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Thread: For the chiller guys
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07-09-2010, 04:51 PM #1
For the chiller guys
I was looking at an antifrost fault on a MultiClima chiller today. (Just so you know why I had it open)
I don't get much practice on chillers in general, so wanted to ask a couple of general questions on parts of the fridge circuit itself:
a) What is the purpose of liquid injection (controlled by a solenoid valve) into the evaporator just after the TEV?
b) What is the purpose of hot gas 'by-pass' (controlled by a solenoid valve) straight back into the suction line?
This specific chiller has 2 x 3 cylinder recip compressors, 1 on each circuit; each compressor has 2 unloaders. It has 1 common plate evaporator with normal TEV's.
While I'm asking, I have also come across a slightly different setup on a Ciat chiller, where they have the discharge line tee off through a capacity valve and also into the evaporator just after the TEV. What's it for?
Thanks
Craig
If at first you DO succeed, try to hide your astonishment!!
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08-09-2010, 07:55 AM #2
Re: For the chiller guys
1) to avoid excessive suction superheat and it's associated high discharge gas temperature from compressor in extremely low part load condition. It is normally actuated by a temperature probe on the discharge pipe and one thermostat set to 100 or 120°C.
2) If you don't have a condensing control device, and in winter time it can be possible to over-condense or over-subcool, you by pass some hot gas into the suction to reduce the effectiveness of the condenser.
If it was me, from a design point of view I would put the liquid injection straight into the suction, but a liquid slugging would then be possible.Last edited by NoNickName; 08-09-2010 at 07:58 AM.
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08-09-2010, 05:06 PM #3
Re: For the chiller guys
Thanks NoNickname, it's good to understand these additional control features.
They have the hot gas bypass on VRV systems I work on, but the liquid injection after the TEV is a seldom-used concept for me. I have seen some bespoke remote condensing units with excessive pipe-runs where they use liquid injection to keep the compressor cool, and that would be the same concept then. Reducing the non-useful superheat value so the compressor doesn't overheat.
Thanks for your time.If at first you DO succeed, try to hide your astonishment!!
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08-09-2010, 06:19 PM #4
Re: For the chiller guys
Please add to my reputation points.
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08-09-2010, 07:01 PM #5
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08-09-2010, 07:47 PM #6
Re: For the chiller guys
Click on the top right corner of the message. There's a scale icon.
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09-09-2010, 05:21 PM #7
Re: For the chiller guys
Multi-clima really are a bag of turd.....dont you think acnerd?
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09-09-2010, 10:35 PM #8
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09-09-2010, 10:45 PM #9
Re: For the chiller guys
they are pressure regulators for the evap/plate heat exchanger. it helps getting a steady suction pressure. They also have a slight hot gas by-pass function when the pressure is to high. That is why the evaps are cracking inside diu to thermal shocks, and the water and refrig blend.
Ice
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10-09-2010, 04:04 PM #10
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10-09-2010, 04:10 PM #11
Re: For the chiller guys
If at first you DO succeed, try to hide your astonishment!!
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10-09-2010, 06:47 PM #12
Re: For the chiller guys
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12-09-2010, 07:01 PM #13
Re: For the chiller guys
i have one now whit a cracked plate evaporator. the fault was a continuously manual reset from the owner. by-passing the LP switch is the most stupid thing you can do.
we have several CIAT chillers in maintenance, and the problems are no different than the other brands.
Ice
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23-09-2010, 01:25 PM #14
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