Does a full fridge cost less money to run than an empty fridge?

[chrishgv]

With the cost of living crisis. my fridge has a bottle of milk in it by itself most of the time. Would it cost less in energy if i fill the fridge with bottles of water to fill the gaps? hope this makes sense.

 

[PeroK]

With the cost of living crisis. my fridge has a bottle of milk in it by itself most of the time. Would it cost less in energy if i fill the fridge with bottles of water to fill the gaps? hope this makes sense.

Drink the milk and switch the fridge off!

 

[chrishgv]

What would i make my cup of tea with for the week?

 

[PeroK]

What would i make my cup of tea with for the week?

Skimmed or semi-skimmed milk will last a couple of days unrefridgerated. When I was growing up we didn't have a fridge, so we just kept milk, cheese and butter in a cool cupboard.

 

[chrishgv]

ok. my fridge is connected to the freezer. I do keep that filled. The fridge is on anyway. Back to my original question. If iv'e posted on the wrong forum i apologise. Is there a better forum to post on?

 

[Klystron]

With the cost of living crisis. my fridge has a bottle of milk in it by itself most of the time. Would it cost less in energy if i fill the fridge with bottles of water to fill the gaps? hope this makes sense.

For the sake of discussion you could experiment by filling the refrigerator with water bottles as you describe, allow the added bottles to cool then compare electricity usage with an identical period withut the added water bottles. If your electrical usage such as air conditioning remains otherwise consistent and you only open the fridge twice a day for tea, lower energy consumption could be significant.

Measuring the refrigerator's on/off cycles may be more significant assuming room temperatures remain consistent during the periods, say one month each, with and without the added water bottles. Thermometers that record or graph internal fridge temperature over time would provide comprehensive data for comparison.

 

[BillTre]

Probably the loss of cool from your frig will occur when you open the door and some cooler air is released to the room containing the frig.

Replacing the cooled air inside the frig with cooled stuff in closed bottles will reduce the losses of cooled air when the door is open.
This seems to me to be the major differences between having more cooled containers in the frig, vs. only the milk.

 

[chrishgv]

very minimal difference then? opening and shutting the fridge quicker would save the same amount of electricity?

 

[chrishgv]

For the sake of discussion you could experiment by filling the refrigerator with water bottles as you describe, allow the added bottles to cool then compare electricity usage with an identical period withut the added water bottles. If your electrical usage such as air conditioning remains otherwise consistent and you only open the fridge twice a day for tea, lower energy consumption could be significant.

Measuring the refrigerator's on/off cycles may be more significant assuming room temperatures remain consistent during the periods, say one month each, with and without the added water bottles. Thermometers that record or graph internal fridge temperature over time would provide comprehensive data for comparison.

I,m just a soccer player . I can do 500 keepy uppers. Iv'e come on here for your knowledge because i don't have it! Thanks for your reply

 

[Wrichik Basu]

With the cost of living crisis. my fridge has a bottle of milk in it by itself most of the time. Would it cost less in energy if i fill the fridge with bottles of water to fill the gaps? hope this makes sense.

This is an interesting question. Let us suppose that the fridge hasn't been on for quite some time, such that its cavity is at room temperature. Now, I switch it on and put some items inside it. The amount of time the compressor will take to bring down the temperature of the cavity will depend on how many items are there inside the fridge because the compressor will have to extract heat from all the items. Therefore, if there are more items in the fridge, the compressor will take longer to bring down the temperature, and hence, the energy consumption will be more compared to when there are lesser number of items.

Now, if the refrigerator is one of the modern ones with inverter technology, the compressor is never actually off, but its speed is reduced such that the items remain cool. If, for the sake of the argument, we consider that no items in the fridge are replaced or added, then I think energy consumption will mostly depend on how many times and for how long the fridge door is open because the longer it is open, air at room temperature will enter the refrigerator, and the compressor will have to work to bring down the temperature again.

If the refrigerator is one of the old ones in which the compressor turns on and off, then the energy consumption will certainly depend on how many times (and for how long) the door is opened. Now consider this situation: the compressor brings down the temperature of the cavity to a certain temperature and then shuts down, and after a certain interval, turns on again. If we assume that no items have been added/replaced and the door of the fridge hasn't been opened even once during this interval, when the compressor turns on after the interval, will the number of items in the fridge have an effect on how long it takes to again bring the temperature down?

 

[DrGreg]

With the cost of living crisis. my fridge has a bottle of milk in it by itself most of the time. Would it cost less in energy if i fill the fridge with bottles of water to fill the gaps? hope this makes sense.

The advice I've heard in the past is just to fill the empty space in the fridge with containers full of air. When you open the door you want to minimise the amount of cold air that falls out and gets replaced by warm air; if most of the air is sealed inside boxes it can't fall out.

But I've never conducted an experiment to see if the advice is correct.

 

[JT Smith]

You can try to minimize the amount of cold air displaced by room temperature air when you open the door but how much is that really going to save you?

Tell me if I did the math right:

Assume:
25 cubic foot refrigerator @ 4°C
ambient air temperature: 20°C
complete displacement of air each time you open the door
heat capacity of air = 1.3 x 10^-3 J/cm3-K
open the door 25 times per day
cost of electricity $0.25/kWh

Cost per day: $0.04

 

[256bits]

You can try to minimize the amount of cold air displaced by room temperature air when you open the door but how much is that really going to save you?

Tell me if I did the math right:

Assume:
25 cubic foot refrigerator @ 4°C
ambient air temperature: 20°C
complete displacement of air each time you open the door
heat capacity of air = 1.3 x 10^-3 J/cm3-K
open the door 25 times per day
cost of electricity $0.25/kWh

Cost per day: $0.04

I didn't check your calculation, but the heat capacity used is for dry air AFAIK.

Note that if there is humidity in the air, the fridge will probably attempt to condense that water vapour to ice.
At ~2500 kJ/kg for heat of vapourization of water, the fridge will work a bit harder and the cost goes up.
For a cubic meter fridge, and 100% humidity, that's 25g of water vapour that has to be condensed for each door opening - 62,500 J. ( 62kJ ) 50% relative humidity would be half that.
versus the 1000 kJ to cool the kg of dry air.

( Note , I didn't take into account the energy required to cool the water vapour from ambient to 0C, nor to turn the liquid water to ice, nor to cool the ice to the coil temperature. )
So on the napkin, about 1.1 that of dry air, if the ambient air is at 100% relative humidity.
If I did my calcs correctly too.

 

[JT Smith]

I did ignore the humidity intentionally. I imagined that the cost of electricity varied more than the effect of humidity but maybe I'm wrong.

The bigger thing I left out is energy efficiency. How many joules of electricity does it take to move a joule of heat out of the refrigerator? I thought to look this up but instead encountered a concept called C.O.P. which just left me confused.

But I still think that this is a silly way to try and save money. If the refrigerator is empty because of the cost of food what are you doing, fasting? Eating in restaurants? Dumpster diving for scraps?

 

[crashcat]

I think your question has been mostly addressed. A lot of fridges run on a simple control scheme, where the compressor is either on or off. It's not regulated on how much it's cooling, but gets colder the more it runs. So once it warms up above some threshold it runs until it reaches the set point, or a few degrees below, and then waits to warm up again. Here are factors affecting how often it runs:

• Bad efficiency because it's too full, blocking air flow and cooling. So it runs but the temperature sensor isn't measuring right and it runs more often than it should because it's confused.
• Loss of heat when you open the door (a full fridge loses less heat when you open the door because you have more goods and less air inside. The air convection is greater than other losses).
• Loss of heat because of gaps in the seals, or an old fridge that doesn't have as good wall insulation as a new fridge.
• Bad efficiency because it cannot exchange heat: the coils are dusty, the air flow to the coils is blocked by dust in the vents or bad placement of the fridge around cabinets, or the fridge is in a hotter place than most of the house.
• The fridge is being heated by direct sunlight.
• The fridge is being heated by proximity to heater vents or radiators.

But also, check your fridge online. In the US they are legally required to tell you the energy efficiency of your model. A fridge made in the last 10 years will cost about $60-$100 per year to run. Older fridges can be up to $300. So stressing about your fridge and doing the best you can is going to save you maybe $20 a year? Not worth the stress. I say just clean the coils and vents of dust, make sure it's in a good position to be properly vented and efficient, and look for other reasons why your energy bill is high.