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shogun7
27-04-2004, 03:33 AM
When refrigeration engineers design supermarkets, they tend to use reach-in glass door cabinets as their low-temperature display cases. Although this makes shopping a little less convenient for customers, they are less problematic than open display cases because open display cases at low temperatures are more sensitive to a store’s environment.

Engineers will use either mechanical or electronic temperature controls to regulate case temperature; electronic controllers are used more often today. The temperature controls are wired to control either a liquid line solenoid or suction stop valve, depending on the design.

The refrigeration system normally is tied into a parallel rack system located either on the roof or at the rear of the building. To ensure that the evaporator is fully active, a service technician can measure the superheat at the outlet of the evaporator coil. An acceptable superheat setting for the thermostatic expansion valve on these cases is 3 F to 5 F. This will ensure that the evaporator is being used to its fullest capacity and that there is no liquid returning to the compressors at the rack.

When checking or adjusting the superheat setting, it is important to make sure the evaporator is not iced over and that the case is within 10 F of its desired operating temperature. When making adjustments be sure not to make more than 1/4 to 1/2 turn at a time. Once an adjustment has been made let the system stabilize for a minimum of 15 minutes, recheck the setting and make any additional adjustments.

The defrost systems on reach-in glass door cases can be either electric heaters or hot gas, and the service technician must be able to identify which defrost system is being used. Exposing the electrical wiring at the kickplate and inspecting it can aid the technician in identifying the type of defrost system. Each system has its advantages. The electric defrost systems normally will obtain a better and less problematic defrost, but are more costly to operate. Hot gas systems essentially are cost-free since they employ the system’s hot gas to defrost the evaporator. However, these systems are more problematic and can cause an incomplete defrost of the evaporator coil if not properly set up.

The service technician may need to adjust the termination setting to allow the case to properly defrost. A common location for the defrost termination sensor is at the return elbow at the coil end opposite the thermostat expansion valve. On some electric defrost systems, it may be located upstream of the evaporator coil in the rear channel of the case. On some hot gas systems it may be located on the dump line of the evaporator.

A typical setting for termination is 55 F to 60 F for hot gas systems and 65 F to 75 F for electric defrost. The actual termination setting should be obtained from the manufacturer’s specifications.

Mark
27-04-2004, 07:57 PM
My apologizes shogun7 but supermarket refrigeration engineers might take this as a pi** take

LOL

Andy
27-04-2004, 08:44 PM
Hi Shogun :)
those superheats seem very low for degrees C never mind degrees F. I have never set a valve that low, even EEV systems, it will hunt like nothing you have ever seen :confused:
To me static superheats on a deep freeze case should be 6 to 9K
Kind Regards. Andy

Mark
27-04-2004, 09:27 PM
Least someone read it :D

Dan
28-04-2004, 12:28 AM
One manufacturer, Hussmann, published in its literature specifications for 3 to 5 deg F superheat settings. What Shogun failed to mention was that the method for achieving this superheat is to measure temperature midway through the evaporator with one probe and measure the temperature of the evaporator outlet with another. No pressure readings. I am not sure how important that is.

As I recall the instructions refer to the superheat hunting between 5 deg and 0 deg F but returning to controlling at 3 to 5 deg F. Basically Hussmann was advising to set the valve on the outermost edge of its control and to use every available inch of the evaporator.

shogun7
28-04-2004, 03:19 AM
Thanks Andy at least that was quite civil!
Quite so Dan, and Mark what is pi** take please speak english so we in the Colonies understand. Please don't hold back be a man like Adolf. You have every right to disagree with my evaluations but as a moderator you flunk when you sink to that level. I write all my articles on research and experience because thats what I do "TEACH". You and I both know that there will always be disagreements on what we think is the "RIGHT" way to do something But never ,never ,never try to make someone less because you have a penus size ego. Is that clear enough for you? If I misunderstood your motives then please accept my deepest apoligies. "ab absurdo"
CHEERS

Mark
28-04-2004, 06:28 AM
Shogun i thought you were making some witty post :) my apologizes :o

And please,you dont score points by making personal comments :(

Kind Regards Mark :)

FreezerGeezer
28-04-2004, 09:46 PM
Perhaps Shogun7 is using us as a testbed for his classes? We correct his mistakes, so he can look like 'da man' in the class? Or is he offering to teach us? If so, perhaps a bit more detail around the edges of the article? Like why he's posting it here? If anyone's willing to teach those of us less experienced / knowlegable, I'm all for it. But I don't like Shogun's style - it's a bit 'I'm telling you this is how it is - disagree at your peril, for I am the deity of refrigeration!' Sorry, but that's how I see it. No malice intended, Shogun7

shogun7
28-04-2004, 10:30 PM
Mark “DIDDO”

Freezer , Where in the world did you get that idea?

cum grano salis :D

shogun7
29-04-2004, 08:41 PM
Adolf;
Jealousy will get you nowhere. So stuff the culch for someone else!

shogun7
29-04-2004, 08:52 PM
I am not old, I am not old .....am I?

Andy
29-04-2004, 09:26 PM
Shogun
that's the last time I reply to one of your posts :D
Kind Regards. Andy :)

shogun7
30-04-2004, 12:05 AM
Piss Take. Australian vernacular for an obstructionist joke - a joke whose butt can't reply for fear of making themselves look more ridiculous.
Andy you got me all wrong this is a big mistake and Mark was way off the mark. My intentions are only honorable.Please keep on talking!
Love ya buddy,but I have to take a piss....take