Refrigerant piping question
Refrigerant piping question
(OP)
Hello friends,
We are about to start commissioning our HVAC system. However, I just noticed the following refrigerant piping connection that has been made at the outdoor/compressor unit.

Will the U-pocket not accumulate an oil plug? (Refrigerant is R407C). Also, does the filter-drier need isolation valves around it to facilitate changing it?
We are about to start commissioning our HVAC system. However, I just noticed the following refrigerant piping connection that has been made at the outdoor/compressor unit.

Will the U-pocket not accumulate an oil plug? (Refrigerant is R407C). Also, does the filter-drier need isolation valves around it to facilitate changing it?





RE: Refrigerant piping question
No on the filter because a closed refrigerant system should not continually have moisture or particulates that need to be continually filtered or dried out. That filter is just to catch whatever got into the opened system during installation. Same with the moisture and hopefully a vacuum was pulled on the system over night before charging so there should've been very little moisture but what was there will be trapped permanently in the filter.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Refrigerant piping question
I have no idea what gas velocities are in a small refrigerant system.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Refrigerant piping question
RE: Refrigerant piping question
He confirms while having a removable section for the dryer is convenient it's not necessary and wouldn't typically be done.
As for the oil... That low loop is acting as suction accumulator. The intent is to prevent any slugs of oil from falling from above straight into the compressor and so they should instead deliberately pile up in that U.
He goes on to say that the refrigerant velocity in that pipe is insane and once the oil piles up deep enough the gas will pick it up and in the short vertical section atomize it so a slug never does make it to the compressor. He said it's a poor-mans suction accumulator. He'd rather a proper suction accumulator but that will do. It works because of the short vertical and then the long sloped horizontal. It's acting as a P-trap.
He went on to say the most important thing is that the system should have pump-down to be reliable so you should make sure it does have that feature.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Refrigerant piping question
RE: Refrigerant piping question
Keith Cress
kcress - http://www.flaminsystems.com
RE: Refrigerant piping question
It's a relief to hear about the poor man's suction accumulator. I was not looking forward to redoing that piping :) Also good to hear about the filter/dryer not needing isolation.
Inside is a Copeland Scroll compressor (w/ crankcase heater). Why the difference with regard to pump-down importance between the scroll and the reciprocating?
RE: Refrigerant piping question
Scroll compressors, since they don't have pistons, can't easily be slugged because a bunch of refrigerant has come wandering back during the off cycle and filled the compressor cylinder(s). While they can be controlled exactly the same way and may need to be in some applications they aren't as likely to be slugged and so are often controlled by the thermostat directly banging on and off without benefit of a liquid line solenoid.
Here a spectacular little demo link
Keith Cress
kcress - http://www.flaminsystems.com
RE: Refrigerant piping question
RE: Refrigerant piping question
Yes, except in special fully constrained systems engineered to avoid the need. Absolutely not for long term situations but for safe daily functioning.
Yes, the compressor should then be fully controlled by pressures.
Low side #1 => start/stop control.
Low side #2 => Low pressure Lockout. (Loss of refrigerant. Running will fry the compressor because of the loss of cooling.)
High side #1 => condenser fan(s).
High side #2 => Lockout for over pressure protection. (Clogged condenser fins, dead condenser fan. Running will either cause a burnout as more HP is demanded than is available or the crank or rods will break. It's a race to disaster.)
Lockouts require human intervention for obvious reasons.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Refrigerant piping question
RE: Refrigerant piping question
Keith Cress
kcress - http://www.flaminsystems.com
RE: Refrigerant piping question
RE: Refrigerant piping question
They come combined. Separate. Integrated. What Ever.
Pressures switch madness
Keith Cress
kcress - http://www.flaminsystems.com
RE: Refrigerant piping question
RE: Refrigerant piping question
Typical example:
Keith Cress
kcress - http://www.flaminsystems.com
RE: Refrigerant piping question