Measuring Airflow

[marc5180]

What is the general rule of thumb to determine enough airflow for condensors and evaporators? I've read that is around 300 cubic feet per minute per kw, is this right?

Also i have the testo 510-2 that measure airflow, temperature and humidity but it measures airflow in metres per second or feet per minute.
How do i convert cubic feet per minute to feet per minute?

[Brian_UK]

Take area of grille, coil etc.

Width x height in metres or feet-inches

Metric:-

1.5m x 0.5m = 0.75 sq.m.

Measured velocity in m/s

Lets say m/s = 2.5

Volume or air flow rate = 2.5m/s x 0.75sq.m = 1.875 cu.m/s

Imperial would be ft x ft x fpm = cfm.

When measured airflow across the coil using an anemometer divide the coil face into equal areas and take a velocity reading in the centre of each area. Then take the average of those readings.

[Abby Normal]

that will work with return grilles the air is not jetting out of them

for supply grilles you need to get an "Ak" factor or "Free area" to correct the jetting air stream's velocity

[mzk2009]

I have thermo king sbIII it is 1996, whats is corectly arpm in my unit.
thanks

[Brian_UK]

Some duct measuring details here for position of anemometer/pitot static tube.

http://www.omega.co.uk/green/pdf/AIRFLOW_MEAS_REF.pdf

[marc5180]

Thanks Brian, i'll have a read through that.