For the chiller guys

[acnerd]

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

[NoNickName]

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.

[acnerd]

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. :)

[NoNickName]

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[acnerd]

Please add to my reputation points.

Sure no problem, just let me know how :o

[NoNickName]

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[wilko123]

Multi-clima really are a bag of turd.....dont you think acnerd?

[icecube51]

Multi-clima really are a bag of turd.....dont you think acnerd?

as long as they do the job wright, there good. any brand that shows allot of the same failures are bags of dirt.

Ice

[icecube51]

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
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

[acnerd]

Multi-clima really are a bag of turd.....dont you think acnerd?

Did you rhyme that on purpose, or is it just me. :p

First one i have worked on. And I'm not a fan of any chiller that uses belt-driven condensor fans. :mad:

[acnerd]

. 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

Thanks Icecube51. When you say the pressure is too high, do you mean the discharge pressure? So for example, the hot ambient even with the fans at full speed, causes it to bleed hot gas into the evaporator to avoid HP cutout?

[Gary]

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

On some of the Hussman supermarket systems, warm gas from the top of the receiver is used for defrosting in order to minimize thermal shock in the evaporator. I wonder if this wouldn't work just as well in other systems, thus avoiding evaporator cracking.

[icecube51]

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

[wilko123]

Did you rhyme that on purpose, or is it just me. :p

First one i have worked on. And I'm not a fan of any chiller that uses belt-driven condensor fans. :mad:


No but it is kind of catchy!