Buried Line

From Chris Georges
Via E-Mail

I live north of Montreal and have a Carrier heat pump. It is presently about 40 feet from my house. The two lines from the pump run underground through an ABS pipe for about 30 feet before they enter the air handler.

I have been reading that it really is not recommended to run piping underground, and I have contacted Carrier; they do not recommend it either. But I think my refrigeration man believes it is OK.

I want to move it. What does your research tell you about my situation? I also find my unit frosting up quickly.

By Dave Anderlik

Your question on buried line sets is an old one. As you found out, Carrier does not recommend this type of installation and I’m sure no other manufacturer does.

When a system is off, refrigerant will migrate to the coldest area because of vapor pressure differential. With the line set buried, that could be the coldest area and refrigerant vapor will condense in the buried vapor line. When your unit cycles on, you have the potential of the compressor slugging liquid. The longer the line set, the greater the problem. Also, with your line set going down into the ground and then back up, you have a possible big oil trap.

With 30 feet of vapor line below or above ground, you are probably losing capacity in the heating mode. As far as the unit frosting up, I assume it is your indoor coil in the cooling mode. If so, with your liquid line exposed to ground temperature, it is acting as an extension of your condenser, and if refrigerant has migrated into your cool vapor line, both could cause a lower head pressure on start-up and not provide enough refrigerant through your metering device.

If your outdoor coil is frosting up in the heating mode, it is probably due to the cold vapor line (discharge) and the time it takes to build up your high-side pressure. The one good thing is, your unit has a suction line accumulator to help protect your compressor.

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Publication date: 09/01/2003