School of Mechanical and Electrical Engineering, Inner Mongolia Agricultural University, Liu Shumin Vacuum Tube Solar Water Heater is a high-tech solar water heater with high borosilicate glass vacuum tube as a heat-absorbing element. The full set of equipment consists of several high-borosilicate glass vacuum collector tubes and diffuser plates, stainless steel inner tanks, insulation materials and brackets. Its characteristic is that the collector tube adopts cylindrical double glass vacuum tube, the vacuum degree between the two glass tubes is P92%, and the emissivity e vacuum tube type solar water heater also has some disadvantages: Firstly, because one end of the vacuum tube is sealed, the other One end is inserted into the water tank, and both hot and cold water are naturally circulated within the tube with an inner diameter of 33 mm and a length of 1.2 m. The circulation resistance is large, and about 1.03 kg of hot water cannot be discharged in each tube, and thermal efficiency is lost. In addition, when adding cold water to the water tank, some impurities in the water will remain in the bottom of the vacuum tube for a long time, and more and more water will affect the normal use of the water heater. Second, when the hot water in the tank is used up, if the cold water is not supplemented in time, the water in the vacuum heat pipe will evaporate in about 2 hours in the summer. The vacuum drying temperature of the vacuum tube is up to 270C or higher. Suddenly adding water will cause the glass vacuum tube to burst due to a sudden change in temperature. Thirdly, the water temperature in the vacuum tube in the summer can reach above 90C. The water in the single-ended closed vacuum tube is naturally convectively circulated. The water flow is slow. The calcium and magnesium ions in the water will form scale on the inner wall of the vacuum tube. As the water heater usage time increases, the scale builds up and the thermal efficiency of the collector decreases.

Some of the above problems are solved by the need to improve the design of vacuum tube solar water heaters. Some problems can also be overcome by proper installation and use.

1 The correct installation of water heaters At present, in cities, solar water heaters are mostly installed on the roof of buildings, and improper installation can seriously affect the supply of hot water.

1.1 Installation Location of Water Heater Where the water heater is installed, there should be no tall buildings blocking sunlight in the front 180 area. If the water heater has been installed in front, the distance between the two water heaters is 23 times the height of the front water heater. In addition, the water heater should not be installed in a place with a lot of smoke and dust, and should not be installed on the air outlet.

1.2 Direction of solar collector installation The collector of the solar water heater should be installed towards the south of the south or the south of the south, especially in the cold regions of the north, mainly to solve the problem of the use efficiency of the water heater in winter. In order to obtain the maximum solar radiation in winter, the dip angle of the collector should be about 10 times larger than the local one. For example, the installation inclination in the Hohhot area is preferably 51°. In order to ensure the installation direction of the collector is accurate, it is best to choose the installation time at the end of December in winter or at midday before and after the winter solstice, and install it against direct sunlight.

1.3 Installation of Exhaust and Return Pipes The exhaust and return pipes of solar water heaters are generally located on the top side of the tank. The purpose is to drain the air when the tank is replenished with cold water and fill the tank with water before returning water. In addition, water vapor generated during the heating of the water can be discharged. Paste quiet: Wei Ge pain: tracheal discharge. The exhaust and return pipes can be connected to the tank with a three-way pipe. The exhaust pipe is installed upwards, and the height of the nozzle from the top of the water heater tank is not less than. 4m. The water return pipe is installed downwards into the room water equipment.

2 The correct use of water heaters Currently, there are many varieties of vacuum tube solar water heaters on the market, which are automatic water supply and manual water supply. However, most are equipped with water pipes, return pipes and exhaust pipes. According to the use methods provided by the manufacturer, the upper water pipe has two functions: one is to add cold water to the water tank; the other is the hot water outlet pipe of the water tank. The upper water pipe is connected to the switch of the water equipment through a hot water switch, a cold water switch and a tee. The function of the return pipe is to return the excess water to the room water equipment after the water in the tank is full, and inform the operator that the water has been filled up. The cold water switch needs to be closed. There are several problems in using water heaters in this way: 1 Every time you use hot water, you must first let go of the cold water in the water pipe, and only after the hot water heats the water pipe, can you run out of hot water. For the low-rise users of high-rise buildings, this problem is even more serious. To highlight.

2.2 Because the use of water heaters often do not know how much water in the tank is the surplus, often the water in the tank is used up and then add cold water, a full tank, a large amount of cold water, solar water heaters to heat this tank cold water takes time , especially in the heating time in the winter, will affect the use of hot water the next day.

2.3 In many cities in the summer, there is a shortage of water. If you run out of hot water in the tank, you will experience low water pressure at the tap water. You will not be able to supply water to the tank. The water in the glass vacuum tube will quickly evaporate and air will appear. phenomenon. At this point, if water is suddenly added, the glass vacuum tube bursts.

2.4 Due to the problems of design and use, each time the hot water is used from the bottom of the tank. The water in the water tank has a temperature gradient during the heating process. The temperature of the upper water in the water tank is higher than the temperature of the water at the bottom, so the hot water flowing from the water tank every time is not the hot water in the highest temperature area of ​​the water tank.

Based on the above issues, the author proposes to use the new party's use and maintenance method to effectively use the water return pipe without changing the original design and installation, and to use the water pipe to add cold water to the water tank and use hot water from the return pipe. Big benefit: 2.4.1 It is not necessary to consider when the hot water in the tank is used up or when it is time to add cold water to the tank. There will be no emptying of the glass vacuum tube.

2.4.2 Because there is no water in the return pipe every time hot water is used, a large amount of cold water does not flow first.

2.1.3 The hot water used each time is hot water in the highest temperature zone in the tank.

2.4.4 In the event that water pressure at the tap water is too low to reach the water, the original designed water method can be used as it is, and the hot water can be taken from the water supply pipe by turning off the cold water switch and turning on the hot water switch. In case of water stoppage due to running water, because the hot water in the water tank is full every day, it can take up to two or three days to save the use of water. It will never be cut off due to water shortage.

2.4.5 The water in the tank is full every day. The weight can increase the installation stability of the solar water heater and increase the wind resistance.

4.6 The method of water extraction using hot water from the top of the cold water can be installed in the pavilion for users of the bungalows. The water heaters do not need to be installed in high positions.

3 Routine Maintenance of Water Heaters Most of the solar water heaters are installed on the roof of a building, and maintenance operations are difficult. The conditional user can solve it by themselves, otherwise the routine maintenance work needs the water heater installation company to help solve it.

3.1 Periodically remove the dust on the surface of the vacuum heat collection tube and the diffuser, and keep the transparent and diffuse surface of the vacuum heat collection tube clean, so that the heat absorption efficiency of the heat collector can be optimized.

3.2 Many hail areas in summer should pay attention to changes in weather and take timely measures to prevent flooding.

3Before the arrival of winter every year, it is necessary to check whether there is any damage to the insulation material and repair it if necessary.

3.4 Remove the snow on the collector after the winter snowfall.

3.5 After the water heater is used for 2 to 3 years, it is necessary to clean the scale in the glass vacuum tube.

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