Sleeping Bag Comparison
Which sleeping bag will keep you warmer?
By: Kyle Layton and Ben Salazar
Introduction
• Camping is fun, but can be cold, especially in the winter.
• Many companies make claims that their brand of sleeping bag is better at keeping you
warm in cold conditions
Research Objective:
• We want to compare two sleeping bags that have very similar materials and
specifications but drastically different prices and experimentally find out which is more
effective at retaining heat
• We will do this by deriving a heat transfer rate for the different forms of heat loss
• We will then plug in values for each sleeping bag that we measure in our experiment
and obtain the heat transfer associated with each sleeping bag
• We will compare these values and determine which brand of sleeping bag is better at
keeping a camper warm
Introduction – sleeping bags
• Sleeping bag 1 – Ledge
Mummy Sleeping bag
• Operating temperatures: +
20º F
• Price: $60.00
• Sleeping bag 1 - Northface
Mummy Sleeping bag
• Operating temperatures: +
20º F
• Price: $200.00
Which is better?
Methods
Materials used:
• 2 Small Zip-Loc bags large enough to
fit 500 ml of liquid
• Beaker
• Water
• Microwave
• Two sleeping bags of the same size
and style, but different brands
• Infrared thermal laser digital
thermometer
• FLIR E5 compact thermal imaging
infrared camera
Assumptions:
• Zip Loc bags have uniform surface
temperature
• Zip Loc bags can be approximated as
as spheres with properties of water
• Sleeping bags can be approximated
as flat surfaces
• Floor can be treated as a semiinfinite solid
• Thickness of material of sleeping bag
can be neglected due to compression
• 1-D heat transfer
Methods
• Filled Zip-Loc bags with a
fixed volume of warm water
• Measured water volume using a
beaker: 475 ml = 475 x 10-6 m3
• Heated water to 49º C using a
microwave
• Measured the temperature of
water, the room, and the
sleeping bag using an infrared
thermal laser digital
thermometer
• Placed Zip-Loc bags in sleeping
bags and monitored
temperature of both the
sleeping bag and the Zip-Loc
bag over a 45 min time
interval.
• Took thermal images using FLIR
E5 Compact Thermal Imaging
InfraRed Camera for
visualization purposes
Methods
• The bag of water at 49º C is assumed to heat at least a small portion of the sleeping bag.
• If we approximate the patch of sleeping bag that was heated as a small plate we can use the
following equations:
• Using these values, the Rayleigh number was calculated for each corresponding measurement: Ra
= Pr(Gr)
• This gave us a way to calculate the average h value for surfaces
• Then, using the equation Qair = hA(ΔT*t), we calculated the heat transfer between each
measurement through free convection.
• The total heat loss through the air was found by summing values for these Qair values( see
appendix)
Methods
• Heat transfer through the ground was calculated assuming a semi-infinite
solid in contact with a uniform temperature surface, using:
• For each measurement, similar to the procedure outlined for Qair, q” values
for each time interval were calculated and then summed
• Heat loss through the air (Qair ) and through the ground (q”) were then
summed to determine the total heat loss
Results – Thermal images
Sleeping bag 1 – Ledge Mummy sleeping bag
Qtotal = 8970 W/m2
Results – Thermal Images
Sleeping bag 2 – Northface Mummy sleeping bag
Qtotal = 7890 W/m2
Conclusion
• A slight difference was detected between the two sleeping bag brands
• At Qtotal = 7890 Sleeping bag 2 more effectively retained heat and thus
would keep a camper warmer
• This represents a 12% better heat retention
• Despite its better performance, we do not believe this justifies the
$140 price difference between the two products
• We therefore recommend the use and purchase of the less expensive
and still effective sleeping bag
Appendix – Experimental Measurements
Ledge
Time
0 min
Ts
Ts Kelvin
5 min
10 min
15 min
20 min
25 min
30 min
35 min
40 min
45 min
26
32
30.3
28.5
29
28.5
27.5
28
27.5
27.5
299.15
305.15
303.45
301.65
302.15
301.65
300.65
301.15
300.65
300.65
Northface
Time
Ts
Ts Kelvin
0 min
5 min
10 min
15 min
20 min
25 min
30 min
35 min
40 min
45 min
27
28
28.5
28.8
29
27.5
27.5
27
28.5
26
300.15
301.15
301.65
301.95
302.15
300.65
300.65
300.15
301.65
299.15
Appendix – Preliminary Calculations
Ledge
Gr
h
Northface
483172.173 Ra
341119.554
1207930.43
Gr
603965.22 Ra
426399.44
852798.886
724758.26
511679.33
1002582.26
707823.075
785154.78
554319.28
785154.781
554319.276
821392.69
579903.24
845551.303
596959.22
845551.3
596959.22
785154.781
554319.276
664361.74
469039.39
664361.738
469039.387
664361.74
469039.39
724758.26
511679.331
603965.22
426399.44
664361.738
469039.387
785154.78
554319.28
664361.738
469039.387
483172.17
341119.55
3.52358034 Nu
13.0502975
4.43066771
16.4098804
3.8994827
14.442528
4.22900991
15.6629997
3.9782999
14.734444
3.9782999
14.7344441
4.0234296
14.901591
4.05269285
15.0099735
4.0526928
15.009974
3.9782999
14.7344441
3.8155738
14.131755
3.81557375
14.1317546
3.8155738
14.131755
3.89948265
14.4425283
3.7257326
13.79901
3.81557375
3.81557375
14.1317546
14.1317546
3.9782999
3.5235803
14.734444
13.050298
h
3.7257326 Nu
13.79901
Appendix – Final Calculations & Results
Ledge
Northface
Q_air
2449.899329 Q_air
2112.714065
Q_floor
Q_total
6519.085264 Q_floor
8968.984593 Q_total
5774.654646
7887.368711