Air Conditioning - Why not insulate liquid line?
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jwcalla
05-25-07, 02:35 PM
Hi,
How hot is the refrigerant liquid typically after leaving the condenser unit? I have about 75' of copper lines going through the attic (~110-120°F air temperature). If the temperature of the liquid is much cooler than 110°F I figured it might be worth it to insulate the liquid pipe. If it's hotter than 110-120°F insulating it would probably have the opposite effect. Don't we want that liquid to be as cool as possible?
Thanks,
John
How hot is the refrigerant liquid typically after leaving the condenser unit? I have about 75' of copper lines going through the attic (~110-120°F air temperature). If the temperature of the liquid is much cooler than 110°F I figured it might be worth it to insulate the liquid pipe. If it's hotter than 110-120°F insulating it would probably have the opposite effect. Don't we want that liquid to be as cool as possible?
Thanks,
John
furd
05-25-07, 03:11 PM
It doesn't really make much difference. The transfer of heat (cooling) is a result of the liquid changing to a gas. The difference between 80 degree liquid, and 140 degree liquid when it is expanded to a gas is minimal.
jwcalla
05-25-07, 03:15 PM
Really? That surprises me. What's the point of the condensor coils and fan? They would seemingly be unnecessary.
Jarredsdad
05-25-07, 04:41 PM
I used to have a link to the basic refrigeration cycle (maybe still do) but I can't find it.
An A/C needs Subcooled liquid and Superheated gas to function properly.
Heres how it works. Starting with the compressor. The compressor takes the low pressure low temp gas from the evaporator and compresses it to high temp high press gas. The condenser and outdoor fan then condense the gas to liquid.
Say the maker of your unit wants 10 degrees subcooling. If the pressure at the liquid service valve is 200 psig the condensing temp of the R-22 is 102 degrees. To get 10 degrees subcooling we would want the liquid line temp to be 92 degrees. This is to ensure that there is liquid R-22 in the line at the metering device at the evaporator. If not you end up with a block of ice not an evaporator.
Now with an uninsulated liquid line you may have 94 degrees at the metering device, big deal it's still liquid. It takes much much more heat (BTU's) to change the liquid to gas than it does to add a degree to the liquid.
R-22 boils at -41 degrees. When the R-22 hits the metering device the liquid goes through a really small hole and hits (for it) a really big space and "flashes" into gas. This is where the cooling effect comes from.
We need this now "saturated vapor" to pick up heat from the air in your home to make sure the R-22 returning to the compressor is all gas and has no liquid. Liquid will kill your compressor.
Why is the suction line insulated? Two reasons. One, to keep water from condensing on the line and ruining your ceiling. Two, to keep the gas cool.
Say your looking for 10 degrees superheat. Your suction pressure is about 70 psig and the suction line temp is 52 degrees. At 70 psig the R-22 will condense into liquid at 42 degrees. 52 - 42 = 10 degrees superheat. This assures there is no liquid returning to the compressor and it's cool enough to keep the compressor motor cool.
The suction gas cools the compressor motor and helps keep it running.
Understand?
Chris
An A/C needs Subcooled liquid and Superheated gas to function properly.
Heres how it works. Starting with the compressor. The compressor takes the low pressure low temp gas from the evaporator and compresses it to high temp high press gas. The condenser and outdoor fan then condense the gas to liquid.
Say the maker of your unit wants 10 degrees subcooling. If the pressure at the liquid service valve is 200 psig the condensing temp of the R-22 is 102 degrees. To get 10 degrees subcooling we would want the liquid line temp to be 92 degrees. This is to ensure that there is liquid R-22 in the line at the metering device at the evaporator. If not you end up with a block of ice not an evaporator.
Now with an uninsulated liquid line you may have 94 degrees at the metering device, big deal it's still liquid. It takes much much more heat (BTU's) to change the liquid to gas than it does to add a degree to the liquid.
R-22 boils at -41 degrees. When the R-22 hits the metering device the liquid goes through a really small hole and hits (for it) a really big space and "flashes" into gas. This is where the cooling effect comes from.
We need this now "saturated vapor" to pick up heat from the air in your home to make sure the R-22 returning to the compressor is all gas and has no liquid. Liquid will kill your compressor.
Why is the suction line insulated? Two reasons. One, to keep water from condensing on the line and ruining your ceiling. Two, to keep the gas cool.
Say your looking for 10 degrees superheat. Your suction pressure is about 70 psig and the suction line temp is 52 degrees. At 70 psig the R-22 will condense into liquid at 42 degrees. 52 - 42 = 10 degrees superheat. This assures there is no liquid returning to the compressor and it's cool enough to keep the compressor motor cool.
The suction gas cools the compressor motor and helps keep it running.
Understand?
Chris
jwcalla
05-25-07, 05:13 PM
Thanks Chris. That nails it and explains why insulating the liquid line is completely unnecessary.
Thanks to both for your responses. They really are appreciated.
Take care,
John
Thanks to both for your responses. They really are appreciated.
Take care,
John
Grady
05-25-07, 11:06 PM
Not to dispute Chris but some manufacturers used to (and may still) specify insulating the liquid line in applications such as yours. York was one of these manufacturers & if memory serves me correctly, Goodman was as well. This may have been one of those extra fractional of a SEER point things which in the real world didn't make a hill of beans worth of difference. BTW, my liquid line which goes thru the attic isn't insulated.