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.
It can also be referred to as a measurement of the energy per unit time of the air flowing through an opening, which is related to the energy that electricity carries through the power cable (wattage).
The airwatt is a useful measurement of vacuum cleaner motor efficiency, since the
power
Power most often refers to:
* Power (physics), meaning "rate of doing work"
** Engine power, the power put out by an engine
** Electric power
* Power (social and political), the ability to influence people or events
** Abusive power
Power may a ...
carried by a
fluid flow
In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) an ...
(in the case of a typical house vacuum the fluid is air) is equal to
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country a ...
times
volumetric flow rate
In physics and engineering, in particular fluid dynamics, the volumetric flow rate (also known as volume flow rate, or volume velocity) is the volume of fluid which passes per unit time; usually it is represented by the symbol (sometimes ). I ...
. 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 may have a difference in efficiency and thus have substantially different airwattage.
Definition
The formula used to compute airwattage differs between vacuum cleaner manufacturers. The standard airwatt formula is from
ASTM International
ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, ...
(see document ASTM F558 - 13)
:
Where ''P'' is the power in airwatts, ''F'' is the rate per minute (denoted cu ft/min or CFM) and ''S'' is the suction capacity expressed as a pressure in units of inches of water.
Some manufacturers choose to use the fraction rather than the ASTM decimal, leading to a less than 0.25% variation in their calculations.
:
Where airflow in Cubic Feet per Minute
FMis calculated using
:airflow = / vacuum
Where D is the diameter of the orifices.
CFM is always given statistically at its maximum which is at a opening. Waterlift, on the other hand, is always given at its maximum: a 0-inch opening. When waterlift is at a 0-inch opening, then the flow rate is zero – no air is moving, thus the power is also 0 airwatts. So one then needs to analyse the curve created by both flow rate and waterlift as the opening changes from ; somewhere along this line the power will attain its maximum.
If the flow rate were given in litres per second (L/s), then the pressure would be in kilopascals (kPa). Thus one watt equals one kilopascal times one litre per second:
The ratio between the Airwatt rating (power produced in the flow) and electrical watts (power from voltage and current) is the efficiency of the vacuum.
Ratings recommendations
Hoover
Hoover may refer to:
Music
* Hoover (band), an American post-hardcore band
* Hooverphonic, a Belgian band originally named Hoover
* Hoover (singer), Willis Hoover, a country and western performer active in 1960s and '70s
* "Hoover" (song), a 2016 ...
recommends 100 airwatts for upright vacuum cleaners and 220 airwatts for "cylinder" (canister) vacuum cleaners.
References
{{reflist
Units of power