GLASSHOUSE FOR IMPROVING CROP PRODUCTION
The possible yield is dependent on the growing conditions. The glasshouse constructor is - when designing the house - responsible for one of the most important conditions of growth, the climate: that is to say the transmission of light, the heating, the ventilation and the watering practice.
Concerning the cost of production the glasshouse constructor is responsible for the contribution to the amortization of the building expenses, the heating expenses, the costs of maintenance - and to some extent: the labour cost. This means that the glasshouse constructor must try to build a house that in the best way combines the many - partly unknown - factors, which influence the final financial result. It is really a hopeless task, which never can be solved in an exact way.
The design of a glasshouse of this kind must of course become a compromise, and the result must differ from one place to another, because the factors that determine the design of the house vary, according to the geographical situation. It thus concerns: the climate, the building expenses, wages, rate of interest, cost of fuel, building regulations etc. It is therefore unavoidable that the conception of the ideal glasshouse must differ from one country to another. One of the things that, most likely, still will be open to discussion is the shape of the glasshouse. That means especially: which width is the best, and ought it to be single or is the block system preferable, the so called ridge and furrow houses.
The main factors, as to which form may be considered ideal', are: the building expenses, the fuel cost, the working conditions and the transmission of light. If a comparison between the different types of houses has to be made, it is necessary to illustrate it in figures, even if the statistical material procured never can become 100% exact.
Building expenses will differ as to the quality of the work performed, with the building firm's cost of production and many other things, which means that any statement of the above mentioned expenses must be considered as approximate. In Denmark the building expenses will be roughly as shown in table I when conditions are as follows:
The glasshouses are built of timber, resting on a construction of steel. This construction is self supporting. The glass is 4 mm, the size is 900 x 800 mm.
The length of the houses is 60 m. The heating system is based on a difference in temperature of 25°C above outside air. The price mentioned only concerns the installation in the glasshouse itself.
In the calculation is used the most advanced heating control in electronic-pneumatic performance.
Ventilators are operated automatically.