Vertical ventilation can not cancel out vertical temperature gradient

Tomato nursery Gardener's Pride in Beetgum invested in a Ventilation Jet and a second screen installation. Researchers of Wageningen University & Research have monitored the climate and crops in the winter of 2018, with particular attention to the vertical air temperature profile, the tomato temperature and the smoke gas concentration.

 

Tube required
It has been observed that in case of significant heat input by radiation (light) on the top of the crop, a vertical temperature gradient in relation to the bottom is created. This temperature gradient cannot be reduced by using only the lowest vertical air circulation ventilators of the Ventilation Jet. This gradient can be minimized by extra heat input through the lower tubes.

VJ reduces moisture
Extra input of heat can result in excess heat that has to be transported by means of natural ventilation or by using the Ventilation Jets when the screens are deployed. During the monitored period around a quarter of the daily gas usage for heating took place at the same moment the Ventilation Jets transported the hot and moist air. The use of the Ventilation Jets at Gardener's Pride is particularly important to prevent too high humidity levels.

Longer growing time when less tubing is used
A vertical temperature gradient has consequences for the growing time of the tomatoes. Measurements have been conducted at both the small snack tomatoes and the bigger tomatoes. The small tomatoes turn out to be better able to, as expected, follow the air temperature than the larger tomatoes. It is known that the growing time of tomatoes is influenced by the temperature.

Smoke gasses not clean enough
It was also determined that Gardener's Pride requires minimal ventilation to make sure (particularly on windless days) the concentration of NOx does not exceed acceptable day levels. The alternative is to dosage cleaner CO2.

Read more about this project (in Dutch)

Source: Kas als Energiebron


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