News

09/09/2019

Better control over the vertical temperature profile in the greenhouse with water cooled LED lighting

For crops, such as roses, tomatoes and cucumbers, it is important to control the vertical temperature profile in the greenhouse. If the bottom half of the crop is colder than the top half, the evaporation within the crop will not be uniform with negative consequences, such as condensation and a higher probability of elevated disease rates as a result.

The temperature profile can be made more homogeneous by supplying heat from below. However, the drawback of this is that there is already too much heat in the greenhouse, and it is being heated while heat is also being removed at the top of the greenhouse.

A study conducted by Wageningen University & Research (WUR)* concluded that a quarter of the gas consumed for heating took place at the same time that heat was being removed.

Lighting is a major source of heating in a greenhouse. It brings between 30W and 200W of electrical energy per square meter into the area, of which a large portion is ultimately converted into heat. In passively cooled LED fixtures, this heat will largely stay suspended at the top of the greenhouse because approximately 50% of the electrical energy is directly converted into heat that is emitted into the environment. This creates a problem for growers who are trying to create a homogeneous climate in the greenhouse.

The major benefit of water cooled LED fixtures is that 40% of the heat they produce is directly removed from the top of the greenhouse and if desired this heat can be added at the bottom of the crop. The grower maintains control over the climate in the greenhouse and is able to better regulate temperature and lighting independently from each other.

This reduces the need for heating with growth tubes and there is a reduced need for opening the windows, which means more CO2 stays inside the greenhouse and the climate becomes much easier to control. Any additional energy needed for cooling and for the water circulation pumps in most cases is amply made up for through the savings in heating costs or air conditioning.

The water cooled LED fixtures therefore make it possible to increase light levels without creating excessively high temperatures inside the greenhouse. Furthermore, water-cooling contributes to increasing the LEDs’ lifespans.

(*https://www.wur.nl/nl/nieuws/Onderzoek-naar-verticaal-temperatuurprofiel-in-tomatenkas.htm)