Greenhouse: CropHouse

Greenhouse quality

In protected cultivation, the first and foremost piece of equipment is the greenhouse. The quality of the greenhouse largely determines its (commercial) success. It must allow for perfect growing conditions in a cost-effective way. A major growth factor is light. An old rule of thumb says 1% light equals 1% production! In a dark or dirty greenhouse the yield is much lower than in a new greenhouse, but the costs to run it are higher. Unfortunately, old greenhouses can never be upgraded to ‘modern’ and ‘efficient’ greenhouses.

Energy

In most locations, greenhouses require energy input (fuel) for maintaining good growing conditions. In view of rising energy prices, greenhouse growers must improve their energy efficient. The focus is here on greenhouse heating, since this is where most energy is used for.

Basic repairs

First some basic energy-saving actions can be taken that don’t require high investments. Energy is wasted due to small defects, such as broken windows, leaking pipes, rambling pumps, inaccurate sensors, faulty vent motors, vents not closing, draughts from doors, inaccurate sensors, bust equipment in greenhouse and boiler house. Holes in the roof cladding act as a chimney, and loose a lot of energy. Sometimes the vents don’t close properly anymore due to wear and tear. Proper tuning and adjusting of the vents and vent motors will overcome this problem and will prevent a lot of energy loss.

Insulation

Pipes that transport hot water should be insulated thoroughly, especially if they run outside. Greenhouse walls can be insulated to save energy (but be aware of loss of light). Double glass or synthetic insulating panes are ideal but expensive. Cheaper options are helpful too, such as an extra layer of single plastic, double plastic foil, bubble film, shiny reflective material on the inside of the greenhouse walls. Energy loss via the roof can be greatly reduced by closing a thermal screen, but this requires a large investment.

Hot & cold spots

In most greenhouses we find temperature differences, or ‘temperature gradients’, both in horizontal and vertical directions. Hot spots receive too much heat, which is a waste of energy. Warm air rising from a hot spot cools down against cold glass (wasting energy!) and falls down on another place, creating a cold spot there. Places with 1 °C lower temperature have a 5% higher relative humidity. Plants in cold humid spots stay behind and take up less water. These plants are the first to get fungal diseases such as grey mould (Botrytis), root-diseases and pests. The solution is finding the cause and rectifying what is wrong.

Innovations

Energy efficiency has been a key research topic for the huge greenhouse industry in the Netherlands (Holland). Great progress was made over three decades, but recently there was a real break-through in energy management. Holland now has greenhouses that harvest solar heat in summer, and utilise that heat for heating in winter. Storage is in water layers in the deep underground (aquifer), and sophisticated heat exchangers are used. These greenhouse are called ‘Closed Greenhouse’ and ‘heat generating greenhouses’. They don’t consume energy, but instead provide heat to nearby houses.

Climate control & energy > Greenhouse