PREFACE

With the help of members of the Working Group on Greenhouse Climate Control of the Commission for Protected Cultivation of the ISHS and by the incorporation of the Working Party into the program for energy-saving in protected cultivation out of the Mediterranean program of the second E.C.-program for agricultural research, it has been possible to realise this meeting.

This volume, number 106 of Acta Horticulturae, contains 25 papers on the use of computers in greenhouse climate control.

The assistance of the Agricultural University and of the Institute of Agricultural Engineering - IMAG - at Wageningen has been the base of the success of this meeting with good lectures, discussions and also excursions.

I hope the results of this meeting will, before long, be of value to farmers in protected cultivation.

Ir.H.H. van der Borg
Editor of Acta Horticulture

OPENING ADDRESS

Optimal control of the greenhouse climate as a means for energy saving

The idea to organize this working-party on the use of computers to control the greenhouse climate was put forward at a meeting of the Commission for Horticultural Engineering, which meeting was held during the Symposium on "More profitable use of energy in protected cultivation" at Lund, September 1977.

This working-party and the next one which will take place at Avignon in October 1979, may be considered as preparation for the next international symposium on the "Use of energy in protected cultivation" which will take place at Dublin in September next year.

The continuous rise of the energy prices affects the production cost of the greenhouse production in the Northern countries considerably. Therefore in several countries an intensive research program has been started to find ways for reducing the energy consumption for the crop production in greenhouses.

In this relation we have to mention the efforts to breed less energy requiring cultivars and the culture of crops which can be grown with lower temperatures.

Besides the engineers investigate the possibilities of the use of better insulated greenhouses and construction materials as double skins of glass or plastic sheet.

In this range the improvement of the climate control must not be underestimated. The activities in relation to a better control of the greenhouse climate may have a double effect. Firstly they may result into a direct energy saving, owing to a more efficient use of the energy needed to perform the desired climate. This objective requires more knowledge about the various processes of heat, air and water transfer in relation to the greenhouse type and the controlling system. By the way, a well designed controlling system may also promote a more profitable use of water and nutrients, which is as well a need for the future.

A second objective of the research activities is to get a better insight into the requirements of the crop regarding the optimal greenhouse climate. Because of our rather limited knowledge about the plant requirements we also practise rather simple climate regimes. There seem to be good reasons however, to expect higher production rates with more sophisticated regimes, especially in relation to a more efficient use of the daily solar radiation.

To tackle this type of problems, a close cooperation between engineers and plant physiologists and crop specialists is needed.

In relation to the quickly rising of energy prices both possibilities, a direct energy saving as well as an increase of the production, need to be worked out at short notice.

It goes without saying nowadays, that for the research activities mentioned before, the help of the computer is indispensable. At first for solving the mathematical problems and for working out the calculation-models. Secondly for the realisation and recording of the climatological conditions in the experiments executed to formulate the optimal growing conditions. Finally to create these conditions in the most efficient way in the greenhouses of the growers.

This latter stage is approaching very quickly as already a few hundred growers over the world use process computers for the control of their greenhouse climate. Mostly because it is cheaper than using analogue controllers but also because of the very convenient recording system attached to the computer.

The program for the process computers in protected cultivation is still a relative simple one. The computer however, is able to perform much more complicated programs. Once again technology is far ahead of the plant physiological knowledge. But since we have now the tools it is worth-while to investigate the demands of our crops thoroughly.

The potentialities of these new techniques produce an enormous challenge for the horticulturist and the engineer.

A working-party as the one which is going to start now is one of the means to achieve the task set to us.

This working-party has been organised under auspices of the I.S.H.S. and financially supported by the E.E.C. "Brussels" not only proved their financial responsibility but also showed their interest by the participation of their representative, Mr. Troisgros. As co-sponsor of this meeting we gratefully mention the Agricultural University and the Institute of Agricultural Engineering (IMAG) at Wageningen. The Agricultural University is represented at this opening-session by the Dean of the University, prof. dr J.Schenk.

On behalf of the convenors of this working-party I call to guests and participants a hearty welcome. The Chairman of the Commission for Horticultural Engineering, Mr. A.E. Canham and the Chairman of the Working Group Greenhouse Design and Climate Control, Mr. K.W. Winspear, have sent messages to give their regards and to wish you a very succesful and enjoyable event.

Finally we have to express our gratitude to the organizers, Mr. G. Bot and Mr. W.P. Mulder and their co-workers for all the trouble they took for organizing this meeting.

G.H. Germing
Executive Vice-chairman Commission for Horticultural Engineering of the I.S.H.S.
Institute of Agricultural Engineering (IMAG)
Wageningen, Netherlands