Structures & Equipment
Flowers Canada Growers tests energy recovery technologies to reduce greenhouses’ costs
Dehumidification technology can help reduce energy consumption.
February 16, 2023 By Greenhouse Canada
High humidity levels inside greenhouses are a byproduct of growing crops indoors. Left uncontrolled, humid air can reduce growth and result in poor-quality produce, so growers have traditionally resorted to ventilation to manage the issue. While effective, this strategy causes heat loss, which can increase a farm’s energy costs.
Flowers Canada Growers, a national trade association based in Guelph, Ont., set about to find a solution to this problem, accessing funding through the Greenhouse Renewable Energy Technologies (GRET) Research & Development (R&C) Initiative several years ago and testing four dehumidification and energy recovery technologies for their potential to reduce growers’ costs during the peak greenhouse use period of fall through early spring.
These technologies included:
- A mechanical refrigeration dehumidifier (MRD).
- A liquid desiccant dehumidifier (LDD) that runs humid air past a brine solution to absorb moisture, then heats the brine to regenerate it (system pictured above).
- A heat recovery ventilation (HRV) system outside the greenhouse that warms up the cool, dry air as it enters the facility.
- An energy recovery ventilator (ERV) prototype that combines the liquid desiccant approach with heat exchange in a single system.
“We are looking for alternative ways to decrease energy consumption to reduce grower costs and fossil fuel use,” explains Jingjing Han, research engineer with Flowers Canada.
Building on findings from that initial project, the association was successful in receiving funding from the Greenhouse Competitiveness and Innovation Initiative (GCII) to conduct more in-depth research into the four technologies and better understand how they can be integrated into existing greenhouse control systems. Project partners included Ontario Greenhouse Vegetable Growers (OGVG), Enbridge, Nortek Air Solutions and participating farms.
“By continuing the implementation of programs such as GCII, we are furthering our investments with the greenhouse industry, finding ways to reduce their carbon footprint and supporting farmers as stewards for our environment,” says Lisa Thompson, provincial minister of agriculture, food and rural affairs.
Through the GRET program, an Ontario flower greenhouse had three systems (MRD, LDD and HRV) installed, while an herb greenhouse had four LDD units installed and a tomato greenhouse had an ERV system installed. Despite some setbacks with malfunctioning units that could not be fixed, due to supply-chain shortages and changes in crops and production strategies, the researchers were able to gather and analyze enough data to make some useful assessments about the technologies.
“All systems are able to control humidity much better than conventional ventilation, but each has its own advantages and disadvantages,” notes Han, adding none of the systems were effective throughout the entire year.
The LDD and MRD systems were found to be most cost-effective during the late fall, winter and early spring, but their efficiency dropped off if the outdoor air temperature was above 10 C or high in humidity. HRV was found to provide economic benefits during cold and dry months, while the ERV system was effective at helping reduce condensation on the glass greenhouse cover.
According to Han, any of the systems can be useful tools for humidity control with reduced heat loss, but must be properly integrated into a greenhouse’s internal control system to operate cost-effectively. Energy and cost savings were most impactful from October to March. Some of the systems could result in energy cost savings of more than 10% during January, February or March, but the relative price of energy (e.g. natural gas vs electricity) plays a significant role relative to cost savings among the dehumidification systems.
“It is not feasible for an individual grower to do this type of research with this range of technologies on their own,” Han adds. “We couldn’t have done the project without the funding we were able to access from GCII.”
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