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I have a commercial fridge, without a freezer. It is vertical fridge with one glass door. We have medications we want to keep below 8°C. Most medication tolerate a slight T elevation without problem.

I know that a power outage of 4 h will happen tonight. The fridge will not be opened during that time, so only the usual thermal leak happens.

  • How do I know at how much the temperature in my fridge will increase?
  • Would adding extra water or ice packs help?
  • What does the temperature rise curve look like?
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  • $\begingroup$ Another thing you can do is to put the medication in a thermally isolating container (thermos flask, styrofoam box, …) within the fridge. This will slow down the heating of the medication even further. Add ice into that container if you can live with it melting. If you can get your hands on dry ice, even better. $\endgroup$ – Wrzlprmft May 30 at 19:11
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Let us assume that the temperature of the room is 25°C. The temperature will rise at first almost linearly, then the increase will gradually slow down, with a slow approach to 25°C. From 4°C to - say - 10-15°C, the increase is almost linear.

The curve should be almost exponential. But do not worry for this term: in this case, exponential does not mean that the temperature will increase faster and faster.

It is difficult to give an evaluation of the temperature reached after 4 hours. I think that, for 4 hours, it will be still increasing almost linearly. You could make an experiment: turn off for 30 min, an check how fast the temperature increases. Then multiply the increase by 8. E.g., if you go from 6 to 7°C in 30 minutes,, then in 4 hours you will reach approximately 14°C (something less).

The idea of storing water is good. Try to avoid thermal insulation around them.

Another idea, maybe trivial: try to decrease as much as possible the temperature of the room. If it decreases to 15°C, the temperature increase in 4 hours will be one half.

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  • $\begingroup$ thanks everyone for your great suggestions. Only thing feasable and convenient is to add ice. I don't have packages or dry ice. I cannot test the drop because of lack of time. (leaving work at 16h30). I am going with thermodynamics of ice vs water from my2cts. Should maintain T long enough. This also answer one of my long time question of what happens when your fridge breaks or prolonged power outage happens. $\endgroup$ – kan May 30 at 19:51
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    $\begingroup$ Temp went to 9.2 C. 1 degree over recommended T. is perfect. Best case scenario. Thanks. $\endgroup$ – kan May 31 at 12:52
  • $\begingroup$ I'm happy that you saved your medications! I have a suggestion: the best way to thank the users is to up-vote the answers and comments. See the up and down arrows on the left. $\endgroup$ – Doriano Brogioli May 31 at 13:56
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Safest is to add ice in quantity depending on the size of the fridge. Also turn the thermostat down as low as possible without damaging the content. Alternatively, if you can read out the temperature externally, you could switch the fridge off and measure how fast it heats up. Then of course switch it back on soon enough to have it cooled before the blackout. This allows you to extrapolate to a 4 hour duration. Best is to check a full four hour period. If you find that it will heat up too much add sufficient ice. Note that one gram of ice takes 80 cal of heat to melt while one gram of water or other matter takes typically takes 1 cal to heat up by 1 degree. So using ice is 21 times more efficient than using 4 degree water at the same weight.

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