Here's a description of my latest quiet PC cooling project. I was running a computer with a Zalman "flower" heatsink with a 120mm NMB fan blowing on it, but even with the fan slowed down, it was too loud when running at a CPU temperature under 50°C.
- ECS K7S5A motherboard
- Athlon 1.4 GHZ CPU
- 256 Mb DDR RAM
- 80 Gb Barracuda IV hard drive
- Plextor 12/10/32A burner
- Generic 48X CD ROM
- Generic floppy
- Aopen GeForce 2 video card
- Generic case
- 300 watt Codegen power supply-fan replaced with 80mm Pc Power and Cooling "Silencer"
I had water cooled once before using a homemade copper water block, Danner pump, and a Toyota Supra heater core as the radiator with a 120mm fan blowing through it, but the heater core fins were too closely spaced to get a good air flow. To keep the temperatures down meant running the fan at full speed. Not quiet. For this project, the waterblock and pump were used again.
Early on, I decided to try to make a fanless radiator. The inspiration came as I was looking at the radiators in our house. We have hot water heat with baseboard radiators. They are a copper tube with aluminum fins along the length of the tube. At one point, I was just going to buy one of these and mount it behind my desk. Without a fan, though I didn't feel it was the right solution. The answer was to mount a radiator in a chimney and use the difference in temperature at the ends of the chimney to generate an airflow.
The formula used to calculate airflow in a chimney is:
Q = 60 * Cd * A * sqrt(2 * g * (Ht - Hb) * ((Ti - To) / Ti))
- Q = flow rate in cfm,
- Cd = 0.65 (for unobstructed openings)
- A = opening area, square feet
- Ti = indoor temp (Rankine) (The temperature of the heated air measured at the top of chimney...Joe)
- To = outdoor temp (Rankine) (The temperature of the air entering the chimney...Joe)
- g = gravity.
Here's a website that explains stack effect and has a Java calculator to make calculations a lot easier:http://chuck-wright.com/calculators/stack_effect.html
**Thanks to Rusty075 for the formula and website**
Plugging in the dimensions and measured temperatures for the completed radiator gives a theoretical airflow of 14.28 cfm. Not bad for no fan. An interesting note is that as the temperature of the cooling water rises, the airflow rises, too. More airflow in response to more cooling needed. Very nice...
The completed unit is made from two boxes of 1/2" particle board glued with yellow carpenter's glue. Carpeting is used in several places to quiet vibration from the pump. It's filled with about three quarts of distilled water. Click on any of the pictures to enlarge them.
The top box houses the radiator and is 8" wide x 8" deep x 31" high with two 4" x 6" holes for cool air to enter near the bottom. It has a layer of carpeting on the inside bottom. In addition, the boxes have a layer of carpeting between them. The rectangular clear box is the resevoir, made of 1/4" thick acrylic.
The radiator is made of four 3/4" copper tubes with seven 1-3/16" x 12" copper fins soldered to each tube. They are connected with soldered copper elbows and form a continous loop with the resevoir inline after the first tube.
The bottom box houses the pump and is 10" wide x 9" deep x 8" high, covered on the inside with carpeting. Foam rubber is used to seal any openings in the box. The black strip on top of the board is 1/16" thick black self-adhesive foam from WalMart.
The pump is mounted to a board that drops into the bottom box. The pump is suspended on small stretch cords to isolate it from the board. The vertical wood strips are just there to hold the board up for photographing. The black layer on top of the board is more of the WalMart foam.
The cooler is connected to the waterblock with 1/2" silicone tubing, reduced to 3/8" at the waterblock. The water flow goes from the pump to the radiator/resevoir to the waterblock and back to the pump.
So, how well does it work? As I'm writing this, the computer has been on for five hours and MBM5 reports the CPU temperature at 44°C with a 21°C ambient temperature. The only noise is a slight hum from the pump and a bit of noise from the power supply cooling fan, the only fan in the system. The CPU temperature rises as high as 47°C under stress.
I'm quite happy with this setup, but wondered how the cooler would perrform with a fan placed on top. I did some testing using the SiSoft Sandra Arithmetic Benchmark Burn-In running for 15 minutes to stress the CPU.
Three tests were done, first with no fan, then with a 120mm fan running at 8 volts-about the same noise level as the power supply fan, and last the 120mm fan running at 12v.
The test schedule:
- 0 min No fan Cpu at normal operating temperature
- 0 min Start burn
- 15 min Stop burn-in
- 30 min Fan at 8 volts
- 45 min Start burn-in
- 60 min Stop burn-in
- 75 min Fan at 12 volts
- 90 min Start burn-in
- 105 min Stop burn-in
- 120 min Stop test
The results were not as dramatic as I had imagined. There was only a 2°C differencu in CPU temperature from no fan to really noisy fan. The following graph shows the results. The temperatures are in increments of 1°C because that is the limit of accuracy for the motherboard sensors.
It looks like I'll be using the cooler for quite a while. It is quiet enough and cools well enough for me. In the future I'd like to make a smaller resevoir and veneer the outside to make it look a little better.