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Laundry equipment - Basic Equations and Conversion Factors



Cylinder volume

                                     (Drum diameter) x (Drum diameter) x (Drum depth)
Volume, liters =          ----------------------------------------------------------------------

Extraction G Force
                                     (Drum rpm) x (Drum rpm) x (Drum diameter)
G Force, G's =            --------------------------------------------------------------
rpm is drum rotation speed in revolutions per minute, drum diameter in millimetres

Moisture retention
                                      (Load weight, extracted) - (Load weight, dry)
% Water retention =    ---------------------------------------------------------------- x 100%
                                                            (Load weight, dry)

% Water retention =  350.1 x (G-force, G's)
This formula will provide an estimate of water retention at given G-force for 100% cotton terry material. Reduce for muslin weave or for blends.


1 kW-hr = 3414 BTU   Kilowatt-hours, kW-hr = (Horsepower, Hp) x .7457
                                    1 kcal/hr = 0.252 BTU/hr

To calculate an estimate of daily electrical consumption, use the following formula for each motor in the laundry, then total the results for all the motors.

Power consumed, kW-hr/day = 0.001732 x (Line voltage, Volts) x (Current, Amps) x (Operating hours per day) x (Power factor)

Power factor can be assumed to be 80% for motors running under constant load.

Water hardness

When washing in hard water, soap consumption will be higher than when using soft water. A water softener is recommended if water hardness exceeds 3 grains.

Water hardness definitions:

 Grains per gallon
Parts per million  Description
 Less than 1  less than 17.1
 1 to 3.5  17.1 to 60  Slightly hard
 3.5 to 7.0  60 to 120  Moderately hard
 7.0 to 10.5  120 to 180  Hard
 10.5 & over  180 & over
 Very hard