Open access publications in the SLU publication database

Energy use by individual greenhouse producers depends on a wide range of factors. Features of the external climate such as solar radiation, temperature, wind and rainfall have a direct impact on the heating requirement in the greenhouse and consequently on energy use. These external
factors vary with the season and can also fluctuate sharply from day to day or from year to year. The technical equipment in the greenhouse and its design and condition are also very important. How the technical equipment is used and regulated has a major effect on energy use. This report examines the possibilities for increasing energy efficiency through changes and adjustments in climate-related parameters in greenhouse cultivation.

The report begins by describing the benefits of carrying out an energy analysis and working systematically according to a working model for continual improvements. In order to make comparisons of different types, examples are provided of different ways to describe energy use in greenhouse production. Energy-efficient cultivation technology relating to climate issues is divided into the areas of
temperature strategy, ventilation, screen regulation, lighting and humidity regulation. The temperature strategy aims to exploit the energy provided by solar radiation to the maximum extent possible. Examples show that during the winter, less energy is needed to maintain the temperature at night with the screens closed, than during the day with the screens open. Solar radiation only provides a clear energy boost from 1.5-2 hours after sunrise until 1.5-2 hours before sundown. Energy can be saved by allowing a higher temperature to develop in the greenhouse during the day when solar radiation provides additional energy and a somewhat lower temperature when heat losses from the greenhouse are great. The higher temperature is achieved by raising the ventilation temperature threshold.

An appropriate ventilation strategy and correct settings of the climate computer are critical for a good crop and for energy-efficient production. An important parameter is to have correctly set P-band(regulation function) for vents, which determines how these open and close. This report
describes the P-band function for the most commonly available climate computers.

Having greenhouse screens is the single most important measure to decrease energy use in a heated greenhouse. Keeping the screens closed for a longer period in the morning and closing them earlier in the afternoon results in energy savings. This report provides examples that this
can be achieved without any negative effects on production. However, a dense plant canopy under screens can create very humid conditions and it may be necessary to open the screens
slightly to ventilate out this humidity. Examples of humidity levels to aim for and choice of screen opening width are discussed in the report. From mid-October until mid-March, assimilation lighting is essential for producing good quality ornamental plants or vegetables. Adjustment of the lighting period according to total cumulative light is an interesting strategy for decreasing electricity use and is discussed here as an area for development. Humidity regulation often contributes around 20% of the total energy use in a tomato crop, while in a cucumber crop the corresponding value is around 15%. In a greenhouse without variable climate zones and with efficient regulation of temperature and ventilation vents, it is possible to tolerate a slightly higher threshold at which humidity regulation is activated, and a slightly lower pipe temperature when the humidity is too high. The report describes why different climate zones develop in a greenhouse and how they can be eliminated.