MODELLING OF A GREENHOUSE EQUIPPED WITH A SOLAR ROCKBED SYSTEM AND WITH CARBON DIOXIDE ENRICHMENT

Various ways of greenhouse environmental modification, energy conservation, solar collection, and energy storage and utilization were investigated to utilize the available solar energy more efficiently. A computer simulation model describing the greenhouse thermal behavior has been developed and programmed for a greenhouse with a solar rockbed system to evaluate numerous energy conservation designs.;Based on the developed model, a sensitivity analysis was made to determine the effect of key parameters on certain simulated results. Generally, the key parameters related with the greenhouse environmental modifications showed high sensitivities.;Simulation was made by using the Typical Meteorological Year weather data. Selected greenhouse systems were a conventional greenhouse, a greenhouse supplied with farrowing house exhaust air, and each of the preceding with or without a solar rockbed system. The wall type solar rockbed system showed considerable energy saving effects.;The CO(,2) level of the greenhouse air supplied with exhaust air from an animal shelter was significantly increased. Based on a photosynthetic factor which was defined in three different ways, depending on the way of estimating saturation levels of solar radiation and CO(,2) concentration, plant photosynthetic activity was estimated and compared.;Validation of the model was made based on the measured greenhouse performance data sets obtained from a prototype greenhouse. For validation, eight periods were chosen to encompass a wide range of prevailing weather and environmental conditions inside the greenhouse. The accuracy of the values predicted by this model was very high.;Monthly and annual solar capturing factors were simulated by relating the solar energy absorbed within the greenhouse with the total solar energy impinging on the greenhouse cover surface. To see the effects of greenhouse cover materials on energy requirements, four different greenhouse systems were simulated with four different combinations of cover conditions. Some variations were found depending on the months, but the patterns were very similar in all locations.;Optimum airflow rate depending on the rockbed depth was determined by selecting the airflow rate under which the greenhouse annual operation energy requirement was minimized. The optimum airflow rate was strongly dependent on the rockbed depth, weather condition and the energy price ratio between electricity and heating energy source.