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1. Rationale
Solar absorbent air conditioning systems consist mainly of solar collectors and absorbent chillers。
1. 1 absorption refrigeration principles
Absorption refrigeration is performed using a binary solution consisting of two substances as a work mass. The two substances have different boiling points under the same pressure, where the components of the high boiling point are called absorbents and the components of the low boiling point are called refrigerants. Common absorbent-refrigerant combinations have two types: lithium brominated-water, usually for large central air conditioners, and hydro-ammonium, usually for small air conditioners。
Absorption chillers consist mainly of generators, condensers, evapotors and absorbers。
This paper takes the example of a brominated lithium absorbent chiller. During the operation of the chiller, when the brominated lithium water solution is heated with thermal water in the generator, the water in the solution is vaporized; the water vapour enters the condenser and is condensed by cooling water cooling temperatures; the concentration of the liquid in the generator increases and enters the absorber as the water is continuously vapourized; when the water in the compressor enters the evaporation unit through the throttle valve, it swells and steams, and during the process it absorbs the heat of the refrigerant water in the steamer in order to achieve cooling purposes; in the process, the low-temperature water vapour enters the absorbent, absorbs the concentrate of the concentrate brominated lithium in the absorbentor, the solute concentrations decrease gradually, and is returned to the generator from the solution pump to complete the cycle。
1. 2 activation of solar absorbent air conditioning
Solar absorbent refrigeration is the use of solar collectors to provide thermal water needed by the absorbent chillers for their generators. The higher the temperature of the hot water, the higher the performance factor (also known as cop) for the chiller, the more efficient the air conditioning system will be. For example, if thermal water temperature is around 60°c, the chiller is about 0? 40; if thermal water temperature is around 90°c, the chiller is about 0? 70; and if thermal water temperature is around 120°c, the chiller is over 1? 10。
The conventional absorbent air-conditioning systems consist mainly of absorbent chillers, air-conditioning tanks (or wind hoses) and boilers, on which solar-absorbed air-conditioning systems add solar collectors, water tanks and automated control systems。
During the summer, hot water heated by the collector first enters the water storage tank, where the hot water reaches a certain temperature, and provides heat media to the chiller; hot water flowing from the chiller and cooling back to the tank, then heated by the collector into high temperature hot water; and cooling water produced by the chiller reaches the air conditioning tank for the purpose of cooling air conditioning. Supplementary boilers can be used to supplement heat when solar energy is insufficient to provide high-temperature heat-borne water。
In the winter, the heat from the collector is also put into the water storage tanks, which provide hot water directly to the air conditioner when the temperature reaches a certain level for the purpose of heating. When solar energy does not meet the requirements, supplementary boilers can also be used to replenish heat。
During the non-air-conditioning heating season, cold water in water storage tanks can be gradually heated for use as long as the heat from the collector is delivered directly to the heat exchanger in the domestic water tank。
2. Integrated air conditioning and heating demonstration systems
In order to put solar absorbent air conditioning technology into practice, in september 1999 the beijing city solar research institute, under the mandate of the “nine five” national science and technology targeting programme, established the country's largest solar absorbent air-conditioning and heat-supply integrated demonstration system (see table below)。
2. 1 overview of location of installation
The solar air-conditioning demonstration system is located in the city of ^san in shandong province. The city of ^shan is located at the south-east end of the shandong peninsula, with a smoker in the north, an island in the west and the yellow sea in the south. The region has a better solar resource, with an average daily solar exposure of 17. 3 mj/m2 per year. Local maximum summer temperature 33°c, minimum winter temperature - 7°c, with cooling and heating requirements for the summer and winter respectively, is a suitable location for the installation of solar air conditioning systems。
• the silver beach tour resort in the city of ^shan city, which takes advantage of the natural conditions in the region and is vigorously developing the tourism industry, is preparing the “new energy science park in china”. The cope park plans to build eight libraries and halls, including wind and solar energy. Solar air-conditioning systems are located in the solar library in kopp park。
It is possible not only to visit solar energy exhibits, to increase solar energy literacy, to learn about the latest solar technology, but also to experience the comforts created by solar air conditioning and heating while visiting and entertaining。
2. 2 main technical capabilities
The new solar air-conditioning system consists of thermal tubing vacuum-pipe collectors, the brominated lithium absorbent chillers, hot water storage tanks, cold water storage tanks, household hot water storage tanks, recycling pumps, cooling towers, air-conditioning tanks, auxiliary fuel boilers and automated control systems. Following the completion of the system installation, the diodes, electromagnetic valves, were operated and tested during the winter, spring and summer seasons to reach the main technical capabilities of table 1。
2. 3 system design characteristics
(1) organic integration of solar energy and construction
The overall design of the entire solar complex has enabled the building to be aesthetic, novel and responsive, while meeting the requirements for the installation of a collector. In accordance with this principle, the southern side of the building has a large slant roof structure, one of which is much larger than the plane and allows for more heaters to be installed, and the other is designed without the need to consider front- and back-to-back coverings and in a very beautiful form. The tilt roof is 35°, close to local latitude, and allows the collector to function fully。
(2) heat tube vacuum tube collectors have improved cooling and heating efficiency
Thermal vacuum tube collectors are a major scientific and technological achievement of the beijing city solar institute, which has many advantages, such as efficiency, ice resistance, start-up speed, temperature protection, pressure stress, heat shock resistance, and operation*, and is an important component of high-performance solar air-conditioning systems. Thermal tube vacuum collectors can provide 88°c heat-borne water for efficient lithium brominated chillers, thus increasing the system's cooling efficiency; they can also work effectively in cold winters in the north to heat buildings。
(3) two hot tank sizes speed up the daily cooling or heating process
Based on the inherent characteristics of changes in solar irradiation over a day, hot water tanks not only stabilize the system but also store excess energy in the form of hot water at solar irradiation peaks. The difference between the system and the general solar air-conditioning system is the installation of two large and small hot water storage tanks. Small storage water tanks are mainly used to ensure rapid start-up of the system. Tests have shown that in the summer and winter mornings, water temperature in small hot tanks can reach 88°c and 60°c, respectively, thus meeting cooling and heating requirements。
