Single Compressor for Refrigerator

What do you intend to achieve with the dual compressors?

Higher pressure or more flow?

well i used 2 compressor for fast flowing refrigerant and mantain the temperature during long period of holding.

In the refrigeration applications I have used in the past, we used two compressors to move a larger volume of refrigerant to the coils for fast recovery to temperature. Then when the unit is sitting at temperature we ran the smaller unit to maintain the temperature during long periods of holding. As for design we used the reciprocating compressor made by Copeland (V twin). Now most of the units being made in the U.S. for domestic use are the scroll design. Have not been involved with these lately.

well i am still using two compressor ( Copeland ) and its works just as your definition. but i am wondering wether i can use just a single compressor but cover 2 function at the same time that moving refrigerant for fast recovery and mantain the temperature .

the temperature to mantain is - 85 C..and I am thinking with only single compressor the result will be low energy consumption , low noise etc.

could you help me..the kind of compressor would i need.thanks

Try Hitachi Industrial/ Medical branch what you are looking for is a variable volume scrolling compressor. Space between veins reduce in a progression. Progression is set at 120 degrees to balance loads. Centrifugal force of the spinning refrig' does the re-allocation due to increased density(mass). Through points are on the inside(center) so refrig can only pass through when a certain density is met. First such compressor I saw was on a Saturn Five. Used to maintain temp of fuel and deliver it quickly. Does that help?

Rory

i had looked at hitachi scroll compressor but its only has extend cooling range from 45 C to + 5 C..but i want the compressor cooling range to - 86 C or more.

they used the hitachi scrool compressor for storage fruit and vegetables. I need compressor for ultra low temperature frezzer down to -85C at ambient temperature of 32 C.

From my experience [ standing behind and listening to the person who knows what they are doing ] nearly all ultra low systems are of the two stage variety. They are fairly rugged and easy enough to service as well as get the job done. There are some "one can" designs out there but reliability and serviceability is not that great from my personal experience so far. I leave the compressor issue to those more in the know.

Now as to the more precise control once you are at temperature there are a number of approaches.

- Two or more sets of evaporator coils of ever decreasing size / capacity. All are full open when performing crash cooling and only the smallest one cycles when maintaining Setpoint temperature. Control is not much more complicated than a basic bypass system. Reliability is as good as a basic system. More evaporator coils and solenoids to worry about though as well as the controller(s). You can control such a system with two basic temperature controllers where the one Setpoint is slaved to the other then the differentials are set far enough apart so that the larger would not operate once Setpoint was reached.

- Use a variable stepper solenoid valve to feed the evaporator and a backpressure controlled hot gas bypass. You regulate the temperature very precisely through stepping the opening of the valve. Downside is that this is much more complicated and reliability and ruggedness is much reduced. The valve tends to frost up and freeze if you are not careful as well as condensation in the mechanical stepper system is a real issue.

With either system the temperature control and stability enhanced with very good circulation of the medium being cooled (I deal with air so big honking fans are nice but do add significant heat load at the lower temperatures)

Just a hint from the person in the know over my shoulder ... check out the newer copeland models. ex: Copeland Scroll™ ZFKV Compressors

is it a compound system to reach ultra low temperature? what temperature and refrigerant(s) are you using? what is the total load ( latent as well as sensible)? what is the ambient, min. max.? what is the pull down tume duration you are looking for? what is the r factor of the cabinet?

What about a Sterling Cycle cooling system?

http://www.procooling.com/index.php?func=articles&disp=47&pg=1

we are intresting in used compressor of refrigrators.Can u please send me all specifications and CIF price at Pakistan port regarding 20' countainers.Please contect me on my email ID marifgill@yahoo.co.uk

thanks

Arif