.
Not only should the greenhouse or indoor grow be properly insulated, but distributive piping should also be insulated so the contents of the pipes remain at the correct temperature even when the HVAC system is not heating or cooling that area of the facility. This way, the HVAC system is not running in an area that doesn’t necessarily need to be heated or cooled, Policzer says.
In addition, cultivators should apply weather stripping their facility’s windows, doors and exhaust vents to prevent the HVAC system from working overtime, he adds.
9. Target the roots.
“If the roots are happy, the plants can withstand more temperature extremes, so you can use [a] geothermal [heating system] to essentially have heating in the beds so they’re heating the root system, and then you can let the ambient temperature drop a bit more, and the plants are still going to be happy,” he says. “If you’re growing in a greenhouse that’s going to be in a colder climate, that’s one way of heating a greenhouse without heating the whole greenhouse—just heat the root zone.”
10. Choose local genetics.
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