Greenhouse is also called warm house. A facility that can transmit light, keep warm (or heat) and grow plants. In the season that is not suitable for plant growth, it can provide the growth period and increase the output. It is mainly used for the cultivation or seedling of warm vegetables, flowers, trees and other plants in the low temperature season. There are many kinds of greenhouse, which can be divided into many kinds according to different roof truss materials, lighting materials, shape and heating conditions, such as glass greenhouse, plastic greenhouse, single greenhouse, multi greenhouse, single roof greenhouse, double roof greenhouse, heating greenhouse, non heating greenhouse, double roof greenhouse, heating greenhouse, non heating greenhouse, etc. The greenhouse structure should be sealed and insulated, but it should be convenient for ventilation and cooling. In the modern greenhouse, the equipment which can control the temperature, humidity, light and other conditions is used to create the best environmental conditions for plants by computer automatic control.
Performance index of greenhouse:
1. Light transmittance of greenhouse
Greenhouse is a day lighting building, so the transmittance is the most basic index to evaluate the light transmittance of greenhouse. Light transmittance refers to the percentage of the amount of light entering the room and the amount of light entering the room. The light transmittance of greenhouse is affected by the light transmittance of greenhouse covering materials and the shadow ratio of greenhouse skeleton, and the light transmittance of greenhouse is changing at any time with the different solar radiation angles in different seasons. The light transmittance of greenhouse is the direct factor of crop growth and crop variety selection. Generally, the light transmittance of multi span plastic greenhouse is 50%~60%, that of glass greenhouse is 60%~70%, and that of solar greenhouse is over 70%.
2. Heat preservation performance of greenhouse
Heating energy consumption is the main obstacle of greenhouse operation in winter. It is the most direct way to improve the greenhouse’s thermal insulation performance and reduce energy consumption. The heat preservation ratio is a basic index to measure the heat preservation performance of greenhouse. The greenhouse heat preservation ratio refers to the ratio of the sum of the covering area of the greenhouse light transmitting materials with small thermal resistance to the ground area. The larger the hear preservation ratio, the better the heat preservation performance of greenhouse.