Carrier System Design Manual Oil Traps

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• Carrier System Design Manual Part 3 Piping Design
• Carrier System Design Manual 12 Volume Set

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Hi Im installing a 1hp condensing unit and evap section in a small walk in cooler. I am a bit of an old timer and have serviced a ton of equipment. I have been out of the field for about 15 years but now doing a little work here and there. This is only a 1hp tin can that uses 134a. The condensing unit will be outside on the roof. I have about 5 foot horizontal run and 10 foot vertical.

I am using fan cycle. My question is do i need a oil trap (p-trap) on the low end of the suction line. Back in the day almost everything on roofs needed a trap. Does this still apply?

With the newer refrigerants? Thanks That brings me to another question. Good refrigeration practices have always been preached. However even when i was in trade school the instructors would say in class to use vacuum pump, braze with nitrogen,etc. But when i would be their helper out of school they never used them. Im ok with the vacuum and micron but has something changed in the newer refrigerants that makes it so necessary to use nitrogen?

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I compleatly understand what nitrogen does but back in the day no one really used it with 22,502. Its not like we had premature failures but now i hear from the younger guys say its a must. From what i remember the trap just accumulates the oil from a riser when the unit turns off.

So it really has nothing to do with proper sizeing of pipe. I once had to remove a trap from a rheam ac unit. The trap made the comperssor fail or so i was told by them.But line sizing is very important to oil return. The trap does act to capture oil, but it does it during operation as well as in the off cycle. Oil tends to collect in the base of the trap and as it does it lowers the cross-sectional area of the pipe which increases the velocity of the gas.

This gas velocity is what causes the oil to get atomized into droplets and blown into the rising gas flow. Once it's picked up in that vertical flow it will start to form larger and larger droplets.then start clinging to the pipe wall and rise up in a spiralling motion around the inner wall. (Seen this in a glass tube riser test setup). If the velocity isn't high enough or if the rise is too excessive, this vertical oil entrainment process essentially stops. To better understand all this, it's a good idea to read up on how to proper size dual riser for unloading type compressor.

If you understand the 'WHY' of how these are sized, then I think you will get a good handle on riser sizing in general. It's true the residential and commercial sides of this business have been moving away from the need for 'proper' refrigerant piping practices.

I find this disturbing. In the past, there was most often no need for trapping a resi or light commercial installation simply because their recommended line velocities were so high. Then I believe Trane was one of the first to say no traps were needed back when scrolls were first being introduced.not bothering to say the reason was that the scrolls had such a low oil reservoir capacity, they could run dangerously low on oil if numerous oil traps were in the system. Then when the SEER race to the top was on, one of the resulting changes was increased suction line sizes to reduce efficiency loss due to pressure drop. See where I'm going here? It's just that I don't think the refrigerant or the oil gives a hoot who's units they're running through and whether it's a 2 ton residential or a 200 ton industrial system. The oil is going to return up a riser by the same rules and the refrigerant's gas velocity is the primary means to accomplish that.

Last edited by Educational Committee; at 06:33 AM. Quick Navigation. Site Areas. Forums.

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Carrier System Design Manual Part 3 Piping Design

Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R.

Carrier System Design Manual 12 Volume Set

You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions To gain full access to our forums you must; for a free account. As a registered Guest you will be able to:. Participate in over 40 different forums and search/browse from nearly 3 million posts.

Post photos, respond to polls and access other special features. Gain access to our free AOP (Ask a Professional) Section to get real answers for your questions. All this and much more is available to you absolutely free when you; for an account, so today! We suggest not registering using an AT&T, BellSouth, AOL or Yahoo email address. If you have any problems with the registration process or your account login, please. Thanks for the info and quick response, that makes alot of sense. Does that p-trap have to be there for both walk in coolers and walk in freezer, the type of temp that the cabinet holds has nothing to do with it, like you say if the compressor is above the evaporator then there has to be a p-trap.

Also this make me think even further, next time i find out that a compressor has gone bad because of low oil, or if i look at the oil sight glass, before adding more oil i should check to see if there is a p-trap, if not all the oil is in the line set. Is this correct. It has long been a generally accepted practice in the commercial refrigeration industry to install a P-trap at the base of every suction riser in excess of 4 ft high. For very long risers an intermediate trap is called for every 20 ft thereafter. In addition to applying a trap, the riser must be sized to insure sufficient gas velocities to entrain the oil in the gas flow under all operating conditions. Systems with unloading capabilities such as compressors with unloaders or parallel racks, the velocities at minimum load may require a double riser arrangement for proper oil return.

It is also very important to pitch the suction piping at a rate of about 1/2' per 10 ft of run not only to promote oil return but to overcome the sagging of the piping lines in between supports which can in effect create at unwanted oil trap. There are many publications available that address these refrigerant piping issues. Heatcraft's I & O Manual and Copeland's System Design Manual are two of the better one's I know of. Quick Navigation. Site Areas. Forums.