A common cause of premature reciprocating compressor failure is overheating. A reciprocating that is running too hot will surely fail before its time. A service tech should always look for this potential problem while servicing any refrigeration system.
The hottest location in a refrigeration system is at the discharge port of the valve plate inside the compressor head. It is difficult for a technician to measure the exact temperature at this location. It’s important to know the causes of overheating to repair the system.
Let’s learn the main causes of discharge port overheating: high return air temperature, large motor heating capacity, high compression ratio, high condensing pressure, and improper refrigerant selection.
(1) high return air temperature
The return air temperature is relative to the evaporation temperature. In order to prevent liquid back flow, the return air line generally requires a return air super heat of 20 °C. If the return line is not well insulated, the degree of super heat will far exceed 20 °C.
The higher the return air temperature, the higher the cylinder suction and exhaust temperatures. For every 1 °C increase in the return air temperature, the exhaust gas temperature will increase by 1 to 1.3 °C.
(2) Motor heating
For a return air cooled compressor, the refrigerant vapor is heated by the motor as it flows through the motor cavity, and the cylinder suction temperature is again increased. The heat generated by the motor is affected by power and efficiency, and the power consumption is closely related to exhaust, volumetric efficiency, working conditions, and frictional resistance etc.
About the return air-cooled semi hermetic compressor, the temperature rise of the refrigerant in the motor cavity is approximately between 15 and 45 °C. In the air-cooled (air-cooled) type compressor, the refrigerant does not pass through the winding, so there is no motor heating problem.
(3) The compression ratio is too high
The exhaust gas temperature is greatly affected by the compression ratio, and the larger the compression ratio, the higher the exhaust gas temperature. Reducing the compression ratio can significantly reduce the exhaust temperature, including increasing the suction pressure and reducing the discharge pressure.
The suction pressure is determined by the evaporation pressure and the suction line resistance. Increasing the evaporation temperature can effectively increase the suction pressure and rapidly reduce the compression ratio, thereby reducing the discharge gas temperature.
Some users believe that the lower the evaporation temperature, the faster the cooling rate. This idea has many problems. Although lowering the evaporation temperature can increase the freezing temperature difference, the refrigeration capacity of the compressor is reduced, so the freezing speed is not necessarily fast. Moreover, the lower the evaporation temperature, the lower the refrigeration coefficient, the higher the load, the longer the running time, and the higher the power consumption.
(4) Refrigerant type
Different refrigerants have different thermos physical properties, and discharge gas temperature rises differently after undergoing the same compression process. Therefore, different refrigerants should be used for different cooling temperatures.
If the compressor is operating normally, there should be no overheating such as high motor temperature and high discharge temperature. Overheating of the compressor is an important failure signal indicating a serious problem with the refrigeration system or improper usage and maintenance of the compressor.
During using cold room, there will be some common faults for the refrigeration system, let us check and solve them.
Fault Analysis: After the refrigerant leaking in the system, the cooling capacity is insufficient, the suction and exhaust pressures are low, and the expansion valve can hear the intermittent airflow sound much larger than usual. The evaporator does not hang frost or hang a small amount of floating frost. If adjusting the expansion valve hole, the suction pressure does not change much. After shutdown, the equilibrium pressure in the system is generally lower than the saturation pressure corresponding to the same ambient temperature.
Solution: After the refrigerant leaking, don’t rush to fill the system with refrigerant. Instead, should find the leak point immediately, and fill the refrigerant after repair.
Filling too much refrigerant after maintenance:
Fault Analysis: The amount of refrigerant charged in the refrigeration system after maintenance exceeds the normal volume of the system. The refrigerant will take up a certain volume of the condenser, reduce the heat dissipation area, reduce the cooling efficiency, and generally have high suction and discharge pressures. The evaporators don’t frost and the temperature cooling is slow.
Solution: According to the operating procedure, it is necessary to stop the machine for a few minutes and then release excess refrigerant at the high pressure shut-off valve. At this time, the residual air in the system can also be released together.
Air in the refrigeration system:
Fault Analysis: If there is air in the refrigeration system will reduce the cooling efficiency. The prominent phenomenon is that the suction and exhaust pressures increase (but the exhaust pressure has not exceeded the rated value), and the temperature at the compressor outlet to the condenser inlet is significantly increased. Due to the air in the system, the exhaust pressure and exhaust temperature increase.
Solution: It is possible to release air from the high pressure shut-off valve several times after a few minutes after the shutdown, and it is also possible to properly fill some refrigerant according to the actual situation.
4. The efficiency of compressor is low:
Fault Analysis: The low efficiency of the refrigeration compressor means that the actual exhaust gas volume decreases and the cooling capacity responds less when the operating conditions are constant. This phenomenon occurs mostly on compressors that have been used for a long time, and the wear is large, the clearance of each component is large, and the sealing performance of the gas valve is lowered to cause the actual exhaust gas to decrease.
(1) Check if the cylinder head paper pad is broken down and cause leakage. If it is, replace it.
(2) Check if the high and low pressure exhaust valves are not closed tightly, If it is, replace it.
(3) Check the clearance between the piston and the cylinder. If it is too large, replace it.
The frost on the surface of the evaporator is too thick:
Fault analysis: Long-term use of the cold room evaporator should be timed defrosting, such as no defrosting, the frost layer on the evaporator line is thicker and thicker, when the whole pipeline is wrapped into a transparent ice layer, it will seriously affect heat transfer. Causes the cold room inside temperature can’t reach to required value.
Stop the defrosting, open the cold room door to let the air circulate, and use the fan to accelerate the air circulation and reduce the defrosting time.
Refrigerantoil in the evaporator line:
Fault Analysis: During the cooling cycle, some of the refrigerant oil remains in the evaporator line. After a long period of use, when there is more residual oil in the evaporator, the heat transfer effect will be seriously affected, and the cooling efficiency will decrease.
Solution: Remove the refrigerant oil from the evaporator. Remove the evaporator, cleaned and then dried. If it is not easy to remove, it can be pumped from the evaporator inlet and then blown with a blowtorch.
The refrigerant leakage in the temperature sensor of the expansion valve:
Fault analysis: After the refrigerant leaking in the temperature sensor of the expansion valve, the two forces below the diaphragm push the diaphragm up, the valve hole is closed, the refrigerant in the system can not pass, and the expansion valve doesn’t frost, the low pressure is vacuum, and no sound is heard in the evaporator.
Solution: Shut down the shut-off valve and remove the expansion valve to check if the filter is clogged and replaced when damaged.
The compressor suddenly stopped during operation
For air-cooled condenser:
1 The fan is not turned on.
2 The fan motor is damaged.
3 The fan is reversed.
4 The ambient temperature is high (up to 40 °C).
5 The condenser fins are blocked by oil dust and the air does not circulate.
For water-cooled condenser:
1 The cooling water valve is not open or opened too small, the inlet pressure is too low
Cold room is a building warehouse using refrigeration machine to reach a certain temperature and has insulation to hold the temperature.
2, Cold room classification:
According to the structure
◇ Civil engineering cold room building
◇ Steel structure cold room
◇ Mixed structure
According to the cold room usage
◇ Production type cold room used in food, meat, fish factory
◇ Distribution type cold room used for logistics
◇ Retail cold room used for supermarket
◇ Household cold room
According to the cold room scale
◇ Large cold storage over 10,000 tons
◇ Medium-sized cold storage 1000-10,000 tons
◇ Small cold storage less than 1000 tons
According to the cold room temperature
◇ High temperature cold room design temperature (-2~8°C)
◇ Medium temperature cold room design temperature (-10~-23°C)
◇ Low temperature cold room design temperature (-23~-30°C)
◇ Ultra-low temperature cold room design temperature (-30~-80°C)
According to the cold room goods
◇ Seafood and meat cold room
◇ Dairy and ice cream cold room
◇ Fruit and vegetables cold room
◇ Pharmaceutical and chemicals cold room
◇ Flower cold storage
3, Cold room Floor frost heave and protective measures
It is the frost heaving drum of the soil layer under the cold storage floor. The frost heaving phenomenon in the cold room is related to the thickness of the floor insulation layer, the movement of the freezing point isotherm, the migration of water in the soil, the soil quality and the water content. Although the cold room floor is covered with a certain thickness of insulation, it is not completely isolated from heat transfer. Floor frost heaving is also the biggest problem facing the cold room storage ground structure.
Ways to prevent floor frost heave
Overhead floor (direct and reliable, high cost)
Ventilation floor (with certain limitations)
Heating floor (cost saving, high construction requirements)
When the geological conditions of the multi-layer cold storage are poor, it is recommended to use the overhead floor. When better, the other methods can be considered. When the geological conditions of the single-layer cold storage are poor, it is recommended to use heating or ventilation floor. When the temperature is poor, the overhead floor can be considered.
4, Cold room refrigerant choice
◇Ammonia: the oldest in history, the best choice in the field of industrial refrigeration worldwide. Due to the characteristics of the ammonia system, it is generally used for centralized refrigeration, with a special machine room for large-scale refrigeration systems (more than 10,000 tons of cold storage). There is a trend toward miniaturization and modulation, with an emphasis on improving safety and reducing the amount of charging.
◇ Freon: It is widely used in cold storage to disperse refrigeration. It is suitable for small and medium-sized cold storage and large-scale cold storage with limited ammonia. For environmental protection, large-scale cold storage The Freon system should be avoided as much as possible.
◇ CO2: The cold storage application is mainly based on cascade system and loading system. The low-temperature field is more suitable for cascade. The high-temperature field is suitable for loading. The cascade system is more expensive than the traditional ammonia and Freon system.
5, Cold room defrosting ways
6, Cold storage room mold removal ways
Molds generally grow in dark, damp areas and can withstand lower temperatures. Usually in the high temperature cold room, the situation is the most serious. The mold grows in the cold storage, and the spores fly everywhere, which pollutes the goods and products stored in the warehouse.
◇ Mechanical mold removal (manual cleaning and removal of moldy parts)
◇ Physical mold removal (using temperature, humidity, ultraviolet light, high frequency electricity and copper mesh filters)
As owner, we not only have to consider the construction and material costs of cold storage, also should consider the follow up operating costs of cold storage. It directly affects our cold storage effectiveness.
The keys to managing energy efficiency are reducing operational costs, during managing a cold storage warehouse, we should strictly control the energy costs from five parts “ice, frost, water, doors and lights”. Meanwhile using remote monitoring can have a significant impact on reducing energy, maintenance and overall operating costs. Here we only discuss it from how to correctly operate the refrigeration unit and evaporators and how to do the cold storage management.
1, Reasonably adjust the operating parameters of the refrigeration system to improve equipment efficiency.
According to actual cold storage temperature and goods conditions, adjusting system pressure and temperature parameters which can ensure the safety of machinery and storage products, fully utilize equipment efficiency, and save Water, electricity, oil, etc.
2, Prevent evaporating temperature being too low, in common the temperature difference between evaporating temperature and cold storage temperature is 3-5℃.
When the temperature difference between the evaporating temperature and the cold storage temperature increases, the evaporating temperature will be too low, which will result in a decrease in the refrigeration coefficient and an increase in energy consumption. It is estimated that under the same conditions, when the evaporation temperature is lowered by 1℃, it will consume 1~2% more electricity. In addition, as the temperature difference increases, the dehumidification amount of the air cooler is increased, and the humidity of the cold storage warehouse is reduced, thereby causing an increase in dry food consumption and a decrease in food quality.
3, The refrigeration system is a sealed circulation system, keep the refrigerant circulating in the system is clean and free of impurities.
4, Timely remove the frosts on the evaporator and scales on the condenser.
The second importance is energy saving in the cold storage management.
The cold storage is a special building used for freezing and refrigerating foods and maintaining a certain low temperature. The floor, walls and roof are covered with a certain thickness of moisture-proof layer and insulation layer to reduce the introduction of external heat, and at the same time, in order to reduce the radiant heat of the sun, the surface of the exterior wall of the cold storage is generally painted white or light.
Since the cold storage building has the above characteristics, in addition to ensuring the building quality with strict heat insulation, sealing, sturdiness and frost resistance in design and construction, it should also be based on the characteristics of the cold storage in daily use management. Scientific management is implemented to ensure safe production, so as to achieve the purpose of prolonging the service life, reducing production costs, saving maintenance costs, and improving the economic benefits of enterprises.
1, Cold storage door should be closed tightly; Minimize the frequency door opening and door opening time.
2, Reasonable stacking to improve cold storage warehouse utilization
The utilization rate of the cold storage warehouse directly affects the economic benefits of the cold storage, the utilization rate is low, the cooling capacity of the unit weight is increased, and the dry consumption is increased, and the cost is increased. Therefore, strong packaging, shelves, etc. should be adopted, and the code height should be increased to improve the utilization of the warehouse. When the goods are not full, if the storage characteristics of the goods are the same or similar, and they do not affect each other, they can be mixed for a short time.
3, Cold storage warehouse lighting control
The lighting of the cold storage warehouse not only consumes electric energy, but also increases the heat in the warehouse. Therefore, the lighting of the warehouse should be controlled in groups according to the front, middle and back. After entering the warehouse, the staff should minimize the number and time of turning on the lights, and turn the lights off when go out.
Coordination between preservation and refrigeration technology is an important guarantee to reduce operating costs and improve enterprise efficiency. Adopting modern refrigeration technology and cold storage management will reduce the whole cold storage cost.
Atlascool-your cold room expert, more than 18 years refrigeration experience, from design to installation and maintenance service, we provide one stop cold storage service for your fresh life. Best practice for building cold storage and controlling energy saving.
Atals cold room refrigeration company sincerely wishes all my customers happy mid autumn festivals!
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