Hey gang. Were doing compressors right now in theory and my instructor told me anytime a centrifugal chillers compression ratio goes over 4:1 that the wheel comes to a stop because it wants to go the other way and begins to do what is called "surging"
Does anyone have any recording or stories of a surge? I'm kind of interested in seeing one.
Lots of stories on here about surge . Use surging in the keyword search and you will find what you are looking for . As for a recording ???? All I can tell you is when you hear it you'll know it .
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The wheel does not come to a stop. Never heard of the 4 to 1 ratio.
Surgingis when the gas backs thru the impeller(s) as it exceeds the machines design lift. The machine usually goes into a stall before it goes ito a surge.
The impellers are not a positive displacement type of compression like a screw, a scroll or a recip. This is why you get a surge under adverse condition. .
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Ahh maybe I misunderstood what my instructor was saying. Abs I think you're right maybe what I misheard was it stalls before it does that.
This was the only clip I could find. I think i'll use the handy dandy search function and see if I can find any more about it.
haha, yup, was going to just use the elephant description.
If you've ever heard a really ticked off elephant, that's very close to what it sounds like.
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A impeller is uses "Dynamic Compression" which means large volume at low head or lift. Usually an impeller is designed max around 70 degrees of lift (saturated evap vs sat condensing temp)
Originally Posted by RayD8630
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I think it sounds like elephants in heat. Had an absorber guy with me one time while a 1500 ton CVHB did that. Darn guy got so scared he ran out the room.
The stall is known as rotational stall, which I have some old documents relating to it somewhere.
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Abs has the technical info on a surge correct. When the design lift is exceeded the gas goes thru the impeller in the opposite direction until the lift is corrected which is why they are only momentary. I had a call on a Saturday night on a Trane double ender that was surging in an underground parking garage for a high rise apt building. Man you could hear that thing for blocks.
Hi Ray. Welcome to the world of centrifugal chillers. I have seen two types of surges. 1-because the evaporator doesn't have enough refrigerant vapor/volume to keep the compression cycle going(like a water pump cavitating) and 2- when the condensor pressure is to high and the impeller can't compress the refigerant vapor against the higher head pressure (like dead heading a water pump). A surge needs to be experinced on a large low pressure centifugal! Good luck and have fun learn.
What about when the tower water is too cold for the chiller, that will cause it to surge also. Just heard one today. VFDs on Tower fans help and a bypass valve for the tower alson helps. Condenser water flow is also a factor. Lots of reasons for surging. You will know it when you hear it.
Yup. I put my towers on a wet bulb reset schedule with a min/max entering condenser water temperature (ECWT) limit. The max is to prevent high head surging and the low is to prevent the condenser barrel from running so cool that oil has a hard time returning to the compressor sump.
Originally Posted by ice_cube_30
Low load surge on my 19XRs happens when the ECWT is not reset downward as the load on the chiller falls off. Lower load means lower evap temp/pressure, but if ECWT is held too high, the chiller may surge. Of course, this year I finally got a better handle on tweaking the surge prevention settings on all three machines, so incidences of surging have gone way down.
Keep the towers and sump strainers clean, reset ECWT with design approach of towers (if possible...ideal with VFD and bypass loops), run the condenser barrels cooler during low load operations...the chillers should cruise along happily surge-free.
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Building Physics Rule #2: Higher air pressure moves toward lower air pressure
Building Physics Rule #3: Higher moisture concentration moves toward lower moisture concentration.