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冷蔵システムにオイルトラップが必要な理由?

目次

Why is it Necessary to Set Oil Traps?

When there is a large height difference in the refrigeration piping system between evaporator unit (室内機) and condensing unit ( 屋外ユニット), must install oil traps on the vertical pipe to prevent refrigerant oil from failing to return effectively to the compressor, which could otherwise affect the compressorsservice life.

The Role of Oil in Refrigeration Systems

Oil is essential in refrigeration compressor because it lubricates moving parts, reduces friction, and helps seal components to maintain pressure.

In most systems, oil mixes with refrigerant and travels through the piping. This is necessary for compressor’s health, but it also means the oil must cycle back properly after leaving the compressor.

In low-temperature refrigeration, for instance, the oil’s viscosity changes will make return more challenging.

要約すれば, proper oil management is key to preventing compressor failure, especially in systems handling extreme colds.

Oil TypeViscosity (cSt at 40°C)Miscibility with RefrigerantsCommon UseData on Performance
鉱油32-68Low with HFCsLegacy systems10% lower efficiency in modern setups
ポー (Polyol Ester)22-100High with HFCs/HFOsModern ACImproves return by 20% in low-temp
パグ (ポリアルキレングリコール)46-150High with R-134a自動車Reduces migration by 15%

Compare Oil Types in Refrigeration Systems

Common Issues Without Oil Traps

Issue説明Impact Data
Oil ShortageLow return to compressor25% higher failure rate
Efficiency DropEvaporator oil accumulation5-15% heat transfer loss
Downtime from SlugOil clumps damage valves10-20% elevated repair costs

Benefits of Installing Oil Traps

Install oil traps offers multiple benefits that make them a must-have in many refrigeration setups.

They protect compressor by preventing oil starvation or slugging, which extends the system’s lifespan and reduces maintenance costs.

Energy efficiency improves as the evaporator stays clear of oil films that hinder heat exchange.

In commercial applications, this translates to reliable operation during peak loads.

MetricWith TrapsWithout TrapsBenefit Data
効率90-95%75-85%10-20% uplift
Life Span10-15 年7-10 年20-30% extension
Energy Cost$800/year$1,000/year15-20% 節約

When Should Install Oil Traps?

1. When condensing unit is higher than evaporator unit

There is a vertical pipe between evaporator and the main suction pipe. Since refrigerant oil doesn’t evaporate inside the evaporator, it accumulates at the bottom. When too much oil accumulates, it will block the suction pipe.

If install oil traps at the bottom of evaporator, the amount of oil stored in the trap won’t be excessive. As soon as the trap is nearly full, the pressure difference on both sides will be sufficient to “pump” the oil out of the trap, push it up to the horizontal suction pipe at the top, and then allow it to flow back to the compressor.

If the vertical copper pipe is very long and there is concern that the oil may not be pumped all the way to the top, should install oil trap at intervals along the riser (例えば, every 6~10 meters) to ensure the oil will return to compressor in stages.

2. When condensing unit is lower than evaporator unit with a large height difference

Even without oil trap, the oil would automatically flow back to compressor by gravity. しかし, the concern here is that too much oil might return at once, causing compressor “liquid slug (oil slug).」

To avoid this, should install oil traps at intervals (例えば, every 6~10 meters) along the suction pipe so that the oil returns to compressor gradually in stages.

oil trap 01

3. During low-load operation

Oil may accumulate in the trap, but due to the limited refrigerant velocity, the return effect driven only by the pressure difference when the trap is nearly blocked is very small. The key is to regularly increase compressor output to boost suction velocity and improve oil return.

If the suction velocity can increase to a sufficiently high level, then there is no need to add additional oil traps. しかし, in reality, under low-load conditions, the internal heat exchange effect causes compressor output to increase excessively, which can lead to system control issues such as excessively low suction pressure and lack of suction superheat.

This means the increase in suction velocity is limited. したがって, when there is a large height difference, it is necessary to use oil traps to return the oil step by step.

Principles for Installing Oil Traps

1. When there is a height difference between indoor and outdoor units, install an oil trap on the vertical section of the gas (suction) pipe every 8~10 meters from bottom to top.

The oil trap can be made using two “U”-shaped bends or one “O”-shaped bend, with a height 3~5 times the pipe diameter.

そのうえ, install an oil trap at the lowest point and a trap bend at the highest point.

2. The discharge pipe should design in the same way as the suction pipe, must consider: control pressure drop, ensure proper oil return, and prevent liquid slugging, noise, and vibration.

R
んんインチんんんん
Φ19.053/4
≥34≤105
Φ22.2
7/8≥31≤150
Φ25.41/1≥45≤150
Φ28.69/8≥45≤150
Φ34.911/8≥60≤250
Φ38.112/8≥60≤350
Φ41.313/8≥80≤450
Φ44.457/4≥80≤500
Φ54.117/8≥90≤500

Dimensions for Oil Traps and Trap Bends

(備考: “あ” means Copper Outer Diameter, “R” means Min. Bend Radius of Oil Traps, “ハ” means Max. Straight Pipe Length Between Oil Traps)

Technical Requirements for Installing Oil Traps

outdoor unit located below the indoor unit

Outdoor Unit Below Indoor Unit

 

Outdoor Unit Located Above the Indoor Unit

Outdoor Unit Above Indoor Unit

結論

Oil traps are essential in refrigeration systems to ensure proper oil return to compressor, especially when there are vertical height differences or low-load conditions.

Properly installed oil traps prevent oil accumulation, reduce risk of compressor damage, and help maintain efficient and reliable system operation.

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