The constant temperature and humidity machine belongs to the process air conditioner and is used in the occasions of high requirements for air temperature and humidity precision in the electronics industry, instrumentation, printing, post and telecommunications, communication, computer room, etc. Since the conventional constant temperature and humidity machine is cooled and dehumidified by the refrigeration system, and then reheated by electric heating, the repeated energy consumption is severe, and it is considered to be a high energy consumption air conditioner product. Today, with the increasing shortage of energy, energy conservation has become a major issue to be solved in constant temperature and humidity machines.
2. Working principle of conventional constant temperature and humidity machine The working principle of the conventional constant temperature and humidity machine is: firstly, through the cooling and dehumidification of the refrigeration system, the air is treated to a low temperature and low humidity state, and then the electric heater is used to increase the outlet air temperature to achieve The need for precise control of room temperature; an electrode or steam humidifier is also provided for isothermal humidification to achieve precise control of the relative humidity in the room.
It can be seen that in order to meet the requirements of accurate temperature and humidity control, the conventional constant temperature and humidity machine must use the refrigeration system to cool and dehumidify the air to achieve lower temperature and humidity than the supply air temperature, and then use electric heating and humidifier to compensate. Warming up and compensating for humidification, so that not only the energy consumption is severely depleted, but also the water resources are lost to a certain extent.
In addition, since conventional constant temperature and humidity machines mostly use non-adjustable compressors, and the control uses a simple two-position control mode, that is, the temperature and humidity are realized by the start and stop of the compressor, the electric heater and the humidifier. control. Therefore, even if the large air volume and small temperature difference, the electric heater adopts multi-stage adjustment or even stepless adjustment, the control return air type constant temperature and humidity machine can only achieve the return air temperature ±0.5 °C, and the return air relative humidity ±5%. Control accuracy; while controlling the air-type constant temperature and humidity machine, generally only achieve the outlet temperature ± 1 ° C, the output relative humidity ± 10% control accuracy. Therefore, no matter the energy consumption index or the control precision, the conventional constant temperature and humidity machine is more and more difficult to meet the requirements of the society for energy conservation and the high temperature and precision industry requirements for temperature and humidity.
3. The working principle of energy-saving high-precision constant temperature and humidity machine In view of the high energy consumption and low precision of the current constant temperature and humidity machine, this paper proposes an energy-saving high-precision constant temperature and humidity machine, whose working principle is as shown. Different from the conventional constant temperature and humidity machine, the energy-saving high-precision constant temperature and humidity machine adopts a variable capacity compressor capable of energy adjustment, and an air-cooled reheat condenser is used instead of the electric heater as a reheat compensation component, and a refrigerant is used. As a reheating adjustment mechanism, the three-way proportional control valve adds some necessary system solenoid valves and check valves. The PLC controller and PID control scheme are adopted for control.
The following is a brief introduction to a series of energy-saving technologies used in energy-saving high-precision constant temperature and humidity machines: (1) Variable-capacity compressors with energy regulation are available. Currently, variable-capacity compressors with energy regulation are mainly digital. Scroll compressors, inverter compressors, stepless load transfer compressors and other types. The energy-saving high-precision constant temperature and humidity machine is designed by Copeland's digital scroll compressor.
Compared with other variable capacity compressors, Digital Scroll compressors have a wider range of cooling and heating capacity adjustment (10% to 100%), more precise capacity control and room temperature control, better dehumidification performance, and partial load Higher energy efficiency ratio, low noise and low vibration, no electromagnetic interference, excellent oil return characteristics, simple and reliable system, etc., is the highest level of variable capacity compressor.
(2) Replacing the condenser of the electric heater refrigeration system with an air-cooled reheat condenser will release a large amount of heat of condensation, which is usually discharged as waste heat to the outside world. By using an air-cooled condenser as a reheating component, the condensing heat discharged from the refrigeration system can be recovered and the air can be compensated and heated, thereby eliminating the need to consume additional heating energy. This is a very energy-saving heat recovery scheme. Currently, it is widely used in dehumidifiers. However, due to poor control of temperature, it has been difficult to obtain applications on constant temperature and humidity machines.
(3) Using the refrigerant three-way proportional control valve to adjust the reheating heat. Because the heat of condensation is the sum of the cooling capacity and the input power of the compressor, for the general air conditioner, if the heat of condensation is completely recovered, the air temperature can be raised by 10 to 20 °C. The temperature of the air after the constant temperature and humidity machine is cooled by the refrigeration system is generally 10 to 15 ° C. If the air temperature is reheated by the air-cooled condenser to compensate the temperature rise, the air outlet temperature can reach 20 to 30 ° C. In this way, if the air-cooled reheat condenser and the water-cooled condenser are connected in parallel by the two-way temperature control method, there must be a poor comprehensive temperature performance laboratory certified by the Hefei General Machinery Research Institute. The nominal constant temperature and humidity machine H14 and the improved energy-saving constant temperature and humidity machine JH14 were tested for nominal refrigeration conditions and a series of temperature and humidity control tests.
(1) The nominal cooling condition test is to maintain the indoor side air inlet state dry ball/wet bulb temperature 23°C/17°C, the cooling water inlet/outlet water temperature 30°C/35°C, the conventional constant temperature and humidity machine H14 does not turn on the electric heating When the air-cooling reheat condenser side opening degree of the refrigerant three-way proportional control valve of the humidifier and the energy-saving constant temperature and humidity machine JH14 is set to 0%, the nominal refrigeration condition test of the compressor full load operation is performed. The test results are shown in Table 2 above.
It can be seen that when the compressor is fully loaded and not heated and humidified, the energy-saving JH14 constant temperature and humidity machine has a slightly larger cooling capacity than the conventional H14 constant temperature and humidity machine, but the power is also increased, but the energy efficiency ratio is slightly. Low, overall, the difference is small, indicating that the digital scroll compressor has no advantage over the ordinary scroll compressor under full load operation.
(2) Temperature and humidity control performance test: keep the indoor air inlet state dry ball / wet bulb temperature 23 ° C / 17 ° C, cooling water inlet / outlet temperature 30 ° C / 35 ° C, set 30 ~ 80% different In the case of wind relative humidity, the step size is set at a temperature of 1 ° C, and the temperature regulation performance test at 15 to 30 ° C is performed. Due to the different fluctuations of outlet air temperature, relative humidity and power, the data collection of the outlet temperature, relative humidity and power of each test condition, in addition to recording the average value of the unit operation within 20 minutes, The highest value and the lowest value are each collected 1 point to detect the control accuracy of the wind temperature and humidity and the fluctuation range of the power. The power fluctuation and average power consumption of the H14 and JH14 units are related to the set outlet air temperature. It can be seen that compared with the conventional constant temperature and humidity machine H14, the energy-saving constant temperature and humidity machine JH14 is due to its digital scroll compressor. The cyclic loading and unloading operating characteristics at partial load cause large fluctuations in power, but overall, since the digital compressor can be unloaded and operated with condensing heat recovery technology, it is available under all test conditions. Better energy-saving performance, especially in high-temperature and low-humidity air conditions, the energy-saving constant temperature and humidity machine JH14 has obvious energy-saving advantages.
The problem, and in turn affects the control of humidity. Therefore, if the constant temperature and humidity machine is equipped with an air-cooled reheat condenser, the amount of condensation heat recovery must be controlled and adjusted. By using the refrigerant three-way proportional control valve, the refrigerant flow rate can be distributed between 0 and 100% between the two branches of the air-cooled reheat condenser and the water-cooled condenser connected in parallel, thereby realizing convection through air cooling. The refrigerant flow rate of the thermal condenser, that is, the precise control of the reheating energy, makes it possible to use an air-cooling reheat condenser instead of an electric heater to apply the energy saving scheme to the constant temperature and humidity machine.
(4) Using PLC controller and PID control scheme to apply PLC controller, using dew point control method and taking humidity priority control as the principle, through the stepless loading and unloading of digital scroll compressor, precise control of outlet dew point temperature . The running characteristics of the digital scroll compressor without stopping the unloading can greatly reduce the number of compressor start-stops. Moreover, under some working conditions, the humidity can be accurately controlled, the humidifier running time is reduced, and the system is more energy-efficient.
The PID control scheme is adopted to accurately control the flow rate of the refrigerant flowing through the air-cooled reheat condenser through the refrigerant three-way proportional control valve to achieve precise control of the outlet air temperature. In summary, the new constant temperature and humidity machine adopting a series of advanced energy-saving technologies should theoretically achieve the goal of energy saving and precise control of temperature and humidity.
4. Experimental research on energy-saving high-precision constant temperature and humidity machine adopts the conventional water-cooled constant temperature and humidity machine H14 of Shenling Company as the research object, and transforms into the energy-saving high-precision constant temperature and humidity machine JH14 of the system as shown, the design parameters of the unit. It can be seen that compared with the control accuracy of the conventional constant temperature and humidity machine H14 outlet temperature ± 1.5 ° C, the outlet relative humidity ± 10%, the energy-saving constant temperature and humidity machine JH14 has less fluctuation in temperature and humidity, whether in temperature or Humidity control has higher precision, and it can basically achieve high-precision control with temperature accuracy of ±0.5°C and humidity accuracy of ±5%. This shows that the use of refrigerant three-way proportional control valve to control condensation and heat and PID control scheme is an effective means to improve the temperature and humidity control accuracy of the unit.
5. Conclusions Combining digital scroll compressor, condensing heat recovery technology, refrigerant three-way proportional control valve, PID control scheme and other advanced energy-saving technologies and control schemes, an energy-saving high-precision constant temperature and humidity machine has been developed. Through the experimental research and comparison of our common constant temperature and humidity machine H14 and the improved energy-saving high-precision constant temperature and humidity machine prototype JH14, this new type of constant temperature and humidity machine is proved, even under the condition of full load operation. Compared with the conventional constant temperature and humidity machine, there is no advantage, but in the operation of the variable working condition, there is better energy saving effect, especially the high temperature and low humidity air working condition, and the energy saving advantage is more obvious; moreover, the new constant temperature The constant humidity machine has higher precision in both temperature and humidity control.
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