CONTROL OF HEATING AND VENTILATION IN GLASSHOUSES
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:
- Dry bulb temperature
- Air moisture content
- Carbon dioxide concentration
- Air movement
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.