low temp vrs med temp SH settings?

[gas-n-go]

Im just wondering if anyone has an explination why low temp SH range is lower then a med temp SH range? In my mind if we could dial in perfect SH settings we would want .10 of a degree of SH exiting all evaps regaurdless of thier temp range. Would that not give you maxium efficeny from your valve and your evap? Im just curious what the purpose of the 4 to 8 and the 6 to 12 ranges are? If someone could clear the fog for me ild be very grateful and might be persuaded to even email that said individual a beer. lol

[gerryboy00]

The most desirable operating superheat for a particular system largely depends on the temperature difference (TD)
between the refrigerant and the medium being cooled. The
basic definition of TD is the difference between evaporator
temperature and the air enterring temperature. Systems with a high TD, such as air conditioning , can tolerate higher superheats without appreciable loss in system capacity.
Refrigeration and low temperature systems require low
superheats due to their lower TDs.


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[Andy Schoen]

Mmmm... I believe I wrote that... :D :D


Originally posted by gas-n-go
In my mind if we could dial in perfect SH settings we would want .10 of a degree of SH exiting all evaps regaurdless of thier temp range.

You are correct. Keep in mind the ability of a TEV to control a low superheat setting is a function of of how well air is being distributed across the coil and the refrigerant within a multi-circuited coil. Also, most techs do not have the equipment to measure superheat to within plus or minus 2°F in the field.

So in other words, don't try to get 2°F superheat control when 6°F will suffice. Don't try to get 6°F superheat control when 10°F will suffice.

[brimo]

and......remember too that most your heat is absorbed during the latent change not the sensible change of the refrigerant. That's why people try to invent things like the thermal electric expansion valve which tries to maintain a zero degree superheat.