News - August 12, 2010

PPO tests double glazing in greenhouse

Double glazing can save market gardeners a lot of energy, without lowering the harvest. This hypothesis is being put to the test by Wageningen UR Greenhouse Horticulture in a new greenhouse in Bleiswijk.

The use of double glazed glass in horticulture had been tested thirty years ago during the first energy crisis, says researcher Eric Poot. However, double glazed glass in those days admitted too little light, and the harvest was thus affected. A new type of double glazed glass with a good light transmission factor has now been developed. A greenhouse simulation model at WUR Greenhouse Horticulture has shown that this can result in energy savings of 12 cubic metres of gas per square metre.
Poot's colleague Frank Kempkes is testing the double glazed glass in the Venlow Energy greenhouse in Bleiswijk, a 500-square-metre demonstration greenhouse with cucumbers, where modern breeding methods are also applied. Such modern methods make use of a new ventilation system instead of open windows. As a result, energy use decreases even further by fourteen cubic metres of gas per square metre, according to the simulation model of WUR Greenhouse Horticulture. This would bring the energy use down to 16 cubic metres of gas per square metre, compared with 40 cubic metres being used in actual situations. Kempkes will now find out if this lower energy use also applies in real life.
Whether double glazed glass is profitable in greenhouses will depend on electricity prices. Many horticulturists have a combined heat and power (CHP) generation system in their premises, where they sell the electricity to a network and keep the warmth for their own greenhouses. As long as the electricity price is high compared to the gas price, it would be less profitable for the horticulturist to save energy, explains Poot. He expects that a better price balance between electricity and gas would enable the investment in double glazed glass to be covered within five to six years. This research forms part of the programme 'greenhouse energy source' of the Ministry of Agriculture, Nature & Food Quality and the Product Board for Horticulture.