The installation appeared to work well. The air spread was considered sufficient. In the first year, the air moisture was well-managed, but because of the low RV, the energy savings appeared limited. In the autumn of 2013, two screen installations with transparent cloth were installed. In this way, the glasshouse can be insulated by a double screen at night and a single screen during the day.
The light loss by way of the tube and the screen installation was not measured, but was estimated at 3-5%. In winter, the total light loss was limited, due to the fact that a large amount (up to 60%) of the light was coming from the lamps. The use of a transparent screen rather than a blackout screen in the summer compensated for light loss. The transparent screen protected the crop against too much sunlight.
The crop results in the test were on average slightly lower than the control crop. However, the variations per crop were so extreme that this was probably not caused by the installation.
Turning off heating from below
Because of the low RV and also due to the air movement, the reaction time was shorter. Therefore, they dehmified less and the crop was grown in slightly cooler conditions during the test. There confidence in the manageability of the air moisture increased. Therefore, in 2014, we dared to turn off the heating from below during the first 2 - 5 weeks of each crop. In one crop, caused more brown leaves than in the control crop. However, in the remaining crops, the amount of brown leaves was similar to the brown leaves in the test crop, if not more. The LBU can also be used on a sunny summer's evening to cool under the blackout screen. This was especially effective when the outside temperature was lower than the inside temperature.
The saving on heat usage is shown in the table. In the relatively warm year of 2014, in the test section 8,2 m3/m2 less natural gas equivalents were used than in the control section. In 2013, when the extra screening was installed in the autumn, and when the heating from below had still not yet been turned off manually in the first weeks of the crop, the savings were a lot less high. For 8 m3/m2 per year savings, the investment cost has been calculated at € 12 per m2. In this calculation, the fact that the heating costs with the production of electricity and CO2 can be a lot lower than the natural gas price has not been taken into account. Also not taken into account is the fact that the system can offer cultivation benefits by way of a higher reliability of glasshouse climate and therefore a better crop health.
Source: Marcel Raaphorst (Wageningen UR Glastuinbouw), via Energiek2020