12

To use an example, say I need to take out a carton of milk from the fridge, add some milk to my tea, then put the carton of milk back. There are two methods:

Method A:

  1. Open fridge door.
  2. Take out milk.
  3. Close fridge door.
  4. Add milk to tea.
  5. Open fridge door.
  6. Put back milk.
  7. Close fridge door.

Method B:

  1. Open fridge door.
  2. Take out milk.
  3. Add milk to tea.
  4. Put back milk.
  5. Close fridge door.

Say Method A means leaving the fridge door open for 10 more seconds than Method B. In terms of energy wastage, is this a "big deal"?

(Against this must be weighed what to me is the obvious benefit of Method B --- convenience. But perhaps Method A has other costs too, such as additional wear-and-tear of the fridge door.)

  • 1
    Opening and closing the door of the fridge induces turbulence which might enhance the air exchange between fridge and the outside world. I am not sure how strong this effect is but it probably depends on the opening speed of the door and the size and shape of it. I read some estimation about this some time ago but I do not remember the result/conclusion. – daniel.neumann Aug 2 '16 at 12:41
8

It is common knowledge that hot air rises and cold air sinks. Inside a fridge the coldest air will be in the bottom of the fridge.

As soon as the fridge door is opened cold air from the bottom of the fridge drops out onto the floor of the room where the fridge is located. This air is replaced by room temperature air entering the top of the fridge space.

The longer the fridge door opens the greater the amount of cold air falls out of the fridge and is replaced by room temperature air.

Opening the fridge door for the least amount of time possible is the best way to retain cold air in the fridge. However, opening the fridge too often, even if briefly, in a short period of time will drain the fridge of the cold air inside it.

The best thing to do is know what you want to get from the fridge, get it as quickly as possible and close the fridge door as soon as possible and leave it closed.

  • Agree, and you can ameliorate the effect by having as little air as possible in your fridge that can drop out. I do it by filling plastic bottles (from milk) with water and putting them in all the empty spaces. (They stay cold and don't drop out :-) ) When you come back from the store and need to store more food, simply take them out as needed, then put them back as the space gets emptied again. Other methods may involve crumpled newspaper (etc.) that just traps the air. Or compartments with doors - probably impractical for a fridge. – fr13d Jun 20 '16 at 10:38
  • Clarification on above comment: air-filled containers (or insulation material trapping air bubbles) of any description would work, and probably work better when removing and re-introducing - I just use water-filled ones to have more thermal mass, as we sometimes have long power outages, and the extra thermal mass helps to maintain cold - it also takes longer to cool down when taken from room temp and put back in fridge. – fr13d Jun 20 '16 at 11:23
  • @fr13d : I am not sure your water-bottle technique is beneficial in most cases, as it takes a significant amount of energy to bring the water temperature down to fridge temperature in the first place. The savings would have to outweight those, and I have no way to estimate that but it seems you would have to keep those bottles in for a long time before it is beneficial. You might also have to consider hindered air circulation in the fridge if you fill it up with bottles and paper. – stragu Jun 21 '16 at 22:14
  • @stragu, you might be right about the circulation, but I imagine since the bottles do not sit snug to the sides, this would still leave room for circulation. Regarding the water, do refer to the comment right above yours. Water-filled bottles have kept the fridge at a cooler temp for longer than without during protracted outages - 6-24 hours, so no guesswork there. For the OP the circumstances are a bit different, so I agree that water may not work as well. – fr13d Jun 22 '16 at 9:05
  • 1
    I am not sure whether the answer is correct (see my comment to the question). Opening the door fast and short might have an reverse effect. Open it slowly and leaving it open a bit longer might be a better alternative. – daniel.neumann Aug 2 '16 at 12:43
1

No, leaving the fridge door open for about 10 seconds is not a "big deal". I figure it "wastes" about 3,000 joules of heat energy, or about 1,000 joules of electrical energy, which is equivalent to leaving a light on (60 watts) for about 20 seconds. For full analysis, see my post here: Should I Leave the Milk Out?.

  • I like the detailed numerical analysis in your link, but some of the figures might need refining. The estimate that half the air escapes from a fridge with each opening sounds way too high - the fridge is not midway between room and refrigeration temperature after being opened once. And what refrigerator can go from room to refrigeration temperature in 30 seconds?? – Nuclear Wang Jan 17 at 17:13
  • Thank you for the feedback. I edited my post on the link to clarify things based on your comments. – Kellen Jan 18 at 22:50
-6

your fundamental logic is all wrong in your question. My limited brain cell matter suggests that Method B means the fridge door is open 10 seconds longer than Method A?!!! If you reverse the question you might be able to apply some maths theory to find the correct answer.....! I agree that keeping fridge door open as short a time as possible will help contribute to a significant reduction in global energy usage. I refer you to study by Dr Dr. Claus and Barthel Thomas Götz http://www.bigee.net/media/filer_public/2012/12/04/bigee_doc_2_refrigerators_freezers_worldwide_potential_20121130.pdf . They report about 1,4 billion domestic refrigerators and freezers are in use world- wide. With an average annual electricity consumption of 450 kWh each, altogether they account for almost 14 % of the total electricity consumption from the residential sector and cause worldwide annual greenhouse gas emissions of 450 million tons of CO2eq. Households all round the world are currently using 1,4 billion refrigerators, fridge freezers and freezers. The average annual consumption of all these cold appliances amounts to about 453 kWh. In total, this causes an annual electricity consumption of 649 TWh, which is more than the total electricity consumption of Germany, for example. Now will you close the fridge door as soon as possible ?!!!!

  • 5
    Just answer the question please. There is no calculation about the open door in your answer. And edit out all your opinions and do something about the wall of text – Jan Doggen Aug 17 '17 at 11:35

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