502 conversion project & lengthening piping questions?.?.?

[Krohnie84]

Hello,
First off; thank you for taking a look.

This "project" involves two things:

1. Is replacing the 502 charge with 408a (As far as I can remember it is pretty easy)

2. Moving the evaporator further away.

My questions are:

1. As far as 408a goes, there shouldn't be anything more than changing oil, filter driers and checking the operation of the TXV/s correct? If I am missing something, please toss it right back at me.

2. The evaporator will be getting moved from its current position; which is about 50ft from the compressor, to about 200ft. What are the cons to moving this unit that much further from the compressor? I am thinking that the pressure difference from the evap to the compressor will be too great or that I might have issues with oil return.

Notes: I haven’t done much installing in the last five yrs. So I am going off my memory, and I don't recall having such a large distance to cover.

The system is relatively small:

1) compressor 10hp?
1) evap
condenser is shared with four other systems.

If you want to know about the project or why, it just gives me a headache thinking about it......

[mikeref]

ERR, have to say, firstly, i've never liked R408a as it used to burn the guts out of the oil, and if i couldn't keep the compressor cool enough, it would claim it as well. Running an extra 150ft, (50 meters) is going to test this ability. How is the condenser shared? Common refrigerant for all 5 systems? Going to have to keep an eye on discharge pressure and temperature. Total of 200ft run will strain reciever volume capacity and add more load to condenser with increased heat gain on suction line. I would be inclined to run independant condensing unit on R507 for this evaporator, and install it as close to evap as possible.. Mike.

[Fri3Oil System]

I guess you would change the oil from MO to AB... but I wonder, why don't you switch to a HFC instead R408A? I know in the US you have a different funny HCFC's phase out, but you could go directly to HFC in one step... just wondering. :)

Regards,

Nando.

[Krohnie84]

Thank you for replying Mike & Nando,

Your questions:

How is the condenser shared?
There are separate systems going to this one condenser, none of the piping is shared. The condensing fans run all of the time regardless of which unit is running.

Common refrigerant for all 5 systems?
Four of the five are R-22, and this is the only on that isn't.

why don't you switch to a HFC instead R408A?
408a is the third most common refrigerant we use in this plant (Ammonia being the first, then R-22). Also from what I understand 408 runs at a lower pressure than the other change over’s? I thought this could be a benefit with the added heat gain. From what I have been looking over I think my operating pressures should stay pretty close to what they are now. As long as I size and install the pipe accordingly.

[mikeref]

There still will still be added losses due to the distance increase of evaporator from compressor. Suction temperature to compressor will have to be checked so it doesn't get too warm, causing excessive temperature at discharge and premature mechanical and oil/gas breakdown. Let us know how it works out..Mike.

[Krohnie84]

The project has yet to even begin, I am just trying to put out any fires before they occur.

The main doubts that get tossed my way is that the coil will freeze up with such a long suction line. I was thinking the opposite due to the added heat gain. Which one would be the right concern?

[mikeref]

Is the evaporator being moved to a room of similar heatload? So long as you have liquid to TX valve, capacity of evaporator will be similar to R502.( Remember reading something on temperature glide on 408a?). It's the increased pressure to get liquid to TX, then the extra heat gained on return. I still think a seperate condensing unit for this evaporator at a closer location is the way to go. In the future, when you have this running on 408a, i think condenser will be too small after you find it difficult to control superheat. Opening TX will increase suction pressure and pull down time after defrost will increase as TX fires away and CPR reduces excess pressure to compressor.. Mike.

[iceken]

couple of options change to R404a but would have to change to POE oil
change to r507 have to change oils
or could use r422a which can be used with mo/ab/poe oil and change driers and check seals plus do oil change

[Krohnie84]

Thank you guys for responding, but I don’t think this project is going to go anywhere. Thanks again for letting me pick your brains.