good exam question

[key]

water exitng a water cooled condenser has a 20 degree rise when leaving, what effect will this have on TXV and evaporator temperature?

[joeywpittman]

If your condenser is rated @ 20deg del.T then it is working properly. most water cooled condensers are rated with a 10deg delta Temp. in this case the water is most likely moving to slow, therefore you will have a high head pressure. A high head pressure will result in a high suction pressure. The high suction pressure raises the evap. temp. so the air/water is not getting as cold as it should.

because the machine is not removing enough heat from the condenser it is not running at it's rated capacity. if there is a high load on the machine it would not be able to keep up. so the evap. discharge air/water will start to rise above it's setpoint.

If there is proper subcooling then your txv will maintain the superheat which it is set at.



[Edited by joeywpittman on 03-17-2005 at 09:53 AM]

[john dalton]

Dear Joeywpittman

Great answer.

Respectfully Submitted,
John J. Dalton

[fat eddy]

What is the condenser water temp in and out ? and what is the head pressure ?

( this makes all the difference in the world )

This will affect the temp rise. Please be more specific, this is not a good question it is another form of a bad one .

If one of my techs called me with a question like that and that was all of the info he had, it would be a very short and embarassing phone call for him.

what if you had a twenty degree rise ? so what if you had a twenty degree rise,

what you need to know is what is controlling the amount of waterflow through the condenser,

what if it is done on pressure and everything is working fine, the thing could be running fine and you just tried to fix something that wasn't broke.

[Edited by fat eddy on 03-17-2005 at 11:21 AM]

[service guy]

Eddy: If you read the question again the first line is all you need, a 20 degree rise is improper for a water cooled condenser so you need to reduce delta, T. However loop temp is important but if I see a 20 deg rise I need to fix this first and then check loop Temp. Key's question sounds more like a Text book Question Rather than a In the field problem I think he's looking for a Text book Answer Not a harsh Reply.

[mrhvacmechanic]

Guys,
Just a quick question since were talking about water flow.


Have you ever come accross a water cooled unit where the water is moving too fast through the condensor where it dosn't pick up any heat???
I work with someone who says he has seen this?? Can this ever happen to where you have to throttle the water down where its moving to fast to get your 10F????

I have never come accross this. May I have your answer on this if you have seen it happen?

[fat eddy]

Service guy;

Are you saying, that you could never have a 20 degree temp rise across the condenser and still be running fine ?

Do you think that you can troubleshoot it, by the condenser rise ?

Do you think my reply was harsh ?

If it was harsh, so be it, the difference between my reply and yours is that mine is actually correct,and he can learn from it.

And yours he can't, your answer is as bad as the first guys

To answer the question which was

" water exiting a watercooled condenser has a 20 degree rise when leaving, what affect will this have on the TXV ?

The absolute correct answer to the question,stated the way that it is stated is, none, it will have no effect on the TXV or the evaporator temp !!!!!

And that is the correct answer until more data is posted.

Because to state a question the way it is stated,assumes that if it has a twenty degree rise that there is a problem and that is just the wrong dam assumption.

You need to bring your troubleshooting skills up a bit.

Mr. Mechanic, yes that happens.

[jacob perkins]

Dear fat eddy,

Great answer.

Respectfully Submitted,
Jacob Perkins

[service guy]

Thanks Eddy I'm Glad you cleared that up for me!

[NormChris]

The question is not clearly worded in the first place.

[sigma]

Originally posted by fat eddy

Because to state a question the way it is stated,assumes that if it has a twenty degree rise that there is a problem and that is just the wrong dam assumption.
You need to bring your troubleshooting skills up a bit.
Mr. Mechanic, yes that happens.




Eddy,
Have you ever thought about anger management classes? :D

[mrhvacmechanic]

Eddy,
Your answer was excellent and I should have stated that. My question was not intended to contradict what you said. I have never seen a water cooled condensor that was rated for more than 10F accross it.

My question was for a matter of discussion since a guy I work with said he was on a job where the tower water was 85F and it was moving so fast through the barrel that it wasn't picking up heat. So I said to him, maybe the barrel was dirty or needed a acid cleaning. He said no, I had to throttle the water down with the leaving water valve because the flow was too fast???? I never heard of that before so I posed the question if anyone has seen this before????

Your answer to Key was fine and I would have said the same.I know a cond barrel has a certian drop in water pressure due to friction. But I never heard of the water moving so fast at an 85F entering temp and not picking up any heat???? Maybe I should have started a seperate post on my question, I wasn't disagreeing with your reply to Key.

I didnt mean to make you angry towards me, I just wanted to know if this was possible since I never came accross this situation.

[Edited by mrhvacmechanic on 03-18-2005 at 12:34 AM]

[key]

Thank you for the answer, p.s. it was a text book question

[beenthere]

Originally posted by mrhvacmechanic
Guys,
Just a quick question since were talking about water flow.


Have you ever come accross a water cooled unit where the water is moving too fast through the condensor where it dosn't pick up any heat???
I work with someone who says he has seen this?? Can this ever happen to where you have to throttle the water down where its moving to fast to get your 10F????

I have never come accross this. May I have your answer on this if you have seen it happen?

It happens once in awhile.

If your putting 10 gpm through a condenser that should only have 6 gpm, it will seem like its not picking up heat.

Thats why you should have a flow valve on every unit.

[seaboard]

Originally posted by beenthere

Originally posted by mrhvacmechanic
Guys,
Just a quick question since were talking about water flow.


Have you ever come accross a water cooled unit where the water is moving too fast through the condensor where it dosn't pick up any heat???
I work with someone who says he has seen this?? Can this ever happen to where you have to throttle the water down where its moving to fast to get your 10F????

I have never come accross this. May I have your answer on this if you have seen it happen?

It happens once in awhile.

If your putting 10 gpm through a condenser that should only have 6 gpm, it will seem like its not picking up heat.

Thats why you should have a flow valve on every unit.

I have found it happens even more on the chilled water side. Someone will go to a balancing valve of an area that is a little warm and think "I'll open this valve and move more chilled water through the coil which will make it cooler" but in many cases the water moves so quickly the heat isn't transfered. A low delta on the air side and a low split on the water side will be the indicators.

[fat eddy]

Hey key,

I wasn't trying to be harsh with you,it seems like your trying real hard to learn , and that is admirable.I'm just trying to take you one step further,

I know that the question comes out of a book thats why you need to be real careful about which books you trust and which ones you don't.

( I realize that the question probably came right after a chapter on watercooled condensers and it asumes that you apply the question to what you just read)

I'm just trying to point out the importance of gathering data, when you are troubleshooting.When you get out in the field and you need to make those phone calls to ask questions like that.

The guy on the other end of the phone is going to want all the pertinent data,

Gathering all the data correctly will help you advance quickly, because you will start to see that you will be able to figure it out for yourself. In a short amount of time.

Getting the correct data is the key to troubleshooting.

And troubleshooting is the difference between filter changers and technicians.



[Edited by fat eddy on 03-18-2005 at 07:51 AM]

[simpleman]

I see someone heart getting bigger and his head getting smaller.

Hooray!

[Shophound]

Originally posted by NormChris


The question is not clearly worded in the first place.



Agreed.

[valdelocc]

no too long ago I' was doing PMs in some APW McLean Electrical cabinet coolers, They are R-22,water cooled,axial condenser type (tube w/tube),cap tube MD.
In those units the water valve modulates in reference to the high side pressure,My pressures we're H-200 L-62 SH-8
Evaporator DT 12 ,Condenser DT 14 to 22.
I' checked all four and they we're all the same,I' checked with the guys at APW and I' was told that those reading are considered normal.

[service guy]

I knew It was a Text Book question only books ask that kind of Question!!