Why do some comercial refrigerations systems use R134A and other use R404A ?
It is correct to say that R404A can reach lower temperatures at the same suction pressure of R134A ?
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Why do some comercial refrigerations systems use R134A and other use R404A ?
It is correct to say that R404A can reach lower temperatures at the same suction pressure of R134A ?
R134a is a low pressure refrigerant, very efficient for high temperature applications.Quote:
Originally Posted by Acrisoft
This makes it ideal in air conditioning applications that may leak refrigerant like car air conditioning.
Now it is being phased out because of its high global warming potential and replaced by R1234ry.
R404a is a high pressure refrigerant ideal for applications in low and medium temperature.
You want low pressure refrigerants in household applications like refrigerators that may be inside kitchens with (possible) high ambient temperature, so you make sure nothing will blow up. For the same reason you want R134a in your car air conditioning.
R404a instead has pressures slightly above atmospheric in low temperature applications where R134a would have negative pressures and its heat transmission coefficients would be much lower.
Yes, R404 will have a much lower SATURATION temperature at the same pressure than R134a.Quote:
Originally Posted by Acrisoft
Notice the use of saturation temperature because you could have both gases occupying different volumes and you can make this statement false.
What a great answer, absolutely nothing to add on that one!
Thanks Aramis. Very great answer in a small piece of text.
Is there any formula to calculate the average high side pressure by the suction line pressure ?
Or both sides pressure do not have a relation ?
Moises
Both pressures have a relation but not an easy formula for calculation.
High pressure is given mainly by the pumping rate of the compressor and the condensation rate in the condenser. I say mainly because the pumping rate is affected by the pressure drops in the circuit, in this sense the expansion device also affects high pressure but far less than the other two.
Similarly the suction pressure depends on the mass feed of the expansion device to the evaporator, the evaporator rate of vaporization and the pumping rate of the compressor.
So the compressor is the main actor in defining both condensing and suction pressure but all other system components have something to say.
Specially the thermal load in the evaporator and the heat rejected in the condenser and cold room temperature and condenser's cooling media temperature for they rule the evaporation and condensation rates of refrigerant.
This is why we estimate system pressures with the manufacturer’s information of the compressor, provided you supply a matching condenser, evaporator and expansion device.
Please let me be more specific and go a littler further.
Suppose I have 2 systems, both 300PSI on high side using R404A.
Can I adjust one system suction side to 20PSI to cause the refrigerant to evaporate at -25 degrees Celsius and other at 10PSI to evaporate at -35 degrees Celsius keeping the same high side pressure ?
Only expansion valve or capillary tube changes would be enough to such a difference ?
Moises
Provided both compressors don't share a common suction, yes you can.
From the point of view of the energy spent, this is not a good idea because you are forced to raise the condensing pressure of the smaller or lower compression ratio system to a common pressure.
Supermarkets usually do this to save on a single circuit condenser, save space, probably less noise problems and control equipment.
Another drawback is that if one system fails and you are sharing refrigerant the other system is affected. Separate systems are more reliable at a higher initial cost.
Yes.Quote:
Only expansion valve or capillary tube changes would be enough to such a difference ?