June 13 saw the launch of 360 Energy’s Journey to Energy Excellence for Greenhouses. This program draws on international expertise both in greenhouses and energy management. “The objective of the program is to help growers significantly improve profitability by practising the integrated management of energy,” says Program Manager Lisa Brodeur.
The launch event was a webinar offered to participants from across North America and featuring experts from Canada, Holland and the UK. “A key message focussed on the difference in energy spending between a typical grower and a ‘best practice grower,’ which could be as much as $10,000/acre,” Brodeur explains.
How such savings are accomplished was addressed by Dr. Sjaak Bakker, business unit manager at the University of Wageningen in the Netherlands. He started the webinar with an overview of greenhouse physics – the key points being that 60% of the energy input comes from (free) solar energy and the greatest heat loss is through ventilation at around 57%.
Moving on, he noted that the first practical step is to optimise the operational strategy. This alone can deliver 5-15% savings. Medium-term investments in new technology for the existing greenhouse and long-term significant investments in new houses and geothermal energy are also important.
Dr. Bakker then presented his five-step approach to performance improvement:
1. Maximising the use of solar energy
2. Reduction of energy use/losses
3. Efficient conversion of energy
4. Efficient energy use – unit product per unit energy
5. Replacement of fossil fuels by renewable energy
On the topic of maximizing solar energy, Dr Bakker reviewed the use of anti-reflex coatings and diffuse glass. He stated that the ideal cover is one that maximizes light transmission and has low IR transmission. Anti-reflex coatings can give a 6% increase, while diffuse glass can boost production by 8-10%. In the Q&A session, Dr. Bakker also pointed out that a regular glass-cleaning program can deliver benefits, as long as the control system is correctly set.
He also stated that the key technology for reducing energy loss is the use of thermal screens. As an example, a single glass cover with a thermal screen could deliver a 25% saving. The benefit of screens with double layers is lower, but can still be worthwhile.
Bakker notes that in energy conversion, one technique used in Holland is a mix of co-generation, heat pump and heat storage in an aquifer. This is complex technology and should only be considered when the heat requirement for the greenhouse has been optimized.
For an efficient greenhouse, control of the internal conditions is critical, he says. The temperature requirement determines 50-80% of energy use. Options here include revising set points, temperature integration, maximising pipe temperatures and controlling transitions in climate. Temperature integration looks to maximize the use of solar energy during the day while reducing night-time temperatures. This approach can deliver 4% energy savings with a minimal (1% or less) reduction in production.
An interesting point was made on the balance of energy use in double cover houses. With a single cover, humidity control takes 12.1m3 (gas) but with double cover this increases to 18.5m3 – which is offset by an overall reduction of 12.6m3. Following on from this is the benefit of increasing the humidity set point by 5% can deliver 6% energy saving.
The Dutch experience shows that geo-thermal energy is a viable sustainable energy source. However, one single geothermal source (greenhouse operator) requires in the region of 450 hectares of land. This means in an area with a number of growers only one would be able to use geothermal.
“Dr Bakker concluded by saying that to make significant reductions in energy use, it is important to have a structured and integrated approach to managing energy in greenhouses,” Brodeur says. “And this is what participation in the Journey to Energy Excellence for Greenhouses provides.”
To find out more about The Journey to Energy Excellence for Greenhouses, contact:
Lisa Brodeur, Program Administrator, 360 Energy at lisa.brodeur@360energy.net
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