Trane CVGF Two-Stage Compressor Widens the Application Range, Why Centrifugal Compressors Surge

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Features and Benefits

Two-Stage Compressor

Widens the Application

Range

Why Centrifugal Compressors Surge

Centrifugal compressors produce their pressure differential (head) by converting the kinetic energy of the gas leaving the impeller into static pressure. The velocity of this gas is the result of two components:

•The radial velocity component Vr, which is directly proportional to the refrigerant gas flow Q.

•The tangential velocity component Vt, which is a function of both impeller diameter D and the rotational speed rpm.

Two-Stage Compressors Surge Less and Later

To produce the same head as a single- stage compressor, two-stage machines use two small diameter impellers.

Component Vt is the same as on each stage, though Vr is the same as on a single-stage compressor.This results in a better balance of forces at low loads and produces a machine with a wider unloading capability.

The length of the resultant vector V is proportional to the kinetic energy available for conversion to static pressure in the volute. Consequently, for a given compressor, Vt is fixed and Vr varies with the cooling load. With the chiller unloading, the pressure differential between evaporator and condenser decreases. The compressor matches the new load and the lower “head” by closing the inlet guide vanes.

This reduces the gas flow it draws in and modifies its direction. Component Vr decreases accordingly, the vector diagram shifts and at some point, the balance of forces breaks down.

As pressurized gas rushes backwards through the impeller, the pressure in the gas passages falls, allowing the compressor to restore the balance of forces. If the process repeats itself, the compressor is said to surge.

1 - Vr = f (Q)

2 - Vt = f (D, RPM)

3 - V = Resultant

4 - RPM

5 - D

6 - Q

1 - Load Line

2 - Surge Line

3 - A

4 - B

5 - 40%

6- 90° Vanes

7- 100%

8- Compressor Head

9- Refrigerant Gas Flow

InTrane centrifugal chillers, gas prerotation vanes ahead of the compression stage improve impeller aerodynamic efficiency, resulting in smoother unloading and reducing power consumption.

The curves show that two-stage compressors surge less and later than single-stage machines. Intersection point B, when the load line meets the surge area, corresponds to a higher part load for the single-stage compressor than would be the case with a two-stage compressor.Two stage machines, therefore, have a wider range of applications.

Typical single-stage compressor performance curve

1 - Load Line

2 - Surge Line

3 - A

4 - B

5 - 20%

6 - 90°

7 - 80°

8 - 70° Vanes

9 - 100%

10 - Compressor Head

11 - Refrigerant Gas Flow

Typical two-stage compressor performance curve

CTV-PRC001-GB

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Contents Centrifugal Water Chillers Introduction IntroductionContents Standard Cvgf Features Features and BenefitsEnvironmental Features and Benefits Additional Features and BenefitsDynaView Operator Interface Microprocessor Controls with CH530TechView ServiceabilityFeedforward Adaptive Control Soft LoadingFast Restart Chiller-Tower Optimization Why Centrifugal Compressors Surge Two-Stage Compressor Widens the Application RangeTwo-Stage Compressors Surge Less and Later Condenser Water Limitations TemperatureWater Pumps Water FlowTable GD-1 Model Cvgf Description General DataEnglish Units GeneralJobsite Connections Shipment and AssemblyField Connection Standard FeaturesHeat Exchanger Control Motor Control and Compressor ProtectionExtended Operation Package Controls FeaturesBase-Loading Control Hot-Water ControlPhase-Loss Protection Oil-Temperature ProtectionTracer Chiller Controller Loss of Water-Flow ProtectionHigh Motor-Winding Temperature Protection Momentary Power LossCurrent Overload Protection Surge Detection ProtectionPhysical DimensionsModel Cvgf Water Connection Pipe Size Physical DimensionsMechanical Specifications Unit Control Panel Refrigerant and Oil Charge Isolation PadsPainting InsulationConversion Length Energy and Power and CapacltyServicing of equipment referred to in this publication
Related manuals
Manual 28 pages 34 b

CVGF specifications

The Trane CVGF series is a revolutionary innovation in the world of commercial HVAC systems, designed to deliver unparalleled performance and energy efficiency. This air-cooled chiller line is specifically engineered to meet the demands of modern buildings, making it an ideal choice for various applications such as offices, hospitals, and educational institutions.

One of the standout features of the CVGF series is its use of the Trane Adaptive Control technology. This advancement provides the system with real-time data analytics, allowing it to automatically adjust cooling output based on environmental conditions and load requirements. This level of adaptability not only enhances occupant comfort but also contributes to significant energy savings, aligning with sustainability goals.

The CVGF chillers also incorporate a robust and efficient scroll compressor, which operates quietly and minimizes vibration. This design choice ensures reliability and longevity while reducing operational noise levels, making it suitable for installations in noise-sensitive environments. Furthermore, the scroll compressor's efficiency plays a crucial role in achieving a higher coefficient of performance (COP), which translates to lower energy costs.

In terms of environmental responsibility, the CVGF series is designed with an eco-friendly refrigerant that supports lower global warming potential (GWP). Committed to sustainability, Trane ensures that these chillers not only meet but exceed regulatory requirements, allowing businesses to operate with a reduced carbon footprint.

Another remarkable characteristic of the CVGF line is its modular design, which simplifies installation and maintenance. The units are compact and can be easily integrated into existing infrastructure, minimizing disruption during upgrades or replacements. The straightforward maintenance protocols further enhance the system’s uptime, ensuring users enjoy consistent and reliable cooling performance.

Moreover, the CVGF chillers are equipped with advanced monitoring capabilities, accessible through Trane’s proprietary software. This feature enables facility managers to oversee system performance from any location, facilitating proactive adjustments and timely maintenance interventions.

Overall, the Trane CVGF series stands out as a cutting-edge solution for effective and sustainable cooling in commercial applications. By combining innovative technologies, energy-efficient design, and user-friendly features, the CVGF offers a comprehensive approach to achieving optimal climate control while meeting the challenges of the future.
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