Articles
A COMPARISON OF FOSSIL AND SOLAR HEATING OF GREENHOUSES IN CYPRUS
- Development of light greenhouse structures made from galvanized steel parts, suitable for the application of single or double PE-cover, tight against air and heat leakage at night, to be erected on site without need for electricity.
- Testing of means for reducing energy losses from heated greenhouses, i.e. installation of inflated double PE-cover and thermal screens.
- Improvement of conventional fossil heating systems:by refining layout calculation methods in order to avoid oversizing; by technical improvements of heat exchanger systems in greenhouses; and by improving control systems for the operation of heat generators.
- Development of low cost solar systems composed of solar collectors, heat storage, heat exchanger in the greenhouse and engines for the motion of the medium of heat transport.
- Comparison of fossil and solar heating systems with respect to thermal and operational performance, yield, consumption of non renewable energy, economy.
- Transfer of the more promising solutions into the farming practice at coastal locations on Cyprus.
As a rule all developments of structures and heating systems for greenhouses undertaken by this project should avoid as far as possible the use of imported materials and machinery.
The skill required for the erection of structures and the annual labour for maintenance and operation should not surpass the abilities of the typical farmer of Cyprus.
The concept of using solar energy for heating greenhouses should be justified by the relation between solar irradiation and heating load.
From an analysis (I) of solar and degree-hour data for Nicosia it is evident, that more energy is arriving at the greenhouse cover than the quantity needed for heating the house up to 14°C. But as it is possible to collect only the energy which is transmitted through the cover into the house, it is more realistic to balance the heating load with the theoretical excess heat, that could be extracted from the greenhouse air, if this was cooled down to the usually chosen limits of either 12°C or 14°C. Table 1 presents the results of such calculations for every month of a heating period.
The four combinations of single or double cover (k = 7 or 4.6 resp.) and 12°C or 14°C indoor temperature limit are evaluated separately.
In all but one case the daily excess heat surpasses the daily heating load.
The one exceptional case is that with single cover and 14°C, for which the heating load in January is higher than the excess heat.
These records support the assumption that by collecting part of the solar irradiation into a greenhouse a considerable fraction of the heating