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2 indoor hot and cold load calculation and main equipment selection
2. 1 indoor hot and cold load
The indoor cold load is mainly composed of the cold load formed by the roof solar radiation, the cold load formed by the temperature difference of the glass roof and the cold load formed by the solar simulator. Moreover, since the cold load formed by the solar simulator does not occur at the same time as the cold load formed by the solar radiation, the largest of the two may be considered. The calculated total cold load is 29.38kW.
The environmental simulation laboratory presets the maximum temperature difference to 50. Considering the most unfavorable conditions in winter, the winter outdoor temperature difference in Xi'an is tw = - 5, and the solar radiation is also obtained without considering the maintenance structure and ground heat dissipation. Heat is considered as a margin, and the total heat load is 9kW.
2. 2 refrigeration equipment selection
The environmental simulation laboratory has higher requirements for temperature difference control accuracy (0.5), and the set value of the indoor temperature difference is determined according to the temperature difference of the actual natural environment, that is, the natural temperature difference of a certain day or several days is collected. Change the data and establish a time-varying curve as the temperature difference setpoint for the environmental simulation laboratory. Different from the general thermostatic control method, this puts higher requirements on the selection of the refrigeration equipment and the determination of the control scheme.
Since general industrial refrigeration equipment can not meet the requirements of handling accuracy (0.5), we have used one chiller (including two compressors), two air-cooled condensers and three variable air cooling fans to form an evaporator. Cooling System. According to the calculated cold load, a MCF-200PJ indoor type parallel semi-hermetic compressor unit is selected, and the freezing capacity is 53.45kW, 43.92kW, respectively, when the evaporating temperature difference is -5, -10, -15, -20, respectively. 36. 02 kW, 29.05 kW.
2. 3 Selection of heating equipment According to the calculated thermal load, the environmental simulation laboratory has the characteristics of low heat load, and the defrosting heaters (4 kW each, a total of 6 sets) supporting the refrigeration equipment can satisfy the heating. Needed, so the preset no longer presets the heating device.
3 environment simulation laboratory automatic control system preset
The Environmental Simulation Laboratory is a multi-variable complex system that requires computer control of the system in order to meet the process preset requirements of the simulation room. The preset two-level control system, the first-level computer monitoring level SCC, mainly realizes the main information of the comprehensive monitoring and testing process, the archiving of historical data, the issuing of commands to the lower computer and the realization of advanced control algorithms, etc.; Tasks such as data information collection and process control of each system in the lower layer. The system SCC (host PC) adopts the Pentium IV series IBM compatible machine, and uses the Kingview software of the Asian Control Company to develop the human-machine interface monitoring system in the Windows 2000 environment; the lower computer adopts the PLC programmable controller to realize the process. Real-time PID control. The upper and lower machines use the serial port for communication, and the communication protocol uses the PPI protocol.
3. 1 Temperature difference control system principle The given (set) values ​​of each controlled quantity of the simulation laboratory system are changed according to the predetermined time program. For example, for the temperature difference, to realize the temperature difference change of one day, we pre-set A curve is set so that the actual temperature difference can be varied according to this curve. Therefore, the simulated laboratory control system is a typical program control system.
Here, the controller corresponds to the PLC, the actuator corresponds to the inverter, the refrigeration unit and the heater, and the measurement corresponds to the temperature difference sensor transmitter, and the controlled object corresponds to the environmental simulation laboratory, and the controlled amount is the simulated indoor air temperature difference.
3. 2 realization of temperature difference control Considering the difference of the space temperature difference field, multiple temperature difference sensors are used to measure the temperature difference. Take the average value as the temperature difference of the simulation room. In order to control the precision, automatic control and automatic control and control of the upper and lower limits and set values ​​are used in the automatic control, as shown. When the environmental simulation laboratory is in the refrigeration zone, the compressor and the fan work at the same time. By controlling the number of working platforms of the compressor and the speed of the fan, the temperature difference and the air volume of the indoor air are controlled, thereby adjusting the temperature difference in the room and realizing the temperature difference control requirement. For the heating zone, the temperature difference and the air volume of the indoor air are controlled by controlling the number of heaters and the fan speed, thereby adjusting the temperature difference in the room and realizing the temperature control requirement.
In addition, the heater also has the function of defrosting the surface cooler.
When the measured temperature difference PV> SVH, it is the cooling zone. At this time, two refrigeration compressors are started. The frequency of the inverter is 30Hz. The controller does not adjust the frequency. It runs according to the large cooling capacity and quickly reduces the temperature difference to SVH. When SVH When PV<SV, it is the cooling transition zone, one refrigeration compressor is stopped, and the other refrigeration compressor runs according to the small cooling capacity and adjusts the inverter output. When PV=SV, the compressor stops running, the cooling fan stops after 3 minutes delay, and the system is in standby state. When the temperature and cooling control principle is raised to PV = SVH, run a compressor and start the second delay. If the temperature difference is PV<SVH before the second delay is ON, only run. One compressor, the cooling fan runs according to the small cooling capacity; when the temperature difference is PV> SVH, the second compressor is started and the inverter output is adjusted. The heating process is adjusted in the same way.
3. 3 Human-machine interface development Preset We use the Kingview software of Asia Control Company as the monitoring software of the host computer, and carry out secondary development to realize the monitoring of the system.
There are 7 monitoring interfaces in this system: user login interface, system total monitoring interface (including fan system, inverter, compressor system, solar simulator system, heater and humidification system, etc.), environmental factors Control curves (such as temperature control curve, humidity measurement curve, surface radiation intensity control curve, etc.), fault alarm interface, real-time and historical data reports, real-time trend curves, historical trend curves, reports, etc.
4 simulation experiment results and analysis
First, it is investigated whether the temperature difference range achievable by the environmental simulation laboratory satisfies the aforementioned preset process requirements. It can be seen that the achieved low temperature value and high temperature value reach the preset requirements of -10 and 50, and the peak of the protrusion in the figure is caused by the defrosting of the evaporator. In addition, it can be seen that achieving a high temperature environment is less time consuming than a low temperature environment. This is due to economic considerations and is determined by the capacity of the selected refrigeration equipment. However, for the main work currently being studied in the simulation room, the preset has met the need; when the cooling speed is required, only the cooling is appropriately increased. The number of machines can be.
After the working curve is set, the simulation test can be performed.
5 Conclusion
According to the characteristics of the meteorological parameters on the southern margin of the Taklimakan Desert, based on the economic and research purposes, the process indicators of the environmental simulation laboratory temperature difference were determined.
According to the characteristics of the temperature difference of the simulated object, based on the secondary development of Kingview software, the PID control process is used to realize the computer control of the environment simulation laboratory. The simulation test results show that the process index of the simulated object has reached the preset requirement, that is, the temperature difference range is -1 0 50 and the precision is 0. 5.
In the temperature difference environment simulation, not only the constant temperature control, but also the variable temperature operation can be performed according to the required working curve with the required accuracy.
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