What is the effection of condenser and evaporator on chiller?

- Jul 31, 2018-

Effect of condenser and 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 below the temperature of the object or fluid being cooled. The compressor continuously draws the vapor generated in the evaporator and compresses it to the condensing pressure, then sends it to the condenser, which is isostatically cooled and condensed into a liquid under pressure. The heat released during cooling and condensation of the refrigerant is transferred to the cooling medium (usually the air used in the air conditioner of the computer room), and the condensation temperature corresponding to the condensation pressure must be higher than the temperature of the cooling medium. The condensed liquid enters the evaporator through an expansion valve or other throttling element. 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 and regulates the flow of refrigerant into 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 that outputs heat, and 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.

Since the compressor efficiency has been determined by the investment cost in the four major parts of the chiller, the specific factors affecting the air conditioning refrigeration effect are as follows:

First, the evaporation temperature of the refrigeration system

The evaporation temperature of the refrigerant in the evaporator should be lower than the air temperature, so that the heat in the equipment room is transferred to the refrigerant. The refrigerant absorbs heat and evaporates into a gas, which is sucked away by the compressor, so that the pressure of the evaporator is not increased due to excessive gas evaporated by heat. Thereby increasing the evaporation temperature, thus affecting the cooling effect,The temperature difference is combined with the investment cost of the air conditioner (to reduce the temperature difference, it is necessary to increase the circulating air volume of the chiller, increase the evaporator of the air conditioner, resulting in an increase in the cost of the chiller), and comprehensively determine the energy consumption during cooling work. In our computer room chiller, the evaporator is directly evaporating, this temperature difference is 12 ~ 14 ° C (see chiller and refrigeration technical manual P746). In fact, due to various adverse factors, this temperature difference cannot be guaranteed very well, sometimes above 20 °C (ice on the evaporator), so our energy consumption increases. By calculation, the lower the evaporation temperature, the lower the evaporation temperature of the compressor and the higher the exhaust gas temperature. In the refrigerant of the evaporator in the refrigeration system, the evaporation temperature is reduced by 1 degree, and the same amount of cooling is generated, and the power consumption is increased by about 4%. 

The factors affecting the evaporation temperature are as follows:

1. Evaporator line oil: 

Under normal circumstances, due to the mutual solubility of lubricating oil and Freon, no oil film is formed on the surface of the heat exchanger, and the thermal resistance of the oil film may be disregarded. However, in the case of additional lubricating oil, it is necessary to use the same lubricating oil as the original one to prevent the oil film from being generated.

2. Air filter clogging: The filter must be replaced regularly to ensure the circulating air volume required by the air conditioner.

3. Dry filter clogging: In order to ensure the normal circulation of the cooling enthalpy, the refrigeration system must be kept clean and dry. If the system has impurities, it will cause the drying filter to be clogged, and the system will be difficult to supply liquid, which will affect the cooling effect.

4. Too little refrigerant, additional Freon.

Second, the heavy valve opening degree is wrong

The superheat of the expansion valve must be measured periodically to adjust the opening degree of the expansion valve. Proceed as follows:

Stop. The probe of the digital thermometer is inserted into the insulation layer at the evaporator return port, and the temperature T1 at which the evaporator is returned is prepared. Connect the pressure gauge to the tee of the compressor low pressure valve (the air conditioner without low pressure valve such as HIROSS40UA, connect the pressure gauge to the connector on the evaporator), and prepare to read the temperature T2 corresponding to the outlet pressure of the evaporator. 

Turn on the machine and let the compressor run for more than 15 minutes to enter the normal operating state, so that the system pressure and temperature reach a constant value. The high pressure measured at the site is 18Kg/cm2, and the high pressure switch is always in the closed state, so it has little effect on the system and is not used for special treatment.

The temperature T2 corresponding to the evaporator outlet temperature T1 and the evaporator outlet pressure is read, and the superheat is the difference between the two readings. Note that both readings must be read out at the same time because the expansion valve is a mechanical structure and its action will cause a change in both T1 and T2. 

The expansion valve should be superheated between 5 and 8 ° C. If not, adjust.

Specific adjustment steps:

1) Remove the protective cover of the expansion valve;

2) Turn the adjusting screw 2-4 turns; (The professional air-conditioning expansion valve generally adopts the pressure rod type and the scattered type gear type. The scattered type gear type uses a small gear to drive a large gear, and the number of adjustments is relatively large, and generally can be adjusted by 2 to 4 times; The number of adjustable levers is relatively small, and each adjustment is 1/4 turn; Expansion valve of 065 chiller adopts loose gear type)

3) After 10 minutes, the superheat is measured 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 blockage is serious, use anhydrous ethanol for cleaning, and then reinstall it; The expansion valvethat loses the adjustment function should be replaced; when replacing, pay attention to the installation position and keep warm)

Third, the condensing pressure of the chiller refrigeration system

1. The chiller condenser is dirty

The engine room chiller generally adopts an air-cooled condenser, which is composed of multiple sets of coils, and ribs are added to the coil to increase the heat transfer area on the air side. At the same time, the fan is used to accelerate the flow of air to increase the heat transfer effect on the air side. Because the fin space is small, and the machine room chiller is used for a long time, the flying insects and dust stick to the condenser fins, so that the air cannot flow through the condenser. The thermal resistance increases, affecting the heat transfer effect, resulting in a decrease in the condensation effect, an increase in the pressure on the high pressure side, and a reduction in the cooling effect while consuming more power. For every 1kg/cm2 of condensing pressure, the power consumption increases by 6 to 8%.

Countermeasure: combined with the use environment of the chiller, periodically flush the chiller outside the machine according to the ashing situation. The specific method is to use a water gun or compressed air to flush the air conditioner condenser from the inside to the outside, and remove the debris and dust attached to the condenser. At present, Hangzhou Telecom Branch flushes the computer room air conditioner twice a year to ensure good heat dissipation and save a lot of energy. 

2. The condenser is improperly configured

In order to save costs, some manufacturers pursue profit-making, deliberately deploying a small condenser, so that the cooling effect of the chiller is reduced. This situation should be avoided as much as possible in the design of the chiller, but it sometimes happens. In the summer, the chiller frequently causes high-pressure warnings, and frequent flushing of the chiller outside machine also does not help, seriously increasing the workload of maintenance personnel, and the condenser must be replaced. Such as Hangzhou Zhuantang, new fan room, due to the small condenser configuration, high-pressure failure in two days in summer, maintenance personnel are exhausted, a lot of manpower and resources are wasted. At present, Hangzhou Telecom Branch has replaced the unreasonable condenser, which has solved this problem well.

3. There is air inside the system

If the chiller does not have enough vacuum, if you do not care when adding liquid, it will mix in the air. Air is harmful in the refrigeration system, it will affect the condensation and heat release of the steam in the cooling crucible, and increase the working pressure of the condenser. 

If the condensing temperature is 35 degrees at that time, the corresponding condensing pressure is 12.5kg/cm2 gauge pressure, the pressure of the actual pressure gauge may be 14kg/cm2, and the extra 1.5 kg/cm2 of air occupies in the condenser. Law of Elton) As the exhaust pressure is increased, the exhaust gas temperature is also increased, the cooling capacity is reduced, and the power consumption is increased, so the air in the high pressure system must be removed. Countermeasure: Perform air discharge operation. In the case of a shutdown, deflate from the exhaust port or condenser plug to perform a deflation operation.

4. If the refrigerant is injected too much, the condensation pressure will also increase. Since the excess refrigerant occupies the area of the condenser, the condensation area is reduced, and the condensation effect is deteriorated.

Conclusion: Through the above means, it can ensure the working condition of the chiller, which not only reduces the failure rate of the chiller, but also saves 10-20% of energy in a single chiller in summer. Therefore, strengthening the maintenance of the chiller is of great significance to the cooling effect of the chiller, the life of the air conditioner, and especially the energy conservation.