Pro/Forums - View Single Post - How do I calculate how much rad I really need

bobkoure · 10-12-2004, 07:51 PM

Try breaking the problem down.
Once you have a notion of how much energy you're trying to dump to ambient air (I would guess you're somewhere in the 100 - 120W range) and what delta between ambient and coolant you're willing to tolerate (you can dump a lot of heat through a little radiator if there's a 40C delta). Ignore water flow for this - it doesn't matter.
OK, so that's one part.

The other part is moving heat from the CPU and GPU into the coolant (for the first part of this you just assume it's "magic"). Flow does mater for this (although how much it matters depends on the specific blocks you are using). There's a nice interactive C/W/flow chart (with one line per block) somewhere here at PC - worth looking for... You'll need to know what your flow rate is. You can guess based on your pump's performance curve (beats me what the resistance of your loop is, though) - or you can just set it up outside your PC and see how long it takes to fill a 5 gal bucket (or whatever - you get the idea).

So... now you know as much as I do - go have fun

Bob
PS: For figuring your wattage there's a gizmo called a "Kill-A-Watt" that will tell you how much power you're drawing from a 115VAC circuit. Figure your power supply is no more efficient than 80% - so whatever heat you're getting rid of cannot be more than 80% of the figure this thing gives you. My under-desk box has a XP-M 2600 at 12.5X200, 1G PC2300 mem, 2 optical drives, 2 160G SATA drives, matrox 650 card (less power than your GPU) and never see kill-a-watt readings over 120W - not even when I'm writing to one DVD, reading another, and the CPU usage is at 100% (low priority so the DVD writer doesn't starve) - and I'm running fans, a small motorized impeller and a 12VDV pump on that as well.

10-12-2004, 07:51 PM	#6
bobkoure Cooling Savant Join Date: Feb 2003 Location: USA - Boston area Posts: 798	Try breaking the problem down. Once you have a notion of how much energy you're trying to dump to ambient air (I would guess you're somewhere in the 100 - 120W range) and what delta between ambient and coolant you're willing to tolerate (you can dump a lot of heat through a little radiator if there's a 40C delta). Ignore water flow for this - it doesn't matter. OK, so that's one part. The other part is moving heat from the CPU and GPU into the coolant (for the first part of this you just assume it's "magic"). Flow does mater for this (although how much it matters depends on the specific blocks you are using). There's a nice interactive C/W/flow chart (with one line per block) somewhere here at PC - worth looking for... You'll need to know what your flow rate is. You can guess based on your pump's performance curve (beats me what the resistance of your loop is, though) - or you can just set it up outside your PC and see how long it takes to fill a 5 gal bucket (or whatever - you get the idea). So... now you know as much as I do - go have fun Bob PS: For figuring your wattage there's a gizmo called a "Kill-A-Watt" that will tell you how much power you're drawing from a 115VAC circuit. Figure your power supply is no more efficient than 80% - so whatever heat you're getting rid of cannot be more than 80% of the figure this thing gives you. My under-desk box has a XP-M 2600 at 12.5X200, 1G PC2300 mem, 2 optical drives, 2 160G SATA drives, matrox 650 card (less power than your GPU) and never see kill-a-watt readings over 120W - not even when I'm writing to one DVD, reading another, and the CPU usage is at 100% (low priority so the DVD writer doesn't starve) - and I'm running fans, a small motorized impeller and a 12VDV pump on that as well.