Well insulated slow cooker?

[Fionn]

Hi there,
            I bought a slow cooker in TK Max today with the intention of using it for stews and casseroles etc in the hope that it would do a good job of the cooking and possibly save some energy.
Anyway when I got it home I found the control know was missing so I will be returning it.
However I also noted that it seems to lack any kind of insulation whatsoever.
I did a bit of googling and the first article I came across features a picture of the exact model I just bought:
http://www.cookingmanager.com/slow-cookers-energy-efficient/

Surely if well insulated they will save energy due due to the fact that they draw so little power and the losses should be reduced due to the reduced delta T from inside the pot to outside.

Would be interested in seeing what you guys have bought.

Thanks,
Fionn.

[knighty]

I think.... the article you linked to must either be wrong or old...

I can't see why a slow cooker wouldn't turn on/off as needed ?

what's to stop it getting too hot ? - I'd be surprised if they just depend on it losing enough heat out of the top/sides to not overheat ?


as long as you get one which turns on/off as needed.... (maybe one with a temperature setting instead of a power setting?) you could cover it up to insulate it yourself ?  maybe with a big tea cosy?

[Fionn]

I think may not be a mistake and it's possible that the one I bought may indeed lack any kind of thermostat and just rely on losses.
The max heat input is 350W or so so I would imagine that with the 5litre capacity filled its chances over over heating are slim given that it has ZERO insulation and quite a large surface area!
I will return it and hopefully get another one at a later date.
When I do, I plan to try super insulating it for a run just for fun to see how little energy I can get away with for a 5 litre stew. It would be quite interesting to find out how much energy is actually required in order to cook the food after it has been raised to temperature and losses to the environment are eliminated - in so far as possible.

[Fionn]

This sounds pretty interesting - http://en.wikipedia.org/wiki/Vacuum_flask_cooking
Cant be too much energy required to actually cook the food so once it's held at the required temperature

[Contadino]

I can't say I really understand the excitement around slow cookers (electric ones at least.)  To my simplistic mind, a large burst of energy for a short period vs a small burst of energy for a long period is likely to end up being roughly the same quantity of energy used.  If the slow cooker is badly insulated, from my slender knowledge about these things, it would possibly end up using more energy than an oven.

The vacuum flask cooking technique is really just a modern take on the haybox, which works as well as it ever did.  You can make one yourself.  Here's a load of links to details about them.

http://www.greenwizards.org/?q=node/557

If you're working outdoors, away from home on a cold day, there's nothing quite like opening up the haybox at lunchtime to tuck in to the stew that's been gently cooking away since the crack of dawn.

[EccentricAnomaly]

That first article is so muddled about the units used that I'd treat it with a lot of suspicion. Not checking if the slow cooker uses a thermostat seems like a bit of an omission, too.

Insulation does seem like a good idea, though. Try Googling "hay box cooking".

I've cooked pasta in a vacuum flask as an experiment. It cooks more slowly than in a saucepan on a hob which is OK but makes it difficult to work out when it's done. Finished up with a soggy overcooked result a couple of times. It's worth bearing in mind that the actual cooking process absorbs energy (to break chemical bonds) so even in a hypothetical perfectly insulated container the food will cool.

[Fionn]

Yes, I figured energy has to be consumed in order to create the change in the food.
Contadino, well I figure cooking something like a stew on a hob usually takes an hour or so. A lot of heat is lost to the room with a pot on a hob and I'm just interested to see how much less energy I could get away with using a well insulated cooking vessel. Perhaps I should have posted this in the bodges section! I've returned the one I bought today anyway so will have to look for another.

[martin]

http://www.motherearthnews.com/Do-It-Yourself/1980-01-01/Rediscover-the-Hay-Box-Cooker.aspx

[marshman]

I can confirm that at least 3 slow cookers I am familiar with do not have a thermostat. I think it is a mistake to assume that they save energy or cook food using less energy than a standard cooker. We use ours once a week to cook a stew on the day we are all late back home from work etc. - its for convenience so we don't have to wait for the meal to cook when we get back.

The attached picture shows house energy consumption on two consecutive days, the first with no slow cooker, the second when it was on all day. Look at the consumption between 8:30 and 16:00. there is a constant extra load of around 350W - the slow cooker. It is actually on from 7:45 until about 18:00 so uses around 3.5kWh. Enough to have four rings on a cooker flat out for 30 minutes! or an electric oven on for around 2 hours!.

I don't know why they aren't thermostatic with more insulation - perhaps there is a gap in the market for one to be made and sold as "energy efficient".

Roger

[Fionn]

Thanks for the info Marshman, yes as I suspected they must just rely on losses to prevent overheating.
Definitely room for a proper one I guess.
I lived with a guy from South Korea for a time and he used a rice cooker which was something similar to a slow cooker. It cooked his rice for him and then held it warm and moist for him all day, it was definitely insulated I think.
Anyway it would be pointless insulating one without a thermostat, although I have some adjustable stats that I could retrofit I guess.

Incidentially Marshman, what software and hardware are you using for the energy logging?
I have an Owl meter but the USB PC interface requires the computer to be left on for it to log as I understand it.
Thanks,
Fionn.

[Fionn]

This one has an "auto" setting but without a description of what it does it's not much use!
http://www.argos.co.uk/static/Product/partNumber/4231473/c_1/1|category_root|Kitchen+and+laundry|14418476/Trail/searchtext%3ESLOW+COOKER.htm

[marshman]

Incidentially Marshman, what software and hardware are you using for the energy logging?
I have an Owl meter but the USB PC interface requires the computer to be left on for it to log as I understand it.
Thanks,
Fionn.

I have got 2 Brultech ECM1240's.  One in the house and one in an out building. They allow true net metering. The software is a bit of a fudge at the moment but I have most channels (each one can monitor 7 channels) being fed up to Google Powermeter.I need to find some time to sort it all out and get it feeding my website so it is publically viewable.

Roger

[Fionn]

Cheers Roger, I'll have to check those out.
Thanks,
Fionn.

[stannn]

My Missus has suggested buying a slow cooker not only for fuller cooking of the meat but also because the low wattage (say 250W) would lie within the power output from my PV system for most of the year, ie power which would be exported normally. I have read this thread and it seems that (unbelieveably) slow cookers without thermostat use as much power as the electric oven with thermostat. So what would you advise?
Stan

[HalcyonRichard]

Hi Fionn,
             I had a very old slow cooker with an auto function . When turned on it cooked on "high" for a fixed time then turned itself to "low". This was for putting in cold food. It heated quickly then "simmered" until turned off.

Regards Richard