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A method to quantify the energy-saving performance of greenhouse screen materials
Hemming, S. ; Baeza Romero, E.J. ; Breugel, A.J. van; Mohammadkhani, V. - \ 2018
Acta Horticulturae 1227 (2018). - ISSN 0567-7572 - p. 221 - 229.
Air permeability - Dynamic greenhouse model - Emission - Energy saving - Greenhouse screens - Thermal infrared transmission - Water vapour permeability
Screens used in practice are made from various material compositions (woven fabrics, knitted fabrics, foils, open or closed structures, transparent, diffuse, aluminized, various colours) and for various purposes (energy saving, reduction in light sum, or diffuse light obscuration). An important goal of the use of screens in Dutch greenhouses is to save energy. Unfortunately, to date, there is no objective method to determine the energy-saving performance of a material under standardized conditions. Energy-saving rates are estimated by manufacturers using different methods. Growers have no way of comparing material performances independently in order to make a proper investment decision. In the current research, the goal was to develop a method to quantify the energy-saving performance of greenhouse screen materials under standardized conditions. The method is based on the scientific literature and expertise of different screen producers and growers. The research focused on the three main aspects that affect energy saving of a screen: 1) thermal radiation losses, determined by the emissivity and reflectivity for thermal infrared radiation; 2) air permeability, which determines heat convection losses, characterized at a wide range of air velocities to account for velocities by buoyancy through materials as well as for velocities by forced convection caused by internal fans; and 3) water vapour permeability, which determines latent heat losses, determined under temperature, humidity and air velocity conditions normally encountered in commercial greenhouses. For all aspects, different measurement methods were compared to choose the best method based on reproducibility, accuracy and practicability. Screen material properties were then fed into both steady-state and validated dynamic greenhouse climate models to calculate overall screen energy saving under well-defined conditions. In the current research, different screen materials from different producers were investigated. The paper describes the methodology developed and shows data on different screen materials.
An app to quantify radiative heat loss from greenhouse crops
Zwart, H.F. de; Baeza Romero, E.J. ; Breuge, A.J. van; Mohammadkhani, V. - \ 2018
Acta Horticulturae 1227 (2018). - ISSN 0567-7572 - p. 69 - 76.
Air permeability - Dynamic greenhouse model - Energy saving - Thermal infrared transmission - Thermal screens
Deploying a thermal screen in the night gives a significant reduction in radiative heat losses from the crop and heat losses of the greenhouse in general. The reduced radiative heat loss gives a smaller vertical temperature gradient in the crop. Deployment of a thermal screen results in increases in top-leaf temperatures of 1-2°C, which allows for a higher humidity set point without risk of wet leaves, even at higher humidity in the greenhouse. This increment in tolerance of humidity is the second contribution of thermal screens to energy saving. Both aspects of thermal screens have made increased screening one of the main pillars of “next-generation cultivation”, a term referring to growing strategies that reduce energy consumption while promoting crop production. In order to support knowledge on screens and to stimulate growers to apply the benefits of next-generation cultivation, an app was developed that quantifies the effect of screens on leaf temperature and transpiration. On top of that, the app computes the net radiation from the crop, a figure that has gained attention as more and more growers install net radiation sensors in their greenhouse. The effect of screens is, of course, dependent on the outside and inside climate conditions, the crop, the greenhouse covering material and the type of screens used. The app enables the user to select the screen and covering materials from a number of options and to select from a number of crops. Among the screens, a selection can be made from partly open shading screens to transparent energy screens and completely blocking blackout screens. Also, the effect of artificial light can be shown. The app solves the steady-state energy balance of the greenhouse to calculate the promptly presented output. With the output, a quick exploration of the effect of screens on radiative losses and crop vertical temperature profile can be made, to learn from this for practical use.
LED or HPS in ornamentals? A case study in roses and campanulas
Ouzounis, Theoharis ; Giday, Habtamu ; Kjaer, Katrine H. ; Ottosen, Carl-Otto - \ 2018
European Journal of Horticultural Science 83 (2018)3. - ISSN 1611-4434 - p. 166 - 172.
Energy saving - Greenhouses - Light sources - Ornamentals
The aim of the experiment was to evaluate the effect of novel top-installed high-output light-emitting diodes (LEDs) on ornamental plant production both in terms of productivity and energy use in comparison with conventional HPS lamps in two standard greenhouse compartments. The experiments were performed in late winter period using three varieties of potted miniature roses (Rosa hybrida) and two cultivars of Campanula grown in identical installed supplemental light levels (75–85 µmol m-2 s-1 of PPFD) with temperature set points 18°C at night, 24°C during the day, while 800 ppm of CO2 was supplied. Due to the winter being relatively cold, the set points were equal to the realized temperature as ventilation rarely occurred. The leaf temperature was maintained at the same level by adjusting the top pipe temperature. Two harvests were performed in February and in March to show the potential effect of winter-or early spring-grown plants. The results showed relatively small differences with respect to plant performance between the HPS and LED treatments, and most significant differences were found only in the 1st batch of roses harvested in February regarding plant height and stem fresh and dry weight, indicating that growth was favored under HPS lamps for three out of four cultivars. Both the 2nd batches for roses and campanulas harvested in March showed very limited or no differences between treatments. The energy saving on the electricity side was 60% in LEDs compared to HPS, but due to the increased heat use from top pipes the energy used for heating increased by around 50% over the whole experimental period.
Improving the energy efficiency of a pilot-scale UASB-digester for low temperature domestic wastewater treatment
Xu, Shengnan ; Zhang, Lei ; Huang, Shengle ; Zeeman, Grietje ; Rijnaarts, Huub ; Liu, Yang - \ 2018
Biochemical Engineering Journal 135 (2018). - ISSN 1369-703X - p. 71 - 78.
Anaerobic domestic wastewater treatment - Energy saving - Low temperature - Methanogenic activity - UASB-digester
A pilot-scale UASB-Settler-Digester (USD) system was utilized to treat raw municipal wastewater collected from a sewer system at 10 °C. During the reactor operation, UASB sludge was continuously transferred from the UASB to a settler; concentrated sludge in the settler was then transferred to a digester operated at 35 °C. The results showed that the settler with a hydraulic retention time (HRT) of 3 h increased UASB sludge chemical oxygen demand (COD) concentration from 14.5 ± 2.5 g/L to 29.9 ± 4.1 g/L. With an HRT of 6 h, the USD system achieved a mean COD removal of 49.2%; and 23.9% influent COD was converted to methane. The specific methanogenic activities at 35 °C of the UASB and the digester sludge were 0.26 and 0.24 g CH4 COD/(g VSS d), respectively, and the stability values were 0.21 and 0.16 g CH4 COD/g COD, respectively. The stability of the settled sludge was similar to that of the recirculated UASB sludge. Compared to a UASB-digester system, the system with an added settler achieved similar COD removal and methane production, but reduced sludge recirculation rate (from 16% to 8% of the influent flow rate), which led to a 50% heating energy saving in the digester of the UASB-digester.
Ongoing developments in greenhouse climate control
Montero, J.I. ; Munoz, P. ; Baeza, E. ; Stanghellini, C. - \ 2017
In: 5th International Symposium on Models for Plant Growth, Environment Control and Farming Management in Protected Cultivation, HortiModel 2016 International Society for Horticultural Science (Acta Horticulturae ) - ISBN 9789462611788 - p. 1 - 14.
Energy saving - Humidity control - Passive greenhouses - Thermal inertia - Thermal screens
Passive (unheated) greenhouses are typical of mild winter climate areas. Passive greenhouses seek environmental sustainability by reducing inputs of energy and materials. Besides, they have to be economically viable. This paper reviews recent studies on passive techniques and their effect on the night time greenhouse climate: The effect of covering materials properties on temperature and humidity, humidity issues in semi-closed greenhouses and the role of thermal inertia are examined. Research studies show that most passive techniques give moderate temperature rise (in the range of 1 to 4°C). Even though such effect may seem meager, relevant benefits are derived by extending the growing period, increasing yield and ensuring frost protection. In active high technology greenhouses of cold areas, one of the main focuses is energy saving, and for that purpose, a new generation of semi-closed greenhouses is under development. Main efforts for energy saving are the reduction of heat losses by making greenhouses tighter (with multiple covers), intensive use of screens to minimize radiative losses at the expense of maintaining higher ambient humidity values. Canopy condensation is prevented by means of different dehumidification systems, such as fans that drive cold/dry air from above the screens to the canopy area or systems based on the use of heat exchanges to drive external preheated dehumidified air to the canopy area with the help of perforated sleeves, among other systems which are preferred over rising the heating set point.
Innovations in greenhouse systems - Energy conservation by system design, sensors and decision support systems
Hemming, S. ; Balendonck, J. ; Dieleman, J.A. ; Gelder, A. De; Kempkes, F.L.K. ; Swinkels, G.L.A.M. ; Visser, P.H.B. De; Zwart, H.F. De - \ 2017
In: International Symposium on New Technologies and Management for Greenhouses - GreenSys2015 International Society for Horticultural Science (Acta Horticulturae ) - ISBN 9789462611665 - p. 1 - 15.
Climate model - Crop model - Energy saving - Greenhouse coverings - Greenhouse design - Ray-tracing - Sensors - Web-based models
The targets for energy saving in Dutch horticulture are high. Research follows the two lines: total energy reduction and sustainability. The principles for that are: maximum use of natural sunlight (free energy input to greenhouse, free light for crop growth and production); maximum insulation (prevent energy losses through greenhouse covering); efficient use of energy (e.g. next generation cultivation strategies, mechanical dehumidification, diffuse light, optimum CO2, low temperature heating, high humidity levels); replace fossil fuels by renewable energy sources (e.g. geothermal, biofuels, solar energy, wind). Research results are shown in the Innovation and Demo Centre for Energy in Bleiswijk (IDC Energy). The goal of this paper is to describe some of the newest results of the Dutch research programme on energy saving focussing on energy conservation by greenhouse system design and the use of sensors and decision support systems. Energy savings on heating of 50-70% have been realised for a tomato crop compared to average practice in a highly insulated greenhouse. Another greenhouse concept focusses on the maximum use of natural sunlight during low solar elevation. With 3D ray-tracing models the effect of greenhouse roof angle, orientation, shape and construction materials as well as the effect of different diffuse coverings with anti-reflective coatings and hydrophilic condensation properties on light transmission during winter months has been quantified. It is expected to gain 10-20% more natural light by the new greenhouse concept during winter months. Wireless sensors are used to measure temperature and humidity distribution at many spots inside a greenhouse. Innovative web-based decision support models have been introduced into practice to give insight in the climate distribution and to predict the risk for crop health. For that a new climate control strategy the "Roaming Climate Measuring Box" and a "Botrytis Alert" have been developed. The greenhouse climate is automatically controlled on basis of the most humid or coldest spot in the greenhouse. That way up to 10% of energy can be saved and the risk for botrytis can be minimised. Two new sensors measuring actual crop photosynthesis have been developed and are currently tested in practice. Sensors are based on (i) the CO2 balance of the greenhouse and (ii) measuring chlorophyll fluorescence of a crop by means of laser and camera technology. In the future, such information is envisaged to be directly used for greenhouse climate control or crop management.
The ventilationjet system as a step towards controlled ventilation and adapted properties of insulation screens in greenhouses
Weel, P.A. Van - \ 2017
In: International Symposium on New Technologies and Management for Greenhouses - GreenSys2015 International Society for Horticultural Science (Acta Horticulturae ) - ISBN 9789462611665 - p. 167 - 174.
Dehumidification - Energy saving - Transpiration control - Ventilationjet
Moisture control in a greenhouse based on the creation of screen gaps has many disadvantages. This study describes a new approach where screen gaps are avoided by installing a Ventilationjet system. A speed controlled fan creates an airflow through a small opening in the fully closed screens. A second fan under the screen mixes the cold, dry air with greenhouse air. This system is controlled based on the difference in absolute humidity of the air under and above the screen. This difference, multiplied by the volume of air that is exchanged equals the amount of transpiration produced by the plants. This system was tested in multiple crops including gerbera and roses. This resulted in a 16-23% lower gas consumption in a situation where the screen system was not changed. The reduction was a result of more controlled ventilation and the reduction of horizontal and vertical temperature differences within the greenhouse. Based on these positive results, the development of new screen systems that can be combined with the Ventilationjet system has started. A first test with a cucumber crop resulted in a 63% reduction of energy consumption compared to a standard greenhouse with a single energy screen.
Greenhouse concept with high insulating cover by combination of glass and film : Design and first experimental results
Kempkes, F.L.K. ; Janse, J. ; Hemming, S. - \ 2017
In: International Symposium on New Technologies and Management for Greenhouses - GreenSys2015 International Society for Horticultural Science (Acta Horticulturae ) - ISBN 9789462611665 - p. 469 - 476.
Covering material - Diffuse light - Energy saving - Tomato
Dutch greenhouse horticulture puts a lot of effort in reduction of energy demand. Using (multiple) thermal screens, mainly during night, is the most common way to reduce heat losses in practice. In winter, even during daytime, transparent screens are closed, which saves energy, but results in significant reduction of light at plant level. For additional saving a substantial increment of greenhouse insulation is needed. Double covering materials can reach very high insulation levels, resulting in energy savings of 50% compared to the use of single glass with screens. Drawback of insulating glass panels are high investment and problems with snow accumulation in Northern latitudes. A new greenhouse concept with a new type of covering material has recently been developed. The insulating cover consists of a combination of a high transparent glass panel in combination with a high transparent and durable plastic film (F-Clean). The insulation properties are flexible. By blowing warm air through the split, possible snow accumulation is expected to be avoided. The new greenhouse concept has a new roofing structure including a different type of ventilation for a Venlo greenhouse. In a feasibility study, different combinations of different types of glass with different types of F-Clean have been investigated at Wageningen UR LightLab. Different model calculations have been carried out to study the effects on greenhouse climate and energy consumption. The results of a feasibility study with the search for the best combination of glass and plastic film in terms of transmissivity and light diffusing properties as well as the calculated energy savings of the total greenhouse concept are presented. In summer 2014, this concept was built on a scale of 500 m2 at the research station of Wageningen UR Greenhouse Horticulture in Bleiswijk. The first results of a tomato experiment, using new crop growing strategies are presented.
Energy use for greenhouse heating in organic production in southern European countries
Montero, J.I. ; Baptista, F.J. ; Giuffrida, F. ; Munoz, P. ; Kempkes, F. ; Gilli, Celine ; Stepowska, Agnieszka ; Stanghellini, C. - \ 2017
In: 3rd International Symposium on Organic Greenhouse Horticulture International Society for Horticultural Science (Acta Horticulturae ) - ISBN 9789462611603 - p. 439 - 443.
Energy saving - Passive greenhouses - Thermal curtain
The vast majority of southern European greenhouses are unheated. Nevertheless, during the coldest months growth is retarded, since average minimum temperatures in the warmest European areas are between 7 and 9°C. Therefore heating is highly desirable in the winter, but in spite of the positive response of crops to heating its economic profitability is open to debate. Heating is accepted by most organic regulations in different countries; provided it is done efficiently and if the energy source is predominantly renewable energy, heating fits well with the concept of organic production, since it is aligned with the idea of achieving maximum potential of available resources. Little data is available on the energy use for heating in greenhouse horticulture in southern Europe. This study tries to cover this gap of knowledge since it presents the energy consumption for heating in three locations particularly devoted to greenhouse production: Almeria (southern Spain), Faro (southern Portugal) and Acate, Ragusa province (southern Italy). Daily heat requirements based on the temperature difference between the night set-point temperature and the minimum open air temperature were calculated by a simple model. Cumulative heat requirements were estimated by the summation of daily requirements. Calculations show that heat requirements grow exponentially with the set point temperature. As expected, calculations for Faro and Ragusa presented higher values since the open air night time temperature was lower than in Almeria. Heat requirement can be reduced with the help of energy saving techniques such as double walls and thermal curtains. Our study presents the expected energy savings for the three locations under consideration in greenhouses with a polyethylene thermal screen. It also shows that the greenhouse can benefit from the use of passive means, that is, without the application of external energy.
Heating and dehumidification in production greenhouses at northern latitudes : Energy use
Kempkes, F. ; Zwart, H.F. De; Munoz, P. ; Montero, J.I. ; Baptista, F.J. ; Giuffrida, F. ; Gilli, Celine ; Stepowska, Agnieszka ; Stanghellini, C. - \ 2017
In: 3rd International Symposium on Organic Greenhouse Horticulture International Society for Horticultural Science (Acta Horticulturae ) - ISBN 9789462611603 - p. 445 - 452.
Energy efficiency - Energy saving - Humidity - Sustainable production
The majority of greenhouses in northern latitudes are heated, in the winter mainly for temperature control and year round to control humidity. Heating is accepted by most organic regulations in different countries; if heating efficiently and the energy source is predominantly renewable energy, heating fits well into the concept of organic production, since it is aligned with the idea of achieving maximum potential with available resources. It is a fact that energy use for humidity control is more important than for heating. Indeed, the improved thermal performance (insulation) of high-tech greenhouses has decreased heating requirements while decreasing the discharge pathways of vapour at the same time. The need to control humidity is especially important in organic greenhouses, given the limited options to fight fungal diseases once they develop. Excess vapour can be discharged in three ways: through exchange with dry outside air (ventilation), through condensation on a cold surface and through hygroscopic adsorption. Ventilation can be uncontrolled (natural) or controlled (forced), and in the latter case can be controlled by a heat exchanger, recovering sensible heat in the ventilated air. Even then, however, the latent heat contained in the vapour (the energy used for evaporation) will be lost. In those cases where the greenhouse is dehumidified by withdrawing internal moisture, the loss of latent heat via ventilation is prevented and condensation on an internal surface recovers the latent heat. Obviously, it costs energy to cool the condensation surface and/or regenerate the hygroscopic salt. Experiments with these systems have been performed during the last years. Some growers have installed these types of systems and they have been monitored for their effect on moisture control and energy saving. The results of these experiments and model calculations to compare them are presented. In case dehumidification systems are well controlled they can save significant amounts of the energy and with an increase of technology level the saving can be improved. There is no generally best possible solution for dehumidification. The optimum system and its operation is dependent on desired temperature and humidity level in the greenhouse.
Effect of low temperature during the night in young sweet pepper plants : Stress and recovery
Gorbe Sanchez, Elisa ; Heuvelink, E. ; Jalink, H. ; Stanghellini, C. - \ 2015
In: Acta Horticulturae International Society for Horticultural Science (Acta Horticulturae ) - ISBN 9789462610965 - p. 115 - 122.
Capsicum annuum L. - Chlorophyll fluorescence - Cold - Dark period - Energy saving
The optimization of heating in greenhouses should be an energy saving target in the cultivation of sweet pepper plants; from both an environmental and economical point of view. It is important to understand the effect of low temperatures on this crop. While the effect of low temperature has been studied in plants exposed to light, there are few studies on the effect of cold in the dark, which is a more realistic situation in greenhouses. The objective of this work was to study the effect of low temperatures during the night in sweet peppers and to assess the physiological consequences during the following day. Therefore, we subjected sweet pepper plants of two cultivars to 5 or 7 cycles of 12/12 h warm light (500 μmol m-2 s-1 PAR, 21°C) and cold dark (6°C). After the treatment, several measurements were performed on leaves (first in the dark and cold, and one hour after light was switched on): chlorophyll fluorescence (spot and imaging) and measurements of biomass. Our results showed a decrease in the efficiency of photochemistry in photosystem II (Y(II)) during the dark, cold period related to a stimulation of photoprotection mechanisms in the photosynthetic apparatus. However, 1 h after rewarming in light conditions, leaves had recovered high values of Y(II). In addition, fully expanded leaves increased their specific leaf area and fresh to dry weight ratio during this period. This may indicate that, during the recovery period, dry weight decreased due to redistribution of assimilates to expanding leaves and/or that leaf water content increased. The fast recovery of this crop after several cold nights opens possibilities for new strategies of energy saving in greenhouses. However, more studies should be carried out within this area.
Energy saving in office buildings : Are feedback and commitment-making useful instruments to trigger change?
Lokhorst, Anne Marike ; Staats, Henk ; Iterson, Jochem Van - \ 2015
Human Ecology 43 (2015)5. - ISSN 0300-7839 - p. 759 - 768.
Commitment-making - Energy saving - Feedback - Interventions - Leiden - Organizations
This study focuses on energy saving in an office environment. We developed and tested an intervention that contained both the administration of feedback as well as commitment-making: two techniques that are often described in the literature as successful, especially when combined. Using a sample of 146 employees, we tested the intervention's effectiveness for our sample in terms of behavior change. Our results show some effects, but these were irrespective of experimental category. We use this failed experiment to reflect upon critical aspects of the design and implementation of intervention, and provide ideas on how such interventions can be improved.