As energy prices become less predictable and more prohibitive, many greenhouses are turning to biomass fuels to meet their heating needs and provide cost savings.
As energy prices become less predictable and more prohibitive, many greenhouses are turning to biomass fuels to meet their heating needs and provide cost savings. Energy costs can make up 30 to 50 per cent of greenhouse operating costs for Canadian vegetable producers, and reducing these costs can help growers to meet their bottom line. So when Luke den Haan received an annual fuel bill of almost $600,000 in the early 2000s, he knew something had to change.
|Rails located just above the greenhouse floor pipe in heated water for climate regulation and facilitate transportation and maintenance down the long rows of plants.
Den Haan is the young production manager for den Haan’s Greenhouses, located in the Annapolis Valley of Nova Scotia. The family has been growing greenhouse products in Nova Scotia since 1960 and is onto its third generation of family operators. Luke den Haan’s parents, brother, and sister run the company’s retail garden centre, nursery, and original greenhouse, where Luke’s father, John, still grows English cucumbers and peppers. In 1999, the company built a modern 3.5-acre greenhouse to expand its hydroponic tomato production. Because natural gas is unavailable in the area, the greenhouse was initially outfitted with a propane-fuelled boiler.
“When we built this greenhouse, it was under the assumption that propane was going to stay around 22 cents/litre. As soon as we started using the greenhouse, propane jumped to 40 cents/litre,” says den Haan. Eventually, propane reached 80 cents/litre and even higher. Happily by then, a new biomass boiler was heating the greenhouse. This allowed a reduction in propane consumption from about 1.3 million litres/year for heat and carbon dioxide to about 75,000 litres/year to maintain carbon dioxide production to feed the plants, and virtually halved the greenhouse’s energy costs.
A 400 hp (~4 MW thermal), low-pressure, hot water Boilersmith boiler supplied by Ontario-based KMW was installed and fired up in 2005. Den Haan cites several reasons for this choice of boiler, including its multi-fuel versatility. “This boiler was designed for biomass. We wanted a versatile system that could burn different things. If I ran out of wood this month, I could chop up hay or whatever I want and burn it.” And after purchasing the greenhouse from Holland and having to deal with time delays and exchange rates to obtain parts from overseas, he says he appreciates the convenience of having a domestically manufactured boiler.
Local biomass supply
While researching potential boilers, den Haan also considered possible sources of biomass. He first began burning sawmill waste obtained from several local sawmills, but was unhappy with the quality and consistency of the biomass. “When we first started, I had a fair amount of boiler system alarms because the sawdust had big chunks of slabwood in it, which caused blockages,” he says. “And then the truck that brought it to me hauled steel when it wasn’t hauling wood, so pieces of steel that got left on the truck’s walking floor would come out with the wood.” These didn’t just cause blockages; they caused damage and broken parts. Fed up with these problems, mill closures, and irregular supply, he considered other options.
|Unmarketable roundwood is purchased from local woodlot owners and ground to a consistent size for fuel. This remaining pile of ground biomass would supply about two weeks of greenhouse heating in midwinter.
“There seemed to be a lot of wood producers around and not really a market for the waste wood,” says den Haan. Now, he purchases low-quality roundwood that before would have been left behind because there was no market for it. “It opened up a new industry for the wood producers and makes us feel good because all the money that we used to spend on propane is staying locally.”
The roundwood is delivered directly to the greenhouse, where it is later ground into fuel. Den Haan originally had a chipper service come to chip the wood, but says that it was too slow because the machine could only chip one log at a time. He burns about 2000 cord of wood per year and has it shredded 1000 cord at a time. He now has a grinding service, which he says is cheaper and faster, grind the fuel into small, consistent pieces that won’t clog the boiler.
The ground fuel is piled on an outdoor pad the size of a soccer field. “We have the pile rounded off so it sheds water, so in the spring, summer, and fall, we don’t worry about covering it,” explains den Haan. In winter, the pile is covered with a tarp to prevent the surface layer from getting too wet and freezing because chunks of ice will clog the boiler intake system. Each morning, a front-end loader scoops up biomass and fills the boiler intake area. On average, the boiler consumes about one tractor-trailer load of wood per day.
Works like a charm
Other than having to move biomass manually to the boiler intake area, the boiler is highly automated, with auto start up, shut down, biomass infeed, and ash removal. It heats water that circulates to a huge heat storage tank, and shuts off when the heat storage tank is at 100 per cent capacity. When the greenhouse needs heat, it draws hot water from the heat storage tank and circulates it through pipes located just above the floor between the rows of plants. When the stored heat supply gets low, the system tells the boiler to restart.
|Greenhouses are high energy at once. “When they need it, they need a lot of it, and you need a boiler that will give you the output,” says den Haan.
The greenhouse climate control system regulates the boiler system, and both systems can be accessed remotely, for example, from computers in the office or at den Haan’s home. The computer shows real-time boiler function, including the fuel infeed, the moving grate floor inside the boiler, and combustion and flue gas temperatures. A live camera feed monitors a key point along the infeed so that if there’s an alarm, den Haan can check for plugging without having to go to the site. “I hate to drive all the way here for an alarm and see I just could have reset it at home,” he says. “At two o’clock in the morning, you just feel like sleeping, rather than driving all the way to the greenhouse.”
“Biomass boilers take a bit more maintenance,” he admits. He says he’s heard the same story from almost every greenhouse that has gone into biomass — the first year is terrible, with lots of boiler alarms and little sleep. He can’t stress enough the importance of biomass quality. “If you have really poorly ground wood, you’ll have a lot of alarms and maintenance, and things will break. If you burn good wood that’s ground nicely and is the right moisture content for your system’s design, then it burns fine. Now, I might have an alarm only once every two or three weeks.”
|Luke den Haan displays some clean, consistently sized biomass.
|With internal combustion temperatures reaching 1200°C, clean, uncontaminated biomass is critical because metal objects can begin to melt and fuse the moving grate.
Aside from biomass supply and quality, the most important change in moving from propane to biomass was the difference in payment structure, says den Haan. And it’s something they’re still getting used to. “With propane, we’d burn it and pay 60 days later. With wood, we have to buy it all in the summertime to burn in the fall and winter. With 2000 cord and grinding charges, it’s a lot of money to tie up, up front, and you’re not burning the wood for ages.”
Very few infrastructure changes were required to switch to the biomass boiler. A new boiler building was needed, but the former propane system already included a heat storage tank. So it was simply a matter of hooking into the existing system. The biomass boiler is more than big enough to handle its current load, says den Haan. “I would get more efficiency out of the boiler if I had a heat storage tank three times bigger.”
Den Haan has big plans for the future, including bringing the family’s English cucumber and pepper production into this newer facility and expanding the greenhouse’s production. What he would really like to do, however, is get away from using propane altogether. “We do still use a bit of propane for carbon dioxide production, but they are coming out with technology to extract the carbon dioxide from the flue gases of the biomass boiler, and that’s what we’re going to pursue next,” he states.
“I’m not a boiler operator; I’m a tomato grower. If I don’t have product to pack and sell, I have nothing,” says den Haan.
Although the biomass boiler takes a bit more work than the propane boiler, he doesn’t feel that he’s wasting time working with it now that it’s running smoothly. “I’ve always looked for ways to do more for less and build our business, build our brand, talk to our customers. I couldn’t do that if I was tied up in the boiler room.”
Overall, den Haan seems delighted with biomass. “I’m very happy with my boiler system,” he repeats. “It works like a charm.”
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