"Off-Grid, Solar-Powered, Zero-Battery Refrigerator"

[Guest]

https://www.notechmagazine.com/2019/09/off-grid-solar-powered-zero-battery-refrigerator.html

 

More info here.

 

"Fridge0 consists of a standard chest freezer, an added thermal mass, an inverter, and computer control. It ties into the typical offgrid system of a solar charge controller, battery bank, and photovoltaic panels."

 

https://joeyh.name/blog/entry/fridge_0.2/

 

 

[carlt]

Reading the blog it appears that he had a similar success rate as I had with my Easicool fridge in my 1960 Bedford CA camper. It was simply an insulated box which you poured water through a mesh in the top which cooled by evaporation.

It worked better the warmer the weather but didn't work at all on warm wet days when milk just went off.

No computers though.

 

[WotEver]

His wiki is here, for anyone interested:

https://fridge0.branchable.com/

[rusty69]

There is much benefit to be had from a chest fridge imo. We have a small chest freezer that is used as a fridge in the summer months, running from batteries and solar. It reverts to freezer use during the winter months. Of course, it will not run on solar alone, as there are often days without any sun in this country.

 

 The benefits of a chest fridge/freezer are usually better insulation and  the ability to retain the cold when the door is opened,as it doesn't all spill out as it would in a standard fridge. We also use a thermal mass in terms of water bottles,and the freezer can easily go 12 hours overnight without being powered whilst retaining the required temperature.

Edited September 3, 2019 by rusty69

[doratheexplorer]

1 hour ago, rusty69 said:

There is much benefit to be had from a chest fridge imo. We have a small chest freezer that is used as a fridge in the summer months, running from batteries and solar. It reverts to freezer use during the winter months. Of course, it will not run on solar alone, as there are often days without any sun in this country.

 

 The benefits of a chest fridge/freezer are usually better insulation and  the ability to retain the cold when the door is opened,as it doesn't all spill out as it would in a standard fridge. We also use a thermal mass in terms of water bottles,and the freezer can easily go 12 hours overnight without being powered whilst retaining the required temperature.

https://www.bimblesolar.com/cheap-solar-fridge

[GUMPY]

1 hour ago, doratheexplorer said:

https://www.bimblesolar.com/cheap-solar-fridge

First place I saw that was here

https://mtbest.net/chest_fridge.html

Possibly 10 years ago.

Never was allowed to do it

 

[rusty69]

12 minutes ago, Loddon said:

First place I saw that was here

https://mtbest.net/chest_fridge.html

Possibly 10 years ago.

Never was allowed to do it

 

That is where I knicked the idea from too.

[CompairHolman]

Like I posted in another thread, vacuum panel insulation is becoming affordable and a top loading cabinet with this is the only practical way you can get the highest efficiency, plus you can use a 12 v Danfoss compressor and eliminate the inverter power loss. 

 

A freezer may have thicker insulation but its still no where near the maximum, which is 120 mm with PU foam, a vacuum panel will achieve the same with 20 mm. As far as I've read , this level of insulation could get you down to 25% of the power consumption of a normal fridge cabinet.

 

 

 

[WotEver]

8 hours ago, CompairHolman said:

Like I posted in another thread, vacuum panel insulation is becoming affordable and a top loading cabinet with this is the only practical way you can get the highest efficiency, plus you can use a 12 v Danfoss compressor and eliminate the inverter power loss. 

 

A freezer may have thicker insulation but its still no where near the maximum, which is 120 mm with PU foam, a vacuum panel will achieve the same with 20 mm. As far as I've read , this level of insulation could get you down to 25% of the power consumption of a normal fridge cabinet.

Yes, you have indeed written this before. But you haven’t yet supplied us with any examples. 

 

So which fridges/freezers use this amazing technology?

[Jen-in-Wellies]

How much are these magic vacuum insulated panels?. Several companies making them, but no prices anywhere that I've been able to find. Usually this is a sign that if you have to ask, then you can't afford it!

 

Jen

[CompairHolman]

On 08/09/2019 at 08:47, WotEver said:

Yes, you have indeed written this before. But you haven’t yet supplied us with any examples. 

 

So which fridges/freezers use this amazing technology?

https://youtu.be/1h8-OdkGflc

[rusty69]

22 minutes ago, CompairHolman said:

https://youtu.be/1h8-OdkGflc

Looks interesting. I guess they were designed with increasing internal space for a given footprint rather than power saving but will be interesting to see if the idea takes off and prices come down.

[CompairHolman]

On 08/09/2019 at 09:10, Jen-in-Wellies said:

How much are these magic vacuum insulated panels?. Several companies making them, but no prices anywhere that I've been able to find. Usually this is a sign that if you have to ask, then you can't afford it!

 

Jen

In the region of £8 / 10 per square ft. 

 

You have to factor in the cost of the fuel you save recharging your batteries to run a badly insulated fridge over the long term. Like investing in solar panels.

 

 

4 minutes ago, rusty69 said:

Looks interesting. I guess they were designed with increasing internal space for a given footprint rather than power saving but will be interesting to see if the idea takes off and prices come down.

Well if you want a seriously insulated fridge you would need to go up to 120+ mm of PU foam and that's not practical on a boat.

Edited September 9, 2019 by CompairHolman

[rusty69]

4 minutes ago, CompairHolman said:

Well if you want a seriously insulated fridge you would need to go up to 120+ mm of PU foam and that's not practical on a boat.

I would find the space if it meant I could loose a battery or two.

[WotEver]

38 minutes ago, CompairHolman said:

https://youtu.be/1h8-OdkGflc

Apparently only available as a 743l upright fridge freezer in Australia for $4000 au. 

 

Perhaps if they ever manufacture an affordable under counter fridge and make it available in the UK it might have some relevance to inland waterways boats. 

[Jen-in-Wellies]

1 hour ago, CompairHolman said:

In the region of £8 / 10 per square ft. 

 

You have to factor in the cost of the fuel you save recharging your batteries to run a badly insulated fridge over the long term. Like investing in solar panels.

 

 

Well if you want a seriously insulated fridge you would need to go up to 120+ mm of PU foam and that's not practical on a boat.

So for a 2'x2'x3' high box, the panels alone will be £256 to £320 to cover all six sides, including the lid. Add on the cost of the compressor, controller, hinges, seals and so on. Expensive, but not totally impractical. Anyone actually sell these panels to individuals in small quantites of a size suitable for making a fridge?

[Murflynn]

On 03/09/2019 at 12:08, rusty69 said:

 

 

.............................. the ability to retain the cold when the door is opened,as it doesn't all spill out as it would in a standard fridge. 

I believe that is a bit of a miscomprehension.  The only thing that spills out is cold air - that represents a very small loss of the energy required to cool down a few grams of air.  It only becomes an issue when the lid is left open long enough for the food contents to begin to warm up.

[rusty69]

36 minutes ago, Murflynn said:

I believe that is a bit of a miscomprehension.  The only thing that spills out is cold air - that represents a very small loss of the energy required to cool down a few grams of air.  It only becomes an issue when the lid is left open long enough for the food contents to begin to warm up.

Yes, some cold air falls out each time the door is opened.More so in an upright fridge than a chest fridge.It was a bit of an exaggeration on my part so say it all falls out, it clearly doesn't. Still, I would rather keep the cold air in the fridge than in the boat,especially if it is running off the boats batteries and the door is opened many times a day.

 

 

Extract from one of the links above:-

Quote

Vertical doors in refrigeration devices are inherently inefficient. As soon as we open a vertical fridge door – the cold air escapes, simply because it is heavier than the warmer air in the room. When we open a chest freezer – the cool air stays inside, just because it’s heavy. Any leak or wear in a vertical door seal (no seal is perfect) causes significant loss of refrigerator efficiency. In contrast, even if we leave the chest freezer door wide open, the heavy cool air will still remain inside. 

 

Edited September 9, 2019 by rusty69

[Murflynn]

24 minutes ago, rusty69 said:

Yes, some cold air falls out each time the door is opened.More so in an upright fridge than a chest fridge.It was a bit of an exaggeration on my part so say it all falls out, it clearly doesn't. Still, I would rather keep the cold air in the fridge than in the boat,especially if it is running off the boats batteries and the door is opened many times a day.

 

 

Extract from one of the links above:-

 

The thermal mass of a few litres of air is insignificant.  The effect is probably no worse than putting in a dessert-spoon full of water at room temperature. The matter of poor door seals is more relevant, because if the seals are really so bad that heavy cold air continually escapes from the bottom of the door seal, this may represent a huge amount of air over 24 hours.

[rusty69]

10 minutes ago, Murflynn said:

The thermal mass of a few litres of air is insignificant.  The effect is probably no worse than putting in a dessert-spoon full of water at room temperature. The matter of poor door seals is more relevant, because if the seals are really so bad that heavy cold air continually escapes from the bottom of the door seal, this may represent a huge amount of air over 24 hours.

Fair enough. Though I presume the cold air that escapes is replaced by air of an ambient temperature that subsequently requires cooling.The less content in the fridge , the more volume of air present, another reason we keep the fridge full.

[Jen-in-Wellies]

Say we lose 100 litres of air from a front opening fridge at 5C, which is replaced by 100l of air at 21C. That 100l needs to be cooled 16C. Assuming this all happens at normal atmospheric pressure and ignoring changes in volume. Air has a density of 1.225 kg/m³ at STP, so 100l weighs 0.1225Kg. Specific heat capacity of air at constant pressure is around 1kJ/kg.K at the temperatures we are dealing with, so around 2kJ of heat needs to be extracted from the fresh air each time the door is opened.

 

By comparison, putting a 1l bottle of 21C water in the fridge, ignoring the bottle. Water has a heat capacity of 4.185kJ/kg.K, so cooling this down 16C will need 67kJ of heat extracted. Equivalent to opening the fridge door 33 times!

 

I think the claimed super efficiency of the chest freezer conversion is more down to the extra thickness of the insulation compared with a normal fridge than it is to the lid being in the top, rather than the side.

 

If you wanted to improve the efficiency of a front opening fridge you could fill it with bottles of water to reduce the volume of air changed, but that would need lots of energy to cool it down initially. You could fill any areas not with food with an open cell foam that would let air circulate, have a low thermal mass, yet resist air replacement when the door is open. Another idea is a transparent strip curtain inside the door, so you can see the item you want and grab it without losing much air!

I'm overthinking again...

 

Jen

[rusty69]

1 minute ago, Jen-in-Wellies said:

I'm overthinking again...

 

...But  but  how many ants per hour is that out of my battery please miss?

[Jen-in-Wellies]

Just now, rusty69 said:

...But  but  how many ants per hour is that out of my battery please miss?

It's ant.hours not ants per hour!

[rusty69]

8 minutes ago, Jen-in-Wellies said:

Say we lose 100 litres of air from a front opening fridge at 5C, which is replaced by 100l of air at 21C. That 100l needs to be cooled 16C. Assuming this all happens at normal atmospheric pressure and ignoring changes in volume. Air has a density of 1.225 kg/m³ at STP, so 100l weighs 0.1225Kg. Specific heat capacity of air at constant pressure is around 1kJ/kg.K at the temperatures we are dealing with, so around 2kJ of heat needs to be extracted from the fresh air each time the door is opened.

 

By comparison, putting a 1l bottle of 21C water in the fridge, ignoring the bottle. Water has a heat capacity of 4.185kJ/kg.K, so cooling this down 16C will need 67kJ of heat extracted. Equivalent to opening the fridge door 33 times!

 

I think the claimed super efficiency of the chest freezer conversion is more down to the extra thickness of the insulation compared with a normal fridge than it is to the lid being in the top, rather than the side.

 

If you wanted to improve the efficiency of a front opening fridge you could fill it with bottles of water to reduce the volume of air changed, but that would need lots of energy to cool it down initially. You could fill any areas not with food with an open cell foam that would let air circulate, have a low thermal mass, yet resist air replacement when the door is open. Another idea is a transparent strip curtain inside the door, so you can see the item you want and grab it without losing much air!

I'm overthinking again...

 

Jen

Quote

The thermal mass of a few litres of air is insignificant.

You could have just said^^^^^^^Wot he said.

[Jen-in-Wellies]

1 minute ago, rusty69 said:

You could have just said^^^^^^^Wot he said.

Why use ten words when you can use two hundred and seventy four! But, yes, what @Murflynn said.