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OT: insulating refridgerent lines

Bill D

Diamond
Joined
Apr 1, 2004
Location
Modesto, CA USA
Off Topic: I am installing a split ac in my house. I need to run the refridgerent lines about 20 feet down one side of the house. Plan is to run a 3"( or maybe as small as 2" if I can fit it) in conduit with the low pressure line insulated and the power wires inside the same conduit. So shoud I put the high pressure line inside the insulated bundle or leave it in free air so it does not heat the return line to the pump.
Normally the high pressure line is left uninsulated so it can shed heat to the air. If I bundle both lines together it will warm the return flow and that will raise pump temps.
Also how far apart can I have supports of 3" ridgid conduit?
Bill D.
Modesto, Ca often over 100 in summer
 
I'd suggest the power get it's own conduit. The heat will adversely effect the wire and adding heat from the lines will make it worse. Most any rigid conduit needs to be supported 3' from it's box / starting point and then every 10' there after. If it were me, and it was a 20' run, I'd strap it a couple feet from either end and then once near the middle.
I would also slightly increase the size of wire required to feed the unit, from that which is spec. With out details I'll spare the code stuff, and just suggest you do it.
 
The power lines will be 240 volts but the only run a fan motor so I think #14 should be fine for that. Somehow the control is done with 240 as well there are only four wires to the air handler. ground, two hots and one control wire.
Bill D.
 
Get a second opinion on this because it is a long time since I did anything with refrigeration, but it may be to your advantage to wrap the high pressure and return lines together. The idea is to cool the high pressure line so the expansion starts at a lower temperature. At the same time, the compressor gets warmer gas that it is happier with. As I recall from 20 years ago, some of the better systems incorporate a heat exchanger for that purpose. You might even run the lines coaxially, putting one inside the other and separating them with a Tee at each end. I looked through my book collection for something on this but couldn't find any refrigeration texts. I know there is one somewhere, but I have a ridiculous number of books. You definitely don't want to run the wires with the lines.

Bill
 
The units I have seen have the small diameter HP line insulated, not the larger LP return. Same on cars. There is small diameter foam insulation designed for the purpose of insulating the line.
 
Why would you insulate something that has just been fed through a condenser coil to cool it unless it was passing through an area that was warmer than the air through the condenser?

Bill
 
9100. the return line, in a properly working ac system, is still cold. This is then returned to the pump cold and it helps cool the ac pump. In my installation the return line will be outside the house so it will warm up some as it returns to the pump.
Normally the high pressure line goiung to the evaporater is left bare so it can throw off more heat to the air. In a car it might be better to insulate both since underhood temps may be higher then at the radiator.
Bill D.
 
Down here, where it also gets hot. Industry standard is to insulate both lines. Pre-insulated twin pipe is about the only thing I’ve ever seen used for split systems.
Photo of it here I just ripped from EBay.
http://i11.ebayimg.com/07/i/001/28/a5/f7b7_2.JPG

I think that’s done to protect the plumbing when the system is off. The position of the external unit nearly always means the lines will be coming down a wall and in the sun. If you come home in the afternoon and it’s a hundred degrees in the shade. The lines have been baking all day. The temp and pressure in the return line is enough to upset the compressor until it handles the load. Not sure that applies in your situation.

Regards Phil.
 
Lot to consider like ambient temp, but in general I think you can leave the HP line from condenser to TXV open to ambient, and definitely insulate suction line from evap coil to compressor. You can get a heat exchange section to improve efficiency but if you want to home brew it by running the pipes together you'll do a lot of pump downs and evac/recharges before you get it right.
 
AC power

As I read it, the compressor and condenser are outside, and the evaporator coil and its fan are inside. The compressor usually draws a lot of power, and a wire larger than 14 ga (15 amp) is required. The indoor evaporator unit's fan is low drain, and #14 wire will surely suffice. The high pressure line carries the refrigerant in a liquid form to the evaporator coil, and it certainly should be insulated. The low pressure line may be cooler than ambient, or it may not. It usually is not insulated, but it doesn't hurt if it is.

Good luck:)
 
Since my last post, I discussed this with a friend who has made some really wild refrigeration systems, like a super cold one with three compressors cascaded ( he works for the Washington University Medical School and is often called on to make strange setups ). His response was that a heat exchanger between the two lines would improve efficiency but you could not warm the return too much or the compressor would run hot. Just about the same opinion expressed by others here. I am also dredging up some of my old memories. I made an air dryer with a refrigerator that ran subzero. It froze the water out and periodically shut down to allow the ice to melt and drain away. The return was so cold that the side of the compressor was covered with frost, so we made a heat exchanger with many feet of copper tubing coiled up in it. While the theory is the same as an air conditioner, the parameters were a long way from your application and not all that pertinent. It was really effective, though. We could supply 50 CFM of 100 PSI desert air.

Bill
 
refrigerant line

Bill, I originally went to trade school for air conditioning. I guess I am wondering why you want to cover the refrigeration lines to begin with? I put in plenty of systems that required running the pipes down the outside of the house. Some went to the up-stars as well. I can only guess you are concerned about something hitting the lines and causing a leak. If that is the case why not just guard tyhe bottom 5 or 6 feet with a conduit or a cover as long as the conduit is quite a bit larger than the pipes to allow heat to escape. Also, I do not believe the national electrical code allows 240 volt porer lines to run in a conduit with refrigeration lines. As far as heat transfer concerns go: Do not insulate the smaller high pressure liquid line. Leave it bare so heat will continue to transfer to the ambient air as the refrigerant flows to the evaporator coil. The refrigerant is in a liquid state as it is in the high pressure line after the condenser but still gives off heat. The larger low pressure or suction line has refrigerant in a saturated vapor state as it travels to the compressor. This saturated vapor is at a low temperature when it arrives at the compressor and this is what cools the compressor. That is why there are no fins on the compressor housing. This line should be insulated and not placed in a hotter than ambient environment.
Brock
 
In FL the lines are run down the outside of building insulating only the suction line as it will condense lots of water and cause building damage. A hat channel sheet metal duct is fastened over the lines to hide them. The suction needs to be cold to cool the compressor motor and colder suction gas is more dense which improves compressor efficiency. Suction gas is superheated 10 - 20 deg. in the evap. to make sure no liquid refrigerant enters the compressor. Compressors do not pump non compressible liquids well. It breaks the valves and foams the lubricating oil from the crankcase.
 
In FL the lines are run down the outside of building insulating only the suction line as it will condense lots of water and cause building damage.

Ding ding. Finally, we have a winner.

I always understood the primary reason for insulating the cold return line was so that it didn't cause moisture from the hot/humid attic to condense and cause wet spots.
 








 
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