top of page
  • Writer's pictureKai Zhang

Comparison Between Screw Chillers and Centrifugal Chillers

  • 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.

centrifuge-chiller-structure

  • 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 150-3000RT, so generally, centrifugal chillers are designed with only one centrifugal compressor to meet the cooling needs.


centrifugal-chiller-unit

  • 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%.


screw-chiller-unit

  • 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.


office

  • 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 2950 revolutions per minute, and its noise value is generally around 75dB (A), while centrifugal units are generally above 80 dB (A).

  • Centrifuge Chillers: Generally 9000-40000 rpm, and uses blades, impellers for suction and exhaust, so its noise level is slightly higher than that of screw machines and sharper.


building

  • 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 5632Kw (1600 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=1200 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=239884 kWh.


During the 4-month operation of the 650 cold ton unit, the total power consumption of the screw unit was 239884.6 kWh; The total power consumption of the centrifugal unit is 276719 degrees. That is to say, the screw unit saves 36834.4 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=276719 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.

91 views0 comments

Comments


library

library

air condtitioning projects

wood

wood

air condtitioning projects

bridge-crane-electric-room

bridge-crane-electric-room

air condtitioning projects

home-vrf-system

home-vrf-system

air condtitioning projects

hvac-for-hotel-project

hvac-for-hotel-project

air condtitioning projects

Tanzania-office-building

Tanzania-office-building

air condtitioning projects

ethiopia-railway-station

ethiopia-railway-station

air condtitioning projects

1-TG-Tower

1-TG-Tower

air condtitioning projects

russia-gymnasium-stadium

russia-gymnasium-stadium

air condtitioning projects

power-plant

power-plant

air condtitioning projects

villa-view

villa-view

air condtitioning projects

air-conditioning-project-Bangladesh

air-conditioning-project-Bangladesh

air condtitioning projects

Get in touch

bottom of page