Characterization of air velocities near greenhouse internal mobile screens using 3D sonic anemometry

In Dutch greenhouses, different screen types are used for different purposes (shading, energy saving, black-out, light emission, etc.). In order to quantify the energy and mass transfers through screens, characterization of air permeability through the screens is required. In the case of energy-saving screens, it is an essential parameter to estimate the energy saving of each screen. Air permeability can be measured under defined conditions in a laboratory. In order to select the appropriate equipment for air velocity measurements, the air velocity vector near screens in a practical situation in a greenhouse needs to be identified by measurements. Sonic anemometry techniques have been used extensively in different types of greenhouses: a) to study natural ventilation, with and without insect screens, and in different positions; b) to study airflow patterns in greenhouses with mechanical ventilation/pad and fan systems; c) to study airflow patterns induced by different types of heating systems, and d) for the estimation of crop evapotranspiration (i.e., eddy covariance). However, to the best of our knowledge, no research has been carried out to study the airflow near different types of screens in a greenhouse. Many Dutch growers are increasingly using various types of fans with different positions in the greenhouse for dehumidification and improved climate uniformity purposes. The effect of such fans on the air velocity near screens, and therefore the effect on energy and mass transfer, is unknown. For this purpose, air velocities near different types of screens in commercial greenhouses were measured using ultrasonic 3D anemometers. The results show that, in the absence of fans, air velocity near the screens is affected by vent opening. With vents closed, air velocities are hardly ever above 0.2 m s-1. Therefore, a simple air-suction device can be used to characterize permeability of screens at a very low Reynolds range.</p

An algorithm for optimal fertilization with pure carbon dioxide in greenhouses

Pure (bottled or piped) carbon dioxide is commonly supplied to increase productivity of greenhouse crops. As ventilation is necessary for controlling temperature, particularly under sunshine (when a high CO2 concentration would be most desired) there is a need for optimal management of supply, in order to ensure the maximum net return from cost of carbon dioxide supplied and increase in harvest. The optimal concentration depends on many factors: the expected increase of yield thanks to carbon dioxide supply under given climate conditions; the actual ventilation rate; the value of yield and the cost of carbon dioxide. We combined a calculation of the “value” of carbon dioxide supply with an algorithm to calculate the ventilation rate, into a calculation on-line of the optimal supply rate. The algorithm was implemented and tested into a commercial climate control computer

Performance of a day/night water heat storage system for heating and cooling of semi-closed greenhouses in mild winter climate

A novel system for heating/cooling greenhouses based on air/water heat exchangers connected to a thermally stratified water storage tank was tested in a small greenhouse compartment at the Experimental Station of the Cajamar Foundation in Almería, Spain. The system maintained a closed greenhouse (no natural ventilation) throughout the winter and spring during which a truss tomato crop was grown. Atmospheric CO2 concentration could be maintained during the daytime allowing for greater net photosynthesis in relation to a reference greenhouse in which traditional natural ventilation was used to control temperature and humidity. Three fine wire heat exchangers (Fiwihex®) were installed 1 m above the crop when at full development. The heat exchangers allowed for a very efficient transfer of the sensible and latent heat accumulated in the compartment. During the winter, the daytime temperatures were maintained below the ventilation set point (30°C). During the night, the system was able to maintain temperatures above the heating set point (12°C), with stored warm water temperatures between 15 and 17°C after clear days. After cloudy days, with water temperatures between 11 and 13°C, the system could always keep a temperature gradient with the exterior of 4-6°C, enough to maintain greenhouse air temperatures above 8°C the entire night. When seasonal night air temperatures exceeded the heating set point, the hot water at the top of the tank was cooled to the wet bulb temperature by means of an open cooling tower. The cooled water was used for cooling the greenhouse, which allowed for closing the greenhouse for a longer period. The water condensate during the cooling mode, allowed for a high water saving and maintained the relative humidity very constant during the day (around 80%). During the night, humidity was kept at 90% without ever reaching saturation

Impact of previous tobacco use with or without cannabis on first psychotic experiences in patients with first-episode psychosis

Objective: There is high prevalence of cigarette smoking in individuals with first-episode psychosis (FEP) prior to psychosis onset. The purpose of the study was to determine the impact of previous tobacco use with or without cannabis on first psychotic experiences in FEP and the impact of this use on age of onset of symptoms, including prodromes. Methods: Retrospective analyses from the naturalistic, longitudinal, multicentre, “Phenotype-Genotype and Environmental Interaction. Application of a Predictive Model in First Psychotic Episodes (PEPs)” Study. The authors analysed sociodemographic/clinical data of 284 FEP patients and 231 matched healthy controls, and evaluated first psychotic experiences of patients using the Symptom Onset in Schizophrenia Inventory. Results: FEP patients had significantly higher prevalence of tobacco, cannabis, and cocaine use than controls. The FEP group with tobacco use only prior to onset (N = 56) had more sleep disturbances (42.9% vs 18.8%, P = 0.003) and lower prevalence of negative symptoms, specifically social withdrawal (33.9% vs 58%, P = 0.007) than FEP with no substance use (N = 70), as well as lower prevalence of ideas of reference (80.4% vs 92.4%, P = 0.015), perceptual abnormalities (46.4% vs 67.4%, P = 0.006), hallucinations (55.4% vs 71.5%, P = 0.029), and disorganised thinking (41.1% vs 61.1%, P = 0.010) than FEP group with previous tobacco and cannabis use (N = 144). FEP patients with cannabis and tobacco use had lower age at first prodromal or psychotic symptom (mean = 23.73 years [SD = 5.09]) versus those with tobacco use only (mean = 26.21 [SD = 4.80]) (P = 0.011). Conclusions: The use of tobacco alone was not related to earlier age of onset of a first psychotic experience, but the clinical profile of FEP patients is different depending on previous tobacco use with or without cannabis. © 2021 The Author

Effect of greenhouse films on climate, energy, light distribution and crop performance – measuring film properties and modelling results

Greenhouse growers would like to choose an optimum plastic film for their greenhouse production. In parallel, greenhouse supply industry is looking for quantitative information on their product performance. All are looking for answers on the following questions: which film do I need to create an optimum greenhouse climate? Which one do I need to choose for low energy consumption, or for low summer temperatures? What will be my crop yield under the different films? Is an expensive but long-lasting film economic feasible (for my crop, my climate, etc.)? Models can help to find answers to these and other questions and are faster and often cheaper than agronomic trials.</p

Feedback from growers and experts about Euphoros tools - A combined report from experts meetings in three testing sites: Almería (Spain), Morahalom (Hungary) and Bleiswijk (The Netherlands).

The overall objective of the four years project EUP HOROS is the development of a sustainable greenhouse system that minimizes the use of inputs and emissions to the environment, yet with high productivity and resource use efficiency. Working Package 6 of this project deals with implementation of the in the other WP’s developed tools in combinations relevant to three local markets. To ensure that the combinations of elements to be tested in the greenhouse conditions at each site are tuned with the expectations of the local growers, at each site a feedback session has been conducted with a group of relevant stakeholders, potential users of the results from the WP's in practice. Each site has conducted this feedback session in a way that fits the knowledge exchange structures of the area and the crop where the implementation trials are going to be performed. The broadest meeting has been held in Almería, where the meeting was combined with a big seminar. In all three meetings held in the three locations the following goals have been achieved: Growers are aware of the existence of the project; Growers are involved in the choice of the tools developed within Euphoros; Growers have given preliminary feedback to the developers. Not all developments are equally appealing, either because they do not see application in their greenhouses, or because they can not get a good impression on how this developments work or how they can contribute to a beter greenhouse management and input reduction. The preliminary discussions between the test locations together with the meetings have contributed to a plan of tool combinations to implement in trials

An algorithm for optimal fertilization with pure carbon dioxide in greenhouses

Pure (bottled or piped) carbon dioxide is commonly supplied to increase productivity of greenhouse crops. As ventilation is necessary for controlling temperature, particularly under sunshine (when a high CO2 concentration would be most desired) there is a need for optimal management of supply, in order to ensure the maximum net return from cost of carbon dioxide supplied and increase in harvest. The optimal concentration depends on many factors: the expected increase of yield thanks to carbon dioxide supply under given climate conditions; the actual ventilation rate; the value of yield and the cost of carbon dioxide. We combined a calculation of the “value” of carbon dioxide supply with an algorithm to calculate the ventilation rate, into a calculation on-line of the optimal supply rate. The algorithm was implemented and tested into a commercial climate control computer