So you want to build a system

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.

True. If you are shopping for a compressor. Most of us find a compressor at the junk yard, or get an old refrigerator for free.

And then the question is: 'With this compressor, can I get decent enough performance to justify all the work?'

But the statement that the captube is the single most important device in the system is very true.

Hmm, then you maybe can help me to determine the lenght of the captube im going to use?

Heatload: Around 100w (GPU)
Refrigerant: R134a
Type of system: Direct-Die
Evaporator: http://www.xtremesystems.org/forums/...threadid=24702 (it's made 3,5x3,5cm and the bottom is 3mm thick.
My condenser is a Car a/c condenser with 3/8 fittings. The drier i bought has 1/4" fittings. The tubing i'm going to use is 1/4" for the discharge and 1/4" for the liquidline. Suctionline: 3/8".

Does that sound good? i choosed the tubing that was on the freezer the compressor came from.

The jury is still out on cap tube sizing for these systems, but my best guestimate would be 8 feet of .028 cap tube for 100w with R134A.

Others may have tested this combination and can give you a better guestimate.

Pretty anoying to be pionering something :P. No fit lengths or formula's for cap tube ^^

It's like the transmission in your car. Low gear gives you lots of power but not much speed. High gear doesn't give you as much power, but goes to a much higher speed.

A less restrictive cap tube gets there faster, but the temperature isn't as low. A more restrictive cap tube gets there slower, but goes to a lower temperature.

All of the existing cap tube charts assume you want to get there faster. None of them are designed for lowest temperature, which is what we want.

Well Gary you finally got it through my head that I shouldent worry about the compressor :D Anyway:
direct die setup
evap will be a baker block
refrigerent will be propane
heat load I'm not sure. I dont really know the heatloads on high clocked AXPs but I want the system to be future proof so lets just say 200 watts for starters. Is it to high or to low? I douno :p:

What length cap tube do I want to start with?

I would start with about 8 feet of .028 cap tube. That should be good for about 150 watts or so. You can always shorten it a couple feet for higher wattage.

http://www.benchtest.com/calc.html
there ya go afireinside :)

Nice link. You should add that to the 'where to look for information' sticky. :D

Thanks for the link :D

Anyway I always here like 10 feet and stuff... Never heard anyone using less than 8... Anyway an AXP at 2.1V and 3ghz (not that I'll hit that :p: ) puts out almost 200 watts of heat so I guess thats what I want to be able to remove...

Whats a prommie capable of removing at stock and aproximitly how much with r404a?

I used about 7.5 feet of .028" in my R134a waterchillers. So, for a direct-die setup you probably want some more. 10 feet of .028" sounds good. For propane, add another two feet, or switch to .026".

a lil off topic here..
do i need receiver , oil sepa on a single stage system ?

no

]JR[

Bump... Just because I think its important. :D