Error Alarming in Chiller System and How to solve?
First, The suction temperature is too low
The most fundamental reason for the low suction temperature is the low suction superheat caused by the large liquid supply of the evaporator.
How do you understand it? We understand it in the following way:
The large amount of liquid supplied to the evaporator causes the refrigerant in the evaporator to not evaporate completely, so the liquid refrigerant continues to evaporate in the return pipe, and the evaporation and heat absorption will make the temperature of the refrigerant in the suction pipe low, and the suction temperature will be low. .
The question is again, why is the evaporator supplying too much liquid?
It is understood according to the following ideas: the large amount of liquid supplied to the evaporator means that there is too much refrigerant in the evaporator, and the system is charged too much or the opening of the expansion valve is too large, which will cause this problem.
Cause of:
(1) The refrigerant charge is too much, which causes it to occupy the internal volume of the condenser and increase the condensing pressure, and the liquid entering the evaporator also increases. The liquid in the evaporator cannot be completely vaporized, so that the gas sucked by the compressor contains liquid droplets. In this way, the temperature of the return gas pipeline decreases, but the evaporation temperature does not change because the pressure does not drop, and the degree of superheat decreases. There is no significant improvement even if the expansion valve is closed.
(2) Expansion valve opening is too large. Because the temperature sensing element is tied too loosely and has a small contact area with the return air pipe; or the temperature sensing element is not wrapped with heat insulating material and its wrapping position is wrong, etc., the temperature measured by the temperature sensing element is inaccurate, close to the ambient temperature, and the expansion valve moves. The opening degree increases, resulting in excessive liquid supply.
Compressor frosting analysis:
(1): The evaporator works normally to absorb heat, but the refrigerant supply of the throttle valve is too much (above);
(2): The refrigerant charge is insufficient, and it will be connected from the evaporator to the compressor. (to be verified);
(3): Due to external reasons, the refrigerant does not evaporate enough or even does not evaporate in the evaporator. At this time, it will be seriously frosted and even cause wet compression. (For example, if the return air of the central air conditioner is insufficient or the filter screen of the air conditioner box is seriously blocked, the return air pipe of the main compressor of the chiller will be frosted, and the exhaust temperature will be very low)
Second, the suction temperature is too high
We understand the reasons for the low intake air temperature, so it is easy to analyze the reasons for the high intake air temperature;
The suction temperature is too high - mainly due to the increase of suction superheat. Note that high suction temperature does not mean high suction pressure, because suction is superheated steam.
Under normal circumstances, the compressor cylinder head should be half cool and half hot. If the intake air temperature is too high, the cylinder head will all heat up, and if the intake air temperature is higher than the normal value, the exhaust temperature will also increase accordingly.
Cause of:
(1) The sufficient amount of refrigerant in the system is insufficient
Even if the expansion valve is opened to the maximum, the liquid supply will not change much, so that the refrigerant vapor is superheated in the evaporator to increase the suction temperature.
(2) Expansion valve opening is too small
This situation causes insufficient circulation of refrigerant in the system, and the amount of refrigerant entering the evaporator is small, the degree of superheat is large, and the suction temperature is high.
(3) The filter screen of the expansion valve port is blocked
The liquid supply 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) The suction temperature is too high due to other reasons
If the return air pipeline is not well insulated or the pipeline is too long, it can cause the suction temperature to be too high.
Third, The exhaust temperature is abnormal
Factors that affect the abnormal exhaust temperature: adiabatic index, compression ratio, suction temperature
The compressor discharge temperature can be read from the thermometer in the discharge line who gave you. It is related to the adiabatic index, compression ratio (condensing pressure/evaporating pressure) and suction temperature of the refrigerant.
The higher the suction temperature, the greater the compression ratio, the higher the exhaust temperature, and vice versa. If the suction pressure remains the same and the discharge pressure rises, the discharge temperature rises; if the discharge pressure remains the same, when the suction pressure drops, the discharge temperature also rises.
Both cases are caused by the increased compression ratio. Excessive condensing temperature and discharge temperature are both detrimental to the operation of the compressor and should be prevented. Excessive exhaust gas temperature will make the lubricating oil thin and cause carbonization and coking, which will worsen the lubrication condition of the compressor.
The discharge temperature is proportional to the compression ratio (condensing pressure/evaporating pressure) and suction temperature. If the superheat temperature of the intake air is high and the compression ratio is large, the exhaust gas temperature is also high. If the suction pressure and temperature are constant, when the discharge pressure rises, the discharge temperature also rises.
The reasons for the high exhaust temperature are:
(1) The suction temperature is higher, and the exhaust temperature of the refrigerant vapor after compression is higher.
(2) When the condensing temperature increases, the condensing pressure is also high, resulting in an increase in the exhaust temperature
(3) The exhaust valve plate is broken, the high-pressure steam is repeatedly compressed and the temperature rises, the cylinder and the cylinder head are hot, and the thermometer indicating the exhaust pipe is also increased.
The most practical factors are:
If the intercooling efficiency is low, or too much scale in the intercooler affects the heat exchange, the suction temperature of the latter stage must be high, and the exhaust temperature will also increase.
The valve is leaking and the piston ring is leaking. This not only affects the increase in exhaust temperature, but also the interstage pressure change; as long as the compression ratio is higher than the normal value, the exhaust temperature will increase. In addition, water-cooled machines, lack of water or insufficient water will increase the exhaust temperature. Abnormal condensing pressure and reduced discharge pressure.
Fourth, the exhaust pressure is high
It is mainly caused by the high condensing pressure, not the compressor itself.
The exhaust pressure generally corresponds to the condensing temperature. Normally, the discharge pressure of the compressor is very close to the condensing pressure. When the condensing pressure rises, the compressor discharge temperature also rises.
The compression ratio of the compressor increases and the gas transmission coefficient decreases, thereby reducing the cooling capacity of the compressor and increasing the power consumption. If the exhaust gas temperature is too high, it will increase the consumption of the compressor lubricating oil, make the oil thinner, and affect the lubrication; when the exhaust gas temperature is close to the flash point of the compressor oil, part of the lubricating oil will be carbonized and accumulated in the suction, The exhaust valve port affects the sealing performance of the valve.
Lowering the temperature of the cooling medium can reduce the condensation temperature and the condensation pressure, but this is limited by the ambient temperature, and it is difficult to artificially choose. Increasing the cooling medium flow can lower the condensing temperature a bit (this method is often used). However, the flow of cooling water or air cannot be increased unilaterally, because this will increase the power of the cooling water pump or fan and motor, which should be considered comprehensively. High exhaust pressure will increase the compression work and reduce the gas transmission coefficient, thereby reducing the refrigeration efficiency.
The most critical factor for high condensing pressure remember the following words: The condenser heat exchange is not good! !
The main reasons for this failure:
(1) The flow rate of cooling water (or air) is small and the temperature is high
(2) There is air in the system, which increases the condensing pressure
(3) The sufficient amount of refrigerant is too much, and the liquid occupies the effective condensation area
(4) The condenser is in disrepair for a long time, and the heat transfer surface is seriously fouled, which leads to an increase in the condensing pressure; the existence of scale has a great influence on the condensing pressure.
5. Exhaust pressure is too low
The low exhaust pressure is caused by the small or even stopped refrigerant flow in the refrigeration system pipeline. Exhaust pressure is too low, although the phenomenon changes to the high pressure side, but the cause is mostly at the low pressure side.
The reason is:
(1) The expansion valve is blocked by ice or dirty, and the filter is blocked; it will inevitably reduce the suction and exhaust pressure;
(2) Insufficient refrigerant charge;
(3) The expansion valve hole is blocked, the liquid supply is reduced or even stopped, and the suction and exhaust pressures are reduced at this time.
