Experimental Research on Monomial Cooling Measure of Greenhouse in Summer ()
1. Introduction
With the continuous improvement of science, technology and the modernization of agricultural production, agricultural facilities in China boom rapidly. Greenhouse, as the main type of agricultural facilities, has significant social and economic benefits, and it has been widely used in our country. But there are also a series of problems in the application process, especially for the cooling problem of greenhouse in summer that has always been the concern of agricultural scientific workers. July and August are the hottest months in Chongqing Municipality throughout the year. Mean monthly temperature is about 27˚C - 28˚C [1], and the existence of “greenhouse effect” makes the indoor temperature reach more than 50˚C. Crops are completely unable to survive, resulting in making greenhouse in an “idle” state over a third of time. The greenhouse in summer must be considered to take corresponding cooling measures to organize normal production, so as to improve the utilization rate. And it can provide the crops a good growth environment for achieving a high yield, a high quality, and a high efficiency of the intensive mode of production, so to meet the needs of people’s life, and to improve the land utilization rate.
2. Experiment Conditions and Test Scheme
2.1. Experiment Conditions
This experiment is proceeded in water-saving irrigation efficiency demonstration laboratory of College of Engineering and Technology, Southwest University. The laboratory is four straight across Venlo type, which is a large high-grade glasshouse with one cross and three ridges. As Figure 1 shows, the greenhouse runs north to south, with a total area of 9.6 m/span × 4 span × 36 m = 1382.4 m2. It is divided into four areas: the first area is vegetable area, the second is flower area, the third area is for fruit nursery, and the last is for nursery garden. Each area is 9.6 m × 36 m = 345.6 m2, and there is a central control room in front of flower area. All the top and the board of the greenhouse are covered with 4 mm domestic high quality float glass. Light transmittance is greater than 90%; the coefficient of heat transfer K = 6.6 W/ (m2·˚C); the greenhouse is fixed by special aluminum alloy; it is sealed by rubber strip.
Figure 1. The ichnography of experiment greenhouse.
2.2. Test Instruments and Equipments
1) Greenhouse with natural ventilation system, mechanical ventilation system, wet curtain cooling system and external shading system [2].
2) 16 numbers of thermocouple sensors, one placed outdoor, the other fifteen placed indoor. They are located in three different planes. Thermal performance test system of TRM-2 Solar energy water heater (developed by Jinzhou Sunshine Technology Development Company) is used to record temperature automatically. The recording tome is setted for every 30 minutes.
3) Three wet and dry bulb thermometers are setted, 1 placed outdoor, the other 2 placed indoor, which are used to determine the dry bulb temperature, wet bulb temperature and relative humidity outdoors and indoors.
4) Computer is mainly used for the derivation of data. And some related softwares are also used for data processing.
2.3. Test Arrangement
This test is conducted in the second working place, the area—flower area, as is shown in Figure 2. Greenhouse is divided into two symmetrical work areas by corridor, and six observation positions are set up on the right side of the horizontal plane area for analyzing the temperature distribution rule in the horizontal plane during the cooling process indoors. And in the position 3, a temperature sensor is placed underground with a distance of 20 cm from the ground, which is used to measure the geothermal change rule in the whole test process. An observation point 7 is placed outdoors, which is used for monitoring the change of outdoor temperature. In addition, in the greenhouse there placed two dry wet bulbs, and out of the greenhouse there placed dry wet bulb, which are used to measure the relative humidity change rules outdoors and indoors.
Figure 3 shows the map of temperature vertical distribution of each point. Three planes are set up in vertical direction. The third plane is 500 mm distance from the ground. The first plane is 500 mm distance from the gutter. They are used for measuring the variation of tem-