# Thread: DELTA T IN THE REFRIGERATION CYCLE

1. Hi Moideen, I think even if you answer him he will then come up with something else to berate you with or berate others, if he insists on an answer get him to right the question down, sounds like he has done a lot of theory and spent his life behind a desk not in front of a machine.

2. That ∆T total he is asking for is the discharge superheat PLUS the liquid subcooling.

The compressor discharge point is: the discharge line.
If measured in degrees: that is the discharge refrigerant temperature.

The discharge pressure, converted to temperature (via P/T chart for the specific system refrigerant) is the condensing temperature of the refrigerant inside the condenser.
The difference between the two, expressed in degrees, is the discharge superheat.

The inlet of the expansion device is the liquid line.
If measured in degrees that is the liquid refrigerant temperature.
The discharge pressure, converted to temperature is the condensing temperature of the refrigerant inside the condenser.
The difference between the two, expressed in degrees, is the liquid subcooling.

Expressed as a formula: (his) ∆T = DSH + LSC

PHM
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Originally Posted by moideen
A newly appointed head of maintenance manager tested my knowledge by asking a question in refrigeration cycle that,

"what is the delta T between the compressor discharge point to inlet of expansion valve."

I know delta T and issues in chilled water system. In refrigeration we know the saturation, sub cooling and superheat. But his question is about delta T in the condenser area!!i feel either I couldn’t understand his question or he want to asking something different from the topic. What you feel

thanks
moideen

3. IF the ∆T he is asking about was zero there would no point in having a condenser - the compressor could discharge directly into the expansion valve. <g> The difference that he claims does not exist is 50% of the thermodynamic cycle that Refrigeration IS. <g>

Hey! Maybe he uses magic thermodynamics? You should ask him if he gets his thermodynamic textbooks from the same guy who sold Jack his beanstalk beans. <g>

PHM
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Originally Posted by moideen
I don’t think, because he was screaming indignantly at me by claiming that delta is zero. How??? I felt it was a stupid question, then he shouted me by saying like’’ you people don’t know thermodynamics!!!

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Suggest him to touch by hand TXV inlet tube, and than discharge gas tube with working compressor. And what about delta T?

5. after reading all this, I think he actually meant Delta P, not T......but he had already made the mistake of saying it out loud, and would not allow himself to be shamed by admitting wrong......hence the verbal assault when being questioned.

there will be practically zero delta P, but it's obvious there is a temperature difference.....

6. He is most likely regurgitating someone else’s question and screwed it up! I have no use for people like that, obviously he has never been kicked in the nuts to be humbled.
You may need to accept the challenge!

Sent from my iPhone using Tapatalk

7. The man said: Zero! <g>

Air cooled condenser coil pressure drop can easily be over 5 lbs. in commercial equipment. And liquid line, fittings, the drier, etc. - the discharge pressure and the TXV inlet pressure are never going to be exactly the same.

So even if he meant ∆P - he is still wrong. Less-wrong is not: Correct. <g>

Hopefully we have armed our own Moldeen with sufficient ammunition to set the new man back a step or three.

PHM
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Originally Posted by 71CHOPS
after reading all this, I think he actually meant Delta P, not T......but he had already made the mistake of saying it out loud, and would not allow himself to be shamed by admitting wrong......hence the verbal assault when being questioned.

there will be practically zero delta P, but it's obvious there is a temperature difference.....

8. "Practically" in this argument, is the same as saying "reasonable" in a legal document!

9. Originally Posted by 71CHOPS
"Practically" in this argument, is the same as saying "reasonable" in a legal document!
Kinda sorta

10. I sat with him finally, he was then cool and nice guy. I put the p-h chart on the table. He explained and his argument was the difference between (delta T) the saturated vapor curve towards to saturated liquid curve. The latent heat removal area where the temperature is constant. I told him, here I have no any dispute with you. now the matter is clear, and We were in a different point of view in the first day of incident. Thank you to all

11. there certainly is temperature difference there in both the condenser as it approaches subcooling (none on this graph) and as the evaporator absorbs superheat as it approaches the compressor, the btu/lb refers to different specific properties and heat quantities (available capacity) of specific refrigerants at different conditions. This whole conversation is a bit crazy , the good news is you are now on good terms with new manager.

I can see theoretically the point trying to be made now as I look at it closer , but thats very simplified and in my opinion not quite realistic. After discharge superheat is dissipated the condenser vapor is NOT the same as exiting liquid, and if it is I think theres trouble
Last edited by stanbyyourword; 07-14-2020 at 06:17 PM.

12. moideen, what are the primary make and model of units you are working on?

13. Originally Posted by ehsx
moideen, what are the primary make and model of units you are working on?
I am part of property management, looking at the maintenance of facilities. our HVAC system includes centrifugal chiller water to rooftop packaged units. thanks

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Originally Posted by 2sac
Is he saying the compressor line discharge temperature is the same as the liquid line temperature at the inlet of the metering device? If so, he's incorrect.
Originally Posted by stanbyyourword
YES I thought this such as some watercooled , I think theres a miscommunication somewhere
I think he may have confused the issue.
Avg.25’disharge superheat (1)de superheat at first third of the condenser. (2)Center portion it should be at saturation temperature. (3)Final third; refrigerant should become subcooled. It would be a avg. 35’f temperature differential.
The Discharge pressure between entering and leaving should remain within 2-5dpsig at most. Which can be assumed to be constant, depending if it’s a long run between air cooled Dx air cool condenser or a water cooled (2dp or less).
Last edited by Bklyntek; 10-20-2020 at 12:42 AM. Reason: Correction

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I think that DT between the compressor discharge to inlet expansion valve is a measurement of the condenser's performance; oil separator isolated does not affect to the measurement practically.
It could be interesting to monitorig the state of the condenser to know when it is necessary to clean it. Anyway, it is better to use the DT between condenser inlet and condenser outlet.
That is the only explanation I could think for the question.

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I wrote a comment but I can not see it, so I am going to write something similar again.
It is a strange DT. The only explanation that I can imagine is that he wants to check the condenser's performance, to know if it should be cleaned, but DT between condenser inlet and outlet is better for that. Anyway, if you do not have a probes in those positions, the requested DT could be an approximate measure.

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## DELTA T IN THE REFRIGERATION CYCLE

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Last edited by thatguy; 10-22-2020 at 07:42 AM. Reason: Finished reading post, found out issue was resolved and comment no longer applied.

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