Testing the limits of a heat pack in freezing temps

[Dez]

Hello Everybody

I can't believe it is December already. I hope everybody had a lovely Thanksgiving

I conducted a heat pack test trying to push the limits to the extremes to see what the temp in the box would be.

I should have took photos (sorry) but I will try to explain the best I can what I did:

I had a 8x8x6 shipping box insulated on all sides with 3/4 inch stereotype. The box had one very small air hole punched in only one side.

Inside the box I have a plastic pre-punched deli cup. I put a remote themometer inside the deli cup and snapped the lid on.

I unwrapped and started TWO 40 hour heat packs and let them warm up in a towel for about 45 min. I then took the warming packes and wrapped them in newspaper and placed them on eaither side of the deli cup...as if I where packing a real chameleon.

Newspaper was packed in all the loose areas securing the deli cup in the middle.

I sealed up the box and let it sit inside for a two hours to simulate it sitting inside at the UPS center. Them moved outside where it was slightly cooler. I also had a thermometer to measure outside temp.

Heat packs where started about 10:00 and put in the box at about 10:55

TIME / OUTSIDE TEMP / INSIDE BOX

11:00pm / 76 F / 78 F

3:00AM / 70 F / 88.5 F​

Moved box at 3am (yes I got up at 3 am in the name of science) to the refrigerator set on the highest settings (45 F)
After 4 hours at 45 degrees I turned the temp setting of the fridge down to 32 degrees

7:00 AM / 45 F / 68 F

8:00 AM / 41 F / 67 F

9:00 AM / 39 F / 64 F
​

Now I decide to push the results more and put the box in the freezer The freezer is on its highest setting which is 8 degrees. My outside thermometer started to give me error readings that looked like L L L ( I will just assume that means 'freakin cold'

10:00 AM / ERROR / 51 F

10:30 AM / ERROR / 47.5 F

11:00 AM / 14 F / 42 F

12:00 PM / 19 F / 43 F

1:00 PM / 15 F / 40 F

1:30 PM / 15 F / 38.7 F
​

I ended my experiment there but placed the box back in the fridge just to see how much longer the heat packs would heat the box. I went out to run errands and returned at 5:00 pm

5:00 PM / 39 F / 50.3 F
​

I unpacked the box at 5:30pm after 18 hours inside the box. The heatpacks seemed warm to the touch but not hot. the newspaper not in direct contact with the packs was cold.

This was the only heat pack experiment I have done and I used Two 40 hour heat packs. I found the results very interesting. It seemed to do very well when the outside temp is 40 degrees.

Also I was surprised that the temp inside the box never dipped to freezing (32 degrees) even when the outside temp was 14 degrees.

I also now know that my settings on my fridge and freezer are not accurate.
Setting the temp on the freezer to 8 degrees yeiled a inside temp of 14 degrees and also the fridge set on 32 never got lower than 39..

 

[Ryan Jarosek]

Awesome work! I have been thinking of doing this. A+ if I could give you more rep I would.

 

[Dez]

Thanks Ryan, I have been meaning to do this test for a while and just now getting around to it.

I'm curious how much the results would differ if I used just one heat pack.. or maybe 3 heat packs. I'm guessing each pack raises the temp about 12 degrees since the average temp raised was around 24 degrees over all.


I have done similar tests with cold packs in the summer and found that an ice pack can cool a box about 15-20 degrees during 90+ heat of the day. The problem with the cool packs is they only last maybe 8 hours then they melt and are useless.

 

[draetish]

Great Job and very important info!

 

[Syn]

Great information. I reposting a thread from pangea about someone using a thermometer and checking temperatures a while back. I'll see if I can't find that for ya.
EDIT: Here it is.. https://www.chameleonforums.com/cold-weather-shipping-experiment-results-30988/
Not quite freezing, though.