With its focus on rapid growth and high yields, horticulture has always served as byword for efficiency. The introduction of new technologies and new techniques has led to continued refinement in the cultivation process and the sector as a whole has done much to manage its carbon footprint.
While innovation and new ideas have always played an integral role in horticulture’s history, they’ve never been more important than they are today.
Horticulture is a naturally resource-intensive industry, and rising power and production costs mean that anything that can be done to make growing more efficient should be done.
The humidity challenge
One of the key considerations here is the issue of humidity. Excess humidity is a significant problem in greenhouses; with so many plants in such a confined space, there is a huge amount of moisture in the air. Left unchecked, this limits the plant’s ability to evaporate effectively and prevents it from transpiring.
That has implications from a yield perspective. The more water that a plant can evaporate, the more nutrients it can take on, and the faster and stronger it can grow. The more the air around a plant is saturated, the less water it can transpire and – as a result – that plant will be unable to grow at its optimal rate.
Too much humidity can also lead to greenhouse diseases such as mildew, botrytis cinerea that can severely impact the yield and quality of the crop.
Keeping relative humidity to an acceptable level is a major priority, then, and the primary way that growers have traditionally approached this is via the use of vents in the greenhouse roof. When opened, these allow high-humidity air to filter out while fresh, low-humidity air flows in.
Of course, high-humidity air isn’t the only thing that venting lets out. Heat and CO2 – both expensive to create – will also be expelled through open windows. As a result, growers find themselves needing to strike the difficult balance between optimal humidity and the cost of reheating and re-carbonising their greenhouses.
Improving air circulation
It was with this challenge in mind that we designed our Hyperion Pro grow lights. Since 2018, Hyperion LEDs have included a fan-based active air-cooling system, one that directs the warm air generated by the unit away from it. This has three main benefits:
- Air-cooling enables each unit to run at lower temperatures, which is important from a lifespan and efficiency point of view.
- Active cooling allows for a smaller heatsink, which reduces the size of each unit and minimises their shading profile and weight.
- As well as pushing warm air downwards, which can be beneficial to certain crops, the active cooling system also promotes continuous airflow around each plant.
This third point has the greatest bearing on the issue of relative humidity. By increasing air circulation above and within the crop canopy , the Hyperion helps to reduce humidity, which in turn allows those crops to “grow” harder – whilst reducing the need to ventilate precious heat and CO2.
Distance from the LED to the crop
The distance below the light that the vented air will go depends on several factors relating to the existing greenhouse climate but typically it will be 1-2m
The crops that benefit the most
Not all plants are the same, of course, and this approach benefits some more than others. In our experiences so far, those crops that tend to see the greatest returns as a result of this fan-assisted air circulation are:
- Highwire crops
Be it tomatoes, bell peppers, or cucumbers, these crops can grow as tall as 3m within just a couple of months. With much of the stimulation taking place in the first metre of the plant, the ability to circulate air around that upper end allows a grower to really push those crops without needing to rely so heavily on traditional venting.
One important factor to mention here is that the LEDs also need to be quite close to the plant in this instance. That’s something that we can accomplish by virtue of Midstream’s proprietary lenses, which deliver great uniformity despite their proximity to the crop.
The priority here tends to be on pushing the crop as quickly as possible through its different cycles, as the number that you can get through in one year determines your ultimate yield. In this regard, cannabis production tends to be much more like that of vertical farming, where lights need to be much closer to the plants.
Cannabis is also a hungry plant that consumes a lot of nutrients and evaporates great amounts of water. Heating and humidity are critical as a result, and so air circulation can have a major impact on costs and growth alike.
So, the circulation-related benefits are clear – but what about heat, with warm air being pushed downwards?
Obviously, there are benefits to having an additional source of heat in a greenhouse, particularly when directed at the crops rather than being left to dissipate up in the rafters. The reality is that the extent to which those benefits can be realised is largely on a case-by-case basis, one that comes down to the distance between the grow light and the crops.
Take lettuce, for instance, where there can be a gap of around 4m between the plant and the luminaire. Even when you push warm air down, the distance tends to prevent there from being too much of a benefit. The solution, of course, would be to employ larger fans – but that has an obvious countereffect in that it drives up the amount of power that each unit requires.
Why active cooling works
Here at Midstream, we believe the best way to view active (fan-assisted) cooling is as follows.
Firstly, it extends the lifespan of your lights, which is obviously beneficial. Secondly, it can have a clear positive impact on the growth rate of certain crops by virtue of its impact on circulation. Finally, the warm air that is produced does at least help to slow the escape of warm air in any greenhouse, even if its impact on plant growth is debatable.
More than anything, active cooling enables growers to be smarter, more effective, and more efficient in their cultivation efforts – and that’s good for the bottom line and the planet.