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Low energy consumption LEC-greenhouse

Exploitable results

The main objective of the research was to construct and test an LEC greenhouse, in regard to energy consumption, greenhouse climate and plant growth. The common denominator for the project is energy saving in greenhouse based on substitution of glass with screen materials and adaptation of a growing system based on concept that makes it possible to convert the greenhouse to almost open land. The LEC greenhouse is designed for production of plants with low temperature requirement and high tolerance to variation in air temperature. The LEC greenhouse is heated with hot water from a heat storage connected to a solar collector to diminish the use of non-renewable energy. The heating system consists of PEL tubes placed in soil and the solar collector, consisting of PEL tubes, is placed in the top of the greenhouse. As a supplement in case of exhausting of the heat storage, energy is supplied from the boiler and the heat storage works as a heat exchanger. A standard climatic computer was modified and extended to the operation needed in the LEC greenhouse. The LEC greenhouse is a shed roof construction with a roof slope of 5°, with a span of 10m. Using a shed roof construction gives 3 features: 1) Te wind load on the roof screen is minimized. 2) Rin runs off (screen material is water proof). 3) The LEC greenhouse can be built as a separate greenhouse as well as in block. The screen materials is QLS in the roof because it is most suited for a folding screen, while Solar Woven is used in the side walls because it is most suitable for a rolling screen. Both materials have an appropriate light transmission and when the screens are closed the light transmission is 60-65%. The LEC greenhouse is equipped with an aluminized energy screen, which is closed during night. Argyranthemum frutescens, Campanula potenschlagiana, Petunia hybrid, Osteospermum ecklonis and Pinus pinea were grown in the LEC greenhouse and the growth and development was compared with plant grown in traditional way in a glass greenhouse. The plant species produced in the LEC greenhouse were grown under lower average air temperature than the plant in the reference greenhouse and the production time was increased to the double compared with the time in the reference greenhouse. The slow growth rate of the plants result in a higher dry matter content. The fluctuation in air temperature and the lower average temperature decreases stem elongation, which reduces the need for application of chemical growth retardant. The quality of the plants produced in the LEC greenhouse is high and the plants were produced with an energy consumption of approximately 20% compared to the amount of energy used in a glass greenhouse. The energy consumption per hour was on average 4MJ and the average per day was 21MJ, but with very large variation in energy consumption over the experimental period. The energy accumulated by the solar collector was on average 2.3MJ per hour and the average per day was 49MJ, but with very large variation in energy accumulation over the experimental period. In regard to energy the heating system is able to provide sufficient heat to keep the LEC greenhouse free of frost. The solar collector has a low efficiency, but energy accumulation could be improved by change in the design of heat storage and control system. It is not possible to improve the performance of the solar collector it self as long as it is an integrated part of the greenhouse construction.
The main objective of the research was to construct and test an LEC greenhouse, in regard to energy consumption, greenhouse climate and plant growth. The common denominator for the project is energy savings in the greenhouse based on the substitution of glass with screen materials and the adaptation of a growing system based on the concept that makes it possible to convert the greenhouse to almost open land. The LEC greenhouse is designed for production of plants with low temperature requirements and high tolerance to variation in air temperature. The LEC greenhouse is heated with hot water from a heat storage connected to a solar collector to diminish the use of non-renewable energy. The heating system consists of PEL tubes placed in soil and the solar collector, consisting of PEL tubes, is placed on the top of the greenhouse. As a supplement in case of exhaustion of the heat storage, energy is supplied from the boiler and the heat storage works as a heat exchanger. A standard climatic computer was modified and extended to the operation needed in the LEC greenhouse. The LEC greenhouse is a shed roof construction with a roof slope of 5_, with a span of 10 metres. Using a shed roof construction gives 3 features, 1) the wind load on the roof screen is minimised, 2) rain runs off (screen material is water proof) and 3) the LEC greenhouse can be built as a separate greenhouse as well as in block. The screen materials is QLS in the roof because it is most suitable for a folding screen, while Solar Woven is used in the side walls because it is most suitable for a rolling screen. Both materials have an appropriate light transmission and when the screens are closed the light transmission is 60-65%. The LEC greenhouse is equipped with an aluminised energy screen, which is closed during the night. Argyranthemum frutescens, Campanula potenschlagiana, Petunia hybrid, Osteospermum ecklonis and Pinus pinea were grown in the LEC greenhouse and the growth and development was compared with plant grown in the traditional way in a glass greenhouse. The plant species produced in the LEC greenhouse were grown under lower average air temperature than the plants in the reference greenhouse and the production time doubled compared with the time in the reference greenhouse. The slow growth rate of the plants result in a higher dry matter content. The fluctuation in air temperature and the lower average temperature decreases stem elongation, which reduces the need for application of chemical growth retardant. The quality of the plants produced in the LEC greenhouse is high and the plants were produced with an energy consumption of approximately 20% compared to the amount of energy used in a glass greenhouse. The energy consumption per hour was on average 4 MJ and the average per day was 21 MJ, but with very large variation in energy consumption over the experimental period. The energy accumulated by the solar collector was on average 2.3 MJ per hour and the average per day was 49 MJ, but with very large variation in energy accumulation over the experimental period. In regard to energy, the heating system is able to provide sufficient heat to keep the LEC greenhouse free of frost. The solar collector has a low efficiency, but energy accumulation could be improved by changing the design of the heat storage and control system. It is not possible to improve the performance of the solar collector itself as long as it is an integrated part of the greenhouse construction.