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Step 4RESULTS
After everything is assembled, wrapped, taped, etc. and the box has aired out for a while (important), it's ready to use.
To base my expectations, I did a rough calculation involving the wall thickness, radiant area, thermal conductivity of the foam and the fusion enthalpy of water. Given that the temperature in the vehicle swings from 65dF during the night to as high as >140dF during the day, I found an average of 100-105dF to be reasonable for the calculations. The results indicated that the box should be able to keep 2kg of ice for around 27-30+ hours. Increasing the box dimensions independent of wall thickness will reduce this time. Increasing wall thickness and the mass of the ice charge will increase this time.
After running the box in the car for a few weeks, I can say the calculations are pretty accurate. The ice blocks come out of the fridge at 14dF. With 4kg of ice, it can easily maintain acceptable temperatures for four days even when it's opened four-six times per day. I just rotate different sized ice blocks (frozen beverage bottles and 1/2gal milk jugs) to accommodate different container arrangements and expected durations. It might be a good idea to make your box fit available rectangular ice bottles. Round ice blocks waste a lot of room.
The coldest I've ever had the bottom of the box (coldest part) was about 19dF. The warmest I've ever had the top of the box (warmest part) was about 42dF. Such high temperatures are only reached when the box is in the sun, the ice charge is growing small, or the lid has been recently opened. It averages between 34-38dF most of the days.
To base my expectations, I did a rough calculation involving the wall thickness, radiant area, thermal conductivity of the foam and the fusion enthalpy of water. Given that the temperature in the vehicle swings from 65dF during the night to as high as >140dF during the day, I found an average of 100-105dF to be reasonable for the calculations. The results indicated that the box should be able to keep 2kg of ice for around 27-30+ hours. Increasing the box dimensions independent of wall thickness will reduce this time. Increasing wall thickness and the mass of the ice charge will increase this time.
After running the box in the car for a few weeks, I can say the calculations are pretty accurate. The ice blocks come out of the fridge at 14dF. With 4kg of ice, it can easily maintain acceptable temperatures for four days even when it's opened four-six times per day. I just rotate different sized ice blocks (frozen beverage bottles and 1/2gal milk jugs) to accommodate different container arrangements and expected durations. It might be a good idea to make your box fit available rectangular ice bottles. Round ice blocks waste a lot of room.
The coldest I've ever had the bottom of the box (coldest part) was about 19dF. The warmest I've ever had the top of the box (warmest part) was about 42dF. Such high temperatures are only reached when the box is in the sun, the ice charge is growing small, or the lid has been recently opened. It averages between 34-38dF most of the days.
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