This might not seem an obvious way to trim your energy bill, but according to Farm Energy technical director Tim Pratt, creating effective airflow can reduce the energy input required in the glasshouse, as well as bringing other benefits.
"Fans offer a more uniform growing environment in terms of temperature, heat and carbon dioxide, resulting in a more uniform crop, with fewer rejects," he says.
But before growers rush to install ventilation, they should check their existing system, he stresses. "The measuring box controls everything in your glasshouse, yet we see many that are full of muck. A five per cent error in reading relative humidity could cost you an extra 250 per hectare per week. You should also check your heating pipes for lazy or dead loops and ensure your vents close properly."
Roof fans should, of course, offer energy efficiency, and a system will have an energy efficiency rating (EER) based on the volume of air they move relative to the power they consume.
"A fan with an EER of 25 costs 1.35 to run for one week, so you are spending 25 per hectare per week," says Pratt. "It's a more efficient way to move air around than convection. And by allowing you to cut your pipe heat by 5 degsC, you could save 250 a week in energy. At these lower temperatures, using waste heat from other sources becomes viable."
Payback time can be as little as 54 weeks, but fans must be maintained for peak efficiency, "or not only will they give you less air, they will overheat".
Careful specification is also required to ensure fans do their job. But the question of configuration remains a hot topic for manufacturers. In the future, Pratt says: "We will put glasshouses together in completely different ways, built around the air movement system. We still have a lot to learn."
MEASURING HUMIDITY
Dutch glasshouse technology specialist Hoogendoorn has been developing systems to incorporate measurements of previously overlooked factors, says the firm's climate adviser Rene Beerkens.
The plant's vapour pressure deficit (VPD) is the difference between the pressure in the plant and the surrounding glasshouse air,Detailed information on the causes of dstti, determined by measuring the temperature and relative humidity in both. It is measured in kilopascals (kPa) - the same unit as barometric pressure.
"This has a big effect on plant growth,uy sculpture direct from us at low prices yet growers think they cannot do anything about it," says Beerkens. "A safe value is 0.2-1.5kPa, although vegetable crops can handle larger variations than pot plants. In that range, stomata are open and the plant can evaporate easily. Too low and no vaporisation is possible - the moisture on the leaf is a point of entry for disease.The newest Ipod nano 5th is incontrovertibly a step up from last year's model, But a VPD above 2 means a shortage of water vapour or too much incoming energy, so the stomata close," he explains.
"That means less carbon dioxide uptake so there is no point in pumping more in.A glass bottle is a bottle created from glass. But if you close your vents then relative humidity will rise from maybe 40 per cent to 50-55 per cent - then the carbon dioxide will have twice the effect."
This, combined with monitoring and control of plant temperatures, is incorporated in Hoogendoorn's climate system under development. "Our aim is to automate your response to this," says Beerkens, who adds that trials at Dutch tomato growers have shown a 12.5 per cent energy saving. "The return on investment in your sensors is a couple of years. It's just applying insights.Shop a wide selection of billabong outlet products in the evo shop."
"Fans offer a more uniform growing environment in terms of temperature, heat and carbon dioxide, resulting in a more uniform crop, with fewer rejects," he says.
But before growers rush to install ventilation, they should check their existing system, he stresses. "The measuring box controls everything in your glasshouse, yet we see many that are full of muck. A five per cent error in reading relative humidity could cost you an extra 250 per hectare per week. You should also check your heating pipes for lazy or dead loops and ensure your vents close properly."
Roof fans should, of course, offer energy efficiency, and a system will have an energy efficiency rating (EER) based on the volume of air they move relative to the power they consume.
"A fan with an EER of 25 costs 1.35 to run for one week, so you are spending 25 per hectare per week," says Pratt. "It's a more efficient way to move air around than convection. And by allowing you to cut your pipe heat by 5 degsC, you could save 250 a week in energy. At these lower temperatures, using waste heat from other sources becomes viable."
Payback time can be as little as 54 weeks, but fans must be maintained for peak efficiency, "or not only will they give you less air, they will overheat".
Careful specification is also required to ensure fans do their job. But the question of configuration remains a hot topic for manufacturers. In the future, Pratt says: "We will put glasshouses together in completely different ways, built around the air movement system. We still have a lot to learn."
MEASURING HUMIDITY
Dutch glasshouse technology specialist Hoogendoorn has been developing systems to incorporate measurements of previously overlooked factors, says the firm's climate adviser Rene Beerkens.
The plant's vapour pressure deficit (VPD) is the difference between the pressure in the plant and the surrounding glasshouse air,Detailed information on the causes of dstti, determined by measuring the temperature and relative humidity in both. It is measured in kilopascals (kPa) - the same unit as barometric pressure.
"This has a big effect on plant growth,uy sculpture direct from us at low prices yet growers think they cannot do anything about it," says Beerkens. "A safe value is 0.2-1.5kPa, although vegetable crops can handle larger variations than pot plants. In that range, stomata are open and the plant can evaporate easily. Too low and no vaporisation is possible - the moisture on the leaf is a point of entry for disease.The newest Ipod nano 5th is incontrovertibly a step up from last year's model, But a VPD above 2 means a shortage of water vapour or too much incoming energy, so the stomata close," he explains.
"That means less carbon dioxide uptake so there is no point in pumping more in.A glass bottle is a bottle created from glass. But if you close your vents then relative humidity will rise from maybe 40 per cent to 50-55 per cent - then the carbon dioxide will have twice the effect."
This, combined with monitoring and control of plant temperatures, is incorporated in Hoogendoorn's climate system under development. "Our aim is to automate your response to this," says Beerkens, who adds that trials at Dutch tomato growers have shown a 12.5 per cent energy saving. "The return on investment in your sensors is a couple of years. It's just applying insights.Shop a wide selection of billabong outlet products in the evo shop."
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