Development of a Wall Collector Unit and Phase Change Material (PCM), Air Heat Exchanger for Heating Application in Greenhouses

Greenhouse heating is essential in the northern region of China during winter season in order to maximize crop production in terms of quality and quantity and thus increase their overall efficiency. But the use of heating systems faces the problem of high running cost and noxious gases emission for heating systems based on fossil fuel and there is also a risk of frost cropping for electrical heating systems due to electrical power failure during heavy weather conditions. In this paper the performance of flat plate collector and a PCM serpentine heat exchange is investigated. An eutectic mixture CH3COONa·3H2O-HCONH3 was used as a latent heat storage material, this material possess a melting temperature of 40.5°C, relatively higher compared to commonly used phase change materials for heating applications. The energy capacity of the PCM during charge and discharge phase has been determined based upon the measurement results made in the heating process during February 2012, one of the coldest winter months in Beijing, China. It was observed that the average net energy efficiencies was 45%, therefore the PCM in study, was founded to be suitable for solar thermal storage applications.