POSSIBILITIES FOR THE REDUCTION OF THE ENERGY CONSUMPTION IN GREENHOUSES

Presently the cultivation in Hungary extend to 200 ha glass covered and 2500 ha plastic covered greenhouses. 10 % of latter is provided with technical heating.
Half of the glass covered and more than 80 % of the plastic covered territory is heated with thermal water.
The remaining part is heated with hydrocarbons.
The cost of heating – in spite of thermal water heating – often reaches 50 % of the cultivation costs.
Several ideas exist to reduce the heating costs, some of these one discussed in the followings.

At first the heat transfer coefficient, prescribed in the Standard has been examined.
In 1974 on a plantation in the neighbourhood of Budapest measurements have been executed in the whole winter period, to control the wind velocity, the characteristics of the air and parallel to these the roof temperatures of houses with glass, PVC and polyester reinforced with glass fiber covers.

As a result of measurements a reduction of the wind velocity value to be considered from

4 m.s^-1 to 2 m.s^-1;

of heat transfer coefficient from 5.8 – 6 W.m^-2.K^-1 to

4.8 – 5 W.m^-2.K^-1

and consequently the medium heat requirement factor in case of houses with plastic cover to 6.00 W.m^-2.K^-1; in case of glass cover to 6.5 W.m^-2K^-1 has been proposed.

Considering these recommendations, the investment cost of thermal stations can be reduced with 20 – 25 %.

From the Hungarian climatic data regarding the years 1935–1960, the fuel consumption has been determined in the function of sunshine in case of glass covered houses with room temperatures of 5, 10, 15, 20 25°C. The highest heat gain from sunshine (by room temperature of 5°C) has been found 18.9 %, the lowest (by 20°C) 14.8 %. An average value of 15 % can be proposed.
Considering the sunshine data, the fuel requirement calculation, farther the calculation of the heat energy, required for heating cultivation territories above 100 m² can be adjusted. (Fig. 1.)

Two methods have been tried to utilize low temperature soil and thermal waters (<35°C) and other industrial warm waste waters.

The first one can be used mainly for cultivations with plastic cover.
In this case the warm water is led between the double plastic foil

Symposium on More Profitable Use of Energy in Protected Cultivation

P. J. Karai

https://doi.org/10.17660/ActaHortic.1978.76.32