Climate control & energy > Heating system

There are different concepts of greenhouse heating being used, including hot-air heating, hot-water pipe heating, steam pipe heating, radiant heating, bed heating, bench heating, and water heating in hydroponics. The choice of a heating system depends on the required heat load, the scale of operation, availability and price of heating systems and energy sources, etc.

For large-scale greenhouses in colder climates, the most common way of heating is ‘central heating’ by a boiler and a heat distribution system. The boiler runs usually on fossil fuel and is able to heat water to ca. 100 °C. Hot water is mixed with cold return water to get a certain temperature. It is then recirculated through a closed circuit of hot-water pipes, and returned to the boiler. The hot-water pipes can be fixed in between or above or under the crop (or bench) or suspended from the greenhouse construction. The pipes are often also used as tracks for internal transport systems, (e.g. pipe-rail system on the ground for trolleys).

Hot-air heating is often used in greenhouses that are smaller, or located in a mild climate, or not used in winter, or controlled less. A relatively small heater is placed in the greenhouse or suspended on the greenhouse construction. Hot air is blown out and spread directly, or is spread through plastic tubes into the greenhouse. Larger greenhouses require many of these ‘small’ heaters placed on regular distance from each other. This form of heating is relatively cheap, but has several disadvantages.

Instead of heating the ‘whole greenhouse’, it is possible to direct the heat towards the plants or to the roots. Many ornamental pot plants, bedding plants, young plants and nursery stock plants are grown in heated beds, on heated floors or on benches with bench heating. Heating tubes, mats or pipes are located quite close to the roots.