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 air watt formula is from ASTM International (see document ASTM F558 - 13)[4]

Airwatt = 0.117354 * F * S

Where F is the rate of air flow in CFM (Cubic Feet per Minute) 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 orifice plate

Air Watts = ( Vacuum suction (inches of water) x Air Flow (cubic feet/minute)/8.5 
Air Flow (CFM) = √13.35 X D^2/Vacuum suction

Where D is diameter of orifice holes[6]

In terms of litres per second (L/s).

1 L = 0.035315 ft<sup>3</sup> <ref>http://www.metric-conversions.org/volume/liters-to-cubic-feet-table.htm</ref>
1/s = 60/min 
F = 60 × 0.035315 × <''airflow'' (L/sec)> = 2.1189 × <''airflow'' (L/sec)> 

In terms of kPa or mbar as vacuum cleaner suction measurement.

1 pressure in [[inches of water]] ≈ 2.49 mbar ⇒ 1 mbar = 1/2.49 inH2O
1 pressure in [[inches of water]] ≈ 249 Pa = 0.249 kPa ⇒ 1 kPa = 1/0.249 inH2O
S = 1/2.49 × ''suction'' (mbar)
  = 1/0.249 × ''suction'' (kPa)
cleaning power (air watts) = 0.117354 × [ 2.1189 × <airflow (L/s)> ] × [ 1/0.249 × <suction (kPa)> ]
cleaning power (air watts) 
                            ≈ 0.998 × <airflow (L/s)> × <suction (kPa)>
                            ≈ 0.0998 × <airflow (L/s)> × <suction (mbar)>

Alternative measurement formula[edit]

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

Vacuum cleaners[edit]

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

References[edit]

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