Effect of condenser evaporator on chiller refrigeration

The  industrial chiller refrigeration system consists of a compressor, a  condenser, an expansion valve and an evaporator. The working process is  as follows: the refrigerant boils at the pressure temperature, lower  than the temperature of the object or fluid being cooled. The  compressor continuously sucks the vapor generated in the evaporator and  compresses it to the condensing pressure, and then sends it to the  condenser, which is isostatically cooled and condensed into a liquid  under pressure, and the heat released by the refrigerant cooling and  condensation is transferred to the cooling. The  medium (usually the air used in the air conditioner of the computer  room), the condensation temperature corresponding to the condensing  pressure must be higher than the temperature of the cooling medium, and  the condensed liquid enters the evaporator through the expansion valve  or other throttling elements. Throughout  the cycle, the compressor acts to compress and transport the  refrigerant vapor and cause low pressure in the evaporator. The high  pressure in the condenser acts as the heart of the entire system; the  throttle valve throttles the refrigerant. The  pressure acts and regulates the flow rate of the refrigerant entering  the evaporator; the evaporator is a device that outputs a cooling  amount, and the refrigerant absorbs the heat of the object to be cooled  in the evaporator, thereby achieving the purpose of preparing the  cooling amount; the condenser is a device for outputting heat The  heat extracted from the evaporator and the heat converted by the work  consumed by the compressor are carried away by the cooling medium in the  condenser.
  As the efficiency of compressor has been decided by the investment cost, the specific factors affecting the cooling effect of air conditioner are as follows:
Evaporation temperature of refrigeration system
The evaporation temperature of the refrigerant in the evaporator should be lower than that of the air, so that the heat in the engine room can be transferred to the refrigerant. The refrigerant absorbs the heat and evaporates into gas, which is sucked away by the compressor, so that the pressure of the evaporator will not rise because of the excessive amount of heat evaporating gas, so that the evaporation temperature will also rise, thus affecting the evaporation temperature. The cooling effect, and this temperature difference, is combined with the air conditioning investment costs (to reduce the temperature difference, we must increase the circulating air volume of the chiller, increase the evaporator of the air conditioning, resulting in the chiller cost increases), and refrigeration work energy consumption costs and comprehensive decision. In the water chiller of our computer room, the evaporator adopts the direct evaporation type, the temperature difference is 12-14 (see the manual P746 for water chiller and refrigeration technology). In fact, due to various adverse factors, this temperature difference can not be well guaranteed, sometimes above 20 (ice on the evaporator), so our energy consumption increases. . The calculation shows that the lower the evaporation temperature is, the lower the refrigeration effect of the compressor and the higher the exhaust temperature are. The refrigerant of evaporator in refrigeration system, the evaporation temperature reduces 1 degree, to produce the same cooling capacity, the power consumption increases about 4%.

The factors that affect the evaporation temperature are as follows:

1. Oil deposit in evaporator pipeline: Normally, oil film will not form on the surface of heat exchanger due to the mutual solubility of lubricating oil and Freon. Thermal resistance of oil film can be neglected, but in the case of additional lubricating oil, the same lubricating oil as the original label must be selected to prevent the formation of oil film.

2. air filter clogging: we must regularly replace the filter screen to ensure the required circulating air volume.

3. Drying filter clogging: In order to ensure the normal cycle of refrigeration, the refrigeration system must be kept clean and dry, if the system has impurities, it will cause drying filter clogging, the system is difficult to supply liquid, affecting the refrigeration effect.

4. too little refrigerant and additional Freon.

Two. The opening degree of expansion valve is not correct.

The overheat of the expansion valve must be measured regularly and the opening degree of the expansion valve should be adjusted. The steps are as follows:

Stop. The probe of the digital thermometer is inserted into the insulating layer of the evaporator's air return port to read out the temperature T1 of the evaporator's air return. Connect the pressure gauge to the three-way connection of the compressor low pressure valve (HIROSS40UA and other air conditioners without low pressure valves, then connect the pressure gauge to the connection on the evaporator) and prepare to read out the temperature T2 corresponding to the outlet pressure of the evaporator.

Start up, let the compressor run more than 15 minutes, into the normal operation state, so that the system pressure and temperature to a constant value. The high-voltage pressure measured on the spot is 18Kg/cm2, and the high-voltage switch is always in closed operation, so it has little effect on the system and need not be treated specially.

The temperature T2 corresponding to the outlet temperature T1 of the readout evaporator and the outlet pressure of the evaporator is the difference between two readings. Note that both readings must be read at the same time, because the expansion valve is a mechanical structure, and its action causes both T1 and T2 changes.

The superheat of the expansion valve should be between 5-8 degrees, if not, then adjust.

Specific adjustment steps:

1) remove the protective cover of the expansion valve.

2) Rotation adjustment screw 2-4 turns; (professional air-conditioning expansion valve generally used pressure rod type and scattered gear type, scattered gear type is a small gear to drive a large gear, the number of adjustable turns, generally can adjust 2-4 turns; pressure rod type adjustable turns less, each adjust 1/4 turns; 065 chiller expansion valve using scattered teeth Wheel type)

3) After waiting for 10 minutes, measure the superheat again, whether it is in the normal range, if not, repeat the above operation. The adjustment process must be careful. (If the expansion valve oil plug is serious, the use of absolute ethanol cleaning, and then re-installed; the expansion valve should be replaced without regulating function; replacement, pay attention to the installation position and do a good job of insulation)

Three. Condensing pressure of chiller cooling system

1. the condenser of the cold water machine is dirty.

Air-cooled condenser is usually used in water chiller of machine room. It is composed of many coils with fins added to the coil to increase the heat transfer area on the air side. At the same time, fan is used to accelerate the air flow to increase the heat transfer effect on the air side. Because of the small distance between the sheets and the long-term use of the water chiller in the machine room, the flying insects and dust stick to the fins of the condenser, so that the air can not flow through the condenser with a large flow rate, the thermal resistance increases, affecting the heat transfer effect, resulting in the decrease of the condensation effect, the increase of the pressure on the high-pressure side, the decrease of the cooling effect and the consumption of more electricity. When the condensing pressure increases by 1kg/cm2, the power consumption increases by 6 to 8%.

Countermeasure: According to the use environment of water chiller and the condition of ash deposit, wash the outside chiller regularly. The concrete method is to wash the air conditioner condenser with water gun or compressed air from inside to outside, and remove the sundries and dust attached to the condenser. Now Hangzhou Telecom Branch washes the outside chiller twice a year. While ensuring good heat dissipation, a great deal of energy is saved.

2. improper condenser configuration.

In order to save costs and maximize profits, some manufacturers deliberately allocate small condensers to reduce the cooling effect of water chillers. This situation can be avoided as far as possible in the design of water chillers, but it sometimes occurs. In summer, frequent high-pressure warning of water chillers and frequent flushing of water chillers are not helpful and aggravated seriously.

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