why does R134a take so damn long to come down?

[Eddy87]

Hi there

I am at my first year of fridge school and posed a question to an Engineer earlier who had no answer for me. The question was why does R134a take so long to come down to temperature as apposed to, say, R404a?

Any replies will be appreciated

Eddy

[frank]

Why do you say this happens?

Do you have identical systems operating on the different refrigerants?

Is your question based on actual data?

[Eddy87]

Hi Frank

No I do not have identical systems running on different refrigerants. I have noticed, though, that similar systems, say small Pattisserie fridges, one running on R404a will drop drastically in temperature and achieve temp in say 4-5 mins whilst a similar sytem running on r134a will take more like 30-45 mins to make temp. I assumed, maybe naively, that this is down to the difference in the make up of the two gases?

[install monkey]

probably because r134a leaks more!

[paul_h]

Hi Frank

No I do not have identical systems running on different refrigerants. I have noticed, though, that similar systems, say small Pattisserie fridges, one running on R404a will drop drastically in temperature and achieve temp in say 4-5 mins whilst a similar sytem running on r134a will take more like 30-45 mins to make temp. I assumed, maybe naively, that this is down to the difference in the make up of the two gases?

Small commercial fridges like you are talking about are designed around a high TD. R134a can't operate too cold before it's running in a vacuum, R404a can run colder, so manufacturers use that to run an even higher TD, so the air coming off the evap on a r404a evap is just colder. Look at a PT chart for both R134a and R404a and see what temps they would be at 300kPa. ie when first turned on. Look at what temps they would be if the manufacturer designed the system running at 100kPa at normal running temps.

Also R134a sucks and should just be propellant for aerosols, canned air, air duster and all the stuff it was before it was used as a refrigerant etc
R134a pros - low carbon footprint, better than R404a. Edit: By that it mean low global warming potential (GWP)
R134a cons - everything else.

[Peter_1]

Eddy, your statement is wrong, it only depends on the capacity /versus load installed and the refrigerant has nothing to do with this.

In fact, the COP of R134a is even better than R404a for fridge applications, do once some research on this one.

[mikeref]

COP of R134a for fridges in general = 2.83, R404a and R507 for same application = 2.65. COP is the ratio of input energy, in watts, to heat pumped, in watts. Think Eddy87's fridge may be a little dodgy.. Mike.