How to use Refrigerators/AC in efficient manner so that it remains cool inside?

[blake09]

Whenever I open Refrigerator two things come in my mind

Open door with fast speed, take the object out of it and close with fast speed.[so that less cool air escape]

2)Open door very slowly, take out object and close slowly.[assuming the cool air will escape slowly]

Both the above conditions have pros and cons like in 1st opening fast may cause more cool air to disturb and in 2nd cool air gets more time to escape.

Same condition is with Air Conditioner.

 

[Arjan82]

The most thermal capacitance of a refrigerator is not in the air but in the food inside. You can compute how much energy it takes to cool a cubic meter (or so, probably less) of air from 20 to 4 degrees C. This is roughly 17kJ. With this amount of energy you can change the temperature of 1 liter of water (one bottle of milk, say) by 4 degrees...

So, the two options do not differ by that much...

 

[kuruman]

The longer you leave the door open, the more cool air comes out of the refrigerator to be replaced by warm air. The air in the refrigerator doesn't know whether you intend to open the door quickly or slowly and adjust its speed of escape accordingly. The only assumption you can make is that the cool air will escape at the same speed (at least initially) and keep escaping until you close the door.

Maybe I misunderstood what you meant by "slowly". If you meant "with the door not all the way open", then you might save some coolth by opening the door wide enough to stick one arm in and feel around for what you want. Of course, if you spend too much time looking for the item you want, you will lose the advantage.

 

[bob012345]

The longer you leave the door open, the more cool air comes out of the refrigerator to be replaced by warm air. The air in the refrigerator doesn't know whether you intend to open the door quickly or slowly and adjust its speed of escape accordingly. The only assumption you can make is that the cool air will escape at the same speed (at least initially) and keep escaping until you close the door.

Maybe I misunderstood what you meant by "slowly". If you meant "with the door not all the way open", then you might save some coolth by opening the door wide enough to stick one arm in and feel around for what you want. Of course, if you spend too much time looking for the item you want, you will lose the advantage.

I think option #1 is implying some kind of suction effect which draws more cool air out?

 

[Arjan82]

I also think that the fast method will disturb the air significantly, generating turbulence. Turbulence is very good in mixing air, so that is not good either. The slow method will do that to a much lower extent, but indeed gives more time for the cool air to escape... So in the end, this also doesn't make that much of a difference I think. Very hard to quantify this though.

 

[anorlunda]

https://www.physicsforums.com/threads/ideas-for-refrigerator-door-design.902054/page-2

That thread discusses the problem, and it concludes that most air spills in the first 10 seconds. We had a video in the thread that showed the cold air spilling visually, but that video is no longer on the Internet that I can find.

 

[bob012345]

https://www.physicsforums.com/threads/ideas-for-refrigerator-door-design.902054/page-2

That thread discusses the problem, and it concludes that most air spills in the first 10 seconds. We had a video in the thread that showed the cold air spilling visually, but that video is no longer on the Internet that I can find.

Here is a video of a simulation of air flowing out of an open fridge;

 

[bob012345]

I keep water bottles in the unused spaces of my fridge for lots of thermal mass.

 

[JT Smith]

Our refrigerator suffered a failure the day before yesterday. The freezer worked fine but the refrigerator wasn't getting any cold air. I have a little temperature logger and I stuck a probe into the refrigerator (as well as a bunch of ice) to monitor it while I waited for the repair guy to come the next day.

After it was repaired (a broken bimetal switch in the defrost circuit resulted in frost clogging the air pathway to the refrigerator) I monitored the refrigerator first, then the freezer.

This morning I was watching it as I opened the freezer door to get things out and put things away. What I observed was that the freezer air temperature dipped less when I was really quick about it. Taking even a few seconds longer meant that it took longer for the air temperature to drop back down.

On the other hand, if I put the probe in between food items the effect of opening the door was pretty minimal regardless of how fast or slow I was with the door. I suspect it doesn't really matter all that much. There are probably easier ways to save electricity in a typical house.

 

[Baluncore]

When you open the refrigerator door, cold air from inside sinks, and falls to the floor, to be replaced by warm air from above in the room. That circulation exchange could be reduced by covering more of the shelves, but that would reduce circulation within the space while the door was closed. If you had a door, hinged along the front of each solid shelf, that you pulled out and down, the cold air would remain on the shelf unless you accessed that shelf. The smaller and lower shelf spaces would not circulate air as rapidly as the normal full height connected space.

 

[bob012345]

When you open the refrigerator door, cold air from inside sinks, and falls to the floor, to be replaced by warm air from above in the room. That circulation exchange could be reduced by covering more of the shelves, but that would reduce circulation within the space while the door was closed. If you had a door, hinged along the front of each solid shelf, that you pulled out and down, the cold air would remain on the shelf unless you accessed that shelf. The smaller and lower shelf spaces would not circulate air as rapidly as the normal full height connected space.

True but they don't bother because the current designs are good enough. But this could be hacked easily enough for motivated folks.

Also, they use air curtains to good effect in some commercial open air display units.

 

[anorlunda]

An even simpler solution is to use a top loading refrigerator that opens like a chest freezer. But those are almost impossible to find. So, I think the moral to the story is that people value convenience much more than energy efficiency.

 

[bob012345]

An even simpler solution is to use a top loading refrigerator that opens like a chest freezer. But those are almost impossible to find. So, I think the moral to the story is that people value convenience much more than energy efficiency.

Can you buy a chest freezer and just adjust the temp to fridge range? Of course one would then need two units.

 

[JT Smith]

Can you buy a chest freezer and just adjust the temp to fridge range? Of course one would then need two units.

I don't think so. When I looked for one last year they all had unitless settings, not a temperature range. What you could do is plug the freezer into a separate temperature controller. It's kind of silly though, using a top loading freezer as a refrigerator. How much would you save per year? How many years would it take to recoup your investment in the unit? And the impracticality of using a chest freezer for normal refrigerator items would become apparent quickly. They're not set up for ease of access of milk and orange juice and lettuce. Chest freezers are made to pack frozen things in there for the long haul.

But if you're going think that way: What would happen if you laid a normal refrigerator on its back?

 

[bob012345]

I don't think so. When I looked for one last year they all had unitless settings, not a temperature range. What you could do is plug the freezer into a separate temperature controller. It's kind of silly though, using a top loading freezer as a refrigerator. How much would you save per year? How many years would it take to recoup your investment in the unit? And the impracticality of using a chest freezer for normal refrigerator items would become apparent quickly. They're not set up for ease of access of milk and orange juice and lettuce. Chest freezers are made to pack frozen things in there for the long haul.

But if you're going think that way: What would happen if you laid a normal refrigerator on its back?

I was just wondering but agree it's not practical.

 

[Bystander]

if you laid a normal refrigerator on its back?

No air flow to/through the coil/s.

 

[Baluncore]

Can you buy a chest freezer and just adjust the temp to fridge range?

For many years, shops and supermarkets used chest freezers with clear sliding tops. When being opened or closed, a sliding door does not disturb or displace air in the same way that a hinged door does. Chest freezers do not dump the denser cold air when the storage volume is accessed. Commercial chest freezers may still be available, new and used.

In supermarkets, there has been a move toward vertical freezers, with air curtains inside the doors. Air curtains reduce the loss of cold air, at the expense of a continuously running a fan. The vertical style reduces the retail floor space requirement, while increasing retail sales by improving volume access and display.

This is clearly a multidimensional optimisation problem. Different operators will select different compromises or trade-offs, that will change over time.

 

[jrmichler]

Can you buy a chest freezer and just adjust the temp to fridge range? Of course one would then need two units.

Yes. It's been done, with reports of successful results. Check out these threads:

https://ecorenovator.org/freezer-fridge-conversion/

https://ecorenovator.org/diy-superefficient-fridge-1-kwh-day/

https://ecorenovator.org/forum/ is a good forum for people who like to think about, discuss, and try these sort of ideas.

 

[anorlunda]

Yes. It's been done, with reports of successful results.

That's cool. (Pun intended.)

I think it is surprising that manufacturers of chest freezers don't offer that as an option.

 

[jrmichler]

Found it. I had put a Kill-A-Watt on my refrigerator about a year ago. Average power while running was 122 watts. Total power was 10.97 KwH in 237 hours, which averages to 1.11 KwH per day. We must be doing a good job of not leaving the door open because the Energyguide sticker rates this refrigerator at 1.31 KwH per day. This refrigerator was one of the lower efficiency refrigerators in its size range at the time.

This compares to the freezer conversions mentioned in Post #18. One claims 0.395 KwH per day. The other mentions 0.1 KwH per day in the title, but the links to further information are dead.

 

[sophiecentaur]

I keep water bottles in the unused spaces of my fridge for lots of thermal mass.

I thought it was commonly known that a full fridge is better than an empty one for that reason.
I wonder about the energy taken to cool the bottles down in the first. They have many times the mass of the air they displace.
I imagine you’d actually need to comparr consumption for each regime over several days.
Balloons would probably be best.

 

[anorlunda]

I wonder about the energy taken to cool the bottles down in the first. They have many times the mass of the air they displace.
I imagine you’d actually need to comparr consumption for each regime over several days.
Balloons would probably be best.

Neither the bottles, nor balloons would spill out on the floor when the door was opened. In that respect, the improvement by water bottles and balloons may be similar.

Better still would be a fridge with water bottles that are cooled down only at night when electricity demand is low. That may be hard to do DIY, but a fridge designed to sense real time electricity price, and to store energy might succeed. People already do that with hot water heaters, and space heating/cooling, why not refrigerators also?

 

[Baluncore]

There are several reasons for filling the unused space with water bottles.
Thermal mass reduces the warming during power cuts.
The volume of cold air that falls out when you open the door is reduced by the volume of the water bottles. The amount of warm wet air that enters each time, to replace the cold dry air lost, is reduced, so the frost or ice formation is also reduced.
The presence of the bottles obstructs the cold air outflow, so the time the door is open, is not as important.

 

[russ_watters]

No air flow to/through the coil/s.

...and no ability to drain condensation.

 

[russ_watters]

I wonder about the energy taken to cool the bottles down in the first. They have many times the mass of the air they displace.
I imagine you’d actually need to comparr consumption for each regime over several days.
Balloons would probably be best.

It shouldn't matter as long as you are eventually drink the water. You're only interested in the steady state for long term consumption.

Edit: A quick Calc tells me if you put 6 cubic feet of water in a fridge it will take around 1.5-2 kWh to cool it

 

[hutchphd]

Better still would be a fridge with water bottles that are cooled down only at night when electricity demand is low.

Or (salt) water bottles in the freezer. Use the phase change.. Move it into the refridgerator cabinet if you need freezer space.
And sometimes I need the refrigerator spacxe and so I prefer empty sealed containers and blocks of polystyrene beadboard to take up airspace in the fridge. There is a very small penalty for recooling them.

 

[sophiecentaur]

it shouldn't matter as long as you are eventually drink the water.

Good point - but everyone lives differently with their fridge.
I must say, the idea of a fridge that stores its own 'cold', according to the cost per unit, could be attractive. However, the fridge life of most foods is pretty flexible and just running a fridge cooler when the unit cost is low could make sense. That could be a pretty 'smart' fridge but Health and safety issues could make it difficult to find a good solution.
I have a feeling that more energy could be saved with a fridge with a thicker layer of insulation all round. that would be at the expense of storage capacity for fitted units - the 60cm width would be sacrosanct.

 

[hutchphd]

Edit: A quick Calc tells me if you put 6 cubic feet of water in a fridge it will take around 1.5-2 kWh to cool it

If I got it correct about ten liters of (salt) water frozen will sequester 1kWhr (334 J/g is heat of melting) and deliver it at (or below) 32F. So according to

Average power while running was 122 watts. Total power was 10.97 KwH in 237 hours, which averages to 1.11 KwH per day

this represents a full day's supply of cold. This seems a no brainer. Did I screw this up?

 

[bob012345]

I thought it was commonly known that a full fridge is better than an empty one for that reason.
I wonder about the energy taken to cool the bottles down in the first. They have many times the mass of the air they displace.
I imagine you’d actually need to comparr consumption for each regime over several days.
Balloons would probably be best.

But I stock water also because if there is a power outage for a few hours the extra thermal mass helps keep things cool longer.

 

[Baluncore]

I keep it simple.
If you do not have power cuts, store low thermal mass material in the unused space.

If you do have power cuts, increase the thermal mass by filling the long term unused volume with bottles of water. Fill the short term dynamic volume with low thermal mass material.