Every time you open the refrigerator door, you’re letting cool air out , which has to be pumped back into the cooling chamber via a compressor. Perhaps counter-intuitively, the net effect is that you’re warming your house up since the heat technically has to be pumped out of the fridge using extra energy, though the instant blast of cool air can certainly be refreshing during the summer. Although cold air does escape, the real point it to keep food cold and hopefully unspoiled, and the food and drink would normally have more thermal mass than the air anyway, taking much longer to heat up.
All that to say, while you should close the fridge door ASAP, you may not have a good understanding of the actual effect of doing so. Rather than accept this situation, Ryan Bates decided to actually log what happens when he leaves the fridge open too long. For this experiment, he used a DHT22 sensor to log temperature and humidity. He found that upon opening the door — sensed and recorded with a photoresistor — the humidity immediately spikes, while there is a more subtle change in temperature.
Finally, Bates used TMP36 sensors placed at different locations in the fridge, including taped to a pickle jar. What he found after examining the log, was that the jar only heated up around 1 degree (F) per second of the door being open. Maybe it’s not critical that you immediately slam the door shut as you previously thought. If you’d like to duplicate the experiment yourself, or even take thanks further, code and the circuit used are available here.
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Author: Jeremy S. Cook