08. Greenhouse Heating

Greenhouse Heating

The first greenhouse heating systems enabled Dutch growers to extend their growing season over a century ago. Today, heating systems remain a crucial element in commercial greenhouses around the world. When looking at the climate, the first things to notice are the temperature during the day, the temperature at night and the levels of relative and absolute humidity. Many greenhouse crops require a temperature difference between the day and night for proper fruit set. In many cases, the 24-hour average temperature should be above 18 degrees Celsius. To achieve these conditions, a greenhouse heating system is in most cases the first technical installation that should be considered. The maximum possible temperature difference in the Dutch greenhouse, the Delta T, is on which the heating systems are designed.

Heating the Greenhouse

The heating of a greenhouse is traditionally done by using a central gas boiler which heats water that is distributed into the greenhouse. This radiant heating method works on the same principal as the average central heating installations in homes. The temperature and flow of the heated water throughout the greenhouse can be accurately controlled with automated pump- and valve systems.

In some cases, heating the greenhouse is done by installing air heaters in the growing areas of the greenhouse. These hot air heaters run on either natural gas, petroleum and diesel. This direct combustion generates the by-product carbon dioxide, which can be advantageous for plant growth.

The most common heating system in commercial greenhouses is the multi-purpose tube rail. Especially in vegetable crops, the tube rail heating system has been widely applied as it has a significant logistical advantage.

Another common hot-water circuit in the vegetable production is the grow tube. The grow-tubes are situated at the fruits throughout the greenhouse which enables the grower to control the ripening process.

In severely cold climates, the tube-rail system and the growing tube are supplemented with a snow-tube circuit. This to melt off the fallen snow from the deck of the greenhouse, without having to open the climate screens and to disorder the temperature at crop-level.