Satellite launch towers

Tuesday, December 19, 2017

No compromise on reliability for satellite launch tower cooling in China

A challenge for temperature and humidity control overcome with Danfoss cooling solutions
In this case, the Satellite Launch Center is one of China’s bases for the launching of test satellites, applications satellites and carrier rockets. In the past, the Launch Center has successfully utilized the CZ-4 carrier rocket to deliver China's first and second FY-1 mete-horological satellites into sun-synchronous orbit. The satellite launch tower is a service structure providing access for personnel and equipment to satellites and their carrier rockets, allowing operations like assembly, testing, maintenance, compressed gas charging and final launch.

The tower is a vital facility in the satellite launch environment. The temperature and humidity of a rocket are critical parameters which require accurate control from initial positioning of the rocket until the launch.

The special environment of the rocket launch poses stern challenges for temperature and humidity control. First, a rocket may stand outdoors for weeks, where it is exposed to rapid and wide temperature fluctuations. For example, temperatures may drop below -5°C at night or exceed 20°C in the daytime, while there is always the possibility of wind and rain. Second, rocket launching demands a high level of reliability and stability. Regardless of environmental changes, the temperature and humidity of the rocket itself must be maintained within strict limits. Once the launch process is initiated, continuous operation of the refrigeration system is essential. Moreover, the electronic components of the satellite and the rocket are very sensitive to changes in temperature and humidity. In order to ensure optimal working conditions for components and avoid potential risks such as frosting, stringent requirements are imposed on temperature and humidity fluctuations during satellite launch. But the required temperature and humidity control parameters differ for each launch task, necessitating that control devices have wide control latitude.

Advantages of Danfoss inverter compressors for precise temperature and humidity control

Previously, the launch tower was fitted with air conditioning equipment from another domestic supplier, which employed a system design integrating four fixed speed compressors. Control of temperature and humidity could only be achieved by adjusting the air supply or via staged modulation. The control requirements were unable to be met without the use of supplementary means such as electric heating. At low-load conditions (particularly at night), the evaporator would often frost over, making it difficult for units to run continuously. To better safeguard the satellite launch environment, the launch center demanded a solution to this problem, one which would ensure the stability and reliability of the HVAC system.

As one of the top players in China's refrigeration and air-conditioning industry, Wuzhou Refrigeration was invited to participate in the renovation project. A detailed feasibility analysis concluded that, due to constant varying of fresh air load, variable capacity modulation technology would be essential to ensure the stability of air supply parameters and the reliable operation of the HVAC unit. The results of analysis and testing showed that the energy profile generated by the four systems featuring fixed-speed compressors is a step-like curve unable to realize continuous step-less adjustments in cooling capacity. For this reason, it was decided to try a system combining two Danfoss inverter scroll compressors VZH117 with three fixed speed compressors.

No frosting of the evaporator reduces system stops

Danfoss inverter compressors deliver a highly efficient and stable modulation of cooling capacity by controlling motor speed through a frequency converter drive. Most crucially, VZH inverter scroll compressors can adjust cooling.

This was accompanied by an extension of modulation range, with the low-speed operation of the compressors under low load conditions ensuring the matching of cooling capacity to load. The resulting continuous adjustment of energy was the perfect solution to the problem of discrete cooling output generated by the previous combination of staged modulation with fixed speed compressors.

The advantages of Danfoss inverter scroll compressors VZH are not limited to modulation scale exten-ion, but also include enhanced precision in the control of temperature and humidity. Compared with the staged modulation with fixed speed compressors, variable speed solutions make smoother temperature control in air conditioning systems. In this project, fuzzy PID control was employed to control the running conditions of the Danfoss inverter scroll compressors VZH so as to regulate temperature and humidity, making continual adjustments of cooling capacity output in response to load requirements. The project demanded a temperature precision of ±1℃. The Chief Engineer of Wuzhou Refrigeration Mr. Tan comments: "Since installing the all fresh-air air conditioning equipment with Danfoss inverter scroll compressor VZH, the temperature is more precisely controlled - up to 0.2℃ and relative humidity between 3 to 5%. Compared to the previous solution, the close controls reach more easily stable performance.

This has resulted in safer and more reliable operations in summer and transition seasons, with no more instances of overrun. On top of this, "there has been no frosting of the evaporator causing system stop" adds Mr. Tan.

The benefits are also for contractors. The all fresh-air air conditioning equipment employs a modular design, and the exterior units are lightweight and compact, making installation a breeze", says the installer of these units.

VZH compressors win customer trust with a reputation for outstanding performance

As pioneer in HVAC technology targeting environmental and energy challenges, Danfoss offers a range of mature variable-speed solutions. Danfoss inverter scroll compressors VZH boast unique advantages in the field of precise temperature and humidity control, combining high precision with convenience. VZH inverter scroll compressors also represent a new design in variable speed operations. The use of high performance motors featuring rare earth permanent magnets allows full-load efficiency as high as 96%, retaining efficiency above 92% throughout the entire motor speed range. At the same time, there is less heat transfer from the motor to the refrigerant, resulting in higher compression efficiency. The performance of the tailor made drive dedicated to VZH compressors has been verified by testing in a range of different application scenarios, so that the pairing of drive and compressor is now a mature solution that reduces the time and costs spent on system development. 

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