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Comment by daveguy | Hacker News Reader

Hey Joey, fan of your projects. I'm not sure if the fridge you have pulls a vacuum when it is closed, but pulling a vacuum can make a fridge much more efficient. I worked with some of the engineers that designed this -80C freezer for the International Space Station (where power is at a premium):

https://en.wikipedia.org/wiki/GLACIER_(General_Laboratory_Ac....

One of the key efficiency factors was being able to pull and hold a vacuum. And obviously the more efficient the engine that pulls the vacuum the better.

If it's a modern high efficiency unit, it probably already pulls a vacuum. If not, it may be worth physically hacking.

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It probably goes without saying but if you're pulling a vacuum in the fridge you have to consider how often you'll open it. If it's for long term storage and you open it a couple of times every month at most it probably makes a lot of sense but if it's your main fridge you open potentially dozens of times every day it might not make sense to make a full vacuum every time.

That being said since the system doesn't use batteries to store energy it might make sense to use any leftover energy to pump the air out of the fridge even if you don't reach a full vacuum.

You could also use excess energy to pull a vacuum in an external tank, then use that stored vacuum to quickly return the fridge to a near vacuum after opening.

Or maybe just build up the vacuum externally throughout the day until a certain time, then use it to pull the air out of the fridge for the night when it won't be opened and won't have power.

Talking about high-efficiency systems like this it's a given that we're testing for the best-case scenarios.

But you do make a really good point. In cruising, people who choose to have a fridge have systems for this.

It is usually to get saltwater really really cold or frozen in some kind of containers: it is popular to use PVC pipe, capped off of course, filled with seawater (or a mix of fresh and sea).

You store your food in the freezer and charge up these pipes, cycling them on to the top of your food in your cooler (not powered) once every 3-4 days.

This: "1 kilowatt of solar panels has managed to cool the fridge down close to standard fridge temperatures."

Is kind of silly to me though... because that's an "incredible" amount of power.

1kW is 'peak' rating, to get the real power a rule of thumb is that they'll run at that peak for 3-5h each day (depending on climate)

Pessimistically that means 3kWh/day, which if you're storing it efficiently (in a battery or as thermal mass like OP) gives you a nominal 125W supply

Yep, and the actual kWH per day with the fridge has so far been in the range of 1-2, and bear in mind that also runs everything else in my house including a rather energy hungry satellite modem.

The link is broken, I think it was renamed https://en.m.wikipedia.org/wiki/GLACIER_(refrigerator)

Non-mobile link:

https://en.wikipedia.org/wiki/GLACIER_(refrigerator)

With the vacuum technique, I imagine you would have to think more carefully about the containers you use (e.g. lids would probably pop off tupperware-style containers).

And unwrapped fruit or veg would dry out really quickly. I wouldn't want this in my regular fridge.

Theoretically, I'd think you could just wrap most of the central compartment(s) with a (permanent/sealed/static) vacuum chamber--like a big thermos.

http://www.greenbuildingadvisor.com/blogs/dept/energy-soluti...

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