Heat Pump Installs with Long Lines Technical Questions

Joe

I sometimes install heat pumps with tubing runs in the 100 to even 150 foot range. I noticed in the Carrier Infinity heat pump install documents that it is suggested (or directed) that on lines over 100ft, a solenoid valve be placed in the smaller "liquid" line at the compressor when the run exceeds 100ft. I have the following questions please.

1) What is the solenoid supposed to do? In heat pump mode, I am supposing that it keeps the liquid charge inside the inside inside coil from migrating out the line to the outside coil, but I am not sure why this is bad as this does remove heat from the house.

2) In Cooling mode, I am thinking that such a valve would prevent liquid in the outside coil from migrating into the (cooler) inside the house coil. I am thinking this would not be good as it would just have to be pumped out again, but in the process, you might get "slugging" of some liquid out the suction line into the compressor if a lot of the liquid migrated inside.

3) Then third.. If preventing this migration is a good thing, why do the heat pump engineers not just install a second two way expansion valve in the liquid line of the outdoor unit where the two way piston regulator is normally installed? It seems like this would be more efficient in heating mode (particularly if some of the charge has leaked out) and would take care of both problems and not cost any more than a solenoid valve.

How about someone giving me an education here? Thanks
Joe

beenthere

In winter time. It prevents the liquid refrigerant from migrating back and forth between the 2 units. And washing out oil from the outdoor unit. Along with preventing flooding the compressor with liquid during off cycles. The accumulator could fill with liquid without it.

In summer time, it does the same basic thing. Keeps the indoor coil from becoming flooded with liquid, and then slugging liquid back to the compressor.


Since its the installing company that buys the solenoid valve, and the end customer that pays for it on those installs. The manufacturers aren't going to add extra cost to all units.

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Joe

Thanks for the explanation. Would a second two way expansion valve mounted external to the outdoor unit on the liquid line be even better than using a solenoid valve?

RoBoTeq

The solenoid valve holds a higher pressure of liquid refrigerant between the compressor back flow preventer and the solenoid which provides the initial higher pressure on start up to open the TXV.

Joe

In a heat pump, the bidirectional indoor TXV is only operational as a TXV in cooling mode. In heating mode, the indoor TXV acts as a check valve and simply opens fully whenever refrigerant flow in the HEATING mode is called for. A piston orifice in the outdoor unit of a heat pump normally provides the TXV function for the outdoor coil when operating in HEAT PUMP mode.

I am thinking that the solenoid valve is recommended to prevent refrigerant flow BACK into the outdoor unit and thru the piston orifice in winter when the machine is IDLE and in HEAT PUMP mode. This is when the outdoor unit is colder than the indoor coil and so refrigerant will tend to migrate backward thru the bidirectional expansion valve and into the outdoor coil. Thus possibly providing a "slugging" opportunity when the heat pump is started up in winter time.

Actually, I do not think I have seen a recommendation for a solenoid valve for an air conditioning only system.

An expansion valve is a more efficient metering device than a piston/orifice expansion device I am told. I have seen it suggested that replacing the outdoor piston/orifice and solenoid valve with a TXV at the outdoor unit (where the solenoid would be installed) is more efficient than the piston/orifice and that the second bidirectional expansion valve also will provide the function of the solenoid valve and prevent backflow into the outdoor coil when the system is IDLE in HEAT PUMP mode. Is this true??

Am I missing something here?

RoBoTeq

It's not this complicated. The only reason for the solenoid valve is to maintain a solid line of higher pressure liquid in the liquid line so that the compressor does not have to try to compress a lot of gas before the txv will open.

beenthere

No it is not.

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costello

Make sure you use the carrier valve as it is a byflow valve and you have to put the arrown facing the condenser as well for it to work.. I found out the hard way that you can not just buy a standard one and think it will work on a heat pump. I have a customer that has 12 of 200' foot lineset and he has them on all of them the ones that did not have them when got there have had there compressors replaced.

repj2y

Are you serious ? I've never heard of a line-set longer than 50' if at all
possible! Talk to your manufacturer engineering department ! Bohn
Engineering will not honor any warranty what so ever if a line set is longer than 50 ft. The primary reason: insufficient oil return and premature compressor failure. Even if you can prove installing U-traps
every 21' of vertical lift. No cigar ! If you do find an existing system amongst your customer base; I would still call your manufacturers engineering department.

beenthere

ICP approved and designed 180 foot line set for a 7.5 ton A/C
York Approved and designed 88 foot line set for a 2 ton A/C
Trane Approved 170 foot line set for a 40 ton condenser and barrel
York Approved 72 foot line set for a 7.5 ton heat pump


And I've done more long line sets then those. Those are just the few I remember off the top of my head. Oil return is not the concern on heat pumps. Not having the liquid refrigerant over flowing the accumulator is on heat pumps.


Oh, and I use to work on some old GE 20 ton splits, that had a vertical up to the condenser of 120 foot, and no traps were in the lines. This was a GE design. And 26 years later, still had the original compressor in it.

Long line sets are more common then people realize.

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repj2y

Like I said: Talk to the Mfgs' Engineering depart. on any new installs. Dual suction
risers with pressure actuated -or-electrical operated unloaders are installed all the time. I've been installing them for years ! I'm talking best practice. You can
actually do what you want on any installation. Your name is behind it.
I'm very informed about reference tables for equivalent length of feet. They have
tables up to 500' ! There are many cases everywhere because of the architecture
design, which; decide the basis of the installation. Based on the rapid advances
in Bldg. automation, equipment, commercial applications etc; there comes time
when you should be preparing your customer for an upgrade ! It doesn't matter
that 26 yrs. accumulated on any system. That's attributed to good maintenance
practices, and; keeping records to spot trends before failures.

RoBoTeq

JCI brands of horizontal discharge condensing units 1-1/2 to 5 ton approved for 200' linesets out of the box.

repj2y

I probably should of said: line sets longer than 50' are not common in residential cooling in Florida. I've worked in every corner of the state. What the mid-states used for heat pumps I'm aware of used R-500; azeotropic blend of 80% R-22. We can't run heat pumps below 50* (R-22) in Florida based on no heat transfer near that
point. Auxiliary heat strip would actuate and the unit would be in defrost because of our higher humidity ratios in the winter for Florida. I was attending a REVCO Scientific class in Ashville, N.C. in 1987. The instructor kept arguing we run our units
to 0* ! Well; not with R-22 ! What blends are you using now? Check valves seem to be the standard implemented vs solenoids.

costello

yes these are infinity r-410 systems and carrier has said that the line set is ok with the length and the size. You just can not bury them underground for that long. They lose all there heat in heat mode and don't do anything.

repj2y

I googled the Carrier Infinity program. I found alot complaints from both technicians and home owners about the 2 stage systems. But; who knows if the system was installed correctly with the home owner given ample time to really learn how to operate it ! I sometimes have to
catch myself when I start talking tech. info to a home owner and they're
doing this !

beenthere

Those units had hardly any maintainence done to them,.

Most fears about long line sets are from listening to people that have very little if any experience with long line sets(not implying anything toward you).

If its not over 100 foot. I don't worry about its length. Unless it has a large vertical in it.

Main point, is there isn't as much of a limit to line set lengths as people think.

Running them underground, has more hazards then just having a long line set.

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beenthere

The refrigerant has no bearing. The outdoor coil will be the same temp no matter which refrigerant you use.

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repj2y

I'm actually referring to heating mode. Outside temps in mid-states like
Tenn. are very low. What would you set the cross-ambient thermostat at ? You'd be in defrost so frequent; a heat pump would be useless !
I think I've seen enough refrigerant charts to know condensing temps are
the same no matter what refrigerant.

beenthere

Tenn is any colder then my area. And we have lots of heat pumps. Defrost is either time and temp, or on demand. And temps staying in the 20's or teens for days weeks at a time is not unusual.

After the coil gets X cold, yes it will go into defrost every 30, 60, or 90 minutes of compressor accumulated run time on time and temp boards. With on demand, it will only go into defrost when the liquid line temp and the ambient air temp have a great enough temp difference.


If you know the refrigerant temps are the same, then why did you post the above?

They use R22 heat pumps in areas that are in the single digits for weeks at a time.

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beenthere

Cross ambient? Guess you mean lock out temp for the compressor/ heat pump.

No reason to lock out a heat pump. Until its COP drops low enough that it becomes less efficient then electric resistance heat. Some heat pumps maintain a high enough COP, that they still produce more heat at -10°F for less money then resistance heat, that even with the cost of defrost cycles, its cheaper to let it run.

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