Suction line accumulator vs. pump-down w/ hard start kit

[tmoritz]

I would like to relocate our residential 3-ton A/C condensor so I can build a patio. I'm planning on running the line set underground in a 4" PVC chase. The underground run will be 15' to 20' long and sloped back towards the evaporator. I'm debating on if I should have the contractor install a suction line accumulator or convert the controls to a pump down configuration and install a hard start kit on the condensor.

Any feedback would be appreciated.

Thanks in advance,

Tom Moritz
Mechanical Engineer
US Bureau of Reclamation

 

[MintJulep]

If the compressor is higher than the evaporator and the lines are sloped to the evaporator then you probably could get away with neither.

 

[Allen1973]

Hi Tmoritz,
The vapor lines should be pitched in the direction of flow, to aid in oil return.
What is the length of the line-set before the move?
What is the OD of the liquid line and suction line?
What type of refrigerant does your system use?
Is this a heat pump or cooling only?
These are all factors to determine the amount of additional refrigerant needed by the additional piping.
Allen

 

[DrRTU]

Do that application if you like to change compressors. A pump down with blocking solenoid and accumulator will help minimize slugging. Charge migrates towards the coolest piping location. Installing the DX lines in a sleeve with heat tracing will also help. Compressor damage occurs at first startup from liquid slugging. A properly sized suction accumulator is the best defense. Pump down adds to the complexity & wiring of the system. If you have to this piping route, install an accumulator and heat trace the suction line in the underground run. Make sure you have a valid warranty. Example:

http://www.stanref.com/sa/a6118.htm

It’s big but will help.

If you are a gambler, heat trace the below grade piping and slope the buried piping away from the compressor and add the trap at the riser at the entrance to the ground. This may breakup the slug before the pump.

 

[imok2]

I would install an accumulator
becaus of its simplicity.Flood back can occur when the ASHP is reversed, such as the defrost mode, or when the compressor is subject to low ambient temperatures.
Accumulators are typically installed in the “true suction line” upstream of the suction port of the compressor. There is only one typical problem that can occur with a suction accumulator other than a leak,and always use the proper replacement accumulator based on manufacturer’s criteria.
The refrigerant oil aspirator hole is how the refrigerant oil circulating in the system (it’s always circulating) can get out of the accumulator. If the small orifice is plugged, oil will “log” in the accumulator, eventually to the extent that the compressor may fail from lack of lubrication.
The diagnosis is easy. Just tap the accumulator for the “ring” of an empty one or the “thump” of an accumulator with significant refrigerant oil in it. The solution is to replace the accumulator, as it is not normally serviceable. And, there is no guarantee that you will remove all of the debris that plugged it up to begin with. This problem is not encountered often.