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Old 03-10-13, 10:52 AM   #1
Thepprof
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Default What the heck?? (HP line set sizing)

I'm still a novice at HVAC and questions keep piling up. Ok I just spent a number of hours reading about sizing of the line sets on a heat pump.. why? My 5 systems heat as much as they cool so this reverses all of the velocities etc. that I have been reading about. Common sense in this event tells me that since the lines are used for the most part equally for heating as well as cooling that the lines should be the same size. Any thoughts out there???

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Old 03-10-13, 01:40 PM   #2
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Gas is much less dense than liquid.
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Old 03-10-13, 02:07 PM   #3
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I wondered about that too.

Since the Cool Only units use a large and small tube lineset,
maybe it's just a carry-over thing.?. Since the basic units are for cooling..?.
It would be easier not to change the lineset connectors when making the heat & cool model?
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Old 03-10-13, 06:14 PM   #4
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Quote:
Originally Posted by Xringer View Post
I wondered about that too.

Since the Cool Only units use a large and small tube lineset,
maybe it's just a carry-over thing.?. Since the basic units are for cooling..?.
It would be easier not to change the lineset connectors when making the heat & cool model?
You would think with all of the "Engineering" involved and with basically equal cooling and heating seasons here in Va. My brain is still smoking from reading a few pages explaining why the line sets had to be a particular size. Some one has some splaining to do...thanks Owen
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Old 03-10-13, 07:06 PM   #5
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Seems like bigger lines are used with bigger systems. More BTUh..

www.usair-eng.com/pdfs/long-line-piping.pdf
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Old 03-10-13, 11:56 PM   #6
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i think i understand what you are asking: Why is one line larger than the other? The answer is this: The large one is the vapor line, the small one is the liquid line.

During cooling season, liquid is fed indoors through the small line at high density and pressure, and is expanded in the a-coil. The expanded cool vapor is sucked back through the large line to the compressor after absorbing heat. This cool vapor helps keep the compressor from overheating. The large diameter helps keep pressure drop to a minimum.

During heating season, gas is fed indoors through the large line at high pressure and low density. When it reaches the cool a-coil, it shrinks into a liquid as it releases its latent heat. The large diameter allows the compressor to supply lots of superheated vapor to the hungry a-coil. The shrunken, cooled liquid returns to the outdoor unit through the smaller line at high pressure and high density.

No matter which way the refrigerant is flowing, gas is speeding through the large line at low density, and liquid is crawling through the small line at high density. A much larger volume of gas must flow than liquid, around 1000-2000 times more, so the gas line is larger.
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Old 03-11-13, 07:21 AM   #7
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Default What the heck???

Note; REVERSING VALVE. Thanks for the response but when I look at the diagrams of my newest HVAC unit (Goodman packaged unit) In the heating cycle the reversing valve sends the compressed gas through the (what was the liquid line during the cooling cycle) to the indoor coil and the liquid returns through the gas line to the outside coil, which totally negates all of the engineering regarding flow during the cooling cycle. My brain is easily confused when things are not clear cut and absolute.
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Old 03-11-13, 03:56 PM   #8
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Default What you are saying is illegal

Quote:
Originally Posted by Thepprof View Post
Note; REVERSING VALVE... In the heating cycle the reversing valve sends the compressed gas through the (what was the liquid line during the cooling cycle) to the indoor coil and the liquid returns through the gas line to the outside coil, which totally negates all of the engineering regarding flow during the cooling cycle. My brain is easily confused when things are not clear cut and absolute.
NOPE! I don't believe it. Compressors and reversing valves only work with gases. The only liquid that flows through these 2 devices is OIL unless something is very wrong. The liquid line is always on the opposite side of a heat exchanger from the reversing valve.
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Old 03-11-13, 09:57 PM   #9
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I am looking at the hvac schematic for a Goodman Package unit.

When in cooling, the compressor via the reversing valve sends the hot gas to the outdoor coil where with the application of pressure and the passing of cooler air throught the coils. the liquid forms. The heat is released outside and the liquid forms in the outside coil and is pumped to the inside coil through a metering device where it evaprates and cools the coils in the process. The gas then returns to the compressor where the process starts all over.

Now in the heating process the compressor forces the superheated gas via the reversing valve at high pressure into the inside coil where the heat is removed and the gas turns into a liquid returning by the same line that in the cooling cycle was the liquid line... check it out...
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Old 03-13-13, 05:37 AM   #10
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You just confirmed my statement. The liquid line is the liquid line is the small one. Less liquid volume = smaller line.

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