How Water-Cooled Screw Chillers Work

Dec. 16,

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Water-cooled screw chillers also belong to chillers, because their main components use screw compressors, so the name can be called water-cooled screw chillers. Widely used in plastics, electroplating, electronics, chemical, pharmaceutical, printing, food processing and other industrial refrigeration process using chilled water, or large shopping malls, hotels, factories, hospitals and other areas requiring central air conditioning projects. Use chilled water to cool the area centrally.

Water cooled screw chiller working principle

Unit refrigeration, the compressor will send the low temperature and low pressure refrigerant in the evaporator into the cylinder, through the compressor work, the refrigerant vapor compressed into high temperature and high pressure gas.

It enters the condenser through the exhaust pipe. The high-temperature and high-pressure refrigerant gas is exchanged with cooling water in the condenser, and the heat is transferred to the cooling water to take away, while the refrigerant gas is condensed into high-pressure liquid. The high pressure liquid from the condenser enters the evaporator by throttling the thermal expansion valve. In the evaporator, the low-pressure liquid refrigerant absorbs the heat from the chilled water and makes the chilled water vaporize and cool to become the required low temperature water. The vaporized refrigerant gas is re-absorbed by the compressor and discharged into the condenser for repeated circulation, thus cooling the chilled water.

Water Cooled Screw Chiller

The chilled water flowing out from the unit enters the indoor fan coil, variable air volume air conditioner and other terminal equipment for heat exchange with convective air indoors, in which the temperature of water rises due to absorbing heat from indoor air (heat to indoor air), and the indoor air temperature drops through the indoor heat exchanger, driven by the fan, and enters the room, thus lowering the indoor air temperature, while the chilled water in the pump after the temperature rises re After the temperature rises, the chilled water in the pump enters the unit again, and so on, so as to achieve the purpose of continuous cooling.

Features of water cooled screw chiller 

(1)The compressor of the unit is semi-hermetic screw compressor and electric control components, equipped with heat exchanger and high-efficiency high-quality copper tube condenser and evaporator.

(2) Equipped with all kinds of safety devices, stable performance, low noise, long life, simple operation; LCD human-machine interface, simple and convenient operation, clear operation at a glance.

(3) Models have a single compressor or multi-compressor combination of refrigeration system. The compressor can be automatically turned on and run according to the change of load, balancing the running hours of the compressor to achieve the effect of saving energy and extending the service life of the chiller. Easy energy regulation and more energy in the load section.

(4) Open structure, beautiful appearance of the machine, simple structure, can check the operation of the unit at any time, easy installation and maintenance.

System composition: water-cooled screw chiller is mainly composed of semi-closed screw compressor, shell and tube condenser, dry filter, thermal expansion valve, shell and tube evaporator, electrical control part, etc.

If you want to get more information about the best water-cooled screw chiller , welcome to contact us today or request a quote.  

• Structure:

• Screw Chillers: In a screw compressor, the meshing of two female and male rotors completes the suction, compression, and exhaust processes by rotating inside the casing. Its main components include screw compressors, condensers, evaporators, thermal expansion valves, and other control components, which are fewer than centrifugal machines. It has the characteristics of compact structure, balanced and reliable operation, few vulnerable parts, high partial load efficiency, and long service life.
  

• Centrifuge Chillers: It relies on the centrifugal force generated by the high-speed rotating impeller in a centrifugal compressor to generate power for refrigeration. Its main components include a centrifugal compressor, evaporator, condenser, throttling mechanism, extraction and recovery device, lubrication system, and electrical control cabinet. It has the characteristic of large refrigeration capacity per unit, but there are drawbacks such as surge.
  

• Capacity:

• Screw Chillers: The refrigeration capacity of a screw compressor is smaller than that of a centrifuge compressor, usually ranging from 30RT to 500RT. Therefore, nowadays, screw chiller with large refrigeration capacity adopt a multi head method, controlled and regulated by a microcomputer, and each compressor has a separate refrigeration system.
  

• Centrifuge Chillers: The refrigeration capacity of a centrifugal compressor is relatively large, ranging from 150-RT, so generally, centrifugal chillers are designed with only one centrifugal compressor to meet the cooling needs.

• Working:

• Screw Chillers: The electric motor directly meshes with the main rotor and auxiliary rotor to rotate at low speed.
  

• Centrifuge Chillers: The electric motor drives the impeller to rotate at high speed through a pair of speed increasing gears.
  

• Efficiency:

• Screw Chillers: The screw machine uses oil pressure to push the slide valve switch to control the capacity, and there is no unbalanced impact phenomenon when under partial load. For multi head screw units, the energy regulation range is generally between 10% and 100%, and continuous energy regulation is possible. Especially in civil and commercial places, such as hotels, shopping malls, conference centers, etc., the air conditioning load varies greatly with seasonal and human flow changes, requiring refrigeration units to have a wide range of energy regulation.
  

• Centrifuge Chillers: Generally speaking, the energy regulation range of a centrifugal unit is 40-100%. When operating at a load below 40%, the centrifugal unit is more prone to "surge". When the "surge" is severe, it can damage the entire core component of the unit - the impeller. At present, many centrifugal unit manufacturers use "air replenishment" methods to achieve a critical point of "20%" or "10%" for the unit's "surge", which requires a large amount of energy consumption, resulting in relatively low efficiency of the unit below 50%.

• Maintenance:

• Screw Chillers: The screw machine is in the form of multiple compressors and has an independent refrigeration system. In this way, during maintenance and repair, it is necessary to shut down a single damaged compressor while others continue to operate as usual.
  

• Centrifuge Chillers: Generally speaking, centrifuges adopt the form of a single compressor. During maintenance and repair, the entire machine needs to be shut down and the refrigeration operation stopped. The structure is complex, with many vulnerable parts and high maintenance costs.

• Noise:

• Screw Chillers: It relies on the meshing and rotation of the female and male rotors to complete suction and exhaust. Its speed is relatively low, usually revolutions per minute, and its noise value is generally around 75dB (A), while centrifugal units are generally above 80 dB (A).
  

• Centrifuge Chillers: Generally - rpm, and uses blades, impellers for suction and exhaust, so its noise level is slightly higher than that of screw machines and sharper.

If you want to learn more, please visit our website Air Conditioning Chiller.

• Consumption:

Both centrifuges and screw chillers consume a large amount of electricity, but under the same refrigeration capacity, the energy efficiency of screw chillers under partial load is higher than that of centrifugal units under partial load.

With a total cooling capacity of Kw ( cold tons), if three units are used, each unit has a cooling capacity of approximately 650 cold tons. Taking the 650 ton chiller unit as an example, the power consumption of two types of units will be compared and analyzed. According to statistics, the full load or 100% operating time of the chiller unit accounts for 2.3%, 75%, 50%, and 25% of the total operating time.

The running time accounts for 41.5%, 46.1%, and 10.1% of the total running time, respectively. This project is calculated based on an annual air conditioning time of 4 months: the overall operating time is 4 x 30 x 10= hours. Then the unit is 100%, 75%, 50%, and 25%. The running time is 27.6 hours, 498 hours, 553 hours, and 121 hours respectively.

• Screw Chiller:

For example, the screw chiller unit has a COP of 5.24 at full load. The COP of the unit at 75%, 50%, and 25% load is 6.63, 7.23, and 6.03, respectively.

The power consumption of the unit at 100%, 75%, 50%, and 25% load is as follows:

650 x 3.517 x 100% ÷ 5.24=436Kw;

650 x 3.517 x 75% ÷ 6.63=259Kw;

650 x 3.517 x 50% ÷ 7.23=158Kw; 95kW 650 x 3.517 x 25% ÷ 6.03=95kW.

The total power consumption for 4 months is 436 x 27.6+259 x 498+158 x 553+95 x 121= kWh.

During the 4-month operation of the 650 cold ton unit, the total power consumption of the screw unit was .6 kWh; The total power consumption of the centrifugal unit is degrees. That is to say, the screw unit saves .4 degrees of electricity compared to the centrifugal unit, which saves nearly 15% of operating costs.

• Centrifugal Chiller:

For example, the centrifugal chiller unit has a COP of 5.58 at full load. The COP of the unit at 75%, 50%, and 25% load is 5.97, 5.74, and 3.87, respectively.

The power consumption of the unit at 100%, 75%, 50%, and 25% load is 650 × 3.517 × 100% ÷ 5.58=410Kw, respectively;

650 x 3.517 x 75% ÷ 5.97=276Kw;

650 x 3.517 x 50% ÷ 5.74=199Kw;

650 x 3.517 x 25% ÷ 3.87=148Kw.

The total power consumption for 4 months is 410 x 27.6+276 x 498+199 x 553+148 x 121= kWh

After comparison, you may know how to select the right water-cooled chillers according to your actual situation, or contact with us for professional solutions.

For more information, please visit Dc Chiller.