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Thread: superheat
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30-08-2014, 03:17 PM #1
superheat
can anybody tell what is the normal suction superheat of R134a gas in central air conditioning system..???
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30-08-2014, 04:11 PM #2
Re: superheat
.
Normal is very vague
But if it is working with an expansion valve, most
valves come pre-set to about 6 - 8 degs of superheat.
That is measured out of the evaporator. If you measure the
suction closer to the compressor the superheat will be higher.
Regards
Rob
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31-08-2014, 05:26 PM #3
Re: superheat
6-8 deg f or deg c ... txv is using in this chiller, am measuring suction near compressor..
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31-08-2014, 08:24 PM #4
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31-08-2014, 10:41 PM #5
Re: superheat
It is degrees Kelvin not C or F.
Brian - Newton Abbot, Devon, UK
Retired March 2015
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01-09-2014, 07:52 AM #6
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01-09-2014, 10:25 AM #7
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Re: superheat
Use in conjunction with Celsius[edit]
In science and in engineering, degrees Celsius and kelvins are often used simultaneously in the same article (e.g. "...its measured value was 0.01028 °C with an uncertainty of 60 µK..."). This practice is permissible because the degree Celsius is a special name for the kelvin for use in expressing Celsius temperatures and the magnitude of the degree Celsius is exactly equal to that of the kelvin.[10]Notwithstanding that the official endorsement provided by Resolution 3 of the 13th CGPM states, "a temperature interval may also be expressed in degrees Celsius", the practice of simultaneously using both "°C" and "K" remains widespread throughout the scientific world as the use of SI prefixed forms of the degree Celsius (such as "µ°C" or "microdegrees Celsius") to express a temperature interval has not been widely adopted.[4]
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01-09-2014, 10:53 AM #8
Re: superheat
You are right up to a point Moideen but what Brian said is correct
When we explain a difference in temperature we explain it as degrees Kelvin
that means you are talking about a difference between two temperatures and not
the temperature in Deg C.
If the saturation temp is 0 deg C and the suction is 8 deg C then the difference is 8K
(8 degrees Kelvin).
To avoid confusion temperature difference is always expressed as Degrees Kelvin.
Regards
Rob
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01-09-2014, 11:52 AM #9
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02-09-2014, 11:30 AM #10
Re: superheat
17 psi suction and suction line temp is 7-8 degree C.... R134a gas.. FILTRINE CHILLER using for MRI machine
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02-09-2014, 12:22 PM #11
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02-09-2014, 12:56 PM #12
Re: superheat
is it ok sir for this chiller
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02-09-2014, 02:07 PM #13
Re: superheat
Check the suction superheat value when pull down is complete and steady full load operation has been established. 15.5 is high. Bring down to 6-8k.
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02-09-2014, 07:55 PM #14
Re: superheat
pls mention in deg c or deg f........
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02-09-2014, 10:08 PM #15
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Re: superheat
It is already explained earlier in this thread.
This practice is permissible because the degree Celsius is a special name for the kelvin for use in expressing Celsius temperatures and the magnitude of the degree Celsius is exactly equal to that of the kelvin.[10Last edited by nike123; 02-09-2014 at 10:18 PM.
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02-09-2014, 11:17 PM #16
Re: superheat
Hi 17psi = (minus) -8 degrees C, using R134A
Suction pipe temperature 7 to 8 deg C
So (minus)-8 Saturation temperature to +7 to 8 deg C actaul pipe temperture= approx15.5 degK superheat
R134A is a very stable refrigerant and normally I would expect to get a steady superheat of between 5 and 8 deg k using a thermostatic expansion valve
If using an Electronic expansion valve (stepper valve) I would expect a superheat of between 4 to 7deg C superheat.
Your evaporating Pressure/Temperature ie 17psi/ (minus)-8 degC is low for an air conditioning system as AC systems normally work in the positive temps ie +5 deg C not in negative temps ie minus 8
By opening your expansion valve a few turns you should see the suction guage rise a few psi and the suction pipe temperature should fall a few deg C.
So in reality you should see a suction pressure of about 27psi/0 degC with an actual pipe temperature of about 6 degC .So 0degC to 6 degC = 6degK actual superheat
This all depends if the system is fully charged , the drier is clean etc etc
I always fit electronic expansion valves as they always give superior control,a more stable suction condition and give better system efficiency by running with a lower superheat condition thereby utilising the evaporator surface more efficiently
Are you cooling air or water or some other fluid?
Kr Glenn