Is there a rule of thumb on the amount of refrigerant a system will use. I am currently having a walk-in freezer installed using a copeland discus 2DL3-040E 4HP compressor and was just wondering how much R507 should I purchase.
Ricky
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Is there a rule of thumb on the amount of refrigerant a system will use. I am currently having a walk-in freezer installed using a copeland discus 2DL3-040E 4HP compressor and was just wondering how much R507 should I purchase.
Ricky
There is no rule of thumb.
Simple
With remote air-cooled condenser coil?
Any liquid receiver installed?
What is the total refrigerant copper pipe distance from compressor to condenser, condenser to evaporator coil and evaporator back to compressor?
What is the pipe size use?
In my opinion,
the rule of thumb on the amount of the refrigerant of the refrigerator is that there is no "liquid" refrigerant and therer is no "dry-out" of refrigerant in the outlet of a evaporator.
a "liquid" refrigerant in the outlet of a evaporator means the amount of the refrigerant is too much or a evaporator`s capability is small.
a "dry-out" of a refrigerant in the outlet of a evaporator means the amount of the refrigerant is too small or a evaporator`s capability is large.
Then, How to decide whether it is a "dry-out" or not?
Simple experimentally, You can decide it by measuring the temperature of the evaporator`s inlet and outlet.
If there is no temperature`s differance between the inlet and outlet, you can find the optimal amount of the refrigerant.(actually if the differance of the temperature is within 1 ~2 degree Celsius, it is acceptable.)
Strictly speaking,the amount of refrigerant can be calculated by the system inside volume and operation condition . In practical application ,we judge the amount of refrigerant by the system paremeters (low /high pressure ,temp,power consuming etc)and confirm if it's fittable. Because the system usually worked on different condition,the amount of refrigerant must meet the different quantity,so normally the refrigeration system has buffer tank for refrigerant flow varying.
Only measure the evaporator inlet and outlet temp diff can't decide if the amount is reasonable,for it's related to the TEV matching evaporator issue.In many cases,the inlet and outlet temp is affected by the TEV performance.
It's my opinion. pls corect me if i'm wrong.
rgds
LC:-)
Main role of a capillary tube or TEV is to drop the pressure with maintaining the same enthalpy(h). The enthalpy is not concerned with the mass(or amount) of the refrigerant.(So, the unit of the enthalpy is kJ/kg.)
I think that how to decide the amount of the refrigerant is related to how much heat load is.
So, before we decide the amount of the refrigerant, at first we design the basic component of the refrigeration cycle(capillary tube or TEV etc...) and then we decide the amount of the refrigerant in the standard heat load condition(Usually we test at RT 30℃). The amount of the refrigerant can be changed by the heat load condition.
gregorius
Quote:
Originally Posted by t_gregorius
Yes, so in another words the " Rule of Thumb" for correct amount of refrigerants is...........
SUPERHEAT
The amount of refrigerant present has little to do with poor or inadequate evaporator design. One can be a symptom of the other. If the evaporator is wrong you will never cure it by altering the charge.
When all is said and done, the objective is to optimise the evaporation rate of the refrigerant.
Put simply, you need to keep the saturation temperature in the evaporator as close as possible for as much of the time as possible to the entering temperature of the medium being cooled. This is called the ?approach?.
This can be done in a number of ways, depending on your system and, of course, the size.
Believe it or not, this is relatively straightforward with very big systems, providing that you can guarantee a continuous and full load.
In many small systems that are expected to operate over a range of capacities, this can become meaningless in practice, so the manufacturers provide a specified amount that is augmented by extra refrigerant to accommodate longer lines.
In other small commercial systems you simply need to keep the dip tube in the receiver submerged at all times.
In big low temperature freezers, it was an accepted practice at one time to ?borrow? refrigerant to accomplish the pull down, then when the system was at its running temperature, take the excess out, as it was not needed.
I don't know that this is used much nowadays because of emission rules.
So, in my opinion, whatever the system type, there is no rule of thumb, except one:
Know what you are doing.
.
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herb scales