Analysis on the difference between air energy compressor and air conditioning compressor

With the rapid growth of the domestic air-energy water heater market, the previous model of "external air conditioner structure design" will gradually be broken. Following the promotion of heat pump compressors in 2009, many compressor manufacturers in China have invested in the development of heat pump compressors in order to provide core guarantees for the healthy development of heat pump water heaters. The operation mode of the heat pump water heater is very different from that of the air conditioner, which determines the difference in the design concept between the heat pump special compressor and the air conditioner compressor. With the rapid growth of the domestic heat pump water heater market, the previous model of "external air conditioner structure design" will gradually be broken.

Trouble-free long-term stable operation

Compared with air conditioners, heat pump water heaters have a big difference in running time. The running time of heat pump water heater systems is much longer than that of air conditioners. The operating time of the heat pump water heater depends on the following factors:

Air conditioners are frequently used in summer, but water heaters are daily necessities, and they operate particularly long in winter. The heating time for a tank of water in winter is several times that in summer, so it is necessary to confirm the operation mode of the heat pump water heater in winter. According to statistical calculations, 2/3 of the life of the heat pump water heater is consumed in winter.

Because the outlet water temperature of the heat pump is above 55 degrees, the temperature of the water tank will drop as the use progresses. When it drops to about 45 degrees, the compressor needs to start up, so the compressor basically runs in the area with higher condensation temperature. . The condensing temperature is the main factor that affects the life of the compressor. Under the same operating time, the comprehensive load of the compressor in the heat pump water heater is much higher than the compressor in the air conditioner.

The main motivation for consumers to purchase heat pump water heaters is energy saving and convenience. Consumers will use more water for this, which also increases the working time of the heat pump.

If the heat pump water heater is used for heating + domestic hot water, it may run for a long time throughout the heating season.

Based on the above various factors, it can be seen that the main engine of the heat pump water heater will be miniaturized, and the actual running time will be greatly increased. To ensure that no failure occurs during the life cycle of the heat pump water heater, the compressor needs to be able to withstand 20,000 hours of actual operation. Therefore, it is very necessary to use a heat pump special compressor.

Comparison of operating modes of air conditioner and heat pump water heater

Matters needing attention in system design

In the actual system design, the rules of heat pump operation must also be followed, so that the function of the heat pump special compressor can be truly utilized. Specifically, the following aspects should be noted:

The throttling device must ensure a wide range

Whether it is a split type or an integrated heat pump water heater placed outdoors, its evaporation temperature is very wide. In order to effectively throttling in a wide range, it is recommended not to use a single capillary tube, but to use an expansion valve or multiple sets of capillary tubes to cope with changes in ambient temperature and ensure that there is suction superheat under all operating conditions. At the same time, avoid the direct entry of liquid into the compressor, especially in winter.

Observe the phenomenon of liquid impact and immersion, and evaluate the risk

For static heating storage heat pump water heaters, "refrigerant migration" is an unavoidable problem: that is, after the compressor stops working, the condenser is in a high water temperature environment, the compressor/evaporator is gradually cooled, and the temperature difference causes the refrigerant to gradually migrate to evaporation And compressor.

The refrigerant "accumulates" and when the compressor restarts, the refrigerant accumulated in the evaporator is likely to enter the compressor directly. In other words, the degree of liquid shock in the heat pump water heater is much more serious than that of the air conditioner. This phenomenon has been verified through many experiments. This is also one of the reasons why the heat pump special compressor adopts a super large-capacity arc-shaped accumulator (to relieve liquid hammer and increase suction superheat). Therefore, when developing heat pump water heaters, it is necessary to observe the phenomenon of liquid hammer and immersion and assess the risks. For example, Ariston, Gree and other companies have carried out detailed observations in the development of heat pump water heaters, confirmed the reliability of the system design, and did a professional job.

Pay attention to the problem of overheating at the bottom of the compressor

This point is easily overlooked in system design, but it is extremely important. The so-called compressor bottom superheat is defined as: compressor bottom temperature-condensation temperature. If the value is zero or less than zero, the compressor body becomes a "condenser" at this time, and the refrigerant will slowly condense into liquid in the compressor shell and deposit at the bottom of the compressor, which is pumped as "lubricating oil" Each sliding surface of the compressor pump body. Liquid refrigerant has no lubrication function. As a result, the friction couple of the compressor pump body wears out, and the occurrence of "cylinder blockage" is only a matter of time.

When the compressor is running in winter, if there is "suction with liquid", the liquid refrigerant entering the compressor will quickly reduce the temperature of the compressor body, and the low ambient temperature will cause the bottom temperature of the compressor to drop relatively low. Since the heat pump water heater needs to produce higher temperature hot water, the condensing temperature is relatively high, and it is easy to happen that the temperature at the bottom of the compressor is lower than the condensing temperature. The system experiment shows that when there is liquid inhalation, when making 55 degrees hot water, the bottom superheat will be less than zero when the ambient temperature is about 5 degrees. The lower the ambient temperature, the more serious.

Ordinary air-conditioning compressors are prone to "motor overheating" when there is suction superheat, especially when running at a high compression ratio. This is exactly what the heat pump dedicated compressor needs to solve. At a high compression ratio, the heat pump dedicated compressor can still operate reliably.

Safety margin for heat exchange on the condensing side

No matter what type of heat pump water heater, after long-term operation, the heat exchange effect on the water side (condensing side) will decrease (scaling, loosening, aging, etc.), and the heat exchange temperature difference will increase. Therefore, at the beginning of the design, it is considered how the temperature difference of the condensing side may change in the future, and a certain safety margin is reserved to ensure that the compressor operates within a safe range for a long time.