Airwatt

Airwatt or air watt is a measurement unit of the effectiveness of vacuum cleaners which refers to airflow and the amount of power (watts) a vacuum cleaner produces and uses.[1][2] It can also be referred to as a measurement of the energy of the air flowing through an opening which is the same as the energy that electricity carries through the wire (watt).[3]

The airwatt is a useful measurement of vacuum cleaner motor efficiency, since the power carried by a fluid flow (in the case of a typical house vacuum the fluid is air) is equal to pressure times volumetric flow rate. The airwatt relates to actual airflow, while part of the electrical power (watts) consumed by a vacuum cleaner is dissipated into heat due to necessarily imperfect efficiency; two vacuum cleaners of the same airwattage have essentially the same suction, while devices of the same electrical wattage produce a difference in efficiency and may have substantially different airwattage.

Formula

The formula for airwatt differs between vacuum cleaner manufacturers.

The standard airwatt formula is from ASTM International (see document ASTM F558 - 13)[4]

$P = 0.117354 \cdot F \cdot S$ Where P is the power in airwatts, F is the rate of air flow in cubic feet per minute (denoted cu ft/min or CFM) and S is the suction capacity expressed as a pressure in units of inches of water. This makes one airwatt equal to 0.9983 watts.[5]

Below are some of the published formula of airwatts by different vacuum cleaner manufacturers

In terms of the orifice plate,

 Air Watts = Vacuum suction (inches of water) x Air Flow (cubic feet per minute)/8.5 Air Flow (CFM) = √13.35 X D2/Vacuum suction

Where D is the diameter of the orifice holes.[6]

Using coherent SI units, power equals flow times pressure by definition. That is, where the power is expressed in watts (W), the flow is in cubic metres per second (m3/s) and the pressure is in pascals. Since one pascal (Pa) equals one newton per square metre (1 Pa = 1 N/m2), then:

$1~\mathrm{m}^{3} \cdot \mathrm{s}^{-1} \cdot 1~\mathrm{N}\cdot \mathrm{m}^{-2} = 1~\mathrm{N}\cdot \mathrm{m} \cdot \mathrm{s}^{-1} = 1~\mathrm{J}\cdot \mathrm{s}^{-1} = 1~\mathrm{W}$

The power of the flow times the pressure will always be less than the power applied via the voltage and current (1 W = 1 V·A). The ratio of the power produced in the flow and pressure divided by the power from the voltage and current is the efficiency.

Alternative measurement formula

 cleaning power (air watts) = airflow (CFM) × suction (inches of water) / 8.5

If the flow rate were given in litres per second (L/s) instead of cubic metres per second (m3/s), then the pressure would be in kilopascals (kPa). Thus one watt equals one kilopascal times one litre per second: $1~\mathrm{W} = 1~\mathrm{kPa} \cdot \mathrm{L}\cdot\mathrm{s}^{-1}$

Vacuum cleaners

Hoover recommends 100 airwatts for upright vacuum cleaners and 220 airwatts for cylinder vacuum cleaners.[7]

References

• ASTM Standard F558 Standard Test Method for Measuring Air Performance Characteristics of Vacuum Cleaners