Sunday, October 23, 2016

Your freezer is a battery of coldness



File this under the category of things I don't know much about but will talk about anyway, but it seems like home refrigerators and especially freezers could be much better managed for power variability that we'd see in a system dominated by solar and wind. They use more power than anything in the home other than heating and cooling, so adapting to variability seems like a big deal.

Received knowledge is the ideal maximum temps are -18C for the freezer and 5C for the refrigerator. My oh-so-genius insight is they could both get colder, especially the freezer, when power is available and then allowed to drift upward when it's not. So in power system with lots of solar, both the fridge and freezer should kick in at mid-afternoon. The fridge drops to 1C and the freezer to -23C or maybe colder, and then power demand is ended or sharply reduced by late afternoon, when solar is disappearing and other power demands are ramping up.

My other maybe/maybe-not insight is that if the max temps are constant temps, maybe those maximums could be exceeded periodically during the daily cycle without limiting food storage times. Maybe a freezer could spend two hours daily rising -18C to -13C without too much of an issue, and maybe a refrigerator could drift up to 7C before it has to start cooling back to 5C.

Refrigerators get opened a lot and can't be cooled as much as freezers, so the benefit isn't as great, but still exists. For freezers, ones that aren't opened or rarely opened might get through to sunrise without demanding power.

Systems with just a clock and a calendar could make use of solar availability to store coldness. Smart systems on the internet could do even more, especially with wind. If wind turbines somewhere start dumping extra power in the system at 10 p.m., your fridge and freezer turn on and run as long as the power lasts or until they get as cold as they should go.

Just a thought.

More info on managing power availability here. Also here on commercial scale storage of coldness.

26 comments:

Nick Stokes said...

"is they could both get colder, especially the freezer"
There is a cost to that. The energy required to pump heat is proportional to the temperature difference from source to sink. So if you are trying to move heat to sink at 20°, the theoretical cost increases by 43/38 = 13%. And you have to move more heat, because the leakage of heat in from outside is also more or less proportional to the temp difference.

EliRabett said...

Insulation is pretty damn good today and a large temperature difference may not be necessary. Eli thinks Brian is right, the key is how many times the door is open, which is why in door hidey holes like door within a door or external third door for the things you most often reach in for (beer, milk, etc) and especially the gizmo in doors that provide ice w/o opening the freezer are energy savers.

Russell Seitz said...

We should draft an Aide Memoire to Acme Corporation pointing out they can build and deliver humongous cold sinks for Cheap.

A hollow walled 100 pound box of tough and flexible polypropylene ( a carbon sink in itself) can be delivered like a conventional freezer and filled on the spot with a tonne of the wonder heat capacity material, water, which the gizmo's heat piump will freeze as usual.

Once frozen , the aerogel insulated ice-walled ice box will maintain an even thermal keel even if the power goes down for a cloudy week.

In bad neighborhoods, the ice can be spiked with sawdust to add ballistic value to the mighty Pykrete cryolith, and add to its internal insulation.

JohnMashey said...

Tour Stanford Central Energy Facility, here, ~every other Thursday.

The view shows two big tanks of chilled water, one big (red) tank of hot wate, which save energy, also water.

Watch 4 min video at bottom, intro by John Hennessy. (It helped to have a President devoted to quantitative engineering approaches.)

Also, watch the video of panel at Stanford Energy Summit 2015.
"The Future of Energy: Stanford’s Big Clean Energy Gamble - Jack Cleary, Ron Gawer, Bill Kelly, Moderator: Jeff Byron"
I attended that, thought it was a good talk from folks who actually had to do it.

Fernando Leanme said...

It's more practical to put water containers in the fridge to stabilize the temperature. I use tall square containers filled with filtered water. This reduces capacity but also reduces the amount of cold air that escapes. What I need is a clock to change temperature settings, raise it a bit during the day and drop it at night when power is cheaper. I see no need to optimize to help solar power.

Here we have solar power maxed out, it's run using hydro to compensate for solar deficiencies. For example, right now days are shorter, and the country has had over a week of very cloudy and rainy days (the exception being the area where I live, we have a microclimate caused by mountains running close to the Mediterranean coastline). The solar power contribution is anemic when we have these Atlantic fronts, and this is offset by running hydro at full capacity. The excessive use of hydro does mean the water isn't available later, so the system is somewhat out of tune because the water is used for agriculture and drinking.

In conclusion, the experience here is that trying to make solar work beyond what can be covered by hydro doesn't make sense. Wind is more practical, but wind is stronger in the evenings and at night. Which means the price drops and that's when it makes more sense to cool down the fridge. Longer term, I think this country needs more nuclear power. But we do have a bunch of greens touting solutions the economy simply can't stand. An interesting conflict which may be resolved if Spanish politicians can learn a bit of engineering and economics.

Nigel Franks said...

Fernando, you would be better off with a smaller fridge if you have so much spare space.

Instead of a temperature control/time switch, just put your fridge on a conventional timer and only allow it to come on during the cheap rate electricity period. The extra thermal inertia from your bottles will probably keep it cool enough during the day. If not, you can always set the timer to come on for a few minutes a couple of times during the day

Arthur said...

As Nigel''s comment hints at, the principle behind time-of-day pricing is that demand can be adjusedt to meet the supply hour by hour through price mechanisms. With a smart enough refrigerator, it would do all this automatically to minute the cost of keeping things cool. Of course there are always unintended consequences - like the recent DDOS apparently from "smart" home devices...

Victor Venema said...

You can do the same over even longer time scales with the really large cooling houses for produce and the like.

Russell Seitz said...

I had the good fortune as a small child of summering in a town in which enough veritable Ice boxes survived to support the only surviving ice company for fifty miles coastwise

That the coolth came only in 50 and 100 pound blocks ,local footbal coaches reckoned more of a feature than a bug, as a summer spent lugging the stuff proved the making of several Ivy fullbacks.

Nigel Franks said...

One strategy available for balancing the grid is to ask large users to curtail their operations if there is the likelihood of a shortfall in production. The converse could be to ask large industrial freezing plant to "over cool" their products during periods of surplus.

Andrew H said...

What you need is a eutectic refrigerator. Then simply time it to 'store' cold when the sun is shining on the solar panels.

Fernando Leanme said...

If you go to the Barcelona Dust website you will see we have an odd mix of rain with Sahara Dust. They say we may have MUD precipitation over the SE of the country. Not a very good day for solar panels. But temperature is 24 C and the tourists seem to enjoy it.

JamieB said...

Filling your fridge doesn't do anything useful to reduce energy demand because the mass and specific heat capacity of air are both so low. It's useful in a power cut but day to day won't make much of an impact.

Back on topic, we had some good news in the UK recently when there was a demonstration of a technology which sends data that would enable technologies like this over the grid:

https://www.reactive-technologies.com/reactive-technologies-achieves-a-world-first-in-smart-grid-innovation/

It's a no brainer imo, it's just a shame that we didn't mandate these kind of smarts years ago (and still haven't!). The appliance market is quite a slow mover so it'll take a good 10 years before we start to see the benefits even if we act now.

Also in Europe refrigeration is now much more efficient than it was and is getting more so all the time so there's limited scope for using cold appliances to balance the grid (you guys still have a long way to go though). It's still worth doing though as it should be a very cheap technology and we need every tool we can get our hands on.

In my view electric cars are going to be filling those solar-induced dips to a far greater extent. A million EVs plugged in to smart Level 2 chargers would give you close to 7GW of dispatchable demand, plenty to fill in the 2020 duck curve in the post. Smart immersion heaters also make sense.

Phil Clarke said...

"Stern Review (on clim chg) came out 10 yrs ago Predicted weather disasters wld be >0.6% GDP in 2016. Only off by 400%.

https://twitter.com/RogerPielkeJr/status/790620469686775808

And he links to a paper he wrote critical of Stern's methods (to be fair he makes some valid points). What he does not do is give a page reference in Stern for the 0.6% number.

I can't find it, closest seems to be

"The costs of extreme weather events are already high and rising, with annual losses of around $60 billion since the 1990s (0.2% of World GDP), and record costs of $200 billion in 2005 (more than 0.5% of World GDP).New analysis based on insurance industry data has shown that weather-related catastrophe losses have increased by 2% each year since the 1970s over and above changes in wealth, inflation and population growth/movement. If this trend continued or intensified with rising global temperatures, losses from extreme weather could reach 0.5 - 1% of world GDP by the middle of the century."

And in the footnote (27), this methodology is given:

"Based on simple extrapolation through to the 2050s. The lower bound assumes a constant 2% increase in costs of extreme weather over and above changes in wealth and inflation. The upper band assumes that the rate of increase will increase by 1% each decade, starting at 2% today, 3% in 2015, 4% in 2025, 5% in 2035, and 6% in 2045. These values are likely underestimates"

As a first approximation let's increase Stern's number (0.2%) by a fixed 2.5% annually since 2006. That's 0.265% (yeah, I know spurious accuracy), even using 0.3% only gets you to 0.269% of GDP by today.

So I don't know the origin of Pielke's 0.6% global GDP. That would be a rise of 200% over just 10 years. The actual report seems to say 0.5%-1% or between 250% and 500% but in 34 years from now. I must be missing something. Anyone help me out? I don't tweet.

Not sure a single year would be a good metric anyhow, there's HUGE annual variance, as a single bad year for hurricanes in the US such as 2005 gets you to 0.5% …

Phil Clarke said...

Sorry, something chopped the first few lines, here's the totality:

One for Ethan, PR Jr seems to parking his tanks on John Christy's lawn, tweeting

"Stern Review (on clim chg) came out 10 yrs ago Predicted weather disasters wld be >0.6% GDP in 2016. Only off by 400%."

https://twitter.com/RogerPielkeJr/status/790620469686775808

And he links to a paper he wrote critical of Stern's methods (to be fair he makes some valid points). What he does not do is give a page reference in Stern for the 0.6% number.

I can't find it, closest seems to be

"The costs of extreme weather events are already high and rising, with annual losses of around $60 billion since the 1990s (0.2% of World GDP), and record costs of $200 billion in 2005 (more than 0.5% of World GDP).New analysis based on insurance industry data has shown that weather-related catastrophe losses have increased by 2% each year since the 1970s over and above changes in wealth, inflation and population growth/movement. If this trend continued or intensified with rising global temperatures, losses from extreme weather could reach 0.5 - 1% of world GDP by the middle of the century."

And in the footnote (27), this methodology is given:

"Based on simple extrapolation through to the 2050s. The lower bound assumes a constant 2% increase in costs of extreme weather over and above changes in wealth and inflation. The upper band assumes that the rate of increase will increase by 1% each decade, starting at 2% today, 3% in 2015, 4% in 2025, 5% in 2035, and 6% in 2045. These values are likely underestimates"

As a first approximation let's increase Stern's number (0.2%) by a fixed 2.5% annually since 2006. That's 0.265% (yeah, I know spurious accuracy), even using 0.3% only gets you to 0.269% of GDP by today.

So I don't know the origin of Pielke's 0.6% global GDP. That would be a rise of 200% over just 10 years. The actual report seems to say 0.5%-1% or between 250% and 500% but in 34 years from now. I must be missing something. Anyone help me out? I don't tweet.

Not sure a single year would be a good metric anyhow, there's HUGE annual variance, as a single bad year for hurricanes in the US such as 2005 gets you to 0.5% …



Phil Clarke said...

PS PR Jr is my new favourite typo.

Andrew said...

There is a danger to this kind of demand deferment.

The problem is if you have got over a 24 hour period of low production from your renewables mix by turning off freezers, relying on pre-heated water, discharging EVs by whatever percentage is allowed, etc - but we now face another 24 hours of low production. Those smart freezers are now going o be demanding electricity at any price; water needs heating; EVs have to charge. Suddenly we have a big lump of demand. With predictable results.

(Adjust timescales to suit; it's easy to have periods of up to 2 weeks with minimal wind and solar).

Ironically, smart metering/use as a way to flatten the daily demand curve is great for us nuclear-lovers.. but perhaps not as great for those promoting variable sources.


JamieB said...

This is about shifting demand across minutes and hours not days and weeks and it would be quite straightforward to design a demand response system so that any pickup is managed smoothly. There's still a lot of value to be got from this as it reduces the need for very inefficient fossil fuel-based balancing services (and it will be far more responsive).

Not sure I follow your last comment. I'd say it's essential for both. Nukes generally aren't great load followers so if you could reduce peaky demand profiles it would help a great deal.

Ken Fabian said...

I have heard of the use of thermal inertia to stabilise temperature in refrigerators. I'm not sure this is precisely what is being suggested but this study is about the use of phase change materials to do something like it - http://scialert.net/fulltext/?doi=ajaps.2013.56.67

8c7793aa-15b2-11e5-898a-67ca934bd1df said...

Reading through these comments is moderately amusing. These are things that are obvious to anyone who has actually done it on the wild, in the bush and on desert islands. Top loading, lots of insulated inner doors, massive insulation, thermoelectrics powered by solar, delivery of the heat to where you want that heat to be, use of computer fans in the winter, distilled water production using any humidity imbalance.

Etc, etc, ad nauseam. Thermal inertia works better for home heating and a properly designed home is nothing but a very large fridge. Or a pizza delivery box. The problem is that there are a lot of legacy homes that are nothing but big thermal sieves just like modern fridges.

Good luck retrofitting all that in the future carbon negative world.

Jumper said...

Would a gallon of brine stuck in the freezer store the cold more efficiently?

Brian said...

Andrew - if I've understood your comment, I think it might apply to a nearly all-wind power supply, where a black swan event means the wind doesn't blow for a really long time. OTOH I don't see it applying to a system with solar mixed in, because we know that the sun will definitely rise in the morning.

And with a sufficiently-long distance transmission, the wind will be blowing somewhere. Aside from very high latitude areas, solar is always an option, plus some battery storage and hydro availability in real-world scenarios.

Brian said...

Jumper - interesting idea. Either a brine solution that freezes at the max temp you want the freezer to hit, or one that freezes at the average temp you want maintain.

Obviously there are efficiency costs to all these solutions, but addressing power variability may make them worth those costs.

EliRabett said...

8c, everything gets retrofitted in 30-40 years if it does not get knock down, renovated and rebuilt.

8c7793aa-15b2-11e5-898a-67ca934bd1df said...

Unfortunately Eli, that is NOT what I am seeing downtown in the student slum lord rental ghettos, nor in the brand new construction closely space identical suburban Stepfordian Wifian ghettos, nor even in the hard core libertaian box home ghettos of the 50's. What I see everywhere in addition to these nightmares, are perfect chemically treated lawns with big trees being felled every where I look.

You guys sure have your work cut out for you! Myself, I occasionally have to endure 120 MPH sustained winds. I do try to be prepared.

Arpitkakkar said...

With the help of solar freezer, it becomes very easy to store medicines during the summer season.