the btu debate over cooling power..

[hello im sean]

Okay so I was wondering why a lot of people around here seem to believe a 5200 btu a/c system is only good for an oc'd cpu? The conversion for btu to watts is 1 watt = 3.413 btu's so a 5200 btu system should have 1523.6 watts of cooling power, a top end oc'd cpu maybe puts out 300 watts of heat? That still gives a lott of head room for gpu's, nb, ram, etc.. sure the pump and lack of perfect insulation takes some of that cooling power away but still most computers today won't go over 1500 watts of heat.. so wouldn't I be good to use a 7000 btu system (2050.1 watts of cooling) for my whole rig? With dual oc'd gpu's, oc'd cpu and ram and nb all hooked up to the loop? I doubt that'd break 1500 watts of heat even..? Any input here?

[JWB]

Well firstly a lot of people dont know about waterchilling and what that involves. Now your unit is rated at 5200 btu for cooling a room. So in an hour it take that much heat out of the room at its maxium. When conected to a chiller you are cooling a liquid instead of a gas (the air in the room) so the btu will have changed. When you are cooling to a lower temp say -20C instead of 10C your system will be less efficient and have a lower btu rating. The system is rated to cool 5200 btu an hour but you want to cool say 300W to a lower temp constantly. These are the reasons why people think that. For a cpu you should be fine. The reason we can use waterchilling for lots of diffrent components is because ours systems will cooling the liquid we are using to its low temp (say -20C). Then you turn your computer on and the computer will have to warm the entire amount of liquid we have for you to notice a temp difference in your cooling (although not on your cpu because that will be ever changing by say a few degrees from idle to load etc). What your 5200 btu system will be doing is maintaining the coolant temp at -20C. You are using your coolant to not have major temperature swings. Lol sorry my explanation skills arent very good lol. For a system where you want to cool a current generation cpu, n/b, mosfet, sli/cross fire setup. I would advise you to gte a bigger system with the compressor and condensor strong enough to cool that, such as a 12,000 btu system. Your 5200 btu system COULD do it but the coolant temps would be higher.

Erm hope that helps, I think my explanation has been rubbish though. I don't want to try and make it too confusing, but lets say when using a chiller your system will not be producing 1523.6 watts of cooling power. My chiller is 11,000 btu (I think its 12k but anyway...) is supposed to be able to cool 3200W...yes three thousand two hundreds watts. In reality cooling my liquid coolant to the -31C temps its doing I bet its at say 800W at -25C as a guess.

I'm sure a lot of people will have better knowledge and can explain it better though

James

This link might be of some help. It explains how pressures and mass will changed how many btus are need to heat something and therefore cooling something

http://www.refrigerationbasics.com/1024x768/rb1.htm

[hello im sean]

Okay I see what you mean, the lower the temp you'd like to hold gets the more the cooling capacity for that temp decreases got it, I'm curious, how much did you get your 11,000 btu system for and from where?

[underdog1425]

Air is really just a fluid anyways, but I am in the boat of not knowing enough to really provide much more valuable input other than that ^_^

You will still face inefficiencies in water block quality and exchanger design though. I wonder when you start running into diminishing returns with volume of liquid versus cooling efficiency...its prob a function of exchanger design, block quality, pump heat dump etc etc.. don't even want to begin to think of what kind of math and thermo(and fluid)dynamics is going on here.

[JWB]

Well some people have gone down to -50c with there chillers in a single stage. Gomeler was making a dual stage (cascade) for -80/-90 but I'm not sure if he is carrying it on anymore. Chillers that use a heat exchanger will have a lower temp than one with a res but you will have to run only one loop and have it cool your components in series so i think a res design where you can add or change waterblocks quickly is the way to go IMO . Would love to make a cascade chiler one day but I think the only fluid that won't freeze up and is cheap would be pure ethanol but it is very flammable and your loop would have to be totally sealed because of the ethanol vapor being extremely flammable. Well I think the simple answer to the question is the lower temp you go the lower your capacity for cooling is. Thats why when you tune the amount of charge in your system that you dont remove too much because even though your evap/liquid would get colder it could not hold that temperature very well when a load was put on to it.

Sean my unit brand new was £100 which is $153.5 dollars. An identical unit with a sanyo badge is I think 3 times that much! I got a great deal ATM I am thinking of cutting her up and laying her out like a window AC unit so I ca fit it under my desk. Although I would lose the great benefit of being able to just wheel it anywhere I want it. It means though I can add shreader valves to the system and tune the charge for the load I would be using. Plus sorting my condensor cooling out lol!

James

[underdog1425]

@JWB A res design is typically better but I think you confused my post up a bit. Dropping the evap into a res is still a 'heat exchanger' but not in the sense of a plateHX. I wasn't bashing that design at all, the only reason my personal chiller doesn't use a submerged evap design is space and funding limitations.

What it comes down to is what you want to do with the system. If you need it to be portable then a smaller res/evap design works much more in favor but you wouldn't have the luxury of huge volumes of fluid and the ability to run multiple loops.

[JWB]

Yep Underdog totally agree! Lol sorry if there was any confusion I didnt think you bashed any design lol . I did think you meant plate HX though :P. If I was using one loop for cpu for instance I would use a plate hx because of the colder temps and the space saving. Hopfully Sean has gained a little bit of info from this thread . I'm going to change my system because I'm now benching with DI and I want to create a purose built system not a converted AC. Temps lower than -40C for the cpu and mosfet and n/b, which would be in 2 loops. But I would be doing it gradually and using my current compressor and other components due to a lack of $$$ :S,

James

[underdog1425]

That's pretty much what I started with was salvaging my ac but purpose building my own little pipe exchanger with a coil inside. We did kind of threadjack him but its all on topic IMHO =]

[hello im sean]

Nah I don't mind guys, haha I wish I could make a purpose built system.. but all the recycling and charging equipment is so expensive

[hello im sean]

Actually does anybody know what temps a 5200 btu unit could hold a 1000 watt heat load at..? Is there an equation for this?