Oil Traps in risers

[Jasper]

We are in the process of installing a Daikin 100 super inverter system,
When reading through the installation manual (something that we should probably do more often) Daikin state that an oil trap should be installed in the suction riser if the indoor unit is 15m or more above the outdoor unit, this is to prevent oil running back to the compressor during it's off cycle.
They also state that no oil trap is required if the outdoor unit is installed above the indoor unit.
Surely this is the reverse the normal convention where oil traps are required every 3m if the outdoor unit is installed above the indoor unit. Any comments would be greatly appreciated.

Jasper

[chemi-cool]

hi jasper,

maybe you was holding the manual upside down.

if there will be traps on the suction going down, it can not work.
oil is running with the refrigerant in small quatities. oil is heavier then refrigerant. so I dont see whats behind this idea.

when suction is pulling upwards, oil is trapped and when trap is full, it will be pushed by the refrigerant up to the compressor.

could be a printing mistake???

chemi

[Jasper]

Chemi.
Honest this is exactly as it is in the manual, will put a picture of it on this site asap

[frank]

Jasper

I think that you've got the manual upside down as well

[Peter_1]

That's when you need to install the indoor unit upside down.

[frank]

No mention of Oil Traps here http://www.spaceair.co.uk/cgi-bin/pa...121%20tech.pdf - have you been DRINKING??

[Brian_UK]

Haven't seen the manual or pictures yet but.. do they mean a trap at the top of the riser; this would prevent oil drop on the off cycle.

Perhaps as they normally have an oil recovery action they got confused

[Prof Sporlan]

Haven't seen the manual or pictures yet but.. do they mean a trap at the top of the riser; this would prevent oil drop on the off cycle.

The Prof is certain this is the case. The manual would be clearer if it had stated an "inverted trap"

[Jasper]

The Prof is certain this is the case. The manual would be clearer if it had stated an "inverted trap"

The Prof is right again as attached picture shows but i still don't understand why theres no requirement for a trap when the condensing unit is as in our case 6m above indoor unit, How can oil return be gauranteed

[Peter_1]

The Prof is right again as attached picture shows but i still don't understand why theres no requirement for a trap when the condensing unit is as in our case 6m above indoor unit, How can oil return be gauranteed

Brian was right

You don't need a trap in the rising line because speed is in most AC extremely high and mostly under perfect oil return conditions. (high speed, warm gas compared t o freezer application, ..)

[Argus]

For what it?s worth, Jasper?.

Most Japanese manufacturers actually reduce their suction sizes when compared to the normal pipe selections that we are used to, in order to encourage a high gas velocity and oil return. This applies to all types of units.

At least one that I know of (Tosh) discourages oil traps within their stated line length tolerances because of the added resistance to flow.

In the case of VRF in particular and Heat Pumps in general, oil running back to the unit under gravity is not a problem as I see it, because if it lodges anywhere, it will sit in the accumulator first before the compressor. From that point on it is a controlled return to the sump.

All VRF systems have an oil scavenge system of one sort or another, so the question is, are your risers sufficiently high to warrant somewhere for the oil to sit on the off cycle? Factor into this the fact that VRF systems have fewer ?off? cycles than conventional kit because they modulate their speeds and tend to keep running. So, do you need a trap anyway?

Finally, the 64,000 Euro question, what does Daikin say?
________
Lincoln K-series

[chemi-cool]

hi jasper.

ok, so daikin says so.
doesnt make sense. the compressor hold up to 4 litre of oil. if the system is designed right, there should not be any oil problems.

on the contrary, if the trap will hold a large amountof oil on the off cycle, when the unit starts, all this amount will be flushed into the crankcase.

if the trap will be as close to the indoor unit as possible, I can see why.
daikin say every 15M on vertical suction line.

another thing about oil traps is that every manufacturer make them different and when I make them myself to save time and money they are different again, so I think the start should be how to design the trap for best performance.

Prof, are you the one from sporlan website?

chemi

[frank]

If you turn the drawing upside down it looks normal

[Jasper]

Thanks for the info mark.
Most things that are being said make sense (apart from frank LOL )
I come from the old school of fridge engineers and assume that the manufacturer should point out these installation practice changes.

Cheers

Jasper

[Peter_1]

For what it’s worth, Jasper….
Factor into this the fact that VRF systems have fewer ‘off’ cycles than conventional kit because they modulate their speeds and tend to keep running. So, do you need a trap anyway?

When VRF is at partial load, or minimum load, speed is also reduced in the lines and can be that low that oil don't come back anymore.

[Jasper]

peter,
I understand the principle of oil return on VRV/vrf systems.
Theses systems carry out an automatic oil recovery cycle every couple of hours of running time, any traps in a VRV/vrf system will hinder oil return and may damage compressors.
The system i originally wrote about was not a VRV it was only inverter driven.

A side issue to oil return came to mind, why do we allow oil to cuirculate around a system, oil coating in the evaporator must to some extent inhibit heat transfer so why not fit oil seperators to all refrigeration/ac systems.

[yangchenchen]

To fit oil separators to all refrigeration/ac system is a great idea. But, in real refrigeation pipe installation, oil separators are not necessity.

[R1976]

I thought VRF systems had oil separators?

I remember changing one in a Daikin system.

[janezP]

Greetings,

I have encountered a problem during pipe calculation for comercial refrigeration system (R404a). The line from the last evaporator to compressor rises for about 10m. The sofware that I use for calculating pipes warns me, that oil transport on this line is not guaranteed.
I have tried all kinds of tricks (splitting the line in half, reducing diameter....) but nothing works.
I know that this kind of problems have been solved in the past without using any kind of special components (a friend told me that), but i just dont have enought experience (only been in this branch for 1/2 year ).
Can anybody help me with that??

thanks

Johny

[iyadhadi]

what is the length of the oil trap

[brunstar]

in relation to oil traps this is correct, it is the opposite to old school traps that you would install to help the oil back up the riser on a long vertical pipe run.
The reason for installing them when the condenser is below the indoor unit is so that when the compressor cycles off the liquid refrigerant and oil will pick up speed falling down a vertical drop, then if the compressor starts back up again it could cause liquid compression. The trap is to slow the refrigerant and oil down in the off cycle.
If you can imagine dropping something off the top of a building it will pick up velocity on the way down.
This is the reason for the oil trap when the outdoor unit is below the indoor.