ID Greenhouse
‘Production results are satisfactory but we need to raise the bar each year.’
Although their revolutionary greenhouse has had a superb first year, the brothers Duijvestijn see room for improvement. Technically there are still gains to be made. And, although the goal to save 50% on energy by using low-grade heat was achieved in the first year, the businessmen take little pleasure from that. The system’s partners watch and learn. Where can they still make improvements?
The ID greenhouse that Duijvestijn Tomatoes of Pijnacker, the Netherlands, started running in December 2013 is performing well. In the first quarter, the crop was mostly grown in the conventional way in order to eliminate any technical teething troubles without taking any major risks. Then in the very light and closed greenhouse, step by step, they switched to the Next Generation Growing. This greenhouse concept, jointly developed by Technokas, Boal and Scheuten Glass, lends itself excellently to this purpose.
Noteworthy features of the new greenhouse are: A double glazed roof with large format glass (2x3m); insulation glass with four anti-reflective coatings and a structured layer to scatter the incoming light; air conditioning using air drawn in from outside; heating with low grade (primary) and high grade heat (secondary); continuous ridge ventilation with the opening on the top side; and a construction without any light-intercepting trellises. Instead it uses relatively heavy columns and angled sidewalls to support the greenhouse. The screens are tucked under the gutters.
Special year
Ted Duijvestijn calls 2014 a peculiar year, because the reference crop of plum tomato Prunus, performed exceptionally well. “As a result we weren’t able to achieve any extra yield in the new greenhouse,” he said. “If all the components had immediately performed as we wanted them to, we certainly could have got more out of it.”
Apart from the later planting date and the conventional start to the crop, a few other factors contributed to the setback. One of these was the CO2-supply in the new greenhouse. “We had a central control for the CO2 in which a two way valve distributed the CO2 between the conventional greenhouse and ID greenhouse,” explains Duijvestijn. “Measurements inside the greenhouse showed that sometimes too little CO2 entered the new greenhouse so that the concentration measured next to the closed windows was sometimes under the level outside. Then you know you are missing your chance regarding kilos. This year the new greenhouse had its own CO2-control system.”
Insect mesh removed
Another disappointment was that on warm days there was a shortfall in the ventilation capacity. That was directly related to the insect mesh in the ridge ventilation, which the growers had chosen to install at the last minute. “The mesh had a big impact on the ventilation capacity,” says the grower. “On very warm days, which were quite often last year, the plants were sometimes exposed to stress.”
Therefore, the mesh was removed during the crop changeover. Duijvestijn says that it is now more difficult to manage the secondary goal, which is emission-free production, but the ridge ventilation can now very quickly and in line with the original calculations achieve the desired level of cooling.
“The vents open from the top side to obtain the maximum chimney effect,” he explains. When the windows are fully open it’s possible to refresh about 150 m3 air per m2. Due to the diffuse glass that doesn’t have to happen very often but it is good to have such a fast and powerful system available. The capacity to draw in outside air is 10 m3/m2 per hour and is used mostly for the fine-tuning.
Double glass
The advanced and expensive double glazed roof largely meets expectations although Duijvestijn would like to see less condensation.
“That certainly has our attention,” says product manager horticulture Laurens Vlaar, of Scheuten Glass. “We are all convinced that double glazing adds value, but we also know that glass is extremely differentiated and complex. Together with the users and research institutions we want to initiate improvements where possible and offer tailor-made solutions. These could include different structural treatments that you can apply in order to achieve the desired scattering of light. Every type of structure has its advantages and disadvantages. With hindsight we can see that the pyramid structure in this greenhouse roof is a little too coarse. A finer structure would probably lead to fewer problems with condensation.”
Peter Zwinkels, of Technokas, adds: “This has also opened my eyes. In the past condensation was often seen as an inevitable side-effect but in recent years it has started to receive the attention it deserves. Nowadays we always test glass samples that are wet and the differences can be amazingly large. Wageningen has a great setup for taking measurements which we thankfully can use.”
One thing that Zwinkels would like to do differently in this context is take measurements when the glass is at an angle, just like when it is on the greenhouse roof. Currently glass samples are only measured when they are horizontal and that, certainly with respect to condensation, can give a distorted picture.
Potential
Glass producer Scheuten, as a project partner, is closely involved in several new greenhouse concepts in the Netherlands. Despite the still relatively high cost, Vlaar sees a lot of potential for well-insulated, double glazed greenhouse roofs using diffuse tempered glass with AR-coatings.
“The projects which we have been able to achieve so far are fairly small scale and therefore relatively expensive,” he says. “Before there’s a further roll-out, the project volumes need to increase to enable a serious decrease in price. For projects of several hectares that is feasible, certainly now that we are better able to deal with the particular nature of horticultural projects.”
Wageningen UR Greenhouse Horticulture was not only consulted for determining the glass specifications, it also provides the monitoring program. “That’s very valuable,” says Duijvestijn. “Before we invested in this greenhouse I was intensively involved in all kinds of trials for three years. However, I’ve actually learned the most from using it, not least, thanks to the monitoring by the researcher.”
Invest in research
Together with Zwinkels and Vlaar he stresses that the sector and the government should keep up their joint investment in research. The relative reticence that has occurred over the last few years gives him reason for concern. “There have been many cut backs and in my opinion potential financial partners sometimes say no too easily to subsidy applications for research,” according to Zwinkels. “That is partly due to a lack of strategic focus and expertise."
The greenhouse builder cites Next Generation Growing as an example. “I have already seen several requests fail because they were not thought innovative enough. However, many variations are being designed. Growers must be able to make informed choices and that requires comprehensive research and testing. Growers also want to pay but it makes a difference if other parties continue to make a contribution and thereby reduce the business risk to an acceptable level. That is what happened here. Without external help this greenhouse may never have been built."
Summary
The energy target (50% energy savings) was achieved in the first year of production, but by a combination of circumstances no extra yield was achieved in the ID Greenhouse. Now the greenhouse has its own CO2 control system and the insect mesh over the ridge ventilation has been removed, so that may now be possible. The well insulated, double glazed roof made of diffuse glass has excellent transmission properties. The condensation behaviour, in relation to the treatments used to make the glass diffuse, deserves extra attention in future projects.
Text/photos: Jan van Staalduinen
‘The focus points of our brainstorming sessions are sustainability, sustainability and sustainability.’
Duijvestijn Tomaten in Pijnacker was elected ‘world’s best tomato grower’ in the Crop & Process Technology category in 2015. Ted Duijvestijn explains the innovative projects his firm is currently working on and what prompted their development. An interview with a passionate entrepreneur.
We are speaking to Ted Duijvestijn in his company’s Innovation Center.
Why do you have an Innovation Center?
‘When we switched from natural gas to geothermal heat we got a lot of interested visitors. And when we built the ID Greenhouse® in 2013, we realised that we needed a solution to be able to continue receiving visitors on this scale. This gave birth to the idea of the Innovation Center, with a big reception area and a balcony with a view over the entire ID Greenhouse®.
‘We attach great value to hygiene and safety. We can now receive visitors and show them what we do without any concessions to either hygiene or safety. Apart from that, we can now receive our customers in a pleasant environment while our day-to-day operations can be carried out without any disturbance.’
What prompted you to choose that name?
‘Our firm has grown step-by-step to 14.5 hectares. After the last expansion we asked ourselves: “How shall we continue: will we try to cut as many costs as possible or are there other opportunities for growth?” We decided that our greatest affinity lay in the field of innovation and that this is precisely where new opportunities can be found. This is our Innovation Center. We regularly hold brainstorming sessions here. This is where we discuss how to respond to changes and what is really important to us. These discussions have generated several innovative projects, such as the ID Greenhouse®. The focus points of our brainstorming sessions are sustainability, sustainability and sustainability. And of course, we always ask ourselves when we come up with a new idea: is it commercially viable, what will it bring us?’
Did you decide to switch to geothermal heat because it is sustainable?
‘Sustainability was a key issue when we made this choice, but our investment had to be profitable, too. We made the switch in 2011. This summer we even had a heat surplus on account of the warm weather. Due to the EHEC crisis we also had a tomatoes surplus, so we came up with the idea of producing oven-dried tomatoes. This is responding to long-term developments and seeing if you obtain a position in a new market. Of course, there is also the financial aspect to consider: can you get funding and develop more know-how? What happens is that you learn new things that take you another step further. We designed a machine dries tomatoes using geothermal heat. We conducted tests on content, taste, temperature, time, varieties - we tested everything we could possibly think of.’
Duijvestijn shows the result with due pride: wedges of dried tomato, in small round containers and in different flavours. The tomatoes were grown on the Duijvestijn premises and are marketed as “Frezta, oven-dried Dutch tomatoes”.’
Isn’t ‘oven-dried’ misleading? They aren’t dried through and through. like most dried tomatoes.
‘They are semi-dried and we add seasoning plus a little oil. You do have to store them in the refrigerator.’
Was it difficult to find distributors?
‘We are still working on it. It is a question of getting distributors interested and gradually building up a market. We can now count several supermarkets, restaurants and delicatessen shops among our customers. In addition to the tomatoes, we also developed a tapenade that market under the name “Tomade”.’
The next innovative product you came up with was the ID Greenhouse®.
‘Looking at new greenhouse systems, we didn’t see many developments that would actually take you a lot further. The frames became higher, that was all. What’s really important is light. Another key topic is energy consumption, even if you have geothermal heat. We wondered how you can combine the two and further optimize your use of energy and hit upon the idea of double glazing. The K factor (thermal conductivity coefficient) of double glazing is twice that of regular single glazing. So we launched a pilot, in collaboration with the Wageningen University Research Centre, based on the VenlowEnergy Greenhouse study that was being conducted at that time. This resulted in the ID Greenhouse®, with a surface area of one hectare. This lets you perform tests on a substantial scale, without being too small to get genuine results.’
How does the ID Greenhouse® distinguish itself from other greenhouses?
‘The ID Greenhouse® has diffuse double glazing with panes measuring 3x2 metres; twice as big as conventional panes. The greenhouse is tilted, so that the rows are at right angles to the cover. We chose this construction because it lets you get as much light as possible to the crop. This construction consolidates the power where it needs to be in the greenhouse. As the screen runs from gutter to gutter, the screen package closes beneath the gutter and barely takes any light away. A tiny grille at the top edge of the ridge vent prevents rain from coming in when the ventilation grid is left slightly open. The exterior has a sloped wall to reinforce the frame. Besides that, you can mount equipment onto it, such as air handling units.’
Does the greenhouse meet your expectations?
‘We chose this greenhouse to grow tomatoes with smallest energy input possible. The first year we used it we received some guidance from Wageningen University Research Centre and were able to achieve energy savings of 60 per cent, by using only low-quality heat. The water from the geothermal well is 75°C. In the standard greenhouse this is cooled to 45°C - depending on the return flow rate - and is then transported to the ID Greenhouse®. The challenge is to cool the water in the ID Greenhouse® down to 25°C, which means that you’re making optimum use of the geothermal energy. After using it in the standard greenhouse you get your heating water practically for free, but in the first year we unfortunately had to make some concessions to quality.’
So the greenhouse isn’t performing satisfactorily?
‘The level of quality rises every year, as is already apparent in the second year. During the first year it is particularly important to ensure that all your equipment is functioning properly. At this stage, it doesn’t pay to spend a lot of time making all sorts minute adjustments to your climate settings in an attempt to take things to the next level. Now that we’re in the second year we aim to achieve savings of 50 per cent, in combination with a higher production at the right level of quality. In first year we achieved our goal of 50 per cent, but not the production level we were after. The biggest problem was related to light loss on account of condensed moisture on the glass. Both the interior and exterior glazing had been provided with an HR coating to prevent light reflection, because you want to get the same amount of light inside the greenhouse that you would with conventional glazing. This coating creates tiny pyramids on the glass, as it were, onto which droplets of condensed moisture cling. We have since removed the coating on the inside. Now the moisture can flow away more easily. A small percentage of light is still lost in comparison to single glazing, but compared to last year we have gained 5 per cent more light.’
So the greenhouse is performing satisfactorily after all?
‘It’s too early to really say anything about it. We aim to compensate for the loss of light through the frame. You can come up with the best ideas on the drawing board, but you never know how well something is going to work until you’ve put it into practice. Only then can a product be truly tested and will you learn more. The CO2 supply - from Ocap - was adjusted in this second year, for example. It failed to produce the correct values from time to time. Instead of the extension of the CO2 supply in the other greenhouses we managed to put together provisionally there is now a direct supply.
‘We achieved the envisioned energy savings, and now we’re working on raising our production level, step by step. After only one year you can’t rightly draw any conclusions; only after about three years can you truly say anything. In the meantime you identify the challenges, look for improvements and learn from your experiences.’
Is such a small ridge vent enough to meet for ventilation needs?
‘The air vents in the greenhouse had been fitted with mesh. As a result, insects could not enter the greenhouse, which means that we can achieve an even lower maximum residue level in our tomatoes. You could then get even more out of using natural enemies. However, the fine mesh obstructed the flow of air; particularly on days with little wind and warm, humid air. Weather conditions like that put a lot of stress on the plants. We therefore abandoned that idea, since stress has a negative impact on quality and production. Now that the mesh has been removed we are able to control the climate, in combination with the AHUs, more accurately.’
Do you expect more greenhouses to be built with double-glazing on the roof?
‘Taking into account the energy savings, our expectations are high. Economically speaking, however, there is still a way to go. Double glazing is still rather expensive.’
Duijvestijn Tomaten in Pijnacker was elected ‘the world’s best tomato grower’ in the Crop & Process Technology category in 2015 by a jury who also presented the accompanying Tomato Inspiration Award. The jury was composed of experts Gene Giacomelli (University of Arizona, USA), Ep Heuvelink (Wageningen University, the Netherlands), Stefanie de Pascale (University of Naples, Italy) and Tadahisa Higashide (NARO Institute, Japan). Duijvestijn Tomaten grows 14.5 hectares of primarily round and plum tomatoes. Besides these tomatoes, they also grow Silky Pink, an exclusive new variety of pink tomato with an exceptionally fruity flavour.
Visit the website Duijvestijn Tomaten.
Would you like to know more? Download the complete interview with Ted Duijvestijn on innovative projects such as geothermal energy, the ID Greenhouse®, CHP units, LEDs, geothermal energy-dried tomatoes and packaging made from waste foliage (login required).
Copy/photo: Tuinbouwteksten.nl/Theo Brakeboer.