Every now and then the discussion comes up in forums where someone gets the idea that they want to run their radiators passively without out any fan power at all. The discussion recently came up again and I decided to dig out some old test data and share a quick blog on what I found back on my V1 test bench while testing a low density double thickness 480 sized radiator.
When I was testing my TFC480 radiator back on my V1 test bench, I tried exactly that. I even dialed down the heat to a bare minimum 100 watts to test a very small (perfect conditions) scenario. The TFC 480 radiator is a premium double thickness low density radiator that performs really well with low speed fans, so I figured it would be the pefect test case.
So I proceeded to use my very smallest heater, and in the optimal open bench setting with the radiator pointing upward proceeded to test at 100W heat load.
1 hour went by….still not stable
2 hours went by…temps still climbing…
Almost 3 hours later, temps are still climbing…The tubing was hot to the touch and I began to worry about my heaters fracturing in their glass tubes and decided to call it quits. This is what that test data log looked like:
I consider an “Average” radiator setup performance to be around a 10C water/air delta and the radiator nearly doubled that on this incomplete test. Perhaps you could get passive to work in a case where you had a power supply pulling air through the case and radiator, but then that’s not really passive is it?
Bottom line, passive operation on conventional radiators just doesn’t work well enough to consider it a useful option. I would ask why bother when 600RPM fans are quieter than a mouse fart anyhow…:)
It would take a very different type of radiator and much much larger surface areas for passive to work well.