S. Hemming

Wageningen University, Wageningen, Gelderland, Netherlands

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Publications (84)0 Total impact

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    ABSTRACT: Labour is the most dominant cost factor in Dutch cut-rose production. To improve crop production systems and labour management, a generic process modelling approach was developed enabling the impact of different scenarios on labour productivity to be assessed. The crop production system with crop handling processes is defined as a stochastic discrete event system. This paper demonstrates the model flexibility and transferability by adapting an existing model developed for a mobile rose production system to a model for a static growing system for cut roses. The paper describes the adaptation process. The adapted model was validated for the harvest process at a 3.6 ha production site in the Netherlands. Work scenarios were simulated to examine effects of skill, equipment, and harvest management. The model reproduces the harvest process accurately. A seven workday validation for an average skilled harvester showed a relative root mean squared error (RRMSE) under 5% for both labour time and harvest rate. A validation over 96 days for various harvesters showed a higher RRMSE, 15.2% and 13.6% for labour time and harvest rate respectively, mainly caused by the absence of model parameters for individual harvesters. The model was successfully used in scenario studies and indicated that worker skill was an important cost factor, differences associated with harvest trolley type are small, and that an extra harvest cycle per day is only feasible when compensated by product price. Overall, the generic model concept performs well for a static growing system when extended with system specific properties and process elements.
    Biosystems Engineering. 01/2014; 120:34–46.
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    ABSTRACT: Combination of production of algae and tomato increases efficient use of available resources of greenhouse enterprises, such as controlled environment, water and nutrients, carbon dioxide, greenhouse space and infrastructure and knowledge. No information is available, however, about the potential productivity and related costs of a combined tomato and algae production in Dutch greenhouses. The objective was to determine the algae productivity in tubular photobioreactors (PBRs) and the economic feasibility of combined production of tomato and algae in Dutch greenhouses. A model was developed to predict greenhouse climate from outside climate, to predict tomato and algae biomass production and to analyse scenarios of different locations and dimensions of tubular PBR in the greenhouse with regard to algae productivity and cost price of algae production. The results show that algal productivity is low if PBRs are installed under a tomato crop due to limited light levels. Areal algal productivity was calculated to be 5–6.5 kg DM m−2 if PBRs are installed in a separate greenhouse compartment next to tomato. In this case the minimum cost prices of algae production was calculated to be €11 kg−1 DM algae, which give perspectives for the future. The proposed model is important because it gives insight into the feasibility of algae and tomato production in Dutch greenhouses. This novel model approach and the scenario results provide better knowledge about the potential productivity and related costs and returns of algae production in greenhouses.
    Biosystems Engineering. 01/2014; 122:149–162.
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    ABSTRACT: Greenhouse crop system design for maximum efficiency and quality of labour is an optimisation problem that benefits from model-based design evaluation. This study focussed on the harvest process of roses in a static system as a step in this direction. The objective was to identify parameters with strong influence on labour performance as well as the effect of uncertainty in input parameters on key performance indicators. Differential sensitivity was analysed and results were tested for model linearity and superposability and verified using the robust Monte Carlo analysis method since in the literature, performance and applicability of differential sensitivity analysis has been questioned for models with internal stochastic behaviour. Greenhouse section length and width, single rose cut time, and yield influence labour performance most, but greenhouse section dimensions and yield also affect the number of harvested stems directly. Throughput, i.e. harvested stems per second, being the preferred metric for labour performance, is most affected by single rose cut time, yield, number of harvest cycles per day, greenhouse length and operator transport velocity. The model is insensitive for σ of lognormal distributed stochastic variables describing the duration of low frequent operations in the harvest process, like loading and unloading rose nets. In uncertainty analysis, the coefficient of variation for the most important outputs, labour time and throughput, is around 5%. Total sensitivity as determined using differential sensitivity analysis and Monte Carlo analysis essentially agreed. The combination of both methods gives full insight into both individual and total sensitivity of key performance indicators.
    Biosystems Engineering. 01/2013; 116(4):457–469.
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    ABSTRACT: Highlights ► Discrete event simulation model on crop handling in mobile rose cultivation system. ► Model for assessment of designs of automated horticultural production systems. ► Validation accuracy of about 95% on labour time estimation in cut rose harvest. ► Model determines best system settings at given yield for operator and gutter speed.
    Biosystems Engineering. 06/2012; 112(2):108–120.
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    ABSTRACT: In Northern regions of Europe glass is mainly used as greenhouse covering material whereas in Southern regions plastic films are commonly used. The develop-ment of covering material optical properties focuses on high light transmission, reduction of heating energy losses (higher latitudes) and reduction of cooling energy load by radiation (lower latitudes). Solar radiation can be divided into photosynthetic active radiation PAR and near infrared radiation NIR. Whereas the PAR is needed for crop growth and development, the energy fraction of the NIR heats the greenhouse and crop and contributes to transpiration, which is not necessarily always desirable during periods with high radiation. Materials or additives for greenhouse covers that reflect or absorb a fraction of the NIR radiation have become available on the market. Excluding NIR from the greenhouse will reduce the greenhouse air temperature. However, there are several side-effects of the reduction of NIR, which are important to consider, such as a higher energy use in winter and a smaller impact on reduction of heat load as expected because of the high NIR reflection of the crop itself. In this study model calculations of the effect on greenhouse climate of different NIR-absorbing prototype plastic films for the climatic conditions of Southern Spain are presented. The effect on greenhouse air temperature and humidity, and on crop transpiration are analyzed. The most appropriate application of a NIR-selective greenhouse cover for that climate is presented.
    01/2012;
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    ABSTRACT: For a better understanding of growth and development of tomato plants in three dimensional space, tomato plants were monitored using a computer vision system. It is commonly known that leaves of tomato plants do not have a fixed position and orientation during the day; they move in response to changing environmental conditions such as the position of the sun. For better understanding, it was desired to quantify this motion. Using a stereovision concept, two cameras were mounted in an experimental greenhouse a short distance apart from each other to enable depth measurement. Markers were placed on strategic spots on the tomato plant branches and leaves in the field of view of both cameras. Images were taken every ten minutes during daytime on several consecutive days. In the greenhouse, a virtual 3D coordinate system was defined and camera and tomato plant position and orientation were defined in this coordinate system. Image processing techniques were used to trace the markers and the 3D position coordinate of each marker in each image was calculated to obtain the course of a marker during several days. Stems, branches, and leaf nerves were considered as kinematic mechanical, robot like, links and corresponding theory was used to model and calculate the motion of stems and leaves of a tomato plant. Analysis of the images showed both small (1-2 degrees) and large rotations (10 degrees or more) of the branches and the different leaves on a branch during the course of a day. Leaves on one side of a branch showed a parallel motion in the same direction; the leaves on the opposite side of the branch showed a mirrored motion. However, deviating patterns occurred too. The developed method proved to be able to precisely quantify the motion of stems, branches and leaves of tomato plants during several days.
    Biomass & Bioenergy - BIOMASS BIOENERG. 01/2012;
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    ABSTRACT: An optimisation algorithm, as an essential part of a model-based method to design greenhouses for a broad range of climatic and economic conditions, was described. This algorithm – a modified controlled random search using parallel computing – maximised the annual Net Financial Return (NFR) for a tomato grower by selecting the best alternative to fulfil eight design elements: type of greenhouse structure, material of the cover, outdoor shade screen, whitewash properties, thermal screen, heating system, cooling system and CO2 enrichment system. As an example, the algorithm was applied to two locations with different climatic and economic conditions, Almeria and The Netherlands. Due to the warm climate with high radiation levels in Almeria, a greenhouse with a relatively large specific ventilation area (20% compared to 14% for Dutch conditions), seasonal whitewash and a low-capacity direct air heater (50 W m−2 compared to 200 W m−2 for Dutch conditions) was selected. In contrast, for the relatively cold climate with low radiation levels of the Netherlands, a 100% aluminium thermal screen and no whitewash would give the best result. The design method produced realistic greenhouses and related annual NFR, indicating that the method performs well. An analysis of the close-to-best greenhouses showed that, for both locations, a structure with high light transmissivity considerably enhanced the greenhouse performance whereas an outdoor shade screen, geothermal heating and mechanical cooling would be not economical. These results demonstrate the feasibility of a model-based design approach that produces suitable greenhouse designs for given climatic and economic conditions. --------------------------------------------------------------------------------
    Biosystems Engineering - BIOSYST ENG. 01/2012; 111(4):350-368.
  • S. Hemming, F. L. K. Kempkes, J. Janse
    01/2011;
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    ABSTRACT: Referaat In het jaarplan Kas als Energiebron wordt aangegeven in 2011 een strategische verkenning uit te voeren naar de mogelijkheden van benutting van warmte uit zonne-energie voor de glastuinbouw in 2020. Naast de ambitie om in 2020 in nieuw te bouwen kassen klimaatneutraal te telen bestaat de ambitie om een aandeel van 20% duurzame energie in te zetten in 2020. Naast aardwarmte en bio-energie is een flinke bijdrage vanuit zonne-energie nodig om deze ambitie te verwezenlijken. Er is dus behoefte aan een verzameling van nieuwe ideeën en een overzicht van de potenties en nieuwe (deel) voorzieningen die nodig zijn om deze bijdrage uit zonne-energie te kunnen verwezenlijken. De technische en economische mogelijkheden voor het benutten van zonne-energie in de glastuinbouw worden in dit rapport beschreven. Tevens worden de poteniele energetische bijdrages voor de glastuinbouwsector voor het benutten van zonnewarmte of conversie naar elektriciteit geschetst. Een aantal concrete casussen op bedrijfsniveau worden berekend. Deze studie is gefinancierd door het ministerie van Economische Zaken, Landbouw en Innovaties en het Productschap Tuinbouw. Abstract In the yearly program of “Kas als Energiebron” 2011 it is stated to carry out a strategic research on the possibilities of using solar energy for greenhouse production in 2020. The ambitions are to build all new greenhouses in 2020 in a climate neutral way and to use 20% of sustainable energy. Next to geothermal heat and biofuels a large contribution from solar energy is necessary in order to fulfil these ambitions. Therefore new ideas to use solar energy in greenhouse production have to be collected. The energetic and economic potentials of the use of new technologies in greenhouses have to be estimated. The technical and economical possibilities for using solar energy in greenhouse horticulture are described in this report. Next to that the potential energetic contributions of solar heat or solar electricity in Dutch greenhouse horticulture are described. A number of specific cases of using solar energy on company level are calculated. This study is financed by the Ministry of Economic Affairs, Agriculture and Innovations and the Dutch Productboard of Horticulture.
    Applied Spatial Analysis and Policy 01/2011;
  • 01/2010;
  • 01/2010;
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    Ecological Modelling - ECOL MODEL. 01/2010;
  • Staalduinen, S. Hemming, T.A. Dueck
    Onder Glas 7 (2010) 5. 01/2010;
  • New Ag International 2009 (2009) 09. 01/2009;
  • 01/2009;
  • FlowerTECH 12 (2009) 3. 01/2009;
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    ABSTRACT: Only about half of the energy that enters a greenhouse as sun radiation is in the wavelength range that is useful for photosynthesis (PAR, Photosynthetically Active Radiation). Nearly all the remaining energy fraction is in the Near InfraRed range (NIR) and only warms the greenhouse and crop and does contribute to transpiration, none of which is necessarily always desirable. Materials or additives for greenhouse covers that reflect a fraction of the NIR radiation have recently become commercially available. Besides lowering greenhouse temperature, a NIR-excluding cover has quite a few side-effects that may become quite relevant in the passive or semi-passive greenhouses typical of mild climates. For instance, the ratio of assimilation to transpiration (the water use efficiency) should increase. On the other hand, by lowering the ventilation requirement, such a cover may hinder in-flow of carbon dioxide, thereby limiting the photosynthesis rate. In addition, there are obviously conditions where the warming up caused by NIR may be desirable rather than a nuisance. NIR-reflecting materials are becoming available in forms that are suitable for various types of applications, such as permanent, seasonal or mobile. By means of a simulation study, we discuss in this paper the best form of application in relation to the external climate and climate management options available
    Acta Horticulturae 807 (2009). 01/2009;
  • New Ag International 2009 (2009) 09. 01/2009;
  • Gärtnerbörse 2009 (2009) 6. 01/2009;
  • J.A. Dieleman, S. Hemming
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    ABSTRACT: In greenhouse horticulture, energy costs form an increasingly larger part of the total production costs. To increase both the profitability and the sustainability of the sector, energy use per kg produce but also per ha has to be reduced. Energy in the greenhouse is primarily used for temperature control, reduction of air humidity, increase of light intensity and to a lesser extent for CO2 supply. The use of fossil energy can be reduced by limiting the energy demand of the system and decreasing energy losses, by intelligent control of (micro)climate, by increasing the energy efficiency of the crop and by replacing fossil energy sources by sustainable ones. In this paper, recent developments concerning reduction of energy consumption in greenhouse production systems in different climatic areas will be presented, as well as the consequences for crop management. Energy requirement of the greenhouse can be lowered by using greenhouse covers with higher insulating values and the use of energy screens. A prerequisite is that these materials should not involve considerable light loss, since this would result in a loss of production. Efficient screening strategies can save energy saving while maintaining crop production level. Recently, new covering materials have been developed that reduce energy loss in winter, heat load in summer and increase light penetration in the crop, thereby increasing crop production, while saving energy. In energy efficient greenhouse concepts, durable energy sources such as wind energy, solar energy or geothermal energy should be included. In (semi-)closed greenhouses, the excess of solar energy in summer is collected and stored in aquifers to be reused in winter to heat the greenhouse. In this concept, ventilation windows are closed, with specific benefits to the crop: high CO2 levels can be maintained, and temperature and humidity can be controlled to the needs of the crop. This poses new research questions, since the optimal climate for crops in various developmental stages is not known yet. Development of new greenhouse concepts is ongoing. Current examples are greenhouse systems which convert natural energy sources such as solar energy into high-value energy such as electricity. Given a certain technical infrastructure of the greenhouse, energy consumption can be further reduced by an energy efficient climate control. Essential elements are to allow fluctuating temperatures within certain bandwidths, allow higher humidities and create fluent transitions in set points. Consequences for plant growth are related to rate of development, photosynthesis, stomatal opening, assimilate distribution, transpiration and the occurrence of diseases or disorders. Next to physiological research, knowledge has to be gained on crop sensors, interpretation of sensor information and developing new microclimate control algorithms.
    01/2009;