Correction factor

[nike123]

I am going to change condensation unit of walk in freezer from R12 to R22 or maybe R404A. Evaporator is going to stay.
Does anyone knows, or have tables of correction factors for nominal capacity (F1) of evaporator and correction factors for refrigerant(F2) which is originally worked with R12 and now should work with R22 or R404A.
In fact I need correction factors R12-R22 and correction factors R12-R404A for Te -25°C
I already have factors for R22-R404A
Thanks!

[Samarjit Sen]

Hello nike 123,

You may get some information from the site of Bock and Bitzer. They have some documents on retrofitting.

[nike123]

I found it at Bitzer site:
http://www.bitzer.de/_doc/k/kt-650-2.pdf

Thank you Samarjit Sen!

[nike123]

I would be grateful if someone could confirm that capacity of evaporator will be lower by 20% if I change refrigerant (and all the rest of the plant) from R12 to R22 at Te of -25°C.
If I do R12 to R404A conversion, then, does capacity of evaporator will be same?

[SteinarN]

I dont fully catch the idea that it exists some universal correction factors for evaporators when changing refrigerant.

An evaporator can be optimized for a low pressure refrigerant or a high pressure refrigerant or somewhere inbetween.

An evaporator optimized for a high pressure refrigerant will have a number of loops of a spesific lenght. The same evaporator optimized for a low pressure refrigerant will have more but shorter loops to handle the increased volumetric flow necessary for the same capasity.

If a "many short loops" evaporator is running in a system with a high pressure refrigerant, then the refrigerant velocity will be lower than optimum, ie have a more laminar and less efficient flow. If, on the other hand, a "few long loops" evaporator is running in a system with a low pressure refrigerant then the refrigerant velocity will be very high causing an excessive pressure loss in the loops.

I understand an evaporator gets different capasity dependent on which refrigerant is in the system, but i cant fugure out how it can be possible to apply some universal correction factors. At least not among evaporators from different manufacturers and optimized for different types of refrigerant.

[nike123]

Look at this PDF.
http://www.mediafire.com/?ut5ggc1bqth
Table no. 3 has some factors and that is why I asked this questions.

[US Iceman]

If a "many short loops" evaporator is running in a system with a high pressure refrigerant, then the refrigerant velocity will be lower than optimum, ie have a more laminar and less efficient flow. If, on the other hand, a "few long loops" evaporator is running in a system with a low pressure refrigerant then the refrigerant velocity will be very high causing an excessive pressure loss in the loops.

This is one of the major problems for air-cooling evaporators. The number of circuits and length of each circuit is designed for the refrigerant, operating condition (temperatures, refrigerant) and cooling load.

Trying to get correction factors for other conditions is at best an AVERAGE number that MIGHT BE suggested which would allow operation that COULD BE acceptable.

I would expect the re-rating of compressors and condensers might be more forgiving rather than evaporators for this reason.

[SteinarN]

Look at this PDF.
http://www.mediafire.com/?ut5ggc1bqth
Table no. 3 has some factors and that is why I asked this questions.

It says it is less than 10% difference between different refrigerants. I suppose that table gives a reasonable picture of the capasity of todays evaporators from that manufacturer. But i doubt you can be sure that table gives a correct picture of the correction factors of evaporators from other manufacturers and/or old evaporators.

[powell]

nike,

I've never used a correction factor for evap capacity when converting from R12 to R22/R502 .........so I did some research. I have an old McQuay book which list a 2% difference, using a x.98 multiplier when using R12 in a R22/R502 rated cooler evaps. I found nothing on freezers.

I have always supplied the nozzles to help distribute the refrigerant in the existing distributors. So far so good.

Thanks for starting this informative post and please let me know your findings.