Inside View: December 2007
By Gary Jones
By Gary Jones
Feeling the chill? Try warming up to the 3Rs. The more that greenhouse growers investigate high-intensity lighting, the more attractive ‘cogen’ becomes.
Unless you’re vacationing on a southern beach somewhere, it’s a safe bet you’re reading this on about the shortest day of the year and your nights are long, probably wet, and the temperatures chilly. Likely you’ve thought about ‘heating costs.’ Canada is the third largest energy consumer on the planet – demand is up 21 per cent since 1990.
What’s to be done? The ‘Three-Rs’ (‘Reduce, Reuse and Recycle’) might apply.
Reduce. Many greenhouse crops use 45–55 m3 gas/m2/year. Everyone’s tried reducing fuel bills. At the Canadian Greenhouse Conference (CGC), Dr. Xiuming Hao (Harrow Research Centre) outlined projects on heat placement and liquid foam insulation. Heat placement uses grow-pipes placed within raised-trough growing systems. Hao found such pipe placement increased fruit temperature and reduced humidity inside crop canopy (and therefore Botrytis). More importantly, it increased early and overall yield without increasing energy consumption compared to standard systems. Furthermore, Hao and colleagues looked at liquid foam insulation on double-poly structures, finding almost a 46 per cent nighttime energy saving and an overall 24-hour saving of 30 per cent.
Reuse. Used a fuel more than once? Cogeneration (Combined Heat and Power – CHP in Europe) isn’t new, but it is now being utilized here. It’s basically a way to get more from a fuel, specifically natural gas burned in a generator to produce heat, CO2 and electricity. Burning natural gas in engines produces approximately 0.2kg CO2 / kWh of energy input. As this is available to boost crop growth, this is effectively ‘free.’
Also at the CGC, Great Northern Hydroponics of Leamington outlined how their ‘cogen’ project is expected to produce consistent crop yields along with significant cost reductions ($0.10/kg tomato-on-the-vine).
While not without challenges (high capital expenses, big construction risks and significant management resource costs), a simple ‘return on investment’ for a 100 kW generator is currently about six and a half years. The more vegetable and flower growers investigate high-intensity lighting (so employing the electricity produced), the more attractive ‘cogen’ becomes.
Recycle. OK, a bit of a stretch to fit the alliteration, but ‘older’ fuels are making a comeback. Coal, for example, can be cheap compared to other fuels for equivalent energy output. Legislation aside, wood products have become very attractive in some areas. Newer forms of wood waste pellets provide consistency, higher calorific value, low moisture content (4-6 per cent), and low ash residue (+/- 0.3 per cent). Growers are also finding innovative ways to make wood waste burn hotter and longer. And unlike coal, it could be argued that wood waste is ‘CO2 neutral.’ (Apparently, transport has to be less than 200 kilometres to be economical though!) Modular flue gas cleaning now allows almost zero NOx emission and for CO2 dosing to the greenhouse. Corn, propane and fuel oil continue to be locally significant, although on cost or availability these will unlikely be accepted widely.
Other options. Jake DeBruyn and Don Hilborn of OMAFRA investigated and developed anaerobic digestion (A.D.) systems. Their reports outline how this technology provides electricity and heat from biogas produced by organic inputs, providing opportunities to sell refined biogas, sell/replace heat, or sell/replace electricity. (Sustainable ‘cogen’?). A.D. has potential to:
• Reduce manure odour levels
• Reduce farm “greenhouse gasses”
• Provide renewable energy
• Allow incorporation of off-farm organics
• Utilize food byproducts
• Improve manure fertilizer values.
Landfill methane collection is already used by some glasshouses. Landfill sites emit 25 per cent of Canada’s man-made methane emission, so this is also good environmentally.
While unlikely to be employed by large-scale greenhouses, researchers from the University of Manitoba, Manitoba Hydro and the Government of Manitoba have shown that sustainable solar greenhouses are totally possible. Stuart McMillan reported in Canadian Organic Grower about applications that used north walls made of concrete, providing daytime heat storage and releasing it to a greenhouse at night, and the potential of argon-filled poly/nylon pillows or double layers of bubble-wrap for insulation.
In a time of ‘peak-oil,’ maybe we should give such techniques more consideration.
GARY JONES is chair of production horticulture at Kwantlen University College and serves on several industry committees. He can be contacted at Gary.Jones@Kwantlen.ca.