DIY fan test chamber
Starting this to help anyone looking to test the CFM performance of their fan project. I was not able to find anything credible on the web while researching various fan CFM ratings so I decided to figure out how to get it done myself.
The link to the thread on that got me here...
I am using this anemometer to measure the CFM of the fans, it has an averaging function that will take 20 samples and average them. It will also give min/max values along with the average.
AN100 - CFM/CMM Mini Thermo-Anemometer
and using this DC Clamp meter. Unfortunately it does not have a peak hold function so I cannot provide that info.
MA435T - 400A True RMS AC/DC Clamp Meter + NCV
Started out with 1 4x8' sheet of plywood. Did the math against my radiator core and found I was able to cut the test box out of 1 sheet. I did find some errors I made in calculating the cuts. I forgot to include the thickness of the wood for some of the cuts so I ended up having to imrovise as I built it.
My design is intended to allow to connect to the factory radiator which has a 27x30.5" core. The idea is to be able to swap in a plate with the fan mounted to an interface box and measure its performance through a 12x12x21" duct. After building this fixture and firing up the fan it occured to me that this setup is not a true free air flow setup since it is drawing through the 12x12" port so the measurements I'll get out of it will be partially loaded. I think to get this right I'd need a duct with the area of the fan connected to the interface box. I may change the 12x12" measurement box to match the fan dimensions. Not 100% sure yet.
On paper draw up your fan test box and see how the cuts would need to be made so you can use 1 4x8' of plywood. Dont forget to include the wood thickness.
Once I had mine cut & I was ready to assemble I started on the smaller box. I used small brackets with counter sunk screws that would allow me to keep the interior of the measurement box free of obstructions. When tightening up the brackets you can sink the screw heads on the inside of the measurement box pretty easy.
completed measurement box
Next build your interface box
Test fit onto radiator core
Add measurement box panel and cut out opening for measurement box. In my case it was exactly a 12x12" opening.
Mouth the measurement chamber to the interface chamber
Next on the fan mounting plate, cut an opening equal to the fan blade. I beleive the if a fan is attached to an existing shroud it can be mounted to this plate. All openings that are not sealed against the fan mounting plate will need to be sealed.
Next mount the fan to the fan mounting plate
Next mount the fan mounting plate to the interface box and you should be ready to go. In this pic I have everything stacked on top of the interface box. Fan is mounted below, battery, relay conections are also below.
While this is not finished, still need to seal the measurement box and attach to interface box, it's should be clear as to what needs to be done to finish it off.
To take measurements you will need to mark 8 spots on the measurement box, 2 on each side and collect the CFM data from each position. oNce all of the measrements are taken, average the 8 readings, the average of all 8 readings should be a good indicator of the fans capabilities measured in CFM. If you are using a 12x12" measurement box then you need to keep in mind that there is a load on the fan and it is not a free air test.
If you want to have 100% free air test then the measurement box needs to be larger than the area of the fan (I think) and the dimensions need to be plugged into a CFM calculator. I recommend calculating the area of the fan blade and go just over it.
DO NOT FORGET TO FACTOR IN THE SENSOR HEAD AREA IN YOUR CALCULATIONS FOR MEASUREMENT BOX AREA.
Circle Area Calculator
Rectangle Area Calculator
ENGINEERING.com | Air Flow Conversion Calculator
My fan... a '97 volvo 850 fan seems to pull really hard and it will be interesting to see how it does.
If anyone repeats this work with another fan and collects some data please feel free to add it here. (if the thread is closed contact a moderator and have them open it, they will be happy to do it). It would be nice to have good solid data for anyone else who is looking for it. I know it was all hearsay on what the taurus fans & volvo fans pull
If I blew it somewhere and need to be set straight, feel free to let me know. :thumbsup:
I marked the measurement box with 3 positions on each side for 12 data points total. There is a small lip on the probe that allows me to place the probe within the marks and give me repeatable locations for measurements.