high compressor superheat

[rocket]

a friend attended a recent Copeland COSS seminar, where they told him that superheat at compressor is 20 minimum, but they don't care how high that superheat is. I can't believe that high compreesor super heat is not impprtantant, anyone know about this?

[cjcargo]

I have the seminar on tape. It has on this one 15 degrees minimum is recommened; readings taken 6 inches from the compressor inlet. That way they feel with low loads the superheat will not drop below 10 degrees.

[Dchappa21]

Ive always been told 20*-40*. If you get much above 40* you won't have enough cooling for the compressor. And will be changing alot of compressor's.

[dirtyboy103us]

depending on application

med temp is between 30 and 50 degree super heat
low temp below -20 i think it is no less than 20 and between 20 and 40

its been a couple of years now since i've been so i maybe off a little

[d_griff]

i have attended the COSS class. I was told 20 degrees for A/C applications..
As low as 4-6 for low temp.
It is in the book they give you it has a chart in it for med temp/low temp etc.
this is rule of thumb, If you have electronic expansion devices you may see alot lower.
on low temp systems that have de-superheaters and other devices to help control superheat it will differ as well.
I am pretty sure they only meant for straight A/C applications.
Although if you have a manufacturer's charging chart i guess you follow it instead.

[rocket]

the minimum superheat is in the book, also something most of us know. The question was on "Maximum" superheat. An attendee stated that they, "the COSS instructor" said there is no maximun, not important, only a minimum of 20. so 95 superheat is OK? that's not what killed my compressor! WHAT!!! In the older COSS semionars they told us 45 was max, anything above that is BAD! So why the new "no Max" comments?

[refrigraider]

i have attended the COSS class. I was told 20 degrees for A/C applications..
As low as 4-6 for low temp.
.

They are talking about superheat at the compressor, not at the txv

[dirtyboy103us]

the 3 day class was long and hard in the beginning

the first day was on basic refrigeration principles and the cycle which was hard to stay awake, maybe he heard one thing when another was said, at this point one of us ( not me ) should break out the AE book and find the right answer if they have a max superheat on the compressor

just kidding I'm looking also, I would like to have that on the tip of my tongue

[icemeister]

That Copeland doesn't care how high the compressor superheat is both a puzzling and troubling statement. I find it hard to believe that a COSS instructor would specifically say that, but I suppose anything is possible.

While it's true that Copeland doesn't state an upper limit to compressor superheat as many system manufacturer's (like Heatcraft for instance) do, Copeland does in fact care about it indirectly as superheat, along with compression ratio and other factors, have a dramatic effect on compressor discharge temperatures.

Copeland's Application Engineering Bulletin AE-1260 discusses the issue of compressor overheating quite thoroughly. After reading it, one can see that there are many variables that can affect a compressor's discharge temperatures and as such it's impractical to pin down one set number as an upper limit for compressor superheat.

The way I see it, the minimum limit of 20ºF SH is adequate as a general rule for protecting the compressor from liquid slugging and/or oil dilution and works for all nearly all common refrigerants and applications. To establish a hard and fast number for a maximum limit that would cover all the possible system scenarios would be too restrictive in many cases, so Copeland in their infinite wisdom opted for the discharge temperature control approach as the governing method. Manufacturers like Heatcraft on the other hand, produce fairly plain vanilla systems (for the most part) that will run under relatively predictable conditions and therefore have the ability to simplify the overheating issue with a blanket statement like 20ºF min and 40ºF max.

Copeland is essentially saying that as long as the discharge gas temperature measured 6" from the discharge valve does not exceed 225ºF you are OK but if it does, then a lower compressor superheat may be one avenue to correct it.

[dirtyboy103us]

Ive always been told 20*-40*. If you get much above 40* you won't have enough cooling for the compressor. And will be changing alot of compressor's.

what part of N.H. and hows that weather today i hear its snowing again
when i lived in manchester we didn't need a whole lot of refrigeration

[hvacpope]

Basically Copeland like many others compressors manufactures are trying to protect their units (less warranty returns) and don’t give a rat ass about the overall system efficiency.
The refrigeration effect of superheat is sensible and very minimum when it happens in the evaporator, superheat (heat) gains in the suction lines due to poor insulation or pressure drops are just a big waste of energy.
10 degrees of superheat 6 inches from the compressor is more than plenty.

[dirtyboy103us]

10 degrees of superheat 6 inches from the compressor is more than plenty.

better have some thick insulation on suction lines down here in fla to achive that on a 300 ft plus line set on those -25 racks
or it will be raining in the store

[jonny in La]

20-40 for low temp 40-60 for medium temp.At least thats what I was told by a former boss that went to copelands school. And Yes there is a max unless its an open drive the motor depends upon superheat to cool the windings and a desuperheater depending upon the type of gas you're running compressor windings will open if superheat is to high for to long.