Technology
The 1.5 megawatt (MW) Gelliondale Nursery hydronic heating plant comprises a refractory-lined furnace in conjunction with a fire tube heater, connected to a pumping and piping system to distribute heat energy to a glasshouse environment. The system, which runs on locally-sourced wet sawdust, is fed by a hydraulic walking floor in conjunction with three feed augers in series.
Combustion air is provided by an induction fan and a forced draught fan. Flue gases are cleaned through a multi-clone grit arrestor before exiting through a chimney.
The hydronic heating system at Gelliondale, designed and commissioned by engineer Sohum Gandhi of AIS Greenworks, uses energy produced from the heating plant. The system disperses this energy evenly through a glasshouse by moving hot water through a network of pipes around the greenhouse. The system is separated into two climate zones (low level and high level), and controlled by mixing valves, pumps and independent headers.
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System features
A two-zone heating system was chosen to provide a constant temperature underneath the growing benches and a slightly reduced temperature above the benches to control condensation. The system provides a minimum temperature lift of 20° Celsius when external temperatures are 0° Celsius.
One of the key features of the system is the way in which the furnace is fed with the sawdust. The purpose-built bunker can hold up to 100 cubic metres of sawdust which can fire the furnace for three to four days. The bunker has an inbuilt walking floor that delivers fuel to a rear auger that then feeds the furnace on demand.
HVP Plantation’s requirement for this project was to remove the need for double-handling fuel. AIS Greenworks’ solution was to have the fuel truck back into a three-walled concrete bunker. The truck then tips its load while rolling forward; the wet sawdust rests on the walking floor, and from there, the fuel is automatically fed into the furnace via the walking floor pushers and series of augers.
Energy savings and supply
Fuel for the plant is supplied by nearby sawmills in the form of wet sawdust, and the plant is expected to produce 1.9 gigawatt hours (GWh) of thermal energy per annum. The annual greenhouse heat demand of 1.9 GWh will be fully supplied by this thermal plant.
The project is expected to save 400 tonnes per annum of greenhouse gas emissions. More specifically, the approximate thermal annual energy use of the site would be 7,000 gigajoules. Had this demand been supplied by liquefied petroleum gas (LPG), the greenhouse gas emissions from the LPG use would have totalled approximately 400 tonnes.
Thermal efficiency of plant is estimated to be 85 per cent.
Chris Barclay from HVP Plantations says “The glasshouse has been in operation for two years with a full crop running through the complex in 2012-11. To date, we have been more than happy with the concept and the cost of the hydronic heating plant as we are uniquely an end user of our own product that assists us in regenerating that product.
“Using a fuel that would otherwise be a waste stream not only helps us in reducing our running cost, but it also makes us a carbon responsible business.”
AIS Greenworks is an engineering projects company that designs, supplies and installs the mechanical, hydraulic, and energy systems required for competitive greenhouse operation. Greenworks’ systems are related to heating, evaporative cooling, growing systems, and water management technologies. For more information on using biofuels to supply thermal energy demands, contact Sohum Gandhi at sohum@aisgreenworks.com
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