Control of water supply and specific nutrient application in closed growing systems

Keywords:Tichelmann layout, constant drain flow, constant drain concentration, mass-flow, diffusion flow, sensor, Isfet, Chemfet, closed growing system, robust control, loopshaping, SimulinkÒ, MIMO controller, SISO controller, simplex routine, simplex matrix.Plants in modern greenhouses receive water and nutrients from a diluter of chemical solutes. Supply lines of a trickle irrigation system dispense the nutrient solution by means of thin capillary hoses, to each individual plant. Dependent on the type of growing system - either a NFT or a substrate system - the drain will run-off immediately or it will linger for some time in the substrate mat. In a closed system for water and nutrient supply, the drain water returns to the nutrient dispenser, where it is prepared for reuse by mixing it with clean water. The thesis starts with an overview of the state of the art of water supply and nutrient application systems.The purpose of the design study in this thesis is to enable completely closed growing systems for water and nutrients, to be applied in horticulture practise, and to improve the technological level of their control to such an extend that it is comparable to the level of computerised climate controllers in greenhouses. It is argued that as a basic requirement the system should have the ability to control the drain flow and the concentration of individual ions in the drain to any predefined set value. An analysis is given of the dynamics of movement of water and nutrients in substrates in relation to nutrient uptake, supply-flow and mass-flow. From a mass balance of nutrients, a control strategy for nutrient application in closed growing systems is suggested that is useful in the design of control algorithms. This strategy keeps the concentration of the individual ions in the drain constant by feedback of ion concentration and drain flow. In doing so, it compensates intrinsically for the plant's uptake of ions.The creation of a system with feedback control requires appropriate sensors and the ability to blend nutrient solution for values demanded by the controller. The ion specific feedback control of fertiliser application implies that ions need to be measured individually. The thesis describes a novel type of ion specific analyser, based on a set of Chemfet sensors. This instrument, as a result of this research, is the prototype of the first series of commercially available equipment for horticulture. Continuous measurement implies sensors with an electrical output, connected to an automatic data acquisition system with in-line calibration. In horticulture applications the lifetime expectancy of a sensor should at least be 6 to 9 months.In contrast to open loop control based on a prediction of uptake, feedback control automatically compensates for fluctuations in evapo-transpiration and nutrient uptake. Uptake by the plant is treated as a disturbance. Comparison of simulation results, with data from an implemented controller in a greenhouse, shows the success of the design.The so-called "Tichelmann" layout of supply lines is proposed to improve the dynamic properties of the supply system. The design study demonstrates and recommends robust controller design as a tool to achieve robust performance and robust stability as qualities of the controlled process to compensate for seasonal changes in the root mat or imperfect models. The modifications to the ideal design arising from the desire in practice for pulse wise water and nutrient injection, as well as aspects related to the blending are considered as well.</p

A Fresnel lenses based concentrated PV system in a greenhouse

The scope of this investigation is the development and testing of a new type of greenhouse with an integrated linear Fresnel lens, receiver module and an innovative system for tracking to exploit all direct radiation in a solar energy system. The basic idea of this horticultural application is to develop a greenhouse for pot plants (typical shadow plants) that do not like direct radiation. Removing all direct radiation will drastically reduce the need for cooling under summer conditions and the need for screens or lime coating of the glass to reflect or block a large part of the radiation. The removal of all direct radiation will block up to 81% of the solar energy, which will reduce the needed cooling capacity. The second measure is the integration of a solar energy system. When the (linear) Fresnel lenses are designed between double glass coverings and integrated in the greenhouse, the focused solar energy on the Thermal Photovoltaic (TPV) cell in the focus point delivers electric and thermal energy. The TPV module mounted in the focal point requires cooling due to the high heat load of the concentrated radiation (concentration factor of 50×). All parts are integrated in a greenhouse structure with a size of about 36 m2 and the electrical and thermal yield is determined for Dutch climate circumstances

A Prototype Sensor for Estimating Light Interception by Plants in a Greenhouse

Light interception is one of the most important factors for plant growth. The intercepted amount depends on the incoming radiation in the greenhouse and the percentage of interception by the crop and is directly related to the leaf area. Proper crop management requires the measurement of the most important growing factors. In case of application of crop growing models the simulation of the leaf area is one of the major uncertainties in the results of the models. Automatic calibration of the model based on radiation interception increases the accuracy of the model results. For the determination of the crop¿s light interception in a greenhouse, a radiation sensor was used which determines the ratio of the incoming radiation from the upper side and the reflection at a specific wavelength from the lower side. The ratio of reflected radiation versus intercepted radiation can be used to estimate light interception as well as leaf area. However, the measurement of this fraction can only be used after filtering out erroneous data due to technical errors, insufficient diffuseness, insufficient solar height, etc. This paper describes the boundary conditions to be taken into account for proper measurement of reflected radiation. Time series measurements of incoming, reflected and global radiation are used, to filter the data acquired by the sensor. The sensor functioned well during tests on a cucumber crop in a commercial greenhouse

Computergestuurde circulatieregelingen : optimaal bewaarklimaat met minimaal energieverbruik

Bij het bewaren van bloembollen in kuubskisten gestapeld voor een systeemwand in een bewaarcel wordt voor de ventilatie met buitenlucht, en voor de circulatie met cellucht veel energie verbruikt. Door het ventilatiedebiet met de klimaatcomputer te sturen op basis van ethyleenmeting wordt bij het bewaren van tulpenbollen veel energie (gas) bespaard. Het energieverbruik bij de circulatie is uitsluitend voor de stroomvoorziening van de ventilatoren. Het circulatiedebiet wordt niet door de klimaatcomputer gestuurd, maar wordt handmatig via een frequentieregelaar ingesteld. Door ook de circulatie via de frequentieregelaar met de klimaatcomputer te sturen kan door het 3de>machtsverband tussen toerental en energieverbruik veel energie bespaard worden. In tegenstelling tot ethyleengestuurde ventilatie is computergestuurde circulatie niet alleen toepasbaar bij tulp, maar bij alle bolgewassen. Op sectorniveau kan hiermee dus heel veel energie bespaard worden. Doelstelling van dit project is het ontwikkelen van op sensoren gebaseerde computergestuurde regelingen voor de circulatie, waardoor bij een optimaal bewaarklimaat voor alle bolgewassen zeer fors op het elektraverbruik voor circulatie bespaard kan worden

Monitoring of climate variables in semi-closed greenhouses

Growers and Dutch government have concluded a covenant in which they express the ambition to reduce the carbon footprint of greenhouse production in order to improve the energy neutrality of newly built greenhouses. Conditioned cultivation in (semi-)closed greenhouses is seen as one of the instruments to reach this goal. It is appointed in the covenant to arrive in 2011 at 700 ha and in 2020 at 2,500 ha semi-closed greenhouses. This paper describes the instruments used to monitor the results of conditioned cultivation in eight semi-closed greenhouses in practice. It addresses the monitoring process, the installations involved and highlights some of the measured data

Watergy: Infrastructure for Process Control in a Closed Greenhouse in Semi-arid Regions

Abstract A novel solar humid-air-collector system for combined water treatment, space-cooling and ¿heating has been designed in an EU framework-5 financed project called Watergy. The design consists of a construction of two prototypes for applications in architecture and greenhouse horticulture: a South European variant (for arid climate and emphasis on agricultural use) and a Central-/North European variant (for temperate climate and emphasis on integral building design). The core is the development of a collector system, following the principle of a closed, two phase thermo siphon. It achieves combined evaporation and ¿condensation, efficient heat transfer to a central heat exchanger as well as increased heat conduction from (humid) air to water. Main improvements are cost reduction in space heating and -cooling of buildings and greenhouses. Furthermore, viability increases by additional integration of greenhouse irrigation water recycling, desalination and building grey-water recycling. Sensors and actuators, connected to low-level controllers, activate a model-based control system to manage these processes. The paper describes the different appendages, sensor systems, network connections, databases, alarming systems, user interfaces and remote management from the Netherlands to Spain through the Internet