A Heat Transfer Approach to Sleeping Bag Ratings Moises Alcevedo Jordan Ryskamp.

A Heat Transfer Approach to Sleeping Bag Ratings

Moises Alcevedo

Jordan Ryskamp

A Heat Transfer A Heat Transfer Approach to Sleeping Approach to Sleeping

Bag RatingsBag Ratings

Modes of heat transfer

A Heat Transfer A Heat Transfer Approach to Sleeping Approach to Sleeping

Bag RatingsBag Ratings

FactorsRating

Heat Generation Thermal Resistance

Gender Metabolism

Food Exercise level

Hydration Weight

Insulation Clothing

Fit Tent

Shape Moisture

A Heat Transfer A Heat Transfer Approach to Sleeping Approach to Sleeping

Bag RatingsBag Ratings

Different Standards

• Ratings are given as a temperature

• Manufacturers pick their ratings

• Many are “optimistic”

• No recognized standards

• Make different assumptions– Young male in a tent wearing thermals – Older larger female sleeping under the stars

A Heat Transfer A Heat Transfer Approach to Sleeping Approach to Sleeping

Bag RatingsBag Ratings

Our Project

• Use heat transfer principles to compare bags• All bags are limited by the amount of insulation• Approximate as cylinder

Sleeping bag, ( Rcond)

Air inside,( Rair in)

Body ( q gen. Ti)

Air out (To, Rair out)

A Heat Transfer A Heat Transfer Approach to Sleeping Approach to Sleeping

Bag RatingsBag Ratings

Properties and AssumptionsFillings of sleeping bags• Feathers

k=0.02 mK / W

• Polyguard Delta k= .041 mK / W• h= 5

– Why? Rcond < Rconv = 1/ h

• No radiation– Why? Low temperature

A Heat Transfer A Heat Transfer Approach to Sleeping Approach to Sleeping

Bag RatingsBag Ratings

Thermal Circuit

Rair in Rcond Rair out

Ti To

Rtotal = Rair in + Rcond + Rair out

Rair in = 1/hA = 1/h2RbodyL

Rcond = Ln(Rout s.b./Rin s.b.) / 2kL

Rair out = 1/hA = 1/h2Rout s.b.L

A Heat Transfer A Heat Transfer Approach to Sleeping Approach to Sleeping

Bag RatingsBag Ratings

Solution and Conclusion

• qV = ∆T / Rtotal

= Ti - To / Rtotal

To= Ti - qVRtotal

Currently found online at www.littlegreendesigns.com/Sleepingbags.aspx

Model does not give accurate results. However, it does give a good method of comparison.