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1, the suction temperature is too high: mainly due to the increase of suction superheat caused by high suction temperature does not mean high suction pressure, because the suction is superheated steam.
Under normal circumstances, the compressor cylinder head should be half cool and half hot. If the suction temperature is too high, the cylinder head is all hot. If the suction temperature is higher than normal, the exhaust temperature will also rise accordingly. The main reasons for the high suction temperature are:
(1) Insufficient refrigerant charge in the system: even if the expansion valve is opened to the maximum, there will be no change in the liquid supply, so that the refrigerant steam is overheated in the evaporator to increase the suction temperature.
(2) The expansion valve is opened too small: resulting in insufficient circulation of refrigerant in the system, less refrigeration dose into the evaporator, large superheat, and thus high suction temperature.
(3) The expansion valve screen is blocked: the amount of liquid supplied in the evaporator is insufficient, the amount of refrigerant liquid is reduced, and a part of the evaporator is occupied by superheated steam, so the suction temperature rises.
(4) Other reasons cause the suction temperature to be too high: such as bad insulation of the return air pipeline or too long the pipeline can cause the suction temperature to be too high.
2, the suction temperature is too low: mainly due to the large amount of liquid supplied by the evaporator, resulting in low suction superheat.
(1) The amount of refrigerant charged is too much: it occupies part of the volume in the condenser and increases the condensing pressure, and the liquid entering the evaporator increases. The liquid in the evaporator can not be completely vaporized, so that the compressor suction gas with liquid droplets. In this way, the temperature of the return air pipe decreases, but the evaporation temperature does not change because the pressure does not drop, and the superheat decreases. Even if the expansion valve is turned down, there is no significant improvement.
(2) The expansion valve is opened too large: due to the loose binding of the temperature sensing element, the small contact area with the return gas pipe, or the temperature sensing element is not wrapped with insulation material and its wrapping position is wrong, resulting in the temperature measured by the temperature sensing element is inaccurate and close to the ambient temperature, which increases the opening degree of the expansion valve action, resulting in excessive liquid supply.
Due to external reasons, the refrigerant does not evaporate enough or even does not evaporate in the evaporator, which will cause serious frost and even wet compression. (If the central air conditioning return air is insufficient or the air conditioning box filter is seriously blocked, the chiller main press return pipe will frost, and the exhaust temperature is also very low).
3. Abnormal exhaust temperature: influencing factors: adiabatic index, compression ratio, suction temperature.
The compressor exhaust temperature can be read from the thermometer on the exhaust pipe. It is related to the adiabatic index of the refrigerant, the compression ratio (condensing pressure/evaporation pressure) and the suction temperature. The higher the suction temperature, the higher the compression ratio, the higher the exhaust temperature, and vice versa.
When the suction pressure is unchanged and the exhaust pressure is increased, the exhaust temperature rises. If the exhaust pressure does not change, when the suction pressure drops, the exhaust temperature should also rise. Both cases are caused by an increase in the compression ratio. The high condensing temperature and exhaust temperature are adverse to the operation of the compressor and should be prevented. Too high exhaust temperature will dilute or even carbonize the lubricating oil, thus worsening the lubrication conditions of the compressor.
The exhaust temperature is proportional to the compression ratio (condensing pressure/evaporation pressure) and the suction temperature. If the suction superheat temperature is high and the compression ratio is large, the exhaust temperature is also high. If the suction pressure and temperature are constant, when the exhaust pressure is increased, the exhaust temperature is also increased.
The main reasons for the increase of exhaust temperature are:
(1) The suction temperature is higher, and the exhaust temperature of the refrigerant steam is higher after compression.
(2) The condensation temperature increases, and the condensation pressure is high, resulting in an increase in the exhaust temperature.
(3) The exhaust valve disc is broken, the high pressure steam is repeatedly compressed and the temperature rises, the cylinder and the cylinder head are hot, and the thermometer indication value on the exhaust pipe is also increased.
4. High exhaust pressure: mainly caused by high condensing pressure, rather than the press itself. High exhaust pressure will increase the compression work and reduce the gas transmission coefficient, thus reducing the refrigeration efficiency.
The exhaust pressure is generally corresponding to the condensation temperature. Under normal circumstances, the exhaust pressure of the compressor is very close to the condensing pressure. When the condensing pressure increases, the compressor exhaust temperature also increases. The compression ratio of the compressor increases, the gas transmission coefficient decreases, and the cooling capacity of the compressor decreases. Increased power consumption. If the exhaust temperature is too high, it increases the consumption of lubricating oil in the compressor, making the oil thin and affecting lubrication; When the exhaust temperature is close to the flash point of the compressor oil, it will also carbonize some lubricating oil and accumulate in the suction and exhaust valve port, affecting the sealing of the valve.
Reducing the temperature of the cooling medium can reduce the condensing temperature and the condensing pressure, but this is limited by environmental conditions and is difficult to choose. Increasing the flow rate of the cooling medium can reduce the condensation temperature (this method is often used). However, it is not possible to unilaterally increase the flow of cooling water or air, because it will increase the power of cooling pumps or fans and motors, which should be comprehensively considered.
The main reasons for this failure are:
(1), cooling water (or air) flow is small, high temperature.
(2) There is air in the system, which increases the condensing pressure.
(3) The amount of refrigerant is too much, and the liquid occupies the effective condensing area.
(4) The condenser has been in disrepair for a long time, and the dirt on the heat transfer surface is serious, which can also lead to an increase in condensing pressure. The presence of scale also has a great influence on condensing pressure.
5, the exhaust pressure is too low: mainly caused by the refrigeration system pipeline refrigerant flow is small or even stopped.
The exhaust pressure is too low, although the phenomenon is manifested in the high pressure end, but the cause is more in the low pressure end. Common reasons: the expansion valve is blocked by ice or dirty, and the filter is blocked, which will inevitably reduce the suction and exhaust pressure.
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