Over Condensing????

[desA]

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

Would these happen to be of the 'hyper' variety?

[mikeref]

Alright, SO, overcondensing is not a physical event that occurs in any refrigeration system right? Or maybe its taken for granted and called by another name because no amount of quantum physics can make it happen on paper. Just as clouds float with tons of water overhead,( workout the dynamics of that),overcondensing is a real event in my opinion, call it what you will, it will always be around.. mike.

[mad fridgie]

Alright, SO, overcondensing is not a physical event that occurs in any refrigeration system right? Or maybe its taken for granted and called by another name because no amount of quantum physics can make it happen on paper. Just as clouds float with tons of water overhead,( workout the dynamics of that),overcondensing is a real event in my opinion, call it what you will, it will always be around.. mike.

Condensing in refrigeration terms is changing a vapor to a liquid, if all is coverted to liquid then it is condensed, as you cool it the voulme will reduce, then keep cooling it will solidify, 'CONDENSING THE VOLUME" . Incorrect pressure drop is a real event and can be caused by an over sized condensor "thus over condensing" just words, not fact.
I do not think anybody is saying the problems do not occur when the precieved term over condensing is used, just that term its self is incorrect.

[mikeref]

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 was recently working on an old Carrier 50k14 with origional condenser, Thought, this old girl deserves a new condenser with hp stages on 2 of 3 fans BUT NO, owner doesn't agree so it can under condense in summer(with constant breakdowns ref: quote above), or move too much air+ waste energy in the cooler periods..mike

[NoNickName]

And why are you asking the owner in the first place? Is he/she a refrigeration engineer or something?

[TRASH101]

I do not think anybody is saying the problems do not occur when the precieved term over condensing is used, just that term its self is incorrect.

Hello Mad

It would appear that the biggest problem is that people are looking at the term "over condensing" far too subjectively.

Condensing in refrigeration terms is changing a vapor to a liquid, if all is coverted to liquid then it is condensed, as you cool it the voulme will reduce, then keep cooling it will solidify, 'CONDENSING THE VOLUME"

This is not strictly true is it?

Remove heat to reduce the enthalpy therefore increasing the density. i.e. liqiuid doesn't have to be formed to condense! (check the definition if you like)

This is not just my opinion.

The definition of "over" (if we can agree) is in our case a surplus, too much etc...

So if NNN, Mad, Gary can prove that it is impossible to remove "too much heat" at the condenser. Then I will be a convert to the "doesn't exist" state of mind.

[NoNickName]

First of all, it is impossible to solidify a F-gas refrigerant. There are 3 possible states of matter, but only combination of two of them is possible in case of f.gases: vapour (or gas for supercritical state), vapour + liquid (two-phase equilibrium), liquid.
Exactly as vapour can exist in superheated status, so subcooled liquid can exist.
What is commonly referred here as "overcondensed" is actually "subcooled liquid".

Secondly, I never said that it is impossible to remove too much heat at the condenser (too much compared to what?). I stated that the term "OVERCONDENSING" is as wrong as "OVERKILLING" despite the latter being used in several forensics criminology papers, as the status to which a body is being inflicted multiple deadly wounds, but only one of them is the killing hit.

[desA]

Let's inject a theoretical element into the discussion:

Q'evap + Q'comp = Q'cond (1st Law of Thermodynamics)

If the condenser heat output increases due to any reason whatsoever, then so must Q'evap+Q'comp. For Q'cond to increase, the HP must lower on the refrigerant vapour bell (just look at the vapour & liquid end-stops for clarification).

In general, the compressor probably doesn't alter too much => Q'comp~const, so Q'evap must increase.

According to the log(p)-h diagram for the vapour compression refrigeration cycle, this would imply that the LP line must lower itself on the vapour bell, as well. Since the TX controls superheat, there is no mechanism to prevent the whole cycle 'slipping downwards' on the log(p)-h plot.

[TRASH101]

NNN

First of all, it is impossible to solidify a F-gas refrigerant.

I never claimed it was possible to solidify f-gas and I refer you to alternate definitions of condensing that are applicable.

Secondly, I never said that it is impossible to remove too much heat at the condenser (too much compared to what?).

I concede that "over" is in itself a subjective term and DesAs' post helps to highlight this (and this in itself state it must exist for everyone to see if everyone can agree on what is too much)

I stated that the term "OVERCONDENSING" is as wrong as "OVERKILLING" despite the latter being used in several forensics criminology papers, as the status to which a body is being inflicted multiple deadly wounds is found, but only one of them is the killing hit.

From that I can only see that you are convinced that that condensing is a change of state and not a change in density brought about by a change in enthalpy ( A definition I don't subscribe to)

[NoNickName]

From that I can only see that you are convinced that that condensing is a change of state and not a change in density

Condensation is the change in the phase of matter from the gaseous phase (of an element/ chemical species) into liquid droplets

http://en.wikipedia.org/wiki/Condensation


It's not me who is convinced...

[Gary]

I'm not sure what the argument is about. Even if we can twist the definition enough to make "overcondensing" a real word, it still doesn't describe the problem.

The problem is reduction of liquid flow.

In a stable series loop, the mass flow is equal at all points, so reduced flow at any point is reduced flow at every point.

[desA]

I'm not sure what the argument is about. Even if we can twist the definition enough to make "overcondensing" a real word, it still doesn't describe the problem.

The problem is reduction of liquid flow.

In a stable series loop, the mass flow is equal at all points, so reduced flow at any point is reduced flow at every point.

To add further to the discussion - how do we know there is reduced mass flow in the system? How is this measured, or observed?

[Gary]

Reduced suction pressure = Reduced mass flow

Hmmm... unless the compressor is inefficient

[NoNickName]

Reduced suction pressure = Reduced mass flow

Hmmm... unless the compressor is inefficient

Or unless it's inverter driven on suction pressure.

[desA]

Reduced suction pressure = Reduced mass flow

Hmmm... unless the compressor is inefficient

Take a look at the log(p)-h diagram I sketched. As Q'evap stabilises to re-gain thermodynamic equilibrium, it lowers LP.

Could this be interpreted as the lowering of suction pressure, you are observing? Would this then necessarily imply mass flow reduction?

[monkey spanners]

So over condensing causes under evaporating......


Jon

[Gary]

Assuming constant compressor volume and speed, it comes down to density of the vapor being pumped. Higher compressor inlet density (higher LP) means more refrigerant pumped and lower density means less refrigerant pumped.

IOW, on each downstroke of the piston, higher pressure will force more refrigerant into the cylinder and lower pressure will force less refrigerant into the cylinder.

[desA]

Assuming constant compressor volume and speed, it comes down to density of the vapor being pumped. Higher compressor inlet density (higher LP) means more refrigerant pumped and lower density means less refrigerant pumped.

IOW, on each downstroke of the piston, higher pressure will force more refrigerant into the cylinder and lower pressure will force less refrigerant into the cylinder.

Ok, that makes sense. Interesting.

Beginning to look like a runaway downwards unstable situation for the evap in such a way that the cycle continues to slide downwards. Mmhh... must surely stabilise somewhere in the real world - where?

[mad fridgie]

Yes you can solidify just about all refrigerants, helium is however a problem, simple example R744, carbon dioxide, soild commonly known as dry ice. (its all about how cold you go)
Increaseing the density, means reducing its volume by mass.
Over condensing if we are going to use the term simply means incorrect pressure differential over the system,

[Quality]

Yes you can solidify just about all refrigerants,

Its called melting point and yes its that point from liquid to solid or vice versa

[Gary]

Beginning to look like a runaway downwards unstable situation for the evap in such a way that the cycle continues to slide downwards. Mmhh... must surely stabilise somewhere in the real world - where?

The TXV goes wide open, so the flow is governed by the orifice size and current dP, assuming there is solid liquid at its inlet.

It is also possible for the liquid flow to be held back further upstream. Supermarket systems come to mind, where the liquid is held in the condenser because the receiver pressure exceeds condenser pressure.

[Segei]

Actually, a refrigeration plant is selfbalancing system. Assume that refrigeration load has increased. If compressor volume capacity is constant, suction pressure will increase. At higher suction pressure mass capacity will increase. At certain suction pressure and at certain temperature in cold room this system will be balanced. However, we have a question. Does this new temperature in required rage of temperatures? The same is on the high side. During periods of cool weather, condenser capacity will increase. However, at certain point will be the balance between compressor capacity and condenser capacity. Do we have enough pressure to move liquid in the plant?

[lawrence1]

Gary,
Throw in a equilizer line between the inlet of the condenser and the receiver and see what happens.

[Gary]

Gary,
Throw in a equilizer line between the inlet of the condenser and the receiver and see what happens.

Yep... that works as long as the condenser is above the receiver. The pressures are equal and gravity moves the liquid.

[mikeref]

And why are you asking the owner in the first place? Is he/she a refrigeration engineer or something?

No, the owner of the building is the man with the money. I have to have his approval or i don't get paid. Its would suprise you to see the amount of mismatched and struggling refrigeration equipment there is about. Yes it can be fixed but i don't work for free.

[mad fridgie]

No, the owner of the building is the man with the money. I have to have his approval or i don't get paid. Its would suprise you to see the amount of mismatched and struggling refrigeration equipment there is about. Yes it can be fixed but i don't work for free.

What you do not work for free, what sort of refrigeration engineer are you, very good answer!

[mikeref]

What you do not work for free, what sort of refrigeration engineer are you, very good answer!

Yeh, not entirely true, how many times have i pulled "clients" out of trouble, put them on 30 days and they don't pay

[NoNickName]

You see, you're doing it wrong. You ask your customer about what YOU have to know and what you have to to do to fix it.

He doesn't know, wants to keep costs down, you leave and the unit is still broken.

My way of doing it: fix it and get paid for the good job done. Customer doesn't need to know what I did as long as I did it right. A pressure switch is not an excuse for not paying. You don't even need to mention it in your report (10 gbp cost? Less).

[احمد محمود م س]

it nice wards

[Rallings]

I think the term 'over condensing' is a relative term thus relative to the system's condensing requirements.