Greener heating for greenhouses

Because
greenhouse crops can be grown throughout the year, they are becoming
increasingly important for the food supply of countries like Canada, which have
colder climates and shorter growing seasons. However, greenhouse heating can be
one of the highest operating costs for a producer. Heat is typically supplied
by non-renewable fossil fuels, such as oil and natural gas. These fuels are
also frequently used to enrich the greenhouse with carbon dioxide (CO₂)
to enhance plant growth. The high cost and environmental impact of fossil fuels
has led some greenhouse operators to look for alternative heat sources, such as
biomass.

Still, biomass
heating systems are far from a panacea. For one thing, the initial capital
investment necessary to install these systems can be discouraging for small operations.
What’s more, a substantial amount of heat, CO₂, noxious gases, and particulates
are released when any type of biomass is combusted. Enter the Biomass Furnace
Flue Gas Emission Control System (GECS), a process designed to recapture energy
and CO₂ from the furnace and redirect it to the greenhouse.

The brainchild of researchers and several
graduate students at McGill University’s Department of Bioresource Engineering,
GECS is “a greener way to use wood pellets for heating greenhouses,” says Dr.
Mark Lefsrud, the engineering professor spearheading the project. The system
not only recovers heat and purifies noxious gases and particulates from the
furnace’s exhaust, it also recycles CO₂ back into the greenhouse, which enhances plant growth
and yields.

The GECS unit consists of a rigid box air
filter coupled with two sets of heating elements, two catalytic converters and two
forced air fans. The unit is attached to the chimney of a pellet stove
installed in a greenhouse. “Pellet stoves generally produce less harmful
emissions than other stove types because the shape of the biomass allows for a better
distribution of oxygen, which produces a uniform and complete combustion. This
makes the flue gas easier to purify and more suitable for CO₂
enrichment”, explains Dr. Lefsrud.

“The air filter removes the particulate
matter in the flue gas, while the other elements transform the exhaust gases
into less harmful gases,” says Yves Roy, a Master’s student who played a
pivotal role in designing the system. He explains that there are 3 steps in the
purification process: the first is the mechanical collection of large-scale particulates
using a combination of an electrostatic precipitator, and cyclone and a bag
filter. Finally, two sets of catalytic converters and heating elements transforms
all noxious gases to less hazardous gases.  

Once the GECS prototype was completed, the
team tested it on the chimney of a wood pellet biomass furnace. The device passed
with flying colours. “We confirmed that it considerably improves the thermal
efficiency of the wood pellet heating system since no heat is lost through the
flue gas,” says Dr. Lefsrud. The team’s measurements also affirmed the system’s
safety: When the exhaust from the furnace chimney was pumped directly into the
greenhouse, the air remained well within Health Canada’s air quality guidelines
for acceptable levels of indoor gases and contaminants.

The GECS unit is also very cost-effective: “The capital investment required for the GECS is far lower than
for alternative heating systems currently on the market,” says Lefsrud. His experiments show that direct
combustion exhaust gas recuperation through the
purification system reduces greenhouse heating costs by 18.8%. Translated into bottom-line terms, this means both a lower
heating bill and a lower carbon footprint, even for small operations. “End-users
may even be able to claim a carbon credit,” he adds.

“This project demonstrates that university research
can yield marketable products,” says Dr. Lefsrud. BioFuelNet gave legs to the initiative,
supporting graduate students to travel to conferences where they showcased the
technology and networked with other scientists in the field. One of these
students was Roy, who had a chance to present his work at the 2013 International Meeting of Agricultural and Biological
Engineers in Kansas City, Missouri. “Even though some
of the attendees commented on my strong French accent, they seemed to enjoy my
presentation,” he jokes.

Two things need to happen before the GECS goes to
market: a patent and a unit suitable for commercial use. The McGill team has
already applied for a patent, and intends to enhance the product to make it
commercially viable. “We plan to build a control system into the unit to allow
growers to adjust CO₂ levels,” says Dr. Lefsrud, adding that “the
BioFuelNet community is helping us with the commercialization process by
connecting us to the right people and information.”

Lefsrud has high hopes for the new technology. “Our
piece of equipment has the potential to spur economic development in the
agriculture and greenhouse sector and strengthen Canadian food security,” he
says. Roy shares Lefsrud’s enthusiasm. “Greenhouses
are seeing a steady growth as they offer a way to control the environment,” he
says. As weather patterns become increasingly fickle, greenhouses are set to
become more popular than ever. “I’m confident our system will make it
economically- feasible for greenhouse operations of all sizes to use
wood-pellet biomass furnaces.”