Oct. 28, 2009, Wageningen, the Netherlands – The best way for Dutch growers to dehumidify greenhouse air is to let outside air in, according to one researcher. Heating this outside air using the outflowing greenhouse air can lead to considerable energy savings.

This is the result of research carried out by Jouke Campen with which he hopes to obtain his doctorate at Wageningen University. Campen also says that letting dry air in allows horticulturists to keep their energy screens closed longer, offering further significant savings.

The technology for the energy-saving dehumidification of greenhouse air is already available. (PHOTO COURTESY CLIMECO)

Campen studied various technologies for dehumidifying greenhouse air. He initially expected the best results from condensation technologies in which humid air flows past a large cold surface, causing the moisture on that surface to condense. Campen presumed that this method would remove moisture from the air and generate heat through condensation. 

After extensive research, however, he discovered that the best approach is to use comparatively dry outside air. The various condensation technologies he studied turned out to be expensive and uneconomical, partly because they required more energy to be “pumped around” than condensation heat alone. The greenhouse air also appeared to cool quicker than expected and the condensation systems themselves can be complex and costly. 

Based on his research, Campen says that using outside air is the best option. “Pre-heating inflowing outside air with outflowing greenhouse air can result in considerable energy savings,” he reports. “And horticulturists can also save up to 15 per cent by using cheap, dry air to keep their energy screens closed longer. They do not have to open the screens until the solar irradiation is such that greenhouse heating is rendered unnecessary.”

The technology has already been applied in a strawberry greenhouse. “Although the investment is yet to become cost-effective due to low energy prices, there is interest from horticulturists and suppliers,” Campen concludes. “I think there is a good chance that this method for the dehumidification of greenhouse will be a commonly used technology within a few years.”

• www.wageningenuniversity.nl