A recent peer-reviewed study explains how the Mitsubishi Jet Towel® is the best hand dryer for our planet.

The Materials Systems Laboratory at MIT recently reviewed seven hand drying systems, finding hands-in hand dryers to provide the lowest Global Warming Potential (GWP) of any hand drying method, including recycled paper towels. This study found that "dyer impact is dominated by use and dryers with similar dry times (and power ratings) will have similar impacts"1 and while packaging, transportation, and other non-operational factors do contribute to a dryer’s impact, they only account for 3% to 14% of the GWP.2 Since the Jet Towel® has the lowest power rating of any dryer in its class - 1060 watts - we would like to demonstrate how the Jet Towel® is the best hand dryer for the environment.

Calculating GWP

This study compares hand drying methods by the GWP for one use. To calculate the GWP of one use of the Jet Towel®, we multiply Ecoinvent’s GWP coefficient for one MJ of electricity (0.232 kg per MJ)3 by the sum total power required to operate the Jet Towel® for 12 seconds plus the power required for standby. The Jet Towel® uses 1060 watts to dry hands in 12 seconds and 2 watts per day on standby.

Power from Use

For power consumption in use, we simply multiply watts by time in use and divide by the number of seconds in an hour (3,600):

Euse = (watts per hour) (seconds in use) / seconds in one hour

Euse = (1060) (12) / 3,600

Euse = 3.53 watts per dry

Power from Standby

To accurately calculate one use’s power consumption from standby, we must first discover the average number of seconds in standby mode for one use. This study assumes 350,000 uses over a 5-year life span, or 192 uses per day. One day has 86,400 seconds, so to find the number of seconds the Jet Towel® is in standby we must subtract the number of seconds from operation. For 192 uses at 12 seconds, the Jet Towel® is in use for 2,304 seconds each day. Once we subtract this from the number of seconds in a day, we know the number of seconds per day that the Jet Towel® is in standby. As we are calculating a per use number and the Jet Towel® is used 192 times per day, we then divide the number of seconds in standby by 192. As a formula, it looks like:

tstandby =

86,400 – (192 * 12)

192

tstandby = 438 seconds per use

The Jet Towel® uses 2 watts per day on standby, so our formula for standby power per use is:

Estandby =

(Standby watts per day) (standby seconds per use)

Seconds in one day

or:

Estandby =

(2)(438)

86,400

Estandby = 0.01 watt per use

So our total per use energy consumption for the Jet Towel® is 3.54 watts.

GWP per Use

The study in question operates on kilojoules and to convert watts to kilojoules we multiply by 3,600, since joules equal watts per hour. In kilojoules, the Jet Towel® uses

12.76 kJ

per dry. To find the GWP of the Jet Towel®, we simply multiply the Ecoinvent GWP by our KJ number. As the coefficient is in MJ per kg of CO2, multiplying the coefficient by our kilojoules number will provide us with the g of CO2 per use since both numbers are lower by a factor of 1,000. It is:

GWP = (kilojoules) (GWP CO2 coefficient)
GWP = (12.76) (0.232)
GWP = 3.0 g of CO2

Additional GWP Considerations

Energy use is the predominant force for hands dryers, but shipping, packaging materials, and other non-use factors do affect GWP. This study found that non- use factors contribute from minimum 4% to maximum 13% of a hand dryer’s GWP. When we factor in secondary GWP factors using our 3.0 g finding, we see:

4%: use = 3.0g (96%) packaging, etc. = 0.1g (4%) Total: 3.1g

13%: use = 3.0g (87%) packaging, etc. = 0.6g (13%) Total: 3.6g

Comparative Calculations

To support our claim of Best Hand Dryer for the Environment for its class, we need to apply the same logic to other dryers. The following graph shows findings from the same calculations applied to other dryers. Specifications are drawn from manufacturers’ websites.

Metric

Jet Towel®

Dyson Airblade

SaniFlo

Bio Jet

Dry Time

12 seconds

12 seconds

12 seconds

12 seconds

Watts

1060

1400

1750

1100

Standby Power

2

1

1

1

Total Energy Per Day

3.5

4.7

5.8

3.7

Kijoules Per Dry

12.8

16.8

21

13.2

GWP Per Ecoinvent

3.0

3.9

4.9

3.1

GWP at 4% Secondary Materials

3.1

4.1

5.1

3.2

GWP at 4% Secondary Materials

3.6

4.7

5.8

3.7

Conclusion

The above table shows that even with packaging, transportation, and other variables factored into the equation, the Jet Towel® provides the least impact on the environment. Even with variables set to a high GWP percentage for the Jet Towel® and low for other dryers, in all but one scenario the Jet Towel® impacts the planet the least, showing why the Jet Towel® is the Best Hand Dryer for the Environment.

Resources

All facts and figures derived from the following study: http://msl.mit.edu/ publications/HandDryingLCA-Report.pdf

Citations:

1) p.25
2) p.34
3) p.89