Design for an Improved Temperature Integration Concept in Greenhouse Cultivation

Original paper: O. Ko¨rner *, H. Challa Design for an improved temperature integration concept in greenhouse cultivation Farm Technology Group, Department of Agrotechnology and Food Sciences, Wageningen University, Mansholtlaan 10, 6708 PA Wageningen, The Netherlands Received 22 July 2002; received in revised form 15 November 2002; accepted 28 December 2002.

     Heating energy represents more than two-thirds of a typical greenhouse total energy consumption. Is currently well known that the average day and night temperatures are what controls how fast plants develop. As the temperature increases, crops develop much faster, but there is a significant cost associated, which typically leads to an increase in energy consumption. To mitigate the cost and become more efficient in the control environment production, an approach to improve temperature integration concept could play an essential role in energy savings. Temperature Integration Concept is based on the ability of crops to tolerate temperature deviation from their biological set points. The integration concept manipulates temperature, aiming to be compensated within a pre-set period without having adverse effects on plant growth.

     Theoretically, a crop with more dynamic and flexible temperature boundaries could potentially play an important role, so this study aimed to improve the temperature integration concept by introducing dynamic temperature constraints. A modified temperature integration procedure was designed combining the usual long-term temperature average over several days and fixed boundaries for daily average temperature with short-term temperature averages over 24 hours with a very flexible temperature limit. The overall idea is based on a concept called the Freedom for temperature fluctuations. This concept allows the temperature to freely fluctuate due to the environment without being controlled by heating or ventilation. Temperature fluctuation increases with longer averaging period and increasing temperature bandwidth, which allows longer periods of several days, which enables compensation of warm or cold periods resulting in higher energy savings.

     The proposed regimen for temperature integration was performed by modeling and simulation techniques (MATLAB version 6.0) using tomato as a model crop. Variables such as air temperature, outside radiation, relative humidity, and CO2 measurements were input in the model with a fixed time of 5 min over one year. Measurements such as setpoints for heating, ventilation and CO2 concentrations were calculated with a climate control model (CCM) which provide enough information for calculating relative humidity, air temperature, energy consumption, and natural gas consumption. For accuracy, energy loses where also consider into the model. Two reference temperature regimens were used for comparison:  BP= commercial standards, setpoint increase linearly, and a Bpfix= night and daytime heating and ventilation temperature setpoints were fixed (uncommon practice). The heating setpoints were 18, and 19 °C and ventilation set points were 19 and 20 °C for night and day, respectively. The weather prediction was also used for providing data into the model simulation. Validations of the CCM model was performed in four semi-commercial Venlo-type greenhouse compartments.

     Two temperature integration regimens were model by the Autor: RTI (regular temperature integration) and MTI (modified temperature integration) both with a bandwidth of +/- 2, +/- 4 and +/- 6. The modified regime model (MTI) resulted in more energy saved when compared with regular temperature integration model (RTI) and the BP controls. Energy-saving increased with temperature bandwidth in all cases evaluated. Fluctuation during a cold time (winter) was observed. Overall, yearly greenhouse energy saving increased by up to 23% compared with the BP regime (temperature with a bandwidth of +/- 6 C). Compared with regular temperature integration energy-saving increased relatively with 14%. Interestingly, the setpoint for relative humidity profoundly influenced energy-saving suggesting further focus in future evaluations. When evaluating the different temperature dose-response data, they observe than an increase in the duration of maximum and minimum temperature increase energy saving and gross photosynthesis of tomato plants, which can be traduced to more photosynthetic efficiency. In conclusion, the conceptual design for advance temperature integration control seems to be promising for energy reduction. The distinction between short- and long-term processes in temperature integration lead to an increase in energy savings. A more advanced flexible humidity control concept could probably help to decrease energy consumption further since the highest energy saving was achieved when no humidity control was used.

13 thoughts on “Design for an Improved Temperature Integration Concept in Greenhouse Cultivation

  1. This modelling system was highly effective at producing several comparative models when crop behavior, outside radiation, weather conditions, extensive internal sensory components, and other data was incorporated.
    If sensors fail or lose calibration, what would be the impact on the control system? What if a grower cannot afford high resolution sensors or even certain sensors altogether? Is there a way to apply the control system present in this study with less data required? Does that missing information impact the model enough that it actually becomes a poor management strategy?
    Further, how hard is it to make a model that tailors to an individualized cropping schedule, and can it be done by a small-time greenhouse farmer?

    • Definitely calibration and validation using controls plays an essential factor in this study. They validated all their data obtained using four semi-commercial Venlo-type greenhouse compartments. Is the weather broadcast efficiently enough for farmers to verify their data obtained? Is currently unknown. Despite this, there are limitations in terms of applying this to small farmers. Is a fact that modeling is computationally intense and data collection and management plays a significant role, but I will not be surprised if future companies create more targeted instruments with Apps to help farmers with decision-making. If future technology could have a well-known crop model, it could potentially be an automated process based on variety and data collection, which can be traduced to substantial energy savings.

    • This paper suggests that if a high resolution system is not available for dynamic control, a grower can still use static set points by lowering the heating set-point at night and then compensating by increasing the temperature during the day (maintains that same average temperature). This may already be an industry standard practice, I don’t know. The plant response might be species-specific but the results of the paper indicated than flowering and growth were similar between the tested species.

  2. I am always curious about how this type of management affects fruit quality. It is clear that a wider bandwidth can save energy, but does a wider bandwidth decrease fruit quality? I would think that even if growth is not affected or increased, fruit quality will decrease the further the temperature deviates from the biological setpoint. However, this may not be the case, or it may not be a significant decrease in quality, which would make this a very lucrative management strategy.

    • Definitely fruit quality is one of the limitations of this study. We currently don’t know if this could be a potential pitfall. Biologically is currently known that the slower plant metabolic processes occur the more accumulation of sugars. Temperature plays a significant role resulting in higher Brix value and probably high quality. I think before implementing this technique, a formal breeding program has to be done to fix traits such as broader temperature deviations in tomato cultivars.

      • Brix and other quality parameters are not necessarily correlated and quality traits are not all proportional to environmental conditions such as temperature. Brix and other quality parameters have a strong genetic signal and genotype can explain a modest proportion of variance compared to environment. The problem with breeding for higher quality is that there is no price incentive for improvement of a quality trait like brix.

    • It seems like a simple fruit quality experiment could determine whether or not quality is being reduced. I would be most curious to see seasonal variation in fruit quality comparing the highly controlled (+/- 2C) vs loosely controlled (+/- 6C) systems. It seems to me that fruit quality may be decreased in some instances, but perhaps improved in others. It would certainly be interested to find out, but further: is the average consumer going to be able to spot the difference in quality?
      Overall, money is going to take the cake and it is likely a loosely controlled system would be employed preferentially over the tight bandwidth until fruit quality concerns of high importance are discovered.

      • I don’t think the average consumer will notice the difference but it’s all about Marketing strategies, if there is a point where quality can be sligely improve probably they could find a market for it. My only concern is that replicating this into greenhouse farmers seems to be expensive and requires a lot of expertise while the gain is still debatible.

        • For context, we noticed a significant change in fruit quality (initially just based on personal opinion then backed up by significant increase in Ohio Total Soluble Solids:Titratable Acidity ratio) in the same strawberry cultivar when grown in Arizona and Ohio greenhouses. Both growing locations had the same 24-hour temperature average, but nighttime temperature on average was 2C lower in Ohio and daytime temperature was 1C higher in Ohio on average. So within small temperature bands, quality can be noticeably different to consumers and fruit composition can significantly change. Also, while it is well established that there is a negative correlation between temperature and Brix when light is not limiting photosynthesis, fruit quality/taste is also affected by acids and volatile compounds. Thus, it would need to be verified that lower temperatures do not affect acids or volatiles in a way that reduces fruit quality.

  3. Temperature integration seems to be a promising technique to increase energy savings, especially in countries where season change drastically. What could be such an impact in regions where temperature fluctuations are more stable? How can we be sure that every crop grown in the greenhouse will have a positive response to constant temperature fluctuation? Do we currently know temperature bandwidth for all crops? How can this technology positively impact or reduce the Greenhouse industry from a biological perspective?

    • For regions that have a more temperate climate, it seems like this concept would still help decrease costs due to energy usage. I’m sure they still have the majority of their energy being used to maintain set points. And their production could even possibly improve if it were found that some crops produce best in certain conditions that could be maintained by the more dynamic range.

      Also, with plants exposed to conditions in opposite extremes of the set point, I would think it would help them more closely resemble field planted crops. And not only resemble morphologically but also phytochemically. With exposure to differences in environment it may increase the abundances or profiles of phytochemicals in a way that makes them closer to those of crops grown in the field. If this concept is true and the changes are abundant enough, this could help the greenhouse industry fight any claims of less nutritious crops or could even help the taste conform more to the field-crop flavor.

      • Interesting, I hope more research is currently being done in this area since it could be a potential benefit for the farmer as well as the consumer.

    • Although I have little knowledge about crops cultivated by the greenhouse production system, temperature fluctuation could be beneficial to field-grown crops to the best of my knowledge. For example, assimilation is facilitated by appropriate fluctuation of temperature, especially daily temperature difference between day and night. Photosynthesis and transfer of photosynthetic assimilates increase under higher temperature in daytime to some degree. On the other hand, dark respiration decreases under lower temperature at night to some extent, As a result, proper temperature fluctuation can expedite the rate of storage of assimilates. Also, some crops such as barley and wheat need suitable cold treatment (vernalization) to break winter growing habit or dormancy. I think that the same concept could be applied to some crops popularly grown in the greenhouse. Once we figure out the optimal temperature variation which is favorable to a specific crop, I expect that artificial temperature fluctuation could be helpful in terms of net-assimilation, florescence, and dormancy breaking.

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