The 50K1 is a fresh air replenishment system with a wind capacity of 1000m3/h for feeding the standard constant temperature and humidity combustion air to the engine. The 50K3 is a fresh air replenishment system with a wind capacity of 2,400 m3/h and is only operated when equipment load is placed indoors. Once the engine is started, it stops running and is replaced by the 50K2 system. Therefore, it does not work with the fan of the 50K2 system. The 50K2 is a fresh air volume adjustable dual fan circulating air return system. The blower and the return fan also have two speeds for automatic or manual conversion during operation. The 50K2 system needs to be operated after the engine is started. Therefore, the main function of the 50K2 system is to eliminate the large amount of heat emitted during the engine test, so that the indoor temperature is maintained within the range of (20 ~ 40) °C, and the air volume of the blower and the return fan are 26000/17300m3/h and 22000/14600m3 respectively. /h. The automatic control of the operation control of each system uses a centrally centralized digital monitoring device. Since the laboratory is only one of the nearly ten various environmental laboratories in a test center, the total number of air conditioning systems and exhaust systems used in various laboratories is several dozen. Hundreds of parameters of these dozens of systems are centrally controlled, displayed and monitored by a microcomputer. In addition, due to the wide variety of air ducts, water pipes, cold water pipes, oil pipes, electric wire pipes, communication cable pipes, etc. in the test room, in order to reduce the conflict between pipes, pipelines must be summarized in the design. To this end, the air-conditioning professional has drawn all aspects of the duct, the tuyere, etc., which are laid in the test room, including the plan view and the side view (9). The frosting and defrosting problems of the cooler in the fresh air handling unit will be a difficult problem because the fresh air temperature required for replenishment can reach -30 °C at the lowest temperature. To this end, the design decided to adopt a frost-free dehumidification and cooling treatment method, that is, a freeze-adsorption combined multi-stage treatment mode such as freeze dehumidification + adsorption dehumidification + freeze dry cooling. 3) Considering that the minimum temperature setting in the room is low, the air temperature of the air treatment equipment is lower. To reduce the transmission energy loss, the air circulation cooling treatment equipment should be hoisted in the body of the low temperature laboratory. 4) On the one hand, considering the low cooling temperature required for indoors; on the other hand, it is also considered to minimize the transmission loss, and strive to simplify the system. The design does not consider the use of antifreeze as the intermediate cooling agent. Despite its good temperature control characteristics. The design decided to use a direct expansion coil cooling method for the refrigerant. After the screw-type refrigeration unit is clearly adopted, the technical requirements for the performance of the screw compressor are proposed and specified, which is another major task in the design. Although there are many manufacturers that can produce and supply screw-type refrigeration units at home and abroad, there are many models that can meet the required evaporating temperature and cooling capacity. However, when bidding, the companies that dare to cope with the challenge bidding are few and far between. This is mainly due to the particularly high technical requirements for such refrigeration units suitable for wide temperature range environmental tests. Among these technical requirements are: 1 to adapt to the test environment temperature may change in the range of (-30 ~ +20) °C, the evaporation temperature of the refrigeration unit must also be flexible at about (-45 ~ +5) °C Adaptable changes in a wide range. For this reason, in addition to the adjustment of the capacity, the compressor is required to have a function of automatic and manual adjustment of the internal volume ratio of the structure. 2 In order to meet the requirements of indoor temperature control accuracy, the refrigeration unit should have automatic capacity stepless control. Originally, in the case that the compression ratio is likely to vary within a wide range, in order to improve the compression performance as much as possible and reduce the effect of the cooling of the spray oil on the energy efficiency, the compressor body is provided with two spray interfaces for operation. Automatically selected. When the real-time running compression ratio of the compressor is greater than 315, the lower passage of the electromagnetic three-way valve PV-030 is opened, and the passage of the membrane and the suction side of the membrane three-way valve is connected, so that the pressure inside the capsule is lost, so the liquid refrigerant Through the right passage, the right side opening SL2 is accessed to achieve enhanced cooling. When the real-time operating compression ratio of the compressor is lower than 315, the electromagnetic three-way valve PV-030 will be in another position to open the through passage. Flat Top Tower Crane, also known as Topless Tower Crane, has the advantages of quick and easy assembly. Usually many Flat Top cranes have been used on construction projects or near airports where overhead clearance is frequently a concern. 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