Why is refrigerator/freezer door hard to open?
October 13, 2019 10:18 PM Subscribe
My apartment recently got a brand new refrigerator. I've noticed that after opening the freezer or refrigerator door and then closing, I can hear a what sounds like air being sucked in. If I try to open either door, I can't without a LOT of force. After a few minutes of being left alone the door opens okay.
It doesn't do this on every open and close, but enough that I'm questioning what's going on.
Best answer: Here is the answer from GE - (my paraphrase) When you open the door, you let a lot of warm air into the unit. When you close it, the warm air is drawn (rapidly) into the condenser, creating a vacuum which pulls the door tightly shut. If you wait 15-30 seconds, the air distribution readjusts, the pressure is normal again and you can open the door easily.
posted by metahawk at 10:31 PM on October 13, 2019 [10 favorites]
posted by metahawk at 10:31 PM on October 13, 2019 [10 favorites]
Adding a comment to metahawk's answer, if the fridge part is made in any way similar to ours, it should have an opening somewhere at the back where collected condensed water can run out (and into a container somewhere there). Sometimes the little hole gets blocked by debris, and that's when our fridge starts doing this. Sometimes a good rough opening-the-door-move is enough to unblock the duct.
The freezer should totally do this, especially a new one with clean, tight door seals: if not anything else, the warm air gets chilled down rapidly and shrinks, pulling the door tight.
posted by Namlit at 10:38 PM on October 13, 2019 [1 favorite]
The freezer should totally do this, especially a new one with clean, tight door seals: if not anything else, the warm air gets chilled down rapidly and shrinks, pulling the door tight.
posted by Namlit at 10:38 PM on October 13, 2019 [1 favorite]
Above posters explained the phenomenon, but here's a trick, if the fridge configuration allows it, for opening the door when it's tight.
Instead of yanking on the handle to almost no effect, find a place where you can see the fridge seal (tougher on double doors) and peel it back a little to break the seal.
posted by notsnot at 6:37 AM on October 14, 2019 [2 favorites]
Instead of yanking on the handle to almost no effect, find a place where you can see the fridge seal (tougher on double doors) and peel it back a little to break the seal.
posted by notsnot at 6:37 AM on October 14, 2019 [2 favorites]
Refrigerator door seals are good, but they're not perfect. When you open a fridge door, most of the cold dense air inside just falls out and gets replaced by warmer, less dense air from outside. All the cold internal surfaces of the fridge then start to cool that air and increase its density, creating a flow of cooled air out of the bottom of the doorway for as long as the door stays open.
If it's an upright freezer and/or a particularly humid day, you can often actually watch this happening: as cold outfalling air mixes with the room air, it condenses any water vapor present in the room air and creates a visible fog trail.
When you close the door again, the cold air can't fall out any more and no more warm air can come in. Rapid cooling of the air that's now trapped inside the fridge causes its internal pressure to drop quite sharply, sucking the door shut hard.
But as soon as this has happened, that suction makes small amounts of outside air begin to leak in past the seals, cooling as they do, until there's once again enough cooled air inside to reduce the pressure difference between inside and outside - and hence both the ingress rate of outside air and the extra difficulty of pulling open the door - to zero.
At this point, the lower temperature of the interior air once again manifests as increased density with respect to exterior air rather than decreased pressure, and that denser air is therefore primed to fall out again when the door is next opened.
This is why chest freezers are both more efficient than uprights and less susceptible to the being sucked shut effect: opening the lid of a chest freezer sloshes a little bit of dense cold interior air out into the room, but doesn't immediately dump the whole lot.
posted by flabdablet at 6:52 AM on October 14, 2019 [4 favorites]
If it's an upright freezer and/or a particularly humid day, you can often actually watch this happening: as cold outfalling air mixes with the room air, it condenses any water vapor present in the room air and creates a visible fog trail.
When you close the door again, the cold air can't fall out any more and no more warm air can come in. Rapid cooling of the air that's now trapped inside the fridge causes its internal pressure to drop quite sharply, sucking the door shut hard.
But as soon as this has happened, that suction makes small amounts of outside air begin to leak in past the seals, cooling as they do, until there's once again enough cooled air inside to reduce the pressure difference between inside and outside - and hence both the ingress rate of outside air and the extra difficulty of pulling open the door - to zero.
At this point, the lower temperature of the interior air once again manifests as increased density with respect to exterior air rather than decreased pressure, and that denser air is therefore primed to fall out again when the door is next opened.
This is why chest freezers are both more efficient than uprights and less susceptible to the being sucked shut effect: opening the lid of a chest freezer sloshes a little bit of dense cold interior air out into the room, but doesn't immediately dump the whole lot.
posted by flabdablet at 6:52 AM on October 14, 2019 [4 favorites]
Just to apply a bit of math to metahawk's answer:
Air pressure follows the Ideal Gas Law
P = nRT/V where P is pressure, n is the number of molecules of gas, R is a constant, V is the volume and T is the temperature.
When you open and shut the door all of the numbers on the right side of the equation stay the same except for temperature - the number of molecules is the same, volume is the same and the constant R is the same.
This means that the change in air pressure is proportional only to the change in temperature.
Let's say that when you open and close the door you allow in warm air that is quickly chilled by 1 degree centigrade. This is just a conservative ballpark guess assuming most of the cold air stays in the refrigerator and there is only a small amount of mixing with outside warm air.
Temperature in the gas law is measured on the Kelvin scale which starts at 273 degrees below zero centigrade. So a one degree change in temperature is 1/273 or about 0.004 change in pressure.
Normal air pressure is about 15 pounds per square inch, so the change in air pressure due to a 1 degree change in temperature is 15 * 0.004 = 0.06 pounds per square inch.
Wow, 0.06 pounds per square inch doesn't sound like much. But ... if your refrigerator door is 2 feet wide and 3 feet tall, that is 6 square feet or 864 square inches.
Now, 0.06 pounds per square inch times 864 square inches is 52 pounds. That's how much force is holding your door shut. As pointed out, this pressure quickly equalizes in a few seconds through leaks.
The numbers I used are just approximations, but it demonstrates that a very small change in temperature multiplied by a very large surface area can add up to a significant amount of force holding your door shut.
posted by JackFlash at 11:38 AM on October 14, 2019 [4 favorites]
Air pressure follows the Ideal Gas Law
P = nRT/V where P is pressure, n is the number of molecules of gas, R is a constant, V is the volume and T is the temperature.
When you open and shut the door all of the numbers on the right side of the equation stay the same except for temperature - the number of molecules is the same, volume is the same and the constant R is the same.
This means that the change in air pressure is proportional only to the change in temperature.
Let's say that when you open and close the door you allow in warm air that is quickly chilled by 1 degree centigrade. This is just a conservative ballpark guess assuming most of the cold air stays in the refrigerator and there is only a small amount of mixing with outside warm air.
Temperature in the gas law is measured on the Kelvin scale which starts at 273 degrees below zero centigrade. So a one degree change in temperature is 1/273 or about 0.004 change in pressure.
Normal air pressure is about 15 pounds per square inch, so the change in air pressure due to a 1 degree change in temperature is 15 * 0.004 = 0.06 pounds per square inch.
Wow, 0.06 pounds per square inch doesn't sound like much. But ... if your refrigerator door is 2 feet wide and 3 feet tall, that is 6 square feet or 864 square inches.
Now, 0.06 pounds per square inch times 864 square inches is 52 pounds. That's how much force is holding your door shut. As pointed out, this pressure quickly equalizes in a few seconds through leaks.
The numbers I used are just approximations, but it demonstrates that a very small change in temperature multiplied by a very large surface area can add up to a significant amount of force holding your door shut.
posted by JackFlash at 11:38 AM on October 14, 2019 [4 favorites]
Our chest freezer does this and it takes a few *minutes* to equalize. I've never had a refrigerator that was that well sealed. JackFlash is exactly right, though--it's warm room air cooling on all the cold surfaces.
posted by Gilgamesh's Chauffeur at 8:57 PM on October 14, 2019
posted by Gilgamesh's Chauffeur at 8:57 PM on October 14, 2019
Our chest freezer does this and it takes a few *minutes* to equalize. I've never had a refrigerator that was that well sealed.
If that's annoying, you can reduce the seal efficiency a tiny bit with a light coating of paraffin wax, as GE suggests in the answer linked by metahawk.
There's a diminishing-returns effect with the excellence of refrigerator door seals; given that the machine is typically going to be running undisturbed for tens of hours at a time, the difference between minutes and tens of seconds of lag on interior tracking of external air pressure variations is not going to make a perceptible difference to energy consumption.
As long as the seals are good enough to prevent any kind of density-driven continuous flow they're fine, and the physical arrangement of a chest freezer makes that kind of flow even less likely.
posted by flabdablet at 12:01 AM on October 15, 2019
If that's annoying, you can reduce the seal efficiency a tiny bit with a light coating of paraffin wax, as GE suggests in the answer linked by metahawk.
There's a diminishing-returns effect with the excellence of refrigerator door seals; given that the machine is typically going to be running undisturbed for tens of hours at a time, the difference between minutes and tens of seconds of lag on interior tracking of external air pressure variations is not going to make a perceptible difference to energy consumption.
As long as the seals are good enough to prevent any kind of density-driven continuous flow they're fine, and the physical arrangement of a chest freezer makes that kind of flow even less likely.
posted by flabdablet at 12:01 AM on October 15, 2019
Response by poster: Just poppin to say these are all great answers and since I've asked the question I've not encountered this happening again.
posted by 922257033c4a0f3cecdbd819a46d626999d1af4a at 8:28 PM on October 15, 2019
posted by 922257033c4a0f3cecdbd819a46d626999d1af4a at 8:28 PM on October 15, 2019
This thread is closed to new comments.
posted by danielparks at 10:31 PM on October 13, 2019