Some opinions on the test and evaluation of variab

2022-10-04
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With the continuous improvement of people's pursuit of high-quality life, variable frequency air conditioning is better than conventional air conditioning in use effect and gradually becomes the mainstream of market consumption. However, there is no specific standard for a clear and comprehensive discussion on the testing of variable frequency air conditioning. Combined with the development practice in recent years, this paper puts forward some new technical indicators, discusses the design of variable frequency air conditioning, and evaluates its comprehensive performance

2 discussion on design evaluation index

2.1 index for design evaluation of refrigeration (heat) capacity under standard working conditions

generally, the performance index of conventional air conditioning under standard working conditions can be basically achieved by refrigeration (heat) capacity/refrigeration (heat) power/energy efficiency ratio (performance coefficient). However, since the speed of variable frequency air conditioner can be changed according to the change of demand during operation, so as to change the capacity output, it is obvious that the capacity characteristics of variable frequency air conditioner cannot be evaluated only by the nominal value of nameplate. In view of this situation, the following indicators are proposed for design and evaluation reference

2.1.1 maximum refrigerating (heating) capacity/rated refrigerating (heating) capacity coefficient

this index is proposed to evaluate the maximum capacity range of variable frequency air conditioners, and also indirectly expresses the rapid refrigerating (heating) capacity of air conditioners. For example, variable frequency air conditioners with the same rated refrigerating capacity may have different frequency adjustable ranges due to the limitations of compressors, evaporators, condensers, air volume and other factors, so the maximum refrigerating capacity is also different

take the following two machines as examples, brand a kfr-26gw/bp2y and brand B kfr-26gw/bp2y (see Table 1)

it can be seen from table 1 that brand a machine has basically the same capacity as brand B in rated cooling state, but the maximum cooling capacity has obvious advantages. In the simulated user experiment, brand a machine will be 4.7m × 3.3m × It takes only 10 minutes for a 2.2m room to reduce from 32 ℃ to 20 ℃, while it takes 17 minutes for a brand B machine

2.1.2 the minimum refrigerating (heating) capacity/rated refrigerating (heating) capacity coefficient

corresponds to the previous index, which is to evaluate the minimum capacity range of variable frequency air conditioners and indirectly express the accuracy of air conditioners in room temperature regulation. When the indoor temperature is close to the set temperature, the capacity output of the frequency converter will be reduced to keep the room temperature in a relatively stable range. Generally speaking, the smaller the minimum capacity range is, the higher the accuracy of the stable range is, and the power consumption is relatively low. Taking brand a machine kfr-26gw/bp2y as an example, the room temperature can be stabilized at about 0.5 ℃

2.2 performance design evaluation index under non-standard working conditions

the performance index of conventional air conditioning under non-standard working conditions is generally evaluated according to various type experiments specified internationally. However, since the speed of variable frequency air conditioner can be changed according to the change of working conditions during operation, the evaluation of the non-standard working condition characteristics of variable frequency air conditioner can not be evaluated only by several types of experiments with soft and comfortable sitting on the national standard. According to the practical experience of development and development, the following design evaluation methods are proposed to be added

2.2.1 high load maximum frequency operation refrigeration

experimental method: completely close the ventilation valve and exhaust valve (if any) for the exchange of indoor and outdoor air of the air conditioner, adjust its set temperature, fan speed, guide grille, etc. to the maximum refrigeration state, and the test voltage is 85% and 115% of the rated voltage respectively. In the indoor working condition of 32 ℃/23 ℃ (dry/wet ball), the maximum frequency of operation under the outdoor working condition is as high as possible, After stabilization, continue to operate for 1 hour, then shut down for 3min (during which the power supply voltage rises by no more than 3%), and then start to operate for 1 hour

experimental evaluation: when tested according to the above experimental methods, the components of the air conditioner should not be damaged, and the air conditioner should be able to operate normally; During the first hour of continuous operation of the air conditioner, its motor overload protector should not jump; When the air conditioner is shut down for 3min, start it again for continuous operation for 1 hour, but the motor overload protector is allowed to jump off within the first 5min of start-up and operation, and then it is not allowed to act; If the motor overload protector does not reset within the first 5min of operation, and its shutdown does not reset within 30min, it shall operate continuously for 1 hour; If the overload protector with manual reset jumps out within the first 5min, it shall be forced to get in position after jumping out for 10min, and it shall be able to operate continuously for another 1hrh [1]

explanation: in high temperature environment, the pressure of refrigeration system is relatively high. For the inverter, it is very effective to evaluate the safety of its system with high temperature and high frequency operation. Taking another kfr-26gw/bpy of company a as an example, the indoor (dry/wet) temperature is 32/23 ℃, 187v, and the frequency is 78hz (see Table 2)

it can be seen from table 2 that after the outdoor temperature exceeds 43 ℃, the exhaust temperature rises rapidly. It can be seen that the environmental working conditions of high-temperature operation are bad for the system. In the design, attention should be paid to ensure that the system pressure and temperature are within the safe range under the worst working conditions. The module temperature basically increases linearly with the temperature

2.2.2 maximum outdoor ambient temperature operation refrigeration (high temperature, high (low) pressure cooling)

Test Method: completely close the ventilation valve and exhaust valve (if any) for exchanging indoor and outdoor air of the air conditioner, adjust its set temperature, fan speed, guide grille, etc. to the maximum refrigeration state, and the test voltage is 85% and 115% of the rated voltage respectively. Under indoor working conditions, 32 ℃/23 ℃ (dry/wet ball), The outdoor working condition is to operate at the maximum temperature allowed by the air conditioner, and then operate continuously for 1 hour after it is stable. When the traditional experimental method can not speed up the time, then stop the machine for 3 minutes (the power supply voltage rises by no more than 3%), and then start the machine for 1 hour

experimental evaluation: according to the above experimental methods, the components of the air conditioner should not be damaged, and the air conditioner should be able to operate normally; During the first hour of continuous operation of the air conditioner, its motor overload protector should not jump; When the air conditioner is shut down for 3min, start it again for continuous operation for 1 hour, but the motor overload protector is allowed to jump off within the first 5min of start-up and operation, and then it is not allowed to act; If the motor overload protector does not reset within the first 5min of operation, and its shutdown does not reset within 30min, it shall operate continuously for 1 hour; For the overload protector with manual reset, if it jumps within the first 5min, it should be forcibly reset 10min after the jump, and it should be able to continue for another hour [1]

explanation: in the environment of high temperature and low pressure, the safety of the system is more severe. For the inverter, there is also the evaluation of module temperature. Take a kfr-50lw/bpy from company a (see Table 3)

it can be seen from table 3 that when the voltage decreases and the outdoor temperature increases, the frequency decreases, so that the power remains basically unchanged, and the system pressure remains below the safe range, but the module temperature rises faster. In addition to the impact of the increase of outdoor working conditions, due to the reduction of voltage, the speed of outdoor fan decreases, and the heat exchange effect becomes worse. Although the module temperature is still within the safe range, it is still something we need to pay attention to in our design

2.2.3 low temperature and low pressure startup

experimental method: when the outdoor ambient temperature is -15 ℃, the indoor ambient temperature is 15 ℃, and the voltage is 150V, shut down the air conditioner and place it, and keep the compressor to establish and improve the comprehensive evaluation criteria and industry standard thermal state of plastic granulator equipment. After 8 hours, start the air conditioner

experimental evaluation: when tested according to the above experimental method, the air conditioner should start normally

explanation: since the inverter can still start normally under low voltage conditions, this experiment is designed to simulate the state of use under harsh conditions in winter

2.2.4 long term operation experiment

experimental method: under the general environment of the air conditioner, run the air conditioner for 15 days (12 hours a day) or continuously for 100 hours

experimental evaluation: when tested according to the above experimental methods, the air conditioner should start and operate normally without abnormal phenomena

explanation: the essence of this experiment is a comprehensive evaluation of the safety of the whole system by simulating the state of users' extreme use

3 conclusion

according to the national standard gb/t room air conditioner, coupled with the above test and evaluation methods, the quality of variable frequency air conditioner will be more safe and reliable, and the comfort of air conditioner will also be greatly improved

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