What is Surge in Centrifugal Compressor

Summary

In this informative video, Holden Schamburger from Chiller Academy and HVAC Time explains the concept of centrifugal surge in chillers, a potentially damaging phenomenon that can cause significant issues if not addressed. He clarifies the difference between centrifugal and positive displacement compressors, describes the process of refrigerant compression, and details the causes and consequences of surge conditions, including high lift scenarios and the importance of preventing compressor damage. The video aims to educate viewers on recognizing and managing surge to protect chiller systems.

Takeaways

• 🛠️ Surge condition in a centrifugal chiller is a critical issue that can cause significant damage if not addressed promptly.
• 🔍 Understanding the difference between centrifugal and positive displacement compressors is crucial to grasping how surge conditions occur.
• 🌀 Centrifugal impellers work on the principle of velocity, using kinetic energy to compress refrigerant and generate pressure, unlike direct compression in positive displacement compressors.
• 💡 Surge is characterized by a reversal of refrigerant flow through the impeller, which can lead to axial thrust issues and overheating, potentially destroying the compressor.
• 🔧 High lift, the difference between condenser and evaporator pressures, is a primary cause of surge conditions, indicating the compressor's struggle to move refrigerant.
• 📈 Factors contributing to high lift include issues with the condenser, such as dirty tubes or high condenser water temperatures, and low load on the evaporator.
• 🚫 Stalls, which precede surges, are an early warning sign of potential surge conditions and should not be ignored as they indicate the compressor's inability to maintain normal operation.
• 📊 The range of 50 to 60 PSID is where compressors typically start to stall, with 65 to 80 PSID being the surge territory, indicating the severity of the lift condition.
• 🛑 It is essential to address surge conditions to prevent long-term damage to the compressor, as extended surging can lead to catastrophic failure.
• 🏭 Different compressor designs, such as VGD, multi-stage, or single stage, have varying capacities to manage lift values and may influence how surge conditions are handled.
• 📚 For further education on chiller systems, designs, and practices, the Chiller Academy offers resources to deepen understanding and improve industry knowledge.

Q & A

What is a surge condition in the context of a centrifugal chiller?

A surge condition in a centrifugal chiller refers to a reversal of refrigerant flow through the impeller, which can cause significant damage to the compressor if not addressed.

Why can a surge condition be a scary occurrence for someone on site?

A surge condition can be scary because it is accompanied by an unusual noise from the compressor, which can be alarming, especially for those not familiar with the operation of centrifugal chillers.

What is the role of a centrifugal impeller in a chiller system?

The centrifugal impeller's role is to move the refrigerant and create a pumping action by converting the refrigerant's kinetic energy into pressure through the use of velocity.

How does a centrifugal impeller differ from a positive displacement compressor?

A centrifugal impeller does not physically compress refrigerant molecules as they pass through; instead, it uses velocity to move the refrigerant, unlike positive displacement compressors, which force refrigerant through the compressor to create compression.

What is the purpose of the diffuser in a centrifugal compressor?

The diffuser is designed to convert the high-velocity refrigerant's kinetic energy into pressure, which can be used in the system, and is part of the process that creates the discharge pressure.

What causes a surge condition in a centrifugal chiller?

A surge condition is caused by high lift, which is the difference between the condenser pressure and evaporator pressure, leading to a reversal of refrigerant flow back through the impeller.

What are some factors that can lead to high lift and potentially a surge condition?

Factors that can lead to high lift include issues with the condenser, such as dirty tubes or high condenser approach values, cooling tower issues causing high condenser water temperatures, or a very low load on the evaporator.

What are the symptoms of a stall condition in a centrifugal compressor?

Stall conditions, which precede surge, can be indicated by a high-frequency sound and are typically experienced when the lift is around 50 to 60 PSID or higher.

How can surge conditions be prevented or managed in centrifugal chillers?

Surge conditions can be managed by addressing high lift conditions, which may involve cleaning condenser tubes, optimizing cooling tower performance, or adjusting the load on the evaporator to reduce the pressure differential.

What is the potential damage caused by surge conditions to a centrifugal chiller?

Surge conditions can cause axial thrust issues, overheating, and in severe cases, the destruction of bearings and other components, potentially leading to the complete failure of the chiller.

What is the Chiller Academy and how can it help someone learn more about chiller systems?

The Chiller Academy is a resource where individuals can learn the fundamentals of the chiller industry, including different chiller systems, designs, and best practices, to become well-versed and fully understanding of the field.