super heat calculations

[tezzthefridgey]

hi all i am a fridgey in tasmania, australia i am new to re and i am new to supermarket refrigeration, can some one please explain super heat fundamentals and calculations it has been a while since i have used them frequently and id like to make sure i am still checking and adjusting my case superheats correctly,for optimum performance
cheers tezz

[taz24]

hi all i am a fridgey in tasmania, australia i am new to re and i am new to supermarket refrigeration, can some one please explain super heat fundamentals and calculations it has been a while since i have used them frequently and id like to make sure i am still checking and adjusting my case superheats correctly,for optimum performance
cheers tezz

Superheat is the added heat to the vapour above the saturated temperature / boiling point at a set pressure.

So if you were measuring superheat out of the evap then you need to know the tempreature the refrigerant is boiling at / evaporating at and you can only know that by using your gauges.
Then you compare the gauge temp with the actual measured temp using a thermomiter at the point where the refrigerant leaves the evap.

The differance between the two is superheat.

It should be about 6 to 8 difference (maybe as high as 10 and as low as 4)

taz

.

[Magoo]

Here we all go again.
Do a search on superheat
Taz 24, beleive me there are no rule of thumbs. Every system has to be treated individually, to take into account the engineer that designed the system. So relevent to super markets refrigeration racks and partial pressure situations.

[dirk]

If you have correctly selected the expansion valve and orofice you should never need to set superheat a valve does not loose its superheat setting . The only time you should be changing the superheat is when some genius has fiddled with the settings.
Magoo is correct there is no fixed rule of thumb, the perfect superheat setting could be described as the setting at which the valve is least erratic ie its smothest operation or the point at which you have the smallest pressure fluctuations measured at the outlet of the evaporator. all this taking into consideration of the superheat the system was designed at.

[Tesla]

Hi Tezz
Welcome to the forum.
The general rule of thumb that I was taught for R22, 12 and 502 was this. measure suction pressure and allow 2 psi pressure drop to evap. Take the equivalent temp and then measure the outlet temp of evap. This difference gives you the approximate superheat. But things have changed and refrigerants so take advice from the above. Best bet is to get yourself a superheat calculation kit from REs, yellow jacket ritchie. Please search this forum for much more detail.

[tezzthefridgey]

thanks for your input looks like superheats may have been a touchy subject at some time with some of the engineers

[Brian_UK]

Not overly touchy it's just that it should be one of the basics and there is a lot of discussion on this forum due to people not using the search facility.

For example, Gary started a Refrigerant 101 thread which really says it all, have a read and a lot will come back to mind.
http://www.refrigeration-engineer.co...ad.php?t=19701

[Blueboy]

Dirk

I am afraid that my experience of 30 years means what you have written make NO SENSE AT ALL.

TEV's are set at different superheat's- Danfoss choose 5C as a starting point. This is neither correct nor incorrect but will depend on the situation that you and your evaporator are in.

Sometimes, I find 6 C is a good superheat sometimes 4C is much much better there are many factors that will affect getting the maximum refrigeration effect from any specific evaporator or situation. To say that they are correct from the factory for all applications is simply WRONG.

[nike123]

http://www.kueba.de/en-us/Tools/K%C3...s/default.aspx