A guide to greenhouse energy efficiency

Greenhouse operations in Ontario are growing. Here's how producers can make sure their energy use doesn't grow faster than their profits.

From vegetables to flowers, Ontario has long been a hotbed for growing crops.
 
Today, many Ontario growers have turned to greenhouses to boost how much they can grow, partially in response to shoppers seeking out more locally grown foods. In fact, the amount of veggies and fruit grown in Ontario has climbed 30 per cent over the last six years.
 
The energy it takes to power lighting, heat pumps and ventilation in a greenhouse all adds up. The good news is that energy use is well within growers' control.

 

The lighting opportunity

We all know that plants need light to thrive, so unsurprisingly, lighting presents the biggest opportunity for greenhouses to save on energy, regardless of what's growing inside. Vegetable growers typically keep their lights on for eight to 16 hours per day, depending on the time of year and availability of sunlight.

Traditionally, greenhouse operators have turned to high-pressure sodium lights to help mimic sunlight and keep growing even as the weather turns grey and cold. However, LED lighting is much more efficient, using up to 50 per cent less energy than high-pressure sodium lights.


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LED lighting also lasts between five and 10 times longer than high-pressure sodium, cutting down on replacement costs. In many cases, greenhouse operators who invest in energy-efficient LED lighting see a payback within two to three years.
 
For example, SunTech Greenhouses in Manotick, Ont., saved a whopping 3,271,680 kWh by switching to LED lights in its 180,000 square foot greenhouse, which it uses to grow its tomatoes, eggplant, cucumbers and more.
 
LEDs also allow for greater lighting control, which may lead to higher yields. Growers can customize spectral light for the crop or growth stage. For example, a grower may find that more blue light than red light at a certain stage improves quality. LEDs allow for that control.
 
They also run cooler than alternative lighting sources, so growers can place them closer to plants, which may help improve crop yield. Depending on the plants in the greenhouse, using vertical racks, with plants that require less light further down, can also help lessen energy waste.

Finally, using controls for natural light can also help improve growing conditions, while also using energy more efficiently. Retractable curtains are a great option for getting the most out of natural heat and sunlight, while also potentially protecting your plants on excessively hot days.

Get the most out of your HVAC

Reducing the heat that comes from lighting may also help growers manage humidity levels better and reduce the load on their heating, ventilation and air conditioning (HVAC) equipment – meaning even more potential energy savings. Dehumidification, which requires mechanical cooling, is vital for certain crops to avoid mold and mildew which requires mechanical cooling, and like lighting, that can drive up energy use.

Greenhouse operators can gain more efficiency by installing variable frequency drives (VFDs) on exhaust fans, heat buffering systems, zone pumps and mixing valves. VFDs essentially help control the speed of motor-driven equipment, such as fans and pumps, so they don’t use energy unnecessarily. 

Like lighting, consider how you can gain more control over heating and cooling in your greenhouse. Electronic sensors and automated thermostats may help growers maintain more accurate temperatures, which can in turn prevent energy going to waste. 

Consider going a step further by installing integrated environmental controls, too. These controls replace stand-alone control systems for equipment such as thermal curtains, VFDs, heat buffering systems, HVAC systems and irrigation equipment.

Just like homes, offices or any other building, greenhouses also benefit from a well-maintained building envelope that allows heating and cooling technology to work more efficiently. Polycarbonate sheets on side and end walls, insulation board around the perimeter foundation, and weather stripping around doors and windows can all help prevent air leakage. Make a habit of checking for (and repairing) leaks or holes, which will not only help improve energy efficiency in a greenhouse but may also help prevent pests. 

As more growers enter the market, remember that saving on energy is ultimately a competitive advantage. Take the time to upgrade lighting and improve HVAC efficiency within your greenhouse – and get ready to see some impressive growth.


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