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G. Scarascia-MugnozzaROJECT
G. Scarascia-Mugnozza
UNIVERSITY OF BARI-ITALY
The HCM (Human Capital and Mobility) network project titled: "Greenhouse design: functional and structural aspects and test methods of covering materials" was funded by the European Commission, with the aim to collect, rationally organise and improve with synergy the scientific activity on greenhouse technology conducted by different European Research Institutions working on the same subject.
This project has started on March 1st 1994 with duration of 48 months. The project was co-ordinated by Prof. D. Briassoulis, Agricultural University of Athens (AUA), Greece; the participants of the network include: Institute of Agricultural and Environmental Engineering IMAG-DLO, Wageningen (NL); Institute of Technique and Constructions in Agriculture, University of Hannover (DE); CEMAGREF, Montpellier (FR); Institute of Agricultural Structures of the University of Bari (IT).
All the proposed research topics were developed obtaining high level scientific results by means of productive exchanges of the researchers between the different national groups. The results of the co-operation among different partners were eleven joint publications published on International refereed Journals and twelve joint publications presented at International Congresses and printed in the proceedings.
Future perspectives of the nted in the proceedings.
Future perspectives of the research in the field of greenhouse
structures and materials are related to the role, currently underestimate,
of Agricultural Engineering within Horticultural Science.
Greenhouse crops are one of the most innovative examples of modern agriculture and it is predictable for them to expand more and more in future, especially in areas with unfavourable climatic conditions. They are one of the highest man-made forms of agricultural activity, because of the intense technological and bio-agronomic inputs in confined portions of the agricultural environment.
Greenhouses are a means to grow crops by overcoming adverse weather conditions; they exploit solar radiation to condition indoor micro-climatic parameters, also with the use of equipment, aimed at optimising crop production in areas or in periods of the year not suitable for open field cultivation. In 1993 greenhouses covered over 220,000ha world-wide, of wich 80,000ha in the EU, whereas small tunnels and mulched areas in the world amount to 250,000ha and 4,000,000ha respectively, and future increases are expected both in developed and in developing countries.
In the Mediterranean Countries the greenhouse covered area amounts to more than 70,000ha, where the so-called Mediterranean greenhouses or "cold greenhouses" have got established. They consist of low technological inpgot established. They consist of low technological input greenhouses, for vegetables or low-temperature flower crops, of low investment and low running costs and fairly good energy efficiency, built with lightweight steel, or timber and concrete structures, covered with plastic film, without heating system or with simple supplementary heating equipment, based on the exploitation of solar radiation to increase the indoor temperature, situated in vegetable prone areas having more favourable climatic conditions.
The HCM (Human Capital and Mobility) network project titled: "Greenhouse design: functional and structural aspects and test methods of covering materials" was funded by the European Commission, with the aim to collect, rationally organise and improve with synergy the scientific activity on greenhouse technology conducted by different European Research Institutions working on the same subject.
This project has started on March 1st 1994 with duration of 48
months. The project was co-ordinated by Prof. D. Briassoulis,
Agricultural University of Athens (AUA), Greece; the participants
of the network include: Institute of Agricultural and Environmental
Engineering IMAG-DLO, Wageningen (NL); Institute of Technique
and Constructions in Agriculture, University of Hannover (DE);
CEMAGREF, Montpellier (FR); Institute of Agricultural Structures
of the University of Bari (IT).
The HCM project finances the mobility of young and experienced researchers among the participant Countries, funding all their travel and subsistence expenses. Six post-graduated and post-doctoral young researchers were paid for a total period of 47 man-months and more than twenty short visits were carried out by the senior researchers in this network.
During the first period of the project some difficulties arose about the definition of the sharing of the work between the scientists involved in the research topics that were chosen as targets of the network. This problem was overcome identifying a scientist for each task, who was the responsible of the development of the research and of the co-ordination of the work. The task co-ordinators presented the situation concerning the development of the research during the periodic meetings, arousing profitable scientific discussion among the participants. Ten meetings were held, approximately one every four months, during workshops specifically organised in turn in the five participant Institutions, or in occasion of International Congresses. A yearly general report with the most interesting results of the common work and the factual information about the obtained progress was also produced.
All the proposed research topics were developed obtaining high level scientific results by means of productive exchangescientific results by means of productive exchanges of the researchers between the different national groups. The results of the co-operation among different partners were eleven joint publications published on International refereed Journals and twelve joint publications presented at International Congresses and printed in the proceedings.
Another relevant result is the establishing of profitable and
friendly scientific relations among the partners.
The objectives of the network include:
*) the investigation of the current situation, proposing standard testing methods and defining the specific needs for new testing methods for flexible and rigid materials used as covering materials for greenhouses, also taking into consideration the environmental impact of these materials;
*) determining main causes and modes of failure of greenhouse structures;
*) fostering reliable designs of film covered greenhouses, including tunnel and arch structures, and rigidly clad greenhouses;
*) establishing a fundamental model of the greenhouse environment
as a design tool.
The results obtained are a direct consequence of the initial objectives, even though, new ideas for research and applications came out with the progress of the research work.
In more details the following results were achieved:
A review of covering materials of greenhouses in use nowadays in the participant countries was carried out collecting data related to greenhouse cladding materials. A systematic presentation of national and international standards such as ASTM, BS, NEN, UNI, DIN, NFT and ISO for flexible and rigid plastics and glass, together with an analysis of characteristic values of selected mechanical and physical properties of greenhouse covering materials was also performed. The radiometric properties to several radiation bands and the overall heat transfer coefficient were reviewed. The knowledge of the radiation transmission characteristics of a greenhouse covering material is important when assessing the potential benefits of different materials, especially in the UV, PAR and in the thermal radiation bands. The knowledge and exploitation of the physical properties of the covering materials are of great interest to the grower, to the horticulturist, to the agricultural engineer, to the manufacturer and in general to all those related to the greenhouse industry. Therefore new testing methods and the modification of the existing ones have been proposed.
Data were also collected with special reference to the environmental effects of plastic wastes. Experimental research is now in progress for the critical evaluation of the mechanical properties and the dluation of the mechanical properties and the degradation and stabilisation of LDPE films.
Two major review papers on the mechanical properties of covering materials appeared in a refereed journal. Similar work has been now completed and a review paper on the physical properties of covering materials was submitted to a refereed journal.
A work on the critical evaluation of the testing methods for the mechanical properties and the degradation of LDPE films was performed and a full series of experiments was conducted, following the artificial ageing of various types of LDPE films, aiming at the study of degradation on the mechanical properties of LDPE films.
A research on water condensation behaviour on plastic films was
also conducted by means of theoretical and physical methods for
the measuring of contact angle of droplets at the film surface;
also the method of k-value measurement by hot-box, for the calculation
of the heat transmission coefficient, was of central interest
for further optimisation of test equipment.
A study about the structural and functional characteristics of greenhouses in EU and for the investigation of causes and modes of failure of greenhouses was conducted by the network participants.
The study on the analysis of arch structures for tunnel greenhouses
is going on by executing structural analysis of different greenhouse
types to be structural analysis of different greenhouse
types to be situated in different European locations according
to the new European CEN standard for greenhouses prEN 13031-1.
This study includes full-scale testing and non-linear finite element
calculation in order to calibrate a usable design method for greenhouse
steel supporting structures. Linear and non-linear calculations
have been undertaken on tunnel and multispan greenhouses to supply
data for investigating the modes of failure of these greenhouse
types. Moreover the combined effect of wind and snow loads on
greenhouse structures has been investigated.
Computer simulations of greenhouse ventilation have been performed, contributing to the preparation of two papers published in international refereed journals about buoyancy-driven and wind-driven natural ventilation. Ventilation is an essential process influencing the indoor microclimate, strongly contributing to the heat and mass exchange between the interior and the environment: well designed ventilation features can therefore improve both climate control and energy efficiency. Especially, ventilation can contribute to the optimum control of temperature, humidity and concentration of gases, such CO2 and it offers improved possibilities for increasing crop production and product quality, at the same time contributing to the reduction of chemicals for plant protection. The achition of chemicals for plant protection. The achievement of good greenhouse ventilation is a crucial factor both for northern humid winter climates and for Mediterranean hot summer conditions: in fact, under cool conditions, reducing excessive humidity levels is necessary to prevent crop mineral depletion and fungal diseases while, on the other hand, under hot conditions it is important to control inside temperature and relative humidity. In this way, the thermal stress is reduced, the plant photosynthetic and transpiration activity is maintained, and the physiological quality of crop improves.
Moreover, a research on greenhouse geometrical view and shape factors to be used in mathematical simulation energy models of greenhouses has also been performed in order to calculate radiation exchange between greenhouse surfaces inside and outside.
A study of the condensation phenomena under various plastic films
used as greenhouse covering materials and the assessment of droplets
according to the wettability of the material was finally carried
out.
The integration of the combined effect of wind on loading and ventilation of greenhouses has been investigated and comments on the proposed CEN draft standard prEN 13031-1, that gives rules for structural design and construction of greenhouse structures, have been prepared.
Some calculations on load combinations to grepared.
Some calculations on load combinations to greenhouse structures were carried out in comparison of the actual standards and the proposed CEN draft standard. These results were discussed during some HCM Workshops and are basis of some individual proposals for improvement of this standard.
Problems concerning environment and greenhouse pollution were also investigated. The main causes of the general unfavourable effects produced by greenhouses on environment can be summarised as:
- the disposal of plastic materials due to the renewal of transparent covering and mulching;
- the massive supply of pesticides and fertilisers;
- the intense withdrawal of water for irrigation purposes;
- flue gases and emission of suspended particles from the thermal equipment of greenhouses with heating system;
- the effects of safety at work, specially during the application of chemical treatments;
- the quality of food products for the consumer's health;
- the changes in landscape and land morphology.
The objectives of the present project, as a whole, have been achieved
successfully and an important contribution to the European greenhouse
design technology has been made, although many aspects concerning
materials, equipment and environmental effects need more investigation.
Many benefits were obtained from working together at a community l>
Many benefits were obtained from working together at a community level. In all European countries horticulture under cover is a profitable branch of agriculture involving considerable industrial activities with high technological level. Despite the large number of innovations applied in the present day greenhouses, a unique design typology can not be considered the perfect solution, but a flexible design approach has to be pursued. Greenhouse construction must meet local needs and climatic conditions. For this reason, the standardisation of greenhouses at a European level involves difficult technical, economic, social and legal problems. However, a certain degree of European harmonisation is required in order to facilitate the trade of greenhouses and greenhouse components among the EU countries.
The present network addressed several important technical questions in this direction. For this reason, the co-operation among five European Universities and Research Centres has been necessary for successfully attacking the involved technical problems. The participants have provided a large variety and quantity of information which could not be gathered by a single research team. In this way, important review studies concerning European greenhouses have been published.
Moreover, greenhouse design is a highly interdisciplinary field requiring the involvement of diverse expertise. This resulted in a very strong co-operation of the partners and exchange ofong co-operation of the partners and exchange of knowledge and know-how between different disciplines with the involvement of post-doctoral researchers seconded or hired to work under the network project. In this way, the present network produced scientific results that could not be developed when working in separate teams.
Future perspectives of the research in the field of greenhouse structures and materials are related to the role, currently underestimate, of Agricultural Engineering within Horticultural Science.
Also the participation of Agricultural Engineering groups to research programs should be more enhanced.
Future studies concerning greenhouses should further investigate: the environmental effects of the greenhouse production system; the mechanical and physical properties of greenhouse covering materials in relation with crop and energetic requirements; the influence of greenhouse construction materials and equipment on the quality and quantity of horticultural products; the greenhouse simulation and plant growth models; the renewable energy exploitation and the energy management system; soilless culture materials and equipment.
According to the diffusion of greenhouses in several countries and in different climatic conditions the study of greenhouse structure and environment should be an essential tool for sustainable horticultural protected cultivation.
The activity of the HCM network was propoivation.
The activity of the HCM network was proposed to be continued in a new TMR (Training and Mobility of Researchers) project, that was submitted in 1997 to the EU for funding but unfortunately not financed. A new proposal will be submitted when the TMR action will be in force in the EU 5th RTD framework programme.
In the meantime scientific collaboration among the partners will
continue, also in order to prepare and submit other proposals
in different R&D programmes, although these programmes are
often not specific for Agricultural Engineering tasks, when they
include topics that only Agricultural Engineers can investigate
in a proper scientific way.