What is Surge in Centrifugal Compressor
Summary
TLDRIn 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
- đ ïž Surge condition in a centrifugal chiller is a critical issue that can cause significant damage if not addressed promptly.
- đ Understanding the difference between centrifugal and positive displacement compressors is crucial to grasping how surge conditions occur.
- đ Centrifugal impellers work on the principle of velocity, using kinetic energy to compress refrigerant and generate pressure, unlike direct compression in positive displacement compressors.
- đĄ 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.
- đ§ High lift, the difference between condenser and evaporator pressures, is a primary cause of surge conditions, indicating the compressor's struggle to move refrigerant.
- đ 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.
- đ« 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.
- đ 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.
- đ It is essential to address surge conditions to prevent long-term damage to the compressor, as extended surging can lead to catastrophic failure.
- đ 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.
- đ 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.
Outlines
đš Understanding Centrifugal Chiller Surge
This paragraph introduces the concept of surge in centrifugal chillers, a potentially alarming event for those unfamiliar with this type of compressor. Holden Schamburger, from Chiller Academy and HVAC Time, explains that surge is not like the operation of typical positive displacement compressors and emphasizes the importance of not getting hung up on technical terms. He provides a brief overview of how a centrifugal impeller works, comparing it to a water pump and a blower motor, using velocity to compress refrigerant and create pressure. The paragraph concludes with an introduction to the surge condition, which is a reversal of refrigerant flow that can cause significant damage to the compressor, including axial thrust issues and overheating.
đ Causes and Consequences of Surge in Centrifugal Chillers
The second paragraph delves into the causes of surge in centrifugal chillers, which is linked to high lift conditions resulting from the difference between condenser and evaporator pressures. High lift can be caused by issues such as poor heat exchange in the condenser, high condenser water temperature, or low load on the evaporator. The paragraph explains how these conditions can lead to the compressor's inability to move refrigerant, resulting in stalling and eventually surging. Stalls are described as a precursor to surge, with the latter being a more severe and damaging state. The importance of addressing surging conditions promptly is stressed, as allowing a chiller to surge for an extended period can lead to catastrophic damage. The paragraph concludes with a reminder to check out Chiller Academy for more training and to prioritize family time.
Mindmap
Keywords
đĄSurge condition
đĄCentrifugal chiller
đĄImpeller
đĄPositive displacement compressor
đĄDiffuser
đĄLift
đĄCondenser
đĄEvaporator
đĄStall
đĄAxial thrust
đĄSuction superheat
Highlights
Understanding what a surge condition is for a centrifugal chiller, which can be a scary thing on site if unfamiliar.
Centrifugal chillers differ from regular positive displacement compressors, so don't get hung up on the terms.
A surge can be quite terrifying and cause confusion about what is happening and why that noise is being made.
Holden Schamburger from Chiller Academy and HVAC Time specializes in chillers and discusses centrifugal surge today.
Centrifugal impellers create a pumping action for refrigerant by using velocity, similar to a water pump or blower motor.
In a surge condition, refrigerant flow reverses, which is very bad for the compressor and can cause axial thrust issues.
High lift, the difference between condenser and evaporator pressure, can cause a surge condition.
Problems with the condenser, such as dirty tubes or high condenser approach values, can lead to high lift and surge.
Low load on the evaporator with high condenser water temperature can also create a high lift condition and surge.
Most centrifugal compressors start showing symptoms of stalling at around 50 to 60 PSID before surging.
Stalls precede the surge condition, so understanding stalls is important to prevent surge.
High lift conditions that overcome the compressor's ability to move refrigerant can lead to surging.
Surging creates a high-frequency swooshing sound that can be very terrifying, especially for those not used to it.
Surging is very bad for the compressor and can lead to its destruction if allowed to continue for a long time.
Different compressor designs, like VGD or multi-stage, can influence how lift value is managed and surge is prevented.
Between 60 to 80 PSID, you are in surging territory and need to tread carefully to prevent compressor damage.
ChillerAcademy.com offers training to learn the fundamentals of the chiller industry and develop expertise.
Make time for family, as they really need you, in addition to focusing on professional development.
Transcripts
So you will come out the other side of this video understanding what a surge condition is Â
for a centrifugal chiller. And this is kind of a... it can be a scary thing when you're on site Â
and if you're not working... used to working on centrifugals and their differences and how they're Â
not like a lot of regular positive displacement compressors, don't get hung up on the terms, Â
like it's okay. And I have talked about these things in other videos. We'll... Â
I'll recap it here in a minute. So if you're not familiar with all that Â
and then you hear a surge happen and it can be quite terrifying... Â
well what do you do? What is it? What's even happening? Why is that noise being made? Like Â
that is an odd noise for a compressor to make. Let's talk about that today. How you doing? I hope Â
you're having a great day. I am Holden Schamburger with Chiller Academy and HVAC time. I specialize Â
in chillers. We're going to talk about centrifugal surge today and with that let me grab my model Â
real quick. So this is a centrifugal impeller. This is what makes the refrigerant move and you Â
know creates the pumping action. The... this looks very similar to a water pump because what Â
we're using the same theory and these centrifugal impellers, I mean they... it's centrifugal theory. Â
Same thing our blower motors also use to make air move. So how we're doing that is through velocity. Â
These are your veins of... this is where the refrigerant comes in on your suction. This is your Â
discharge side here and as that refrigerant moves through we are able to create a compression. Now Â
this is not a positive displacement. It's not a direct compression. So a scroll compressor for an Â
example or a re-sip or screws. Those are positive displacement. The refrigerant molecules are being Â
physically compressed as they get forced through the compressor and that's how we create that. This Â
is not doing that. This is actually creating a... it's taking velocity. So essentially the Â
refrigerant comes in and as this spins it gets thrown through these louvers or these veins Â
just like a blower motor would do, right? So it gets thrown out and it just slings out into the Â
diffuser section of the compressor and as it goes flying we hit the diffuser and the diffuser is Â
designed to take all that high velocity, you know, kinetic energy and actually convert it into a Â
pressure. So pressure we can work with so that that pressure becomes your discharge Â
pressure which is what your canister pressure is. That's the base summary of the centrifugal. Â
Now what's happening in a surge condition is, in simple, we're reversing flow. So quite literally Â
what's happening refrigerant is supposed to come this way but because of our surge conditions and Â
I'll get into that a little more in a second, the refrigerant ends up reversing back through Â
this into our suction side and a very bad thing to happen. You get a lot of axial thrust issues Â
because it's just it's a lot of force and this will destroy your bearings. All of Â
this will get hot at that point because a lot of the cooling for this impeller in the system Â
comes from that suction gas and it's used to seeing, you know, suction superheats of say Â
half a degree to one or two degrees. Very, very low suction superheats and that helps keep all Â
of this cool and not to overheat. Well if all of a sudden our discharge gas is back flowing, Â
that suction superheat, it turns into discharge superheat. Now quite literally like it's it's Â
very dramatic event and it's bad. That is that will just there are plenty of chillers, Â
plenty of centrifugals who have utterly ripped themselves apart in their life because they were Â
allowed to just constantly surge and surge and surge and nobody ever did anything to address Â
it. So that is what a surge is, a reversal of refrigerant through the impeller. Now what causes Â
that? Well it comes back to high lift. So lift is your difference between condenser pressure and Â
evaporator pressure and by doing that subtraction, it's a PSID, we are able to determine Â
how hard that impeller is having to push refrigerant through it. What causes high Â
lift? Well it depends. So you could have a high lift condition if you have say something wrong Â
with the condenser. You're not exchanging heat, dirty tubes, whatever. Even if you've got proper Â
condenser water, you could be running really elevated condenser approach values. So whole Â
separate videos I've done on condenser approach. I highly recommend you go check that out. But Â
if your condenser approach starts running high, then that could push you into a surge Â
condition. If you say you're having a cooling tower issue and your condenser water begins Â
to run really high and you can't keep it down, that's going to push you into a surge condition. Â
Or let's say you have a really low load on the evaporator. Say we've only got three, Â
maybe four degrees of difference from entering to leaving water. And we're making set point, Â
but we are, we're not able to get the condenser water temperature down. So let's say you've got Â
that low of a load going through the evaporator, but you've still got you know 85 to 80 degrees of Â
condenser water and you can't back that off for whatever your reasons are. A lot of valid ones, Â
so don't take that the wrong way. But anyway, it creates a lot of lift. That difference between Â
those two things stays really high and that lift will overcome what the impeller is able to force Â
through it. Most centrifugal compressors, they usually start to show some symptoms. You know, Â
get into stalling at around 50 to 60 PSID. Now if you don't know what stalls are, I've done a whole Â
video on stalls. I actually should have posted yesterday, so quite literally the video before Â
this if you go to my feed, whatever else. Go check that out if you need to know what stall. So Â
stalls prelude or precede, precede, maybe I don't have that. I guess I don't realize what prelude, Â
prelude, prelude. It doesn't matter. They precede the surge, the surge condition. So it's important Â
to understand what the stall is and for the same reasons we get into a stall state, we get into a Â
surge state. Just the surge is the extreme climax of what happens. When we have those really high Â
lift conditions, we overcome the compressor's ability to continue moving that refrigerant. Â
And it creates this really high pitch or higher frequency. It's not always high pitch, but it's Â
really high frequency just swooshing sound that is, it can be very terrifying, especially if Â
you're not used to dealing with that condition. And it is very bad for the compressor. I cannot Â
stress that enough. We've gotten much better with our compressor designs and their ability to take Â
extended surging, but gee whiz, please don't let that continue for a very long time. That is the Â
fastest way to terra-pus centrifugal is allow it to just surge itself into oblivion. So while Â
we may start dealing with stall conditions at that 50 to 60 going into 65, the higher that lift gets, Â
the more the stalling becomes prevalent. And eventually, once you start hitting 65 to 80 PSID, Â
you're flat out in surging territory. And it depends on your compressor, Â
whether or not you have a VGD video coming, or whether or not you are a multi-stage, like a CVH, Â
where you've got two stages or three stages or a turbo core has got a couple of stages. Â
Or whether you're a single stage. So there's variables and design on how we can increase or Â
manage that lift value. But ultimately, they're all kind of about the same ballpark. Essentially, Â
between 60 to 80 PSID, you're looking, you're in the middle of surging territory and you need to Â
tread very carefully, very lightly. So just bear that in mind as you're moving forward working on Â
these chiller's and just understanding how they function, what they're doing, and why they're Â
doing it. With that, if this was any great benefit to you and if you really enjoyed this training, Â
go check out chilleracademy.com. It's a place where you can come to and learn the fundamentals Â
of the chiller industry and developing yourself and come out the other side well-versed and fully Â
understanding exactly what the different chiller systems, designs, fundamentals, Â
and practices are that we need to follow. With that, MTT. Make the time for your family, Â
for your spouse, for your kids. They really need you. I'll see you around.
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