H.J.J. Janssen

Identification and simulated control of greenhouse closed water supply systems

Direct feedback of drain flow is presented as a basic principle to control the supply of nutrient solutions to plants in a greenhouse. In contrast to open loop control based on the prediction of water uptake, control by means of sensor feedback of the measured drain water flow automatically compensates for fluctuations in evapo-transpiration. A pulse modulated pump keeps the drain flow at a constant set value by a feedback control action on the repetition rate and a feed forward control action on the pulse width. The water uptake by the plant is treated as a disturbance. The simulation is performed on dynamic models for three different growing systems, that are identified on the basis of noise response tests on the real supply system. Experimental results are presented, which show how the controller compensates changes in water uptake by the plant due to variations in global radiation.

Control of Water Supply in Closed Growing Systems in a Greenhouse

Abstract In the tests presented, direct feedback of drain flow, rather than a predictive uptake model, controls the supply of nutrient solution to plants in a greenhouse. Feedback control of the measured drain water flow keeps it on a constant set value. Water uptake by the plant is considered as a disturbance of the drain flow control loop. A dynamic model is constructed from noise response data of the supply process for three different growing systems. Results are presented, that show the compensation as a result of feedback control of changes in water uptake by the plant, due to variations in global radiation.

Static linear Fresnel lenses as LCPV system in a greenhouse

A low concentrating PV system with water cooling (LCPVT system) will result in electrical and thermal energy output from the solar energy excess entering a building or greenhouse. All the direct radiation could be converted, which corresponds to 75% of the incoming solar energy. This will significantly reduce the demand of cooling of the building. For an optimal performance it is beneficial to construct asymmetric roof elements with a steep inclination at the north side (the exact angle of course depends on the latitude of the building site). The Fresnel lens structure is oriented in upwards direction. In the current design, two of them are placed between an AR‐coated double glass structure to prevent pollution and condensation on the lenses. Compared with a previous system, the number of lenses is reduced from 3 to 2 lenses, which reduces the costs of the system by limiting the number of receivers. By the upward facing of the lens structure, the focus quality is preserved over a much broader range of ang...

A computer network with SCADA and case tools for on-line process control in greenhouses.

Climate control computers in greenhouses are used to control heating and ventilation, supply water and dilute and dispense nutrients. They integrate models into optimally controlled systems. This paper describes how information technology, as in use in other sectors of industry, is applied to greenhouse control. The introduction of modern software and hardware concepts in horticulture adds power and extra oppurtunities to climate contol in greenhouses.

PV System Integrated in a Solar Greenhouse With NIR Selective Coating

The scope of this investigation is the development of a new type of greenhouse with an integrated filter for rejecting near infrared radiation (NIR) and a solar energy delivery system. Cooled greenhouses are an important issue to cope with the combination of high global radiation and high outdoor temperatures. As a first measure, the spectral selective cover material, which prevents the entrance of NIR radiation, is investigated. The special spectral selective properties of these materials have to block up to 50% of the solar energy outside the greenhouse, which will reduce the needed cooling capacity. The second measure is the integration of a solar energy system. When the NIR reflecting coating is designed as a parabolic or circular shaped reflector integrated in the greenhouse, the reflected solar energy of a PhotoVoltaic (PV) cell in the focus point delivers electric energy. With a ray tracing computer program the geometry of the reflector was optimally designed with respect to the maximum power level. The PV cells mounted in the focal point require cooling due to the high heat load of the concentrated radiation (concentration factor of 30). The properties of different materials, Ge, GaSb, CIS and Si cells were investigated to find the optimal cell for this application. All parts are integrated in a greenhouse structure with a size of about 100m.

Identification for Ion-based Fertigation Control in Soilless Greenhouse Cultivation

Progress in instrumentation and the need for quality control stimulate the rethinking of irrigation and fertilisation (fertigation) of crops in greenhouses. Feedback control using ion specific electrodes in the drain offers opportunities for automatic demand satisfaction. The fertigation system is characterised by pulse-wise water supply, which puts unconventional challenges to the measurement system. Limitations from practice require identification and control design procedures to be robust and simple. This paper introduces a reduced model for the system and describes the practical identification of the nutrient dynamics in a measurement gully on a time scale that is relevant to the crop.