Compressor housing, low side, or high side and why?

[MrTube]

Hello,

I've noticed many hermetically sealed refrigeration compressors have the compressor housing connected as the lowside of the system so the output of the pump is plumbed directly out. I've also noticed many have the opposite setup where the housing is the highside so the suction line is plumbed directly into the pump.


Does anyone know what the reasons are for this?

I work a lot with antique refrigerators and from 1927-1934 General Electric had the compressor housing as the highside, but they also required a heater to keep refrigerant from condensing in the oil. In 1934-1935 time they swapped and started using the housing as the lowside and omitted the heater. I had assumed this was done for no reason other than it had not been thought of before. Now I just learned many modern compressors are setup with the housing as the highside so I'm guessing there is a whole lot more to it.

I'm hoping someone will know what reasons for and or pros and cons of each setup.

[joe-ice]

The compressors with the shell on the high side are rotary compressors as opposed to piston and scroll types which have the shell on the low side.

[MrTube]

The compressors with the shell on the high side are rotary compressors as opposed to piston and scroll types which have the shell on the low side.


Interesting.
Any ideas on why rotary doesn't use the same as everything else?

[joe-ice]

Dont really know .The rotary compressor is just one big rolling piston or ball that virtually squeezes the gas. Probably just easier to lubricate it and seperate the high from the low side if the shell is on the high side

[MrTube]

I wonder if this answers something else I've wondered for years. We live in a very humid area so often I'll run window A/Cs when its in the low 50Fs out and often the units sound unhappy and just run rough vibrating a lot. I also have seen them ice up as if they are undercharged.

Besides the fact the capillary tube setup isn't the best over a wide temperature range, I would also assume refrigerant could be condensing and staying with the oil in the compressor shell. I believe all of my window units have always had rotary pumps.

I do find it interesting none of these rotary compressors have a crankcase heater. The 1927-1934 Monitor Top refrigerators all used crankcase heaters to keep refrigerant out of the oil and the problem happens even in a warm room. Results are the machine behaves like it has a low charge and is noisy.

[joe-ice]

most rotary compressors these days come with an accumalator vessel already attached .Liquid and rotary doesnt match well as the return goes straight into the chamber.A non return valve on the discharge line is also advised to stop liquid migrating to the compressor on the off cycle

[The MG Pony]

The main reason is oil! Scroll and rotary fling a ton of oil through the high side discharge as they rely on it for the final seal, if this went directly to the evap you'd promptly have all the compressor oil in the evap, and this leads to a useless evap and a seized compressor.

By using the shell as the discharge side it allows the bulk of the oil to settle out of the gass stream befor going on to the condenser, with out need of more advanced oil separator systems.

Due to the fact the suction goes directly into the pump there is far more need for the suction side accumulator to protect the low side intake from flooding of either oil or refrigerant in solid liquid form.

[The MG Pony]

most rotary compressors these days come with an accumalator vessel already attached .Liquid and rotary doesnt match well as the return goes straight into the chamber.A non return valve on the discharge line is also advised to stop liquid migrating to the compressor on the off cycle

neither can seal on the off cycle so refrigerant can migrate to the low side, so if you have a parallel rack of scrolls or rotaries with out a check valve the ones in the off state will undermine the running ones by allowing hot gas to by pass through them to suction, and this is bad for many reasons!

[Peter_1]

I've heard they do it also to have some sort of a pressurized oilflow through different channels in the mainshaft and conrods. As far a I knew, most 'domestic' compressors have a LP shell. Hitachi was one of the 1st to have a HP shell for the above reasons. So I'm learning