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Thread: Superheat
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23-07-2009, 09:43 PM #101
Re: Superheat
Thanks Tony
I would have thought a system could hunt with a low or high superheat, hunting only indicates valve opening/closing to much or too irratic, rather than small adjustments
CB
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23-07-2009, 10:43 PM #102
Re: Superheat
I would have thought a system could hunt with a low or high superheat, hunting only indicates valve opening/closing to much or too irratic, rather than small adjustments
If you look at "hunting" as a process then it could be described as the rate of change versus the rate of compensation.
i.e. the TEV can only respond to the result of an action that happend previously.
The valves own build characteristics provide a reasonable dampening effect at a specific band of operating parameters.
The important parameters are
1) quality of refrigerant at the entry to the valve
2) Amount of change to the quality of the refrigerant at the point of sensing.
So in effect the evap will flood before it is starved and will starve before it will flood.
The TEV characteristics and the above parameters will change the degree of flooding and starving.
I hope this helps...............otherwise it is an example of too much time on my hands X tendency to waffle about stuff .Quidvis Recte Factum Quamvis Humile Praeclarum.
Latine dictum, sit altum videtur.
Si hoc comprehendere potes, gratias age magistro Latinae.
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24-07-2009, 11:38 PM #103
Re: Superheat
That old guy was probably an engineer who worked for Troldahl.....it was the 1st thing we were tought
I find it quite shocking how many engineers these days seem to have grasped a perverted version refrigeration engineering skills.
Just goes to show....there's a certain lack of training and apprentices these days.
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25-07-2009, 06:15 AM #104
Re: Superheat
Im new to this forum and ive been going through a lot of them and i find them very helpful i would like to say thanx! but i have a question regarding superheat. i got this W/I cooler R22 system i cant get the superheat right my head pressure is 200psi suction 44psi full sightglass TXV bulb is about the 4 O' clock position, i know on coolers superheat should be 8`F to 10`F. i got to 10 but then it just dropped to -18`F the closest ive got it was 2`F. could it be faulty TXV? or oversized orfice? or what else could it be? what do you suggest i check for?
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25-07-2009, 06:41 AM #105
Re: Superheat
Are you saying that the superheat dropped to -18F?
I don't think so. Negative superheat is not possible.
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25-07-2009, 06:44 AM #106
Re: Superheat
44psi = 21F
21 + 8 = 29F
21 + 10 = 31F
At 44psi (21F SST) the suction line temp at the TXV bulb should be 29-31F.
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25-07-2009, 01:43 PM #107
Re: Superheat
SUPERHEAT: find your saturated evaporating temperature by converting your low side pressure on your gauges to a temperature using a pressure-temperature chart for that refrigerant.Now take the temperature of the suction line about 100mm after it leaves the evaporator.The difference between these temperatures is you superheat.
EG: evaporating temp= -2 degrees c
suction line at evap= 4 degrees c
Then superheat= 6K
SUBCOOLING: is very similar,you get your saturated condensing temp by converting your high side prssure to a temperature then measure the line exiting the condenser the difference betwwen these is your subcooling
EG condensing temp= 46 degrees c
line exiting cond.= 42 degrees c
subcooling= 4k
good superheat setting is 6 k
good subcooling is 4 k
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27-07-2009, 06:27 AM #108
Re: Superheat
One of my guy call in with almost identical problem as you describe. Negative super heat?? I couldn't beleived my ear.
I went to site. it turned out, Suction valve was broken - split in the middle, sometime it will pump down to negative, sometime not. (it was a semi-hermatic compressor, we take the head apart and replace the valve. problem solved).
Do a pump down test, see if you have the same problem.Be Happy
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27-07-2009, 06:50 AM #109
Re: Superheat
As Gary says, you can't have negative superheat, more like subcooling which suggests that you have liquid floodback to your compressor.
The difference between genius and stupidity is that genius has its limits.
Marc
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27-07-2009, 07:00 AM #110
Re: Superheat
Hi Gary,
How does a tech know if he has proper air flow?. For discussion purpose: I will use this example; a Walk in freezer, approximately twenty years old, unknown brand - label is long gone.
Technician notice: On evaporator; one fan motor is 1/15 HP 1550RPM, the other fan motor is 1/20HP 1500RPM. both fan blade is 14", 4 blade, approx. 23 pitch. Question; how do you determine if you have proper air flow?
Further: On condensing unit: one fan motor is 1/10 HP, 1600RPM, one motor is 1/8 Hp 1600 RPM. How do you know if you have proper air flow?Be Happy
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27-07-2009, 07:32 AM #111
Re: Superheat
Delta-T (dT) is the difference between coil entering and leaving air temperatures. As airflow decreases, dT increases. On a freezer evaporator coil, the dT should be no more than 20F/11K. On a condenser coil, the dT should be no more than 30F/16K. Excessive dT means insufficient airflow.
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07-12-2010, 05:36 AM #112
Re: Superheat
interesting wise and nice people thanks for letting me be in the forum
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26-12-2010, 04:28 PM #113
Re: Superheat
Hello all
how do you masuer to superheat foor sabro compresso
thak you
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26-12-2010, 04:57 PM #114
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01-01-2011, 06:58 PM #115
Re: Superheat
here's a controversial superheat question. As an evaporator coil frosts up does superheat increase or decrease? There's less heat being absorbed but the compressor may pull to a lower pressure.
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01-01-2011, 07:27 PM #116
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02-01-2011, 01:03 AM #117
Re: Superheat
On Starting new Equipment, Only check superheat when you are close to Thermostat Setpoint. Under High load and of course your superheat will higher than target range. Do not change Superheat Setting just to change it unless it is really needed. Of course as Gary as stated, Consider Air Flow and Dirty Coils first but than again Dirty Coils on new Equipment shouldn't be happening. But most Air Conditioning Manufacturers are more concerned with Subcooling on charging their systems correctly. If you notice most installation Manuals will have Subcooling Chart but not a Superheat Chart. But simply making a note of Superheat on new Equipment is probably good practice. Are you going to need to change setting on new Equipment with proper sized TXV. Probably not.
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07-01-2011, 05:54 PM #118
Re: Superheat
hi,iam new to this site,i want to know the what will be the correct super heat for evaporator and compressor in f or c
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07-01-2011, 11:22 PM #119
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08-01-2011, 04:22 AM #120
Re: Superheat
its a cold room temp is -22'c
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11-01-2011, 05:28 PM #121
Re: Superheat
what are basic tips of an installation engineer before instaling the cold storage panels and pipe routing
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18-01-2011, 01:19 PM #122
Re: Superheat
I learn from you guys, thank you
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15-04-2011, 02:34 AM #123
Re: Superheat
hey sir can u tell me v can measure the super heat with out the gauge as u said earlier so whtz the thing which v can come to find the superheat with out gauge.
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15-04-2011, 11:13 PM #124
Re: Superheat
You cannot measure superheat without a gauge only temperatures.
Brian - Newton Abbot, Devon, UK
Retired March 2015
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16-04-2011, 12:41 PM #125
Re: Superheat
You could do it with 2 temperature meters (TM): The 1st TM measures the temperature of the first bend where there's no SH realized yet and the other TM measures the temperature on the outlet of the evaporator.
It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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25-04-2011, 07:16 PM #126
Re: Superheat
Why are temps expressed in C and superheat in K, I assumed it was Celcius and Kelvin but thats not right is it, and quite apart from How we measure and where what ,in simple terms are the desired figures as far as I can make out it's 6C superrheat and 5 to 8 c subcooling is that right, it,s very near to what I learned
Devlin
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25-04-2011, 08:17 PM #127
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Re: Superheat
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25-04-2011, 10:32 PM #128
Re: Superheat
Hi devlin,
'K used in superheat refers to the delta/ temperature difference. Check the kueba.de web site for super TXV super heat checks and settings.
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26-04-2011, 10:24 AM #129
Re: Superheat
Hi, devlin maguire
see this ....
http://www.refrigeration-engineer.co...efinition-reqd
http://www.refrigeration-engineer.co...tive-superheat
you can search RE forums too .... for Kelvin, SC&SH ... a lot of posts ..
Best regards, Josip
It's impossible to make anything foolproof because fools are so ingenious...
Don't ever underestimate the power of stupid people when they are in large groups.
Please, don't teach me how to be stupid....
No job is as important as to jeopardize the safety of you or those that you work with.
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27-04-2011, 11:16 AM #130
Re: Superheat
Hi Frank,
I have installed Cold Room its set point in -22 C but the compressor does not off except defrosting time means remains on and some times temperature reaches to -18 C I measured its super heat which details are below.
Suction line pressure 20 PSI convert to PT chart R-22 temperature is -5 F
Suction line temperature is 71 F so that according to calculation super heat is (71 - (-5) ) = 76 F ? (71-5) = 66 F ?
In both condition the super heat is too high so my question is that in cold room what super heat is ideal at evaporator and compressor side as in A/C
Compressor side Super heat 20~25 is ideal kindly reply I am really confused.
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27-04-2011, 02:35 PM #131
Re: Superheat
Hi Ismail,
I try to get the superheat between 4-8K when working in Celcius. This will let you know that the evaporator is fully flooded with refrigerant but you have enough superheat to make sure the refrigerant is in a vapor state when it enters the compressor.
For a freezer room you should be evaporating at least -25'C. This could just be short of gas but you would need to take more readings and find out what your sub cooling value is. That should also be between 4-8K.
Low subcooling + High Superheat = low gas charge
Also check for clean condenser with correct fan speed. Did you remove all the air with a vacuum pump before charging with refrigerant?
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