crank case heaters in scroll compressors

[abbasi]

In COPELAND scroll compressors we are not using crank case heaters. what is ill effect of not using crank case heater?
please explain?

[jamcool]

What kind of application are the comps. used in? is it medium temp. or low temp.? whats your ambient? here in the tropics not alot of crankcase heaters the ambient is always mid to high 20s ,the use for crankcase heaters is to always have your oil at a high temp. for many reasons.
No heaters can cause the oil to become less misicible also in piston comps. on start up with refrigerant in the oil it can damage the valve plate and reeds.
Scroll comps are more giving than say helical or piston type,of the top of my head dont see a whole lot of trouble if no heaters are used,as long as the ambient is high and the application isnt low temp or below:cool: :)

[NoNickName]

Keeping the oil warm will also help in establishing good lubrication after a short stop, not just preventing oil dilutiojn. I would definitely recommend it, provided it is interlocked with the compressor contactor, in order to avoid unnecessary heating while compressor is running.

[abbasi]

well i just wonder when v heat oil durin off cycle the refrigerant evaporates n v dun want liquid in compressor. Question i may put is is oil soley heated 2 evaporate refrigerant. it has nothing 2 decrease viscosity of oil?
wat is basic difference of use of crankcase heater usage in scroll and semi hermetic compressors?

[US Iceman]

what is basic difference of use of crankcase heater usage in scroll and semi hermetic compressors?

There is no difference.

The crankcase heaters are required to keep the oil temperature warm to prevent refrigerant from being absorbed into the oil.

This also applies to screw compressors. However a screw compressor does not have a crankcase, they have oil separators. The oil separator has an oil sump. This is where a heater is usually provided for the same reason as above.

The oil viscosity will decrease of course as it is heated. For this reason you do not want the oil to get too warm.

The viscosity also decreases when liquid refrigerant is mixed in the oil. This is the main reason for crankcase or sump heaters.

[malik55]

Scrolls are different then reciprocating, and can handle liquid at start up, As there are no valve reeds and scrolls having some clearance as rotary which becomes normal after warm up, with out a oil heater in the system it does not effect compressor operation, many units are working with out any problem.
Any how if you are facing some operational problems you may fix additional clamp type heater externally on the dome as some manufacturers recommends to fix additional oil heater for low ambient areas.

[US Iceman]

Scrolls are different then reciprocating, and can handle liquid at start up, As there are no valve reeds and scrolls having some clearance as rotary...

What you say makes perfect sense. Screw compressors are also more "tolerant" of small amounts of liquid refrigerant for similar reasons.

In any event, my preference would be to recommend a band-type of heater as you suggested for the scroll compressors, when the compressor is first installed.

In my view this is very cheap insurance to protect the compressor.

[NoNickName]

Tolerance is a matter of point of view.
If you want, I can send you a warranty refusal report from Copeland, stating that the spirals and bearings failed due to low superheat. Anyway, I'm not suggesting that the heater will counteract low superheat, but just that suction of liquid will do definitely harm to any compressor, depending on the quantity of it.

[US Iceman]

...not suggesting that the heater will counteract low superheat

I quite agree. The low suction superheat is a distinct problem and independent of the crankcase heater.

The heater should not be used as a means of attempting to cover up another problem.

I am also not surprised that Copeland issued a warranty refusal on the basis of liquid prone damage.

I also agree with the comment that any liquid is not good for compressors. My comment about some compressors being tolerant of small quantities of liquid should not be construed to mean it is OK to allow liquid into ANY compressor.

I was agreeing with the logic, not the argument.:D

[malik55]

Iceman is right, Torlance means it can handle some amount for some time only but not as a low super heat problem which can not compair with an oil heater off cycle operation, It is a functional problem and as refrigerant compressors are built for to pump refrigerant in gas form only, Continuously fed by liquid will sure damage compressor internal parts.

[abbasi]

so folks what do we conclude as we are using scroll and no problem to date is reported can any one tell the manufacturer's point of view.

[abbasi]

Did the compressor damage due to crank case heater, i mean the liquid accumulated during off cycle and at strt up it created damage or there was problem with low superheat during normal operation.
Iyt seizes to amaze me that we experimented with 1 condenser and 2 evaporators by just inducing solenoid valve(w/out any hot gas bypass to save cost ) and when one evap is off liquid floodback 2 comp is likely
it has been months and no damage to rotry compressors. y is it so. idf rotary are not prone 2 damage, y manufacturer is concerned with scroll)

[Lazarus]

My chief concern with not having a crankcase heater would not be a matter of having liquid refrigerant through the vanes/pistons or scroll but having refrigerant boil out of the oil within the bearings. This then removes what lubrication was there and causes premature failure.
So it is not primarily a matter of wehter the compression gear can handle a little refrigerant but can the bearings stand not being lubricated.....
Just a thought!!!

[frank]

We had a 6 compressor VRV system lose No.6 scroll comp due to an undersized CH. The original design was for a 40W CH to each compressor but, as No.6 was only called under full load conditions it spent the majority of it's time just sitting there.

A combination of low usage and small CH caused the oil to be lost in the system and not returned quickly enough and the compressor eventually seized.

The factory issued a 70W CH which seems to have solved the problem.

[abbasi]

what is the maufacturer's say in this matter?
Is it a mandatory accessory?

[NoNickName]

what is the maufacturer's say in this matter?
Is it a mandatory accessory?

No it is not mandatory, but it costs a few euro; consider it an inexpensive insurance. So please buy it.
And by the way: there's no liquid in the oil if you install a liquid solenoid, so please install the liquid solenoid as well.

[frank]

what is the maufacturer's say in this matter?
Is it a mandatory accessory?
It was the manufacturer who designed the system and they came up with the solution. Subsequent systems were changed at the factory.

[Lazarus]

there's no liquid in the oil if you install a liquid solenoid, so please install the liquid solenoid as well.

!!!!!!!!!!!!!

[Guner Edip Riza]

No it is not mandatory, but it costs a few euro; consider it an inexpensive insurance. So please buy it.
And by the way: there's no liquid in the oil if you install a liquid solenoid, so please install the liquid solenoid as well.

Considering the temperature of milk pumped into the milk tanks. I beleive we shoud consider crankcase heaters mandatory for the compressors installed on to the milk coolers.
Rgds
Güner

[powell]

Here's a link to Copelands AE manuals. Start with 4-1312 and then read all the others concerning scrolls.;)

http://www.hvacrinfo.com/ae_index.htm