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Posted by The Daring Dufas on July 29, 2009, 9:48 pm
The King wrote:
> On Wed, 29 Jul 2009 14:53:24 -0500, The Daring Dufas
>
>> The King wrote:
>>> On Wed, 29 Jul 2009 06:13:58 -0400, The King
>>>> On Tue, 28 Jul 2009 22:16:27 -0500, The Daring Dufas
>>>>> The King wrote:
>>>>>> On Tue, 28 Jul 2009 15:53:04 -0500, The Daring Dufas
>>>>>>>>> /Lars S
>>>>>>>> You could use NU-22 as a R22 replacement and you can use mineral oil
>>>>>>>> with it. BTW Stormy is a idiot posing as a hvac tech as his remark
>>>>>>>> about using a low temp ref shows. R-22 is not typically used in a low
>>>>>>>> temp applications. It can be used as such but it has special needs
>>>>>>>> when its used in low temp apps. Your application would be considered
>>>>>>>> high temp. Its all about evap temps not boiling points like the dumb
>>>>>>>> ass mormon thinks.
>>>>>>> Whenever I've used R22 in low temp applications, hell,
>>>>>>> even in refrigeration medium temp applications I always
>>>>>>> have to have a defrost system. A lot of the Domino's
>>>>>>> Pizza stores switched over to R22 in the walk-in coolers
>>>>>>> some years back and they all have to have defrost systems.
>>>>>>> I have to rebuild one here soon.
>>>>>>> TDD
>>>>>> Most of the time med temp ref is off cycle defrost. I suppose Dominos
>>>>>> wants 34 or cooler? as a target temp so a clock might be needed. In a
>>>>>> 36-40F box you shouldnt need anything but off cycle lessen it isnt
>>>>>> sized or adjusted right.
>>>>> The R22 walk-in coolers come from the factory with defrost
>>>>> timers. In order to get the 33-40 box temps, the evap runs
>>>>> a lot colder and of course the darn door does not stay shut.
>>>>> I like to set them at 35 because of all the meat products
>>>>> they stock and of course it helps keep the food temps where
>>>>> the health dept likes to see them with the door being open
>>>>> so much. I have one at a store I service that was an R12
>>>>> system originally, it's now running on 416a and keeps on
>>>>> running better than most. It has a three phase semi hermetic
>>>>> compressor, large receiver and pump down control, it's very
>>>>> reliable because it was installed CORRECTLY. The crap I
>>>>> see when some (techs?) throw them in is astounding. Oh darn,
>>>>> there goes my blood pressure.
>>>>> TDD
>>>> Evaporator temperatures are the same for the application (low - med -
>>>> high temp) regardless of what ref is used. R 12 med temp evaps run
>>>> at the same temperatures as an R 22 med temp evap. No need for a
>>>> defrost clock just because it has R 22 in it. There may be other
>>>> reasons for a defrost clock but the type of ref isnt one of them.
>>> I have a few beore I leave so heres my parting thoughts on your
>>> defrost problem. I use a 6F differential on the control setting. So
>>> with a 35F box cut out air temp would be 32F and cut in temp would be
>>> 38F. So at a target avg of 35.. yeah, you might want a defrost
>>> clock.
>>> I'd bump the temp up a half a degree or so to keep the air temps above
>>> 32F. That way you maintain a more consistant box temp which is good
>>> for the product and the consumer.
>> Since I'm not the worlds leading expert on refrigeration/HVAC,
>> I can only comment on my own personal experience with the various
>> equipment over the last four decades. I would have to research
>> the subject to give you any sort of proper and precise explanation.
>> All I can say is that every R22 walk-in cooler I've ever seen, has
>> had a defrost system except for the homemade ones that didn't work
>> until they were equipped with some sort of defrost system.
>
> Every
>> factory built condensing unit for an R22 walk-in cooler including
>> walk-in freezers has had some sort of defrost system. Passive for
>> the coolers, active for the freezers. I'm always willing to learn
>> new things so if you can tell me more and point me to the source,
>> I have no problem being corrected. When it comes to education, my
>> ego doesn't get in the way.
>> TDD
>
> What do you mean when you say "passive for the coolers"?
>
> I agree every ref system needs some sort of defrost. it could be
> either electric, hot gas, manual, or off cycle.
>
> What you said was every r22 cooler needs a defrost clock. I don't see
> why it would. Most refers are designed to have a 2/3 run time. The
> other 1/3 is off. When it is off the space warms and any light
> accumulation of frost should melt off before the next start. About
> the only time I have seen or had to put a timer in is when the
> customer wants the coldest beer in town and wants the coolers to run
> 30-35F. At those temps there is not enough off time above freezing F
> to allow for a natural defrost and a defrost clock is needed.
>
> Why is it an r 22 cooler needs a clock when a r 12 cooler didn't.
> Just askin..
>
> The evap temps are the same for each and every ref used for medium
> temp work at a 10 delta. The refrigerants pressure/temp relationships
> change with the type of refrigerant and they all have different
> boiling points and properties. Some temps are cooler at x pressure
> and some are warmer. They each have a different capacity per pound
> circulated and all that jazz but those factors are why there are
> different ratings for compressor duty and the type of refrigerant used
> in them.
>
> I hate to type and run but I have to pack the bike now and off to
> Sturgis. :)
Careful out there, the cage drivers are out to get you.
Passive defrost: Cut the flow of refrigerant, leave the
evaporator fan/fans running. Ambient temp rises melting
the frost buildup. Active defrost: Cut the flow of freon,
turn off the evaporator fan/fans, turn on electric heaters
or use a hot gas defrost cycle to melt the ice buildup.
I've never had the R12 systems freeze up unless the temp
was set too low or the evaporator air flow was impeded.
R22 walk-in coolers always seem to freeze up without a
timed defrost cycle. All those years ago when I was at
college studying for my degree in rocket surgery, the
classes never covered walk-in coolers so I can't give you
a scientific explanation.
TDD
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