Fridge/freezer on Economy 7 possible energy-cost-saving trick?

[Deleted User]

Converting water to and from ice needs about 100 times the energy of changing the temperature of either by 1C. (SHC of ice about 2.1kJ/kg/K, SHC of water about 4.2kJ/kg/K, latent heat of fusion over 330kJ/kg)

Don't know how that affects the calculation, just something I remember from chemistry lessons. 

inkydolphin

You'd be better off inventing an inner door that you can retro fit to all fridges to stop the cold air escaping so much when you open the door.

in_my_wellies

I regularly take tomorrows dinner out of the freezer the night before to defrost in the fridge. I've always assumed the cold as it defrosts save a few pennies running the fridge

Ultrasonic

Steve_79_P said:

@QrizB Thanks for explaining - must admit I just assumed that as the ultimate reason a freezer uses energy is to cool things down,  letting warmer things in would result in using more energy.

What I don't get is (f it makes such little difference opening and taking items in and out of) how does a freezer that's on all day without being opened and keeping everything inside it at -20 use 0.6 - 2 kWh a day. Is it because the items within have a different heat capacity?

The surrounding room is much warmer than the inside of your freezer and the thermal insulation cannot prevent all heat from getting in. The compressor uses energy to counteract this, explaining the energy use even when the door is never opened.

As cooling air lost when a freezer is opened was discussed above, I'll just mention that one reason a freezer has drawers rather than shelves is to significantly reduce this the.

mmmmikey

I had intended to try and measure the effect of leaving the fridge door open had on energy consumption, but a few minutes after starting I got cold feet......

devondiver

Deleted_User said:

devondiver said:

Deleted_User said:

- using "phase change technology" (and don't capitalise that, it just means melting/freezing/evaporating/condensing, nothing special about it, it's already in condensing boilers), -

Sorry, - but not correct. Not my capitals - read the reference, and many others. 

Sorry, but the first line of that "reference" that you quote:

"PCM-based thermal energy storage might be the oldest form of energy storage known to humanity, as our ancestors valued ice for exactly that purpose."

They even then say "All this is possible using the best and most abundant PCM: water."

You're going to have to do some serious explaining if you think that freezing water and thawing ice is a new and special technology.

Even they don't capitalise it in most of the book chapter abstracts on the page.

I don't recall anyone saying there was anything new or special about any of this. Quite the contrary.

For anyone actually interested: -

Thermal energy storage (TES) is a technology with a high potential for different thermal applications. It is well known that TES could be the most appropriate way and method to correct the gap between the demand and supply of energy and therefore it has become a very attractive technology. In this paper, a review of TES for cold storage applications using solid–liquid phase change materials has been carried out. The scope of the work was focussed on different aspects: phase change materials (PCMs), encapsulation, heat transfer enhancement, and the effect of storage on food quality. Materials used by researchers as potential PCM at low temperatures (less than 20 °C) are summarized and some of their thermophysical properties are reported. Over 88 materials that can be used as PCM, and about 40 commercially available PCM have been listed.

Abstract from: Review on phase change materials (PCMs) for cold thermal energy storage applications

Ref: https://www.sciencedirect.com/science/article/abs/pii/S0306261912002784

 Be nice.

devondiver

Further to foregoing and also from https://www.sciencedirect.com/science/article/abs/pii/S2352152X220146

It seems that things may be 'hotting up' - or should that be 'cooling down'. Anyway - from Journal of Energy Storage - 1st November 2022 (in progress) -

'Cladding phase change materials in freezing and chilling zones of household refrigerator to improve thermal performance and environmental benefits' Abstract:

The rapid change in the lifestyle of people makes the refrigerator an inevitable appliance in every home and its sales are increasing every year. Since refrigerators account for the major share of energy consumption in homes, many technologies are adopted to improve its energy efficiency for environmental protection. The favourable properties of phase change material (PCM) in terms of its energy efficiency, attracted the use of the same in refrigerators. Among the configurations - [some] - showed better performance with 18.5 % reduction of energy consumption.

Maybe worth a try then with the old freezer packs.  Be nice

QrizB

A couple of decades ago when I knew people with boats, you'd occasionally find one with a phase-change cold plate. The isdea being that you'd only run your fridge when the boat engine was running (as otherwise you'd flatten your batteries) so by having a phase-change system inside your fridge you could "create cold" when the engine ran then store it for when the engine wasn't.

I had a bit of a Google but couldn't find anything quite like that on the current market. Maybe boat fridges have got better since then!

[Deleted User]

"Since refrigerators account for the major share of energy consumption in homes"?  Really?  Are these homes without space heating or hot water?

I'd rather use the "phase change material" of molten salt in concentrating solar power stations with thermal storage than need everyone to change their refrigerator.

Large-scale renewables with energy storage means that there is much less of a peak vs off-peak anyway.

devondiver

QrizB said:

A couple of decades ago when I knew people with boats, you'd occasionally find one with a phase-change cold plate. The isdea being that you'd only run your fridge when the boat engine was running (as otherwise you'd flatten your batteries) so by having a phase-change system inside your fridge you could "create cold" when the engine ran then store it for when the engine wasn't.

I had a bit of a Google but couldn't find anything quite like that on the current market. Maybe boat fridges have got better since then!

Interesting. Sounds a bit like the way I run my '3-way' campervan fridge. This runs either weakly on electricity - 240V (external hook-up) or 12V (weakest, and only with the engine running), or gas (best/coldest but only usable when static). So, when using the van, I keep the tiny freezing compartment filled with three or four freezer packs initially pre-frozen in my home freezer. These act as a 'cold buffer' - keeping the whole fridge colder when on the move (cooler than possible just with the 12V cooling) and are then re-frozen when the van is static and the fridge running on gas. This way, effectively re-freezing the cold packs every night, the packs stay frozen and the fridge cold enough even during exceptionally hot weather. Cool eh?