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Discounting initial power to bring an item into a frozen state, then is the electricity cheaper to leave my fridge empty; or is the cost the same for it being packed with frozen foods?

If my fridge is empty, will it draw less power (and therefore be less expensive) than if it is full of frozen food which needs to remain frozen at, say $0.25 per kW/h, for constant power applied at a cost of:

$$ \mathrm{Number\ of\ hours} \cdot 0.25 \cdot \left(\frac{\mathrm{Voltage} \cdot \mathrm{Amperage}}{1\ \mathrm{hour}}\right) $$

Neinstein
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hein
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4 Answers4

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If you leave a packed fridge and an empty fridge for a week, the same amount of heat will escape through the walls. The cost will be the same.

But it takes more energy to cool the food in a packed fridge than the air in an empty fridge. So the cost when you put room temperature food in is higher.

You will likely be opening the door more often the get food out of a packed fridge than an empty fridge.

mmesser314
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I think there should be some difference in energy consumed by an empty fridge and a full fridge. @mmesser314 says

If you leave a packed fridge and an empty fridge for a week, the same amount of heat will escape through the walls.

I am not sure about that. Maybe the following effect is not very significant, but... So cold (not heat) escapes through the walls, so the temperature of the walls should be somewhat higher than the temperature of the interior of the fridge. That means that the interior of the fridge will absorb some thermal radiation from the walls, and I would think food would absorb radiation better than air. There may be some other effects, but I still think there can be some difference in energy consumption.

akhmeteli
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One more factor (other answers still being good)

A fridge full of food has much more heat capacity inside. This means that the thermostat will switch on and off at lower frequency - it will take more time for the interior to heat up to the point of switching the thermostat on and then will take more time to cool it down to the point of the thermostat switching off.

This can act two ways:

  • On one hand, at switching on, the compressor runs minute or two without actually cooling anything, just to get to the proper working distribution of temperature and pressure. At switching off, the cooling action stops more or less immediately. We have a minute or two worth of electricity wasted, more or less frequently (see above). So the full fridge may actually be consuming somewhat less energy.

  • On the other hand, running the cooling system longer means building up heat around the external heat exchanger and gradually lowering the cooling efficiency. For a properly installed domestic fridge, this is probably the less prominent effect, but it acts against the first one.

Both effects will probably be overwhelmed by the differend temperature field of a full / empty fridge. Full and empty fridges have profoundly different heat transmission properties inside the cooled volume. This will affect the thermostat function and the average temperature (and the heat ingress thereof). The effect can be in both directions, depending on the thermostat sensor placement.

fraxinus
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If the fridge remains closed there ideally is no difference. The heat transport is determined by the temperature difference between inside and outside and the heat conductivity of the walls. This assumes a uniform temperature inside. If some parts of the packed fridge are less well cooled then others the temperature distribution and the heat transmission will depend on the loading. In general this will result in less heat loss at the expense of less adequate cooling.

my2cts
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