Contrary to popular belief, the center of the refrigeration system is not the compressor, nor is the compressor size the primary consideration. The lord and master of the system, the center of the refrigeration universe, is the metering device (cap tube, TEV, EEV, AEV, etc.). The most important question asked in these forums is not, "What size compressor?". It is, "What size cap tube?".
So... Where to start?
Your first question is, "What do I want to cool, and what is its heat output?".
Next, "How do I want to cool it, direct die evaporator or water chiller?".
We can now select an appropriate evaporator, capable of transferring the heat from the cooled product to the refrigerant.
Then, "What refrigerant am I going to use?".
Knowing the heat load and the refrigerant, we can now select the right cap tube (or other metering device) for the job.
Knowing the heat load, which is limited by the metering device, we can add heat of compression (25-50%) to heaviest heat load, and select a condenser/fan combination capable of dissipating the required amount of total heat.
We can also select the proper connecting pipe sizes for the refrigerant flow.
Then we can braze/solder it all together.
But wait. Did anyone notice something missing from our new system? We have built a system, minus the compressor.
It's kinda like building a car and then selecting which engine we want in it, the little economy four banger, or the big powerful V8, or any of the sizes in between. They will all move the car, but some will move it faster.
As I see it, the compressor should be the last item on the shopping list, not the first.
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