4 ms·

This is nonsense (what the author said, not you). The heat capacity of the air contained in a fridge is insignificant when compared to that of the contents. Op

This is nonsense (what the author said, not you). The heat capacity of the air contained in a fridge is insignificant when compared to that of the contents. Opening and closing the door occasionally has almost no effect. The two important variables are thermal mass and insulation.

Xylakant 10y ago
The relative heat capacity of the air and the content is irrelevant. The thermal mass of the content is irrelevant as well since it's the same for a chest fridge and an upright fridge. The relevant comparison is how much heat escapes through the walls of the fridge relative to the heat loss via escaping air. Since fridge insulation has improved massively in the last decade that might actually be a significant share. The paper also mentions that an imperfect seal (due to imperfect closing or plain wear) on a vertical door leads to a constant trickle loss, while it does have much less of an effect on a chest freezer.
- joezydeco 10y ago
  Consumer fridges also consume a lot more energy in the interest of keeping humidity (and, subsequently, frost) out of the compartment. They also run defrost cycles with heaters to keep the evaporators from icing over and locking up the system. That lack of humidity control is what builds up a secondary layer of insulating frost/ice inside a normal chest freezer. It results in that "cleaning flow" of water inside the chest fridge, which doesn't sound as sanitary or healthy as the author proclaims once it builds up to a significant level. "The amount of condensation depends how much moisture is in the ambient air and how often and how vigorously we open and close the fridge lid." Wait. I thought less to no ambient air mixed into a chest fridge cavity according the author.
  - dpark 10y ago
    > Consumer fridges also consume a lot more energy in the interest of keeping humidity (and, subsequently, frost) out of the compartment. Yep. I'm pretty sure if you had an upright fridge built to modern standards but cooled conductively (convectively?) it would be about as efficient as the chest fridge here, but it would also have the same condensation problem.
- rebootthesystem 10y ago
  I think you misunderstood. There's this urban myth that opening the fridge door is a problem because it let's the cold air out. The author of this article falls for that one as well. When you open the fridge door a small amount of cold air is replaced by a small amount of room air. Yet, even if it was open long enough for all of the cold air to be replaced (use a fan to push room air into it) it would have zero effect. In a nicely filled fridge the mass of items cooled to the set temperature has, by means of it's heat capacity and the mechanism involved in heat transfer from solid to gas, a thermal inertia that results in negligible effects from occasional door openings. For example, I'd be surprised if opening the door to a well-stocked fridge and leaving it open for five minutes caused a 1 gallon jug of milk to drop in temperature even as much as 0.1 degrees at the core.
  - Xylakant 10y ago
    You're misunderstanding the point I (and the author) make. It's not a problem that cold air gets replaced by warm air because that might heat up the milk in the fridge (this is where thermal capacity of the fridge content would be relevant). It's an issue because the warm air needs to be cooled down to fridge temperature and that costs energy. So the relevant question is "how much of the total energy loss of the fridge is caused by cooling down warm air repeatedly after every opening)

Xylakant 10y ago

The relative heat capacity of the air and the content is irrelevant. The thermal mass of the content is irrelevant as well since it's the same for a chest fridge and an upright fridge. The relevant comparison is how much heat escapes through the walls of the fridge relative to the heat loss via escaping air. Since fridge insulation has improved massively in the last decade that might actually be a significant share. The paper also mentions that an imperfect seal (due to imperfect closing or plain wear) on a vertical door leads to a constant trickle loss, while it does have much less of an effect on a chest freezer.

joezydeco 10y ago
Consumer fridges also consume a lot more energy in the interest of keeping humidity (and, subsequently, frost) out of the compartment. They also run defrost cycles with heaters to keep the evaporators from icing over and locking up the system. That lack of humidity control is what builds up a secondary layer of insulating frost/ice inside a normal chest freezer. It results in that "cleaning flow" of water inside the chest fridge, which doesn't sound as sanitary or healthy as the author proclaims once it builds up to a significant level. "The amount of condensation depends how much moisture is in the ambient air and how often and how vigorously we open and close the fridge lid." Wait. I thought less to no ambient air mixed into a chest fridge cavity according the author.
- dpark 10y ago
  > Consumer fridges also consume a lot more energy in the interest of keeping humidity (and, subsequently, frost) out of the compartment. Yep. I'm pretty sure if you had an upright fridge built to modern standards but cooled conductively (convectively?) it would be about as efficient as the chest fridge here, but it would also have the same condensation problem.
rebootthesystem 10y ago
I think you misunderstood. There's this urban myth that opening the fridge door is a problem because it let's the cold air out. The author of this article falls for that one as well. When you open the fridge door a small amount of cold air is replaced by a small amount of room air. Yet, even if it was open long enough for all of the cold air to be replaced (use a fan to push room air into it) it would have zero effect. In a nicely filled fridge the mass of items cooled to the set temperature has, by means of it's heat capacity and the mechanism involved in heat transfer from solid to gas, a thermal inertia that results in negligible effects from occasional door openings. For example, I'd be surprised if opening the door to a well-stocked fridge and leaving it open for five minutes caused a 1 gallon jug of milk to drop in temperature even as much as 0.1 degrees at the core.
- Xylakant 10y ago
  You're misunderstanding the point I (and the author) make. It's not a problem that cold air gets replaced by warm air because that might heat up the milk in the fridge (this is where thermal capacity of the fridge content would be relevant). It's an issue because the warm air needs to be cooled down to fridge temperature and that costs energy. So the relevant question is "how much of the total energy loss of the fridge is caused by cooling down warm air repeatedly after every opening)