Over Condensing????

[gazzza]

Who is teaching our poor apprentices this term? I have been a refrigeration mechanic in NZ and OZ and still hear the same thing from people. The system is "Over Condensing" It drives me crazy and doesn't even make any sense. Is this just a cop out for people who don't understand sub cooling?

If i am wrong can some one else please explain?

[nike123]

http://www.refrigeration-engineer.co...ad.php?t=13857

[NoNickName]

A little bit like "overkilling". Once one is dead, can't be killed further.

[Grizzly]

It's sad that you feel that if someone uses the term "over condensing" they are not correct.
I have first hand experience of chillers that have to much "Sub cooling" the politically correct answer maybe.
Either way when an "over condensing" situation does occur.
You loose your Head Pressure control, the "lift" across the Comp.
To low suction pressures can occur and a whole Host of related issues.
OK it's not actually possible to over "Sub Cool" refrigerant.
Surely it's more important than we all understand what is meant?
It's like you get Receiver, reclaim and recovery cylinders.
Just terminology really!
Grizzly

[paul_h]

Who is teaching our poor apprentices this term? I have been a refrigeration mechanic in NZ and OZ and still hear the same thing from people. The system is "Over Condensing" It drives me crazy and doesn't even make any sense. Is this just a cop out for people who don't understand sub cooling?

If i am wrong can some one else please explain?

I use the term when the condenser is cooler than the rest of the liquid line, causing the liquid refrigerant to turn into vapour again before the liquid flow control device.
It's a real thing you can see in systems with a sightglass before the TX. IE you can measure subcooling after the condenser, but if it's a remote condenser, what happens between it and the remote receiver and TXV?
No point adjusting refrigerant level or TXV setting until you ascertain whether the system may be 'over condensing'
I don't know where you are tackling this problem or name from, but it's a real thing, thats why systems have HP fan control, variable speed fan control, or fans come on in stages etc. If the condenser is too cool, you'll get 'over condensing', ie any liquid from the condenser unstable and will boil off when leaving a cold condenser and going to a warm liquid line.

[NoNickName]

will boil off when leaving a cold condenser and going to a warm liquid line.

How is it possible the liquid line warmer than the condenser? Would you please explain to me such scenario?

[Discharge]

Subcooling and over cond. do not go hand and hand. if your over cond. then your wasting energey. it helps to keep a constent pressure on your txv's. If your over cond. than you may be loging refrigerent in the condensor, giving the false impression that your low on gas.

[monkey spanners]

How is it possible the liquid line warmer than the condenser? Would you please explain to me such scenario?

Condensing unit out side in winter running a coldroom in a kitchen, the liquid line section in the kitchen will be above the outside temperature.

Liquid line should be insulated in such conditions.

Jon

[lowcool]

gazza you sound like your undercondensing.if your condensing pressure is lower than the designed system rated pressure then it is over condensed

[NoNickName]

Liquid line should be insulated in such conditions.

That's a unique scenario, and IMHO unlikely. In a controlled condensation, the fan speed in such low ambient will be almost or if not at all OFF.
Liquid will still be warm enough, to avoid such situation, unless a IHE between suction and liquid is installed.
That's more credible. Suction at -20, liquid leaving condenser at 30°C, liquid entering receiver 0°C.

[TRASH101]

I am having trouble with some of the interpretations of "over condensing" and "excessive sub cooling"

If, by definition, over condensing means more liquid is formed by condensation than what is anticipated by normal design parameters then it most certainly does exist when the design parameters are exceded by fault or other.

Excessive sub cooling is a very real concern for proper operation of most expansion devices (both in pressure drop and ability to actively control superheat)

They are both very close in definition but with over condensing there doesn't have to be a significant amount of sub cooling.

[mad fridgie]

There is no such thing as over condensing, what there is; to lower liquid pressure to ensure correct refrigerant mass flow through the evap at a said condtion, and has nothing to do with sub cooling (which is not going to happen at the outlet of the reciever)

[TRASH101]

There is no such thing as over condensing

Why not???

I'snt it correct that, in a thermodynamically balanced state, any change in the physical variables (namely the thermo physical effects on the high side heat exchanger) on a running system will change the proportional volume of liquid to vapor? Is the liquid not condensate (i.e. the product of the process condensing)?

If the above is true then any change to the ratio of liquid to vapor volume past its design must be considered as under or over condensing respectively.

I submit my postulation for your intrest/ amusement/ ridicule.

[desA]

I have to agree with mad fridgie's view. Here's my take.

If additional condensation occurs, then for thermodynamic equilibrium to exist in the cycle, something else must alter to balance the first law of thermodynamics. The evap will then try to balance itself by moving (downwards if cond pressure reduces) on the log(p)-h chart such that Q'evap + W'comp = Q'cond. The evap will then probably run too cold. In other words, the cycle will 'float' downwards.

Controlling the hp end to run where preferable, will 'peg' the cycle to stay where desired.

[TRASH101]

If additional condensation occurs, then for thermodynamic equilibrium to exist in the cycle, something else must alter to balance the first law of thermodynamics.

Hi Des

The above doesn't agree with mads' statement

There is no such thing as over condensing

I agree that it will achieve a balance to whatever the new conditions but if that equilibrium is not the desired condition then that shift has still been caused by a proportional shift in the liquid/vapor ratio which if viewed as a function of the condenser then it could be described as over condensing.

I hasten to add that I agree that the term over condensing is used by others as a " can't be ar5ed to tell you whats wrong " or " I really don't know what is wrong with it " statement but in its purest defined state it does happen and when it does it is invariabley a fault in the system or the system is being used outside of its design parameters.

[NoNickName]

Overcondensing doesn't exist. A variation in the titration of vapor to liquid happens at constant T and P in the 2-phase equlibrium.

[Gary]

In looking through the definitions offered, it seems the term "overcondensing" does not accurately describe the problem.

Being from the old school, we used to call this "low head pressure", although "liquid underfeed" would be more descriptive.

Personally, I prefer terminology that actually describes the problem and overcondensing doesn't accurately describe anything. If anything, it is misleading. You can't overcondense.

[NoNickName]

Agreed with Gary. Let's put this to rest.

[shieldcracker]

Why not???

I'snt it correct that, in a thermodynamically balanced state, any change in the physical variables (namely the thermo physical effects on the high side heat exchanger) on a running system will change the proportional volume of liquid to vapor? Is the liquid not condensate (i.e. the product of the process condensing)?

If the above is true then any change to the ratio of liquid to vapor volume past its design must be considered as under or over condensing respectively.

I submit my postulation for your intrest/ amusement/ ridicule.

Condensation means a change in state from gas to liquid. Over condensation would mean having excess of condensate (liquid refrigerant) period. You can have an excess of liquid refrigerant in the condenser and this is better described as flooded condenser or flooded operation, so essentially the level of liquid in a condensing coil will determine the volume ratio of vapor to liquid. There is no design parameter that fixes the volume of vapor to liquid refrigerant in the condenser, this is a dynamic point in the condenser operation that changes with the operating conditions of the equipment.
Over condensation would imply that one could achieve different rates of condensation from a substance in vapor state which is impossible. The rate of condensation formation is fixed for a given set of state variables.

I hope this clarifies things.

[nevgee]

If you are, you breathe. If you breathe, you talk. If you talk, you ask. If you ask, you think. If you think, you search. If you search, you experience. If you experience, you learn. If you learn, you grow. If you grow, you wish. If you wish, you find. And if you find, you doubt. If you doubt, you question. If you question, you understand and if you understand, you know. If you know, you want to know more. If you want to know more, you are alive.



Does this just mean "I think therefore I am" ?

[Grizzly]

OK. So the purists have explained why I cannot use the term "over condensing!"
OK so I can only get a finite amount of vapour or liquid refrigerant.
My dilemmas usually occur when that Liquid is at a lower temperature than normal.
IE, its a cold windy night and the system temps at standstill (Duty satisfied).
The system starts up but because of the low H.P. side temps/ pressures and therefor the low LP temps/pressures.
The system trips, a common enough occurrence.
Particularly with Chiller packs.
I until now, (for I have been converted from using such terminology).
Would of referred to the system as over condensing!!

So for this situation where there is to little heat in a system.
What do people suggest I use as viable Terminology?
Grizzly

[mikeref]

I have to agree with Paul H, though i see where the term does not make sense. Here's my view.Given any working system. Evaporator absorbs heat, condenser rejects heat. Balance achieved.Condenser fails to reject required heat removal, discharge pressure rises, high temperature liquid/vapour supplied to evaporator,.. undercondensing. Back to "balanced" opperation, now the ambient is lower but all condenser fans are running so the condenser completes heat rejection more efficiently, now liquid is being subcooled where vapour was previously condensing,vapour volume is less, discharge pressure falls, suction pressure drops, it seems the equipment is running short of refrigerant, cool liquid line with liquid/vapour mix. This is my defination of "overcondensing".. mike.

[monkey spanners]

Its just a term for a condition!

Overcondensing = too low a head pressure, its just a word so we know whats wrong. Its simple so the customer can grasp the idea.

Often i have to call a condenser a radiator so that people know which part i'm on about.

Some call a spade a spade, some call it a metal bladed digging implement with a beech wood shaft.

Language is just a tool like any other, so long as people understand what we want to comunicate it has served its purpose.

Jon

[nike123]

Does this just mean "I think therefore I am" ?

In short, yes.
I know lot of zombies around me.

[nike123]

Language is just a tool like any other, so long as people understand what we want to comunicate it has served its purpose.

Jon

That is why I like German word sausages. They are usually explanation by itself.

[desA]

That is why I like German word sausages. They are usually explanation by itself.

Sausage condensing?

[nike123]

Sausage condensing?

You need example?

Donaudampfschiffahrtselektrizitätenhauptbetriebswerkbauunterbeamtengesellschaft

"association of subordinate officials of the head office management of the Danube steamboat electrical services"

[desA]

^ lol

[NoNickName]

What do people suggest I use as viable Terminology?

Poor engineering.

[Grizzly]

Poor engineering.

????
Pardon?
Grizzly

[Quality]

A little bit like "overkilling". Once one is dead, can't be killed further.

You want to try my wife's cooking

[paul_h]

That's a unique scenario, and IMHO unlikely. In a controlled condensation, the fan speed in such low ambient will be almost or if not at all OFF.

Such a perfect world you live in. Some of us have to deal with domestics, static, and cheap units.
If this term "over condensing" doesn't exist because theres fan control, what do you call the conditions that exist when there's no fan control?
Do you call it fiction and say it can't exist just because you believe there's no such system in the world without condenser pressure control?

It's fair to call it another name, or to explain it is something else. But to say it can't happen because you live in an insulated world where you don't see it is ridiculous. Same goes with charging liquid into the suction service valve, it happens all the time because there is no choice.
It happens and is out there because things are built and designed to budget and repaired to budget and compromises and the like are made.

I know we are worlds apart, and you can run rings around me as far as engineering and large systems. I'm not trying to insult, I've worked on large systems though for not a such a long time. I specialised in small systems in order to get self employed. Pauls big industrial refrigeration company wasn't ever going to get of the ground with just me and pocket change, so I've kept with the small stuff to keep me busy. If I ever close shop, and I'm pretty close because I hate constant phone calls etc, yeah I'd like to work more on the industrial side as an employee. But there is completely different conditions, expectations and reality down here - not referring to geographical location either.

[NoNickName]

I didn't say poor engineering doesn't exist. Surely overcondensing doesn't exist.
For what it's worth, a pressure switch connected the fan conctactor costs few euro or gbp or aud. Face it: fixing a unit requires some dedication.

[paul_h]

I didn't say poor engineering doesn't exist. Surely overcondensing doesn't exist.
For what it's worth, a pressure switch connected the fan conctactor costs few euro or gbp or aud. Face it: fixing a unit requires some dedication.

wow, just wow.

[desA]

A thought could be to describe the phenomenon on the log(p)-h chart & then detail what is actually occurring in this situation.

[monkey spanners]

I didn't say poor engineering doesn't exist. Surely overcondensing doesn't exist.
For what it's worth, a pressure switch connected the fan conctactor costs few euro or gbp or aud. Face it: fixing a unit requires some dedication.

Fixing a unit does require dedication, something that is not lacking in the posters on this forum, but out on site it also requires payment for the parts and time, and for this you need the customers permission to carry out the work. Simple economics.

One of my jobs on friday was a milk cooling tank water pump replacement, it should have three pumps but only had two and one of them had failed causing over £1000 worth of milk to spoil, yet the customer wouldn't have a third fitted...
The condensing unit was also covered in milking vacuum pump oil as the exhaust blew directly onto it, i adviced them the system needs a service and clean, this again was declined.

Many customer run equipment on a FOF principal (fix on fail) and don't care so long as the machine is making a noise.

Why not see if you can spend some time working with an engineer out and about servicing stuff, i know you know your stuff with the equipment, but i'm sure it would be a usefull experience with regard to customers and operators of plant.

Jon

[desA]

The words - rock & hard place, come to mind.

[NoNickName]

Many customer run equipment on a FOF principal (fix on fail) and don't care so long as the machine is making a noise.

Sorry for being direct and brutal, but fitting a pressure switch for keeping the condensing pressure high enough to avoid low pressure alarms doesn't involve any of these wasted arguments of yours.
Actually, I think that refrigeration engineers prefer to have themselves payed (read: overpayed) for charging refrigerant than actually spending some time and brain to repair units and fix the problems once and for all.
Then, they come here and whine like sissies about "overcondensing" except that such phenomenon doesn't exist anywhere else than in their huge ignorance.

[Grizzly]

Sorry for being direct and brutal, but fitting a pressure switch for keeping the condensing pressure high enough to avoid low pressure alarms doesn't involve any of these wasted arguments of yours.
Actually, I think that refrigeration engineers prefer to have themselves payed (read: over-payed) for charging refrigerant than actually spending some time and brain to repair units and fix the problems once and for all.
Then, they come here and whine like sissies about "overcondensing" except that such phenomenon doesn't exist anywhere else than in their huge ignorance.

Do you insult everyone that disagrees with you?
Because you certainly seem to do so a lot on this forum.
You are only reading what you want to on this post.
I have accepted that the terminology is wrong!
Along with many others.
And any form of pre-set pressure control is irrelevant when the system fails to reach it.
Or is that down to poor engineering?
I am willing to accept many of your comments but why such a bitter answer?
Grizzly

[r.bartlett]

Years ago we would often get called to look at a split in the winter which running on cooling had the indoor unit iced up solid. We called that over condensing and when we blocked the 'radiator' the suction would come up to 60 psi and not ice again.


So I have used the term 'over condensing' with reference to this particular problem way back in the early eighties and I shall continue to do so. And if someone stands there and say's "Oh I think you'll find it's called excessive sub coolarghhhhhhhhhh"*thud*

That was me throwing him off the roof for being such a bellend

[monkey spanners]

Sorry for being direct and brutal....


Then, they come here and whine like sissies about "overcondensing" except that such phenomenon doesn't exist anywhere else than in their huge ignorance.

Being direct and brutal can be a kindness if it is done with compassion and with the intent to help another being, if not it serves only to boost the ego then why be direct and brutal if it has potential to hurt another?

I'm not whining, i am sorry if you percieve me that way, i had a similar reaction to the term the first time i heard it years ago, "how can a system overcondense?" but realised it is just a word and nothing that important to get upset about.
I have never claimed to be anything but ignorant, it is one of the reasons i visit this site to learn from the many members here, yourself included.

Jon

[r.bartlett]

If you are, you breathe. If you breathe, you talk. If you talk, you ask. If you ask, you think. If you think, you search. If you search, you experience. If you experience, you learn. If you learn, you grow. If you grow, you wish. If you wish, you find. And if you find, you doubt. If you doubt, you question. If you question, you understand and if you understand, you know. If you know, you want to know more. If you want to know more, you are alive.



Does this just mean "I think therefore I am" ?

I'm a small tin of spiced ham "I'm pink therefore I'm spam"

[750 Valve]

Sorry for being direct and brutal, but fitting a pressure switch for keeping the condensing pressure high enough to avoid low pressure alarms doesn't involve any of these wasted arguments of yours.
Actually, I think that refrigeration engineers prefer to have themselves payed (read: overpayed) for charging refrigerant than actually spending some time and brain to repair units and fix the problems once and for all.
Then, they come here and whine like sissies about "overcondensing" except that such phenomenon doesn't exist anywhere else than in their huge ignorance.

I cannot believe the absolute drivel you have posted in this thread, you are taking a tunnel visioned stance based on two words "over" and "condensing".

The situation exists in so many systems across the world (except quite clearly Merate (LC) Italy! which must something akin to a thermodynamic Utopia) and it does not matter what people call it, the fact remains that under much colder than design ambients where systems that have remote condensers operating quite a bit colder than both the system receivers and liquid lines that this phenomena can occur.

In Australia we have to engineer for ambients such as 40C during summer, those same systems can operate at -7C ambient during winter - this brings about challenges in maintaining an achievable operating envelope, say for instance in supermarkets we have remote condensers operating at ambient conditions, plantrooms containing the rack and receiver can be anywhere from ambient temp to conditioned air temps - I am sure someone just wanting to win an argument (which is how No Nickname is coming across) will say engineering dictates that we should place the receiver at the condensers in the ambient air to stop "over condensing", the same genious should also think of the affects this has at max design conditions..... yes - less than desirable isn't it?? So lets insulate the receiver then.... what does this do in summer at design max??? Yes it hinders natural subcooling doesn't it?

To overcome issues we cycle fans and/or run variable speed drives however even with fan cycling you can observe issues in low ambients as a fan cycles on and changes subcooling conditions dramatically. A genius engineer would say just use smaller fans and more of them to alleviate the effect, or even 6 or 8 pole fan motors.... there is a commercial reality we must all adhere to and at the end off the day we are left with less than perfect systems, it is our job to get the best out of them under all conditions.

So when someone comes on here whining about over condensing - my advice to you Mr No Nickname is to just look at another thread, don't let a technician trying to make a system operate better get under your skin, just make a conscious decision not to help him and go back to your thermodynamic Utopia and be happy you don't have to deal with any less than desirable design and operating conditions.

END RANT

[mad fridgie]

The OP did ask about teaching, so a correct description, had to be given!
As monkey said we all use the term over condensing, instead of saying the condensor is oversized, which leads to reduced discharge pressures, this is not be confused with liquid sub-cooling, which completly different. Best engineering is always easy when money is not important, but in these hard times, you look at cost all of the time, do you think the client understands, no he just sees the money and listens to the salemen. The practrical implecations are that we cut corners which are going to give the biggest ruduction cost with minimal risk on reliability, normally at the cost of efficiency and product quality (lower sst, for example dries out fresh product)

[NoNickName]

I don't agree a single word of the rants above. I'm much more used to watch refrigeration engineers (around the world) temporarily fixing the issues with their system to guarantee more problems for the next month to come, and ensure bread and butter for themselves as seasons change.
The overcondensing thing, once again as other posters already stated, doesn't exist. There's no overcondensing whatsoever.
And for what it's worth, there are plenty of systems that all year long experience a range of temperatures much larger than australians.
I install and maintain condensing units in siberia, with 30°C in summer and -50°C in winter. How would you call that: hypercondensing?
Do you happen to know that almost all refrigerants at -50°C is liquid at atmospheric pressure, so that you don't even need a recovery unit for recovering it?
But then again, please go ahead with rants on cutting corners, price driven projects, cost reduction and bla blah.

[mad fridgie]

I don't agree a single word of the rants above. I'm much more used to watch refrigeration engineers (around the world) temporarily fixing the issues with their system to guarantee more problems for the next month to come, and ensure bread and butter for themselves as seasons change.
The overcondensing thing, once again as other posters already stated, doesn't exist. There's no overcondensing whatsoever.
And for what it's worth, there are plenty of systems that all year long experience a range of temperatures much larger than australians.
I install and maintain condensing units in siberia, with 30°C in summer and -50°C in winter. How would you call that: hypercondensing?
Do you happen to know that almost all refrigerants at -50°C is liquid at atmospheric pressure, so that you don't even need a recovery unit for recovering it?
But then again, please go ahead with rants on cutting corners, price driven projects, cost reduction and bla blah.

I do not agree with your statement on bread and butter, although I do believe that many do not understand why they do, what they do, but it works for them. but that is not the same as intentionally ripping the clients.
Hypercondensing, lol
the rest, well that just depends which world you live in. I too was perfect, then I woke up!!!!!!!!!!!

[desA]

How to optmise hypercondensation & negate it's downside potential?

[Quality]

How to optmise hypercondensation & negate it's downside potential?

Easy

Superheat it

[desA]

^ LOL...

Would this not need to be hypersuperheating?

[Gary]

Hmmm... wondering if I should throw equalizer lines and liquid pumps into the discussion... lol