R-407C and Coil Capacity

[glabah]

We've been using Colmac Coil's software for doing coil capacity estimates for system design. However, now we have a specification for designing a system using R-407C, a refrigerant that their coil software doesn't have available in its options.

I know compressor capacity decreases a little bit with the change from R-22 to R-407C - at least the compressor manufacturers are up to date.

Since I was unable to run a set of calculations for a coil for R-407C using the Colmac software, I decided to use Super Radiator Coil's software instead. Their software is a little less user friendly and also I don't have a lot of experience using it. However, when I put in R-22 numbers, and used the exact same numbers for R-407C, their software showed a slight increase in capacity for R-407C over R-22.

Obviously there is an issue with high temperature ambient conditions because R-407C has a critical point about 86 deg C, whereas R-22 has a critical point about 100 deg. C. Therefore, there will obviously be a decrease in condenser capacity in R-407C at high outside temperatures.

However, for normal air conditioning temperatures, say evaporator temperatures in the 5 deg C range and the ambient at the condenser at most about 45 deg. C, do the coils generally show an increase in capacity when going from R-22 to R-407C? I can see this happening due to the nature of the temperature glide in the coils, but my impression has been that if a unit is converted from R-22 to R-407C, generally there is a 5% to 7% decrease in capacity. Is this decrease in capacity based entirely on the decrease that comes at the compressor?

[frank]

This makes for interesting reading and seems to answer your question. http://www.cnpam.edu.my/ICRAMME2005/...rs/PP/PP30.pdf

[glabah]

"However, experimental data in association with this most important refrigerant substitute for R-22 are limited at the present time." and the report is dated May 2005. I suppose that is probably why Colmac hasn't added it to their software yet.

Thanks very much.

[NoNickName]

R407c has been used in Europe since late 90s.
Performance is 7% lower than R22 at the same working conditions, and SH, SC must be kept higher to prevent distillation of blend.

[Renato RR]

Ciat have some research on this subject.They did experiment with same chillers and diferent refrigerants.The R 407c have biger power consuption and small decrease in heat power.

But use R22 calculator and calculate 5% decrease in heat power.

Renato

[Chris Burton]

I think some manufacturers use either the dew or bubble point as design saturation temperature which can give capacitys higher or lower than R22. In practical terms you must use the bubble point & factor in 10k subcooling to ensure a good liquid seal in condensor. If not you'll get a breakdown of the refrigerant called fractionisation. My best advice is to avoid R407c as most manfacturers are switching to R134a on liquid chillers or other more stable refrigerants.