4 ms·

As a counter argument, imagine an infinitely good insulation and 0 standby power (and a spherical cow inside, for illustration purposes). Then keeping it "runni

As a counter argument, imagine an infinitely good insulation and 0 standby power (and a spherical cow inside, for illustration purposes). Then keeping it "running" is clearly better than letting the fridge warm up since power draw is 0 in the former case. Obviously the conditions are not as perfect, but with a very modern fridge, maybe you get sufficiently close that keeping running indeed is superior. I'm not arguing that that's the case here. I'm arguing that you don't "always" expect things to be worse off letting it run. There is a threshold, when approaching the mentioned fantasy conditions, beyond which letting it run may be better.

mlyle 4y ago
> imagine an infinitely good insulation Then it would never warm up, and at this limit the two cases are equivalent (powered and unpowered). > when approaching the mentioned fantasy conditions, beyond which letting it run may be better. Anywhere short of the limit, what I said holds. Anything better than infinite insulation, I don't know how to reason about.
- lazide 4y ago
  I think you're missing the point. Perfect insulation doesn't help if you open the door? If you're saying 'well with perfect insulation it doesn't matter if it has power' - well yeah. It doesn't matter if it has power. So you aren't wasting any either leaving it on.
  - mlyle 4y ago
    Heat losses are proportional to the temperature difference integrated over time, and the refrigerator is more efficient in taking heat from the inside when it is close to the temperature of the room. This means that you are better off letting it warm up, because this results in both types of losses decreasing. This continues all the way up to perfect insulation, though ultimately it's breakeven with perfect insulation. > Perfect insulation doesn't help if you open the door? This doesn't change the picture, but worse, it's just completely unrelated to the scenario. Who's opening the door when everyone has left for weeks?
    - lazide 4y ago
      Uh no. The heat pump may be more efficient during the period it has the largest temperature differential, but that is ensuring it has the largest possible heat differential up front. If you don’t do that (aka keep it on), there is far less total heat to move, unless you’d have it sit so long that you’d get the same total heat transfer. Which if the insulation is good, may take many weeks. Which seems unlikely in this case. My chest freezer for instance turns on for less than 30 minutes a day even with people getting in and out. When I defrost it, it takes a day+ to cool down again. The reason someone would leave the door open is to ensure no one accidentally left a jug of milk in there when they turned it off. Which would pretty much neutralize any possible gains in sheer grossness if nothing else.
      - mlyle 4y ago
        > you don’t do that (aka keep it on), there is far less total heat to move, unless you’d have it sit so long that you’d get the same total heat transfer. I think you're a little confused. I'm a little lost at even how to minimally explain it to you. The rate at which heat leaks into the refrigerator declines as the refrigerator heats up, so this metric too improves with time. > Which if the insulation is good, may take many weeks. Implausible. "Many weeks"? The best 20 cu ft refrigerators use about 375 kilowatt-hours per year according to energystar.gov. At a coefficient of performance of 10, that's an average of 400W flowing into the fridge and needing to be removed by the refrigerator. At 20K of temperature difference, that's about 20W/degK. The contents will warm very quickly, absent phase change. Having ice in there will slow things down until the ice melts; then it will warm very quickly. The typical numbers cited say you have 2-3 days with a full freezer without power before things have mostly thawed and become unsafe-- this is well over half of the way to room temperature in terms of energy budget (and in the best case of a full freezer where there's the most thermal mass inside). (Specific heat capacity of water ~4200 J/(kg*k); heat of fusion of water ~334000 J/(kg*k)). None of this changes the energy balance of the problem, though.

mlyle 4y ago

> imagine an infinitely good insulation Then it would never warm up, and at this limit the two cases are equivalent (powered and unpowered). > when approaching the mentioned fantasy conditions, beyond which letting it run may be better. Anywhere short of the limit, what I said holds. Anything better than infinite insulation, I don't know how to reason about.

lazide 4y ago
I think you're missing the point. Perfect insulation doesn't help if you open the door? If you're saying 'well with perfect insulation it doesn't matter if it has power' - well yeah. It doesn't matter if it has power. So you aren't wasting any either leaving it on.
- mlyle 4y ago
  Heat losses are proportional to the temperature difference integrated over time, and the refrigerator is more efficient in taking heat from the inside when it is close to the temperature of the room. This means that you are better off letting it warm up, because this results in both types of losses decreasing. This continues all the way up to perfect insulation, though ultimately it's breakeven with perfect insulation. > Perfect insulation doesn't help if you open the door? This doesn't change the picture, but worse, it's just completely unrelated to the scenario. Who's opening the door when everyone has left for weeks?
  - lazide 4y ago
    Uh no. The heat pump may be more efficient during the period it has the largest temperature differential, but that is ensuring it has the largest possible heat differential up front. If you don’t do that (aka keep it on), there is far less total heat to move, unless you’d have it sit so long that you’d get the same total heat transfer. Which if the insulation is good, may take many weeks. Which seems unlikely in this case. My chest freezer for instance turns on for less than 30 minutes a day even with people getting in and out. When I defrost it, it takes a day+ to cool down again. The reason someone would leave the door open is to ensure no one accidentally left a jug of milk in there when they turned it off. Which would pretty much neutralize any possible gains in sheer grossness if nothing else.
    - mlyle 4y ago
      > you don’t do that (aka keep it on), there is far less total heat to move, unless you’d have it sit so long that you’d get the same total heat transfer. I think you're a little confused. I'm a little lost at even how to minimally explain it to you. The rate at which heat leaks into the refrigerator declines as the refrigerator heats up, so this metric too improves with time. > Which if the insulation is good, may take many weeks. Implausible. "Many weeks"? The best 20 cu ft refrigerators use about 375 kilowatt-hours per year according to energystar.gov. At a coefficient of performance of 10, that's an average of 400W flowing into the fridge and needing to be removed by the refrigerator. At 20K of temperature difference, that's about 20W/degK. The contents will warm very quickly, absent phase change. Having ice in there will slow things down until the ice melts; then it will warm very quickly. The typical numbers cited say you have 2-3 days with a full freezer without power before things have mostly thawed and become unsafe-- this is well over half of the way to room temperature in terms of energy budget (and in the best case of a full freezer where there's the most thermal mass inside). (Specific heat capacity of water ~4200 J/(kg*k); heat of fusion of water ~334000 J/(kg*k)). None of this changes the energy balance of the problem, though.