The combined effects of cover design parameters on tomato production of a passive greenhouse

The objective of this paper is to demonstrate the need of a multiple design parameter approach to greenhouse design. To illustrate this need, we determined the combined effects of cover design parameters on tomato production of a passive greenhouse, that is a greenhouse with only natural ventilation and seasonal whitewash for climate management. The design parameters investigated in this research were the transmission of the cover for photosynthetically active radiation (PAR) and near infrared (NIR) radiation, the emission coefficient for long wave radiation of the cover and the ventilation area. First, we developed a model to link the tomato yield to the cover design parameters, through their effects on greenhouse climate. The model was validated by comparing the simulated greenhouse climate and yield with data obtained from field studies conducted in Almería, Spain. Thereafter, the sensitivity of the yield to the cover design parameters was analysed for three greenhouse configurations. This analysis gave insight into the effects of the cover design parameters on crop yield. Results showed that the sensitivity of the yield to a single design parameter depended on the absolute values of the other ones. For example, the yield in a greenhouse with a high ventilation capacity was the most sensitive to PAR transmission (0.45 % more yield for each 1% increase of PAR transmission) while in a greenhouse with a low ventilation capacity the crop yield is most sensitive to the ventilation area (0.63 %) and NIR transmission (-0.56 %). In addition, the yield sensitivity to the design parameters also varied over time because of changing outdoor climate conditions. In conclusion, a significant improvement of greenhouse design can be attained only through a multifactorial approach that accounts for the joint effect of design parameters, local climate and desired production period upon crop yield

Optimal greenhouse design should take into account optimal climate management

The objective of this paper is to demonstrate that optimal greenhouse design must account for (and be combined to) optimal climate management. We prove this by showing that different strategies and set-points to control the greenhouse ventilators result in different ¿optimal sets¿ of design parameters. We determined these optimal sets for a passive greenhouse in Almería, Spain where tomatoes were grown. The greenhouse design parameters investigated in this research were: 1) the transmission of the cover for photosynthetically active radiation (PAR), 2) the transmission of near infrared (NIR) radiation and 3) the emission coefficient for longwave radiation of the cover. Six optimal sets of design parameters were determined by maximising the marginal revenues (crop yield minus costs of design parameters), under given climate conditions, and for different ventilation control strategies. Each ventilation control strategy had different set-points for the air temperature and carbon dioxide concen¬tration to control the greenhouse ventilators. To solve this optimization problem we used a dynamic crop-greenhouse model and an optimization algorithm. The model described the combined influence of the relevant design parameters, outdoor climate and ventilation control upon economic crop yield, through their effect on indoor climate. The yearly costs of the design parameters were empirically derived from prices, physical properties and lifespan of a number of greenhouse cover materials. Results showed that indeed for different strategies and set-points to control the green¬house ventilators different ¿optimal sets¿ of design parameters and marginal revenues were obtained. For example, the difference between the highest optimal NIR trans¬mission 1.00 and the lowest optimal NIR transmission 0.40 was 60%, while the highest marginal revenues 16.94 ¿m-2 differed 18,7% with the lowest marginal revenues of 13.77 ¿ m-2. Additionally, it was found that the cover design parameters were time dependent. In conclusion, only a combined optimal control and design approach that takes into account the best climate control strategy and the time dependency of the design parameters will ensure optimal design parameters and maximum marginal revenues

Impact van een schermkier boven het middenpad bij een Ventilationjet systeem

Between growers there is discussion if a (controllable) gap above the central path of the greenhouse is needed toextract the surplus of heat and vapour in a greenhouse equipped with artificial lights and Ventilation Jets. Basedon this discussion, this research was started at a tomato greenhouse with artificial lights to analyse the impactof this gap. To determine the effectiveness of this gap, the air flow through the Ventilation Jet was measuredwith an air flow measurement device, the air flow through the gap at the central path was determined usingair velocity sensors and horizontal temperature differences were measured with wireless temperature sensors.Based on this study we can conclude that: (1) at this grower the measured flow of the Ventilationjet at 2 closedscreens (6.7 m3/m2/hour) was much lower than expected (12 m3/m2/hour); (2) the impact of the gap at thecentral path was small (a maximum of 2.8% of the incoming air through the Ventilation Jets left the greenhousethrough this gap), the gap at this grower is this not needed since almost all air leaves the greenhouse throughthe screens and; (3) in case that the artificial lights were switched on and both screens were closed, largehorizontal temperature differences of maximum 2.7°C occurred

Verwarming van de glastuinbouw in een post-fossiele energie infrastructuur

In the near future the greenhouse horticultural sector wants to produce free of fossil energy. To be able to worktowards this purpose, it is important that the possible roads are mapped out on time. In this report, these roadsare presented in a qualitative sense. In fact, there are 2 types of primary energy sources, namely green electricityand residual heat/geothermal energy, each requiring other technical solutions depending on the type of cultivation(divided in this report into cold extensive crops, not, -moderate and -heavily artificial lighted crops).If greenhouses are heated by electricity, then the heat pump in combination with heat-cold storage, is thebest solution both energetically and economically wise. When using residual heat or geothermal energy, theheat pump can play a role, but less prominent than in an all-electric energy infrastructure. In all cases a gooddehumidification system is important. Energy systems in a fossil-free infrastructure are characterized by highfixed costs and low variable costs. These high fixed costs can be reduced by lowering the capacities using betterisolation and low temperature heating systems.This report has set the spot on the horizon for a CO2 neutral horticulture. How we get there depends on thepreconditions that will change on the way. This calls for energetic and economic indicators for different crops andoptions for the primary energy source that take into account those changing precondition

Energiebesparing door een spouw in het verduisteringsscherm bij Chrysant

The insulation value of a Chrysanthemum greenhouse has been increased by creating a cavity in the blackout screen and by using a transparent energy screen. The dry U value of the greenhouse decreased from 3.00 W/ m²/K for a conventional blackout screen to 1.67 W/m²/K (44% reduction) for a blackout screen with cavity and a transparent energy screen. The transparent energy screen provides the largest U-value reduction of 33% and the cavity in the blackout screen provides a U-value reduction of 17%. However, the substantial U-value reduction does not lead to an equally large energy saving because the higher insulation value of the screens only has an influence on the energy consumed to fulfil the heat demand when the screens are closed. In the better insulated department, the energy consumption through the heating pipes was 27.1 m³ gas/m²/year and in the reference department 30.4 m³ gas/m²/year. The energy savings due to the higher insulation value in the dark period of the greenhouse is 1.9 m3 gas/m2, which amounts to a total energy saving of 6.3%. Due to the energy savings the relatively low additional investment of making the cavity in the blackout screen can be earned back in a Chrysanthemum greenhouse with artificial lights. The investment in the transparent energy screen and associated screen installation cannot be fully earned back by energy saving alone. The application of multiple screen layers had no demonstrable effect on the quality and production of Chrysanthemum

Tuinbouw zonder fossiele energie

Society asks for serious decrement of CO2 emissions, which means that greenhouse horticulture will haveto change from natural gas as the dominant energy source towards alternatives. This report describes suchalternatives and their effects on the energy costs. For this, a model built by AAB Netherlands was used. As inputit uses the time varying demands on heat, electricity and CO2 and the prices for energy-commodities, equipment,taxes and levies. Computations have been made for 6 typical greenhouse cultivations, representing the rangeof greenhouses in the Netherlands. It is concluded that energy costs will go up, but that the increment canbe limited by adopting new ways of heating. Heat distribution systems for large clusters of greenhouses showpromising possibilities, but also low grade heat obtained from surface water bodies or from heat excesses of thegreenhouse itself may serve as a heat source. In almost all cases, heat pumps will be part of the system and thenow widely used combined heat and power will disappear when natural gas is no longer available. Because of themajor role of heat pumps, growers may prepare their greenhouses for the application of low temperature heatingsystems and make preparations for energy conserving measures. The project is funded by Kas Als Energiebron ,an innovation and action program supported by the Ministry of Agriculture, Nature and Food Quality and thegrowers association LTO-Glaskracht Nederland

Model-based design of protected cultivation system - first results and remaining challenges

Abstract: Protected cultivation systems are used throughout the world as a powerful instrument to produce crops. They protect the crops from unfavorable outdoor climate conditions and pests and offer the opportunity to modify the indoor climate to create an environment that is optimal for crop growth and production, both in terms of quality and quantity. A quick scan of protected cultivation systems presently in use reveals that quite a variety of protected cultivation systems can be found throughout the world. They range from fully passive “solar greenhouses” with thick energy storage walls as found in China to the high-tech “closed greenhouses” in Western Europe. This variety is due to local conditions, including the local climate, the availability of resources like water, energy, capital, labor and materials, local legislation and social aspects, to mention a few. This paper presents a methodology of a model based method for designing protected cultivation systems. First results will be reported as well as directions for future research