Accurate control of plant environment in commercial glasshouses is being regarded with ever increasing interest by modern growers, for a variety of reasons. Work at research institutes on plant response to the various aspects of environment, coupled with the experience of growers with up to date structures and control systems is perhaps the main incentive. Nevertheless, just as the manufacturing industries have improved efficiency by the use of automation, so the glasshouse industry must also consider how automatic controls can improve output from a given capital investment and labour force, with better quality and uniformity of the product. The cost of labour and fuel alone is sufficient justification for the adoption of some automatic control, but in England there are still many growers without automatically fired boilers or controlled heating systems. It is difficult for the engineer to present an economic case for the use of automatic ventilation, based on the labour content that the individual grower may allocate to this task. More persuasive is the argument put forward by the plant physiologist that the effect of loss of temperature control during the day is important enough in itself to justify the improved control that only automation can bring.

The main aerial environment factors over which control is desired (and it may not be economic to attempt full control of all these factors) are:

  1. Dry bulb temperature
  2. Air moisture content
  3. Carbon dioxide concentration
  4. Air movement
  5. Illumination

The soil environment is ignored for the purpose of this paper, but cannot of course ignored when considering the whole plant. Knowledge of the plant response to these factors is limited, particularly the interaction of one with another, but within the framework of existing knowledge of the growing plant, the engineer has to design the most effective equipment to provide the most suitable environment. The current approach is to consider each aspect in isolation, and this is perhaps understandable because the grower will add control equipment piecemeal as knowledge is gained by the plant experimenters, and as capital becomes available. The different aspects of the whole environment do not of course act separately on the plant, and the engineer is impatient for further knowledge so that a comprehensive control system can be developed where the interaction of one controlled condition with others is taken into account to provide the best conditions for growth.

Straightforward automatic systems for heating and ventilation control are well advanced, and the desired dry bulb temperatures can be reasonably precisely maintained. In the practical use of those systems, skill is still required on the part of the grower not only in the choice of temperature level according to prevailing weather and the state of the plants, but also in modifying the effect that the systems have on the humidity within the glasshouse.

DOI: 10.17660/ActaHortic.1968.6.6