Pump down vs. suction accumulator

[tmoritz]

I posted a question regarding running DX linesets below grade last week. I have distilled two solutions from the responses I received, modify the system for pump-down operation and add a suction accumulator.

Now I'm wondering, which is better? Which presents greater risk? Is there value in doing both, i.e. the belt and suspenders option?

I'm also considering specifying a suction accumulator with an integrated superheat exchanger. I've seen claims of efficiency improvement but it seems to me these gains are only realized if I operate the unit in off-optimal conditions. Can anybody comment on this?

Thanks,

Tom Moritz

 

[chilled]

If you are convinced you need either of these options, choose the pump down control.

It is easier to install, involves no field basterdization of the outdoor unit and probably no brazing or the removal of the refrigerant charge to flare in a solenoid valve.

You will also need a pressure control to cycle the compressor and your control voltage will now energize the liquid line solenoid coil. Your compressor may also require a hard start kit to be able to turn over against the pressure differential it may now see.

Good luck.

 

[tmoritz]

Chilled,

Why the hard start kit? If I understand the pump down sequence correctly a call for A/C opens the liquid line solenoid valve allowing refrigerant into the expansion coils. The compressor is controlled by a pressure switch on the suction line. I guess if there's not much hysteresis in the pressure switch then the compressor may have a hard start.

What does a hard start kit do? Also, is there any need for a receiver since I'm limiting the volume on the liquid side?

Thanks for the info.

Tom Moritz

 

[chilled]

If the existing system has an orifice for a metering device the low and high side pressures equalize during the off cycle. Most single phase compressors will not start or start properly against a pressure differential. This differential on start-up MAY be created with the addition of a liquid line solenoid. Just something to consider, you may have a TX valve and a hard start relay / capacitor on the system already?? If not, you'll probably see the dashed lines on the wiring diagram for the option.

No receiver, the condensor has plenty of storage volume to accomodate the addition of the pumpdown.