Airwatt

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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."What is an airwatt?". 

Formula[edit]

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[edit]

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[edit]

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

References[edit]

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