Author Topic: Are we wasting energy boiling water?  (Read 4313 times)

HipGnosis

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Are we wasting energy boiling water?
« on: November 13, 2016, 10:52:25 AM »
Boiling is turning water into steam / vapor.
It takes relatively little heat energy to raise the temperature of water to reach its boiling
point.
The BTU (British Thermal Unit) is the standard heat energy measurement.  One BTU is the energy it takes to raise one pound of water one degree Fahrenheit.
A pint of water weighs approximately 1 pound.
So, to cook with a lb / pint of water, it requires 140 BTU's to bring the water from 72F to 212F - of water (this is important).
To keep the water at 212F takes very little energy - just enough to match the heat lost to radiation, evaporation, convection and conduction.   There are to many variables to estimate it. 
It will take more BTUs to return the water to 212F  after we add food.  Again, to many variables.
But, no matter how many BTUs the stove burner makes, the water will NOT get hotter than 212F.  All heat energy added  to the water at that point is used to change the water into steam, ie. boil it.
When all of the pound of water has been vaporized to steam, the stove will have added 970 BTU's to that pound of water to turn the 212F water into 212F steam.
That is almost 7 times the energy it took to heat the water from 72F  to 212F!!

Now, I know we dont boil all of the water in a pan to steam (at least not on purpose).
But..  it IS taking extra BTUs to boil the water, and all its doing for us is showing us that the water is at  212F.
A simmer, slow,  soft, fast or hard boil just indicates how fast we are putting extra heat-energy into the water.  Remember, water never goes above  212F.

My question:  Would it be more frugal  / efficient to use a thermometer instead of boiling the water?

shuffler

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Re: Are we wasting energy boiling water?
« Reply #1 on: November 13, 2016, 12:07:17 PM »
Ah ... you're problem is that you're *wasting* the steam.  Get some turbines and you can either charge up your Tesla power-wall, or sell it back to the grid.

... but really, you're suggesting using a thermometer to modulate the input from the stove, to keep the water *just* under the boiling point, thereby limiting the creation of waste-steam?

That seems like a lot of work for very little benefit.  You're surely not boiling off very much water at all during normal home-kitchen operation.

If it could be achieved, it may be more energy-efficient, but it's certainly not more time-/attention-efficient.  It's not worth your time.  I mean, you could save energy by not getting out of bed in the morning, but you choose to get out of bed and spend that energy because you've got more important things to do with your time than lie in bed.  Same thing here.

If you really wanted to do it, you could use the temp to drive the stove directly (I think of sous-vide machines, since that's what I'm more familiar with).

But even more practically, if it concerns you that much ... put a lid on your pot.

gaja

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Re: Are we wasting energy boiling water?
« Reply #2 on: November 13, 2016, 12:55:06 PM »
Potatoes and porridge are examples of food that can cook at much lower temperatures than you usually use, if you give it time. Instead of boiling the food for 20 minutes, take it to the boiling point and put the pot in bed under the covers for some hours. Wrap it up well, and the heat will keep high enough to cook the food.

seattlecyclone

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Re: Are we wasting energy boiling water?
« Reply #3 on: November 13, 2016, 01:14:43 PM »
You're right that the temperature doesn't change from 212 whether it's at a simmer or a rolling boil. The difference (as you know, since you're concerned about wasting energy on it) is that there's more heat in the water at a rolling boil. When you add colder food to the water, some of the heat will transfer from the water to the food. The more heat that is in the water at that point, the less likely it is for the temperature to drop below 212. Some foods may cook better at a constant 212 than if they start out at 150 (or whatever) and later go back up to 212. Others may not.

Spork

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Re: Are we wasting energy boiling water?
« Reply #4 on: November 13, 2016, 01:28:27 PM »
Potatoes and porridge are examples of food that can cook at much lower temperatures than you usually use, if you give it time. Instead of boiling the food for 20 minutes, take it to the boiling point and put the pot in bed under the covers for some hours. Wrap it up well, and the heat will keep high enough to cook the food.

There is quite a bit to be learned from some of the pre-modern technology.  The method you describe used to be common, as were "fireless cookers."  Fireless cookers were simply a contraption that did exactly what you describe.

Our stove was made in 1951.  It incorporates exactly this.  It has a deep well that is extremely insulated.  You put a pan in it, heat it to a boil, then turn off the gas and let it sit and cook on retained heat.  The oven works similarly.  If I recall, the recipe for roasting a turkey is something like "gas on for 45 minutes, gas off for 3 hours."

obstinate

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Re: Are we wasting energy boiling water?
« Reply #5 on: November 13, 2016, 01:31:11 PM »
Definitely wasting some energy, but most Americans use relatively little energy cooking. Even if 10% of all your energy use is cooking (unlikely), if you cut that by 20% (also a very generous estimate), you've saved 2% of your overall energy usage.

Radagast

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Re: Are we wasting energy boiling water?
« Reply #6 on: November 13, 2016, 07:38:15 PM »
How about an induction top and an inductable pressure cooker?

bobechs

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Re: Are we wasting energy boiling water?
« Reply #7 on: November 13, 2016, 08:11:24 PM »
How much do you plan on spending on thermometers?

You'll have offset that cost against the price of any energy saved by monitoring your water temperature.  At best you will be saving only the cost of the delta between your thermometer-found target temperature and the point where you reach the no-thermometer-required indication for determining a near-boil - bubbles.

Rockies

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Re: Are we wasting energy boiling water?
« Reply #8 on: November 13, 2016, 08:25:01 PM »
Im not picky enough to be concerned with this, but I do have a practical cooking tip related to boiling water and saving time:

If you are making pasta add the pasta when the water is cold and then turn on the heat instead of adding the pasta to boiling water. It will cook faster because as the water warms up you will get extra cooking time.  Just remember to stir it when you add the pasta to the cold water and a few times while its warming. I guarantee you won't notice the difference.

HipGnosis

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Re: Are we wasting energy boiling water?
« Reply #9 on: November 14, 2016, 12:55:20 PM »
Definitely wasting some energy, but most Americans use relatively little energy cooking. Even if 10% of all your energy use is cooking (unlikely), if you cut that by 20% (also a very generous estimate), you've saved 2% of your overall energy usage.
Good point and insight.

zolotiyeruki

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Re: Are we wasting energy boiling water?
« Reply #10 on: November 14, 2016, 01:26:03 PM »
Definitely wasting some energy, but most Americans use relatively little energy cooking. Even if 10% of all your energy use is cooking (unlikely), if you cut that by 20% (also a very generous estimate), you've saved 2% of your overall energy usage.
Good point and insight.
The same could be said for turning off the lights when you leave a room nowadays, between low energy prices and LED or CFL bulbs.  But a multitude of small, painless habits *can* add up to significant savings over time.

OP is entirely correct, BTW.  Your food won't cook any faster with a rolling boil than with a simmer.

catccc

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Re: Are we wasting energy boiling water?
« Reply #11 on: November 14, 2016, 01:43:58 PM »
instead of hard boiling eggs, I steam them.  I use a steamer basket and heat less than an inch of water rather than an entire pot full of water.  Once the water is boiling, I can turn the heat down quite low and still maintain steam to cook the eggs.  Works wonderfully!

Gimesalot

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Re: Are we wasting energy boiling water?
« Reply #12 on: November 14, 2016, 02:18:05 PM »
You can reduce the wasted heat by using a lid and also by adjusting the burner to the size of the pot.  If the flame is too high for a small pot, most of the heat will go around the pot, not towards the actual food.

Spork

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Re: Are we wasting energy boiling water?
« Reply #13 on: November 15, 2016, 08:39:44 AM »
You can reduce the wasted heat by using a lid and also by adjusting the burner to the size of the pot.  If the flame is too high for a small pot, most of the heat will go around the pot, not towards the actual food.

This is actually indicative of a badly designed burner.  Most burners today are round.  The reason is they are marketed with "Now with 25,000 BTUs!"  If they had well designed burners, they wouldn't NEED 25,000 BTUs.  Daisy burners and cloverleaf burners will put a lot more heat into the pan than a simple round burner.

KCM5

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Re: Are we wasting energy boiling water?
« Reply #14 on: November 15, 2016, 09:17:31 AM »
You can reduce the wasted heat by using a lid and also by adjusting the burner to the size of the pot.  If the flame is too high for a small pot, most of the heat will go around the pot, not towards the actual food.

This is actually indicative of a badly designed burner.  Most burners today are round.  The reason is they are marketed with "Now with 25,000 BTUs!"  If they had well designed burners, they wouldn't NEED 25,000 BTUs.  Daisy burners and cloverleaf burners will put a lot more heat into the pan than a simple round burner.

Spork, I love that you spend so much time invested in your Chambers. The only reason I've noticed is that I, too, have a Chambers and think it is just the best thing ever. Only mine's a model D with the "plane of flame" burners. Glorious and so good a temperature modulation!

Really, for the OP, remember that you are not turning all of your water to steam, so if you turn down the burner when the water starts to boil, you shouldn't be wasting much energy on turning water to steam. Certainly not as high as wasting 20% of the energy.

ooeei

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Re: Are we wasting energy boiling water?
« Reply #15 on: November 15, 2016, 10:01:30 AM »
Using an enclosed electric kettle is likely going to save more energy than monitoring your pot with a thermometer.  A lot of heat tends to go out of the sides when using burners.  We have one for tea and I usually use it for getting the water started.

In addition, water isn't at 212F when simmering in an open container. I did some testing with a thermometer to get my soft boiled eggs consistent awhile back, and when simmering (bubbles not quite breaking the surface) the water was around 190F.  The water at the very bottom layer of the pot was at the boiling point, but there was a gradient through the water getting colder as you move away from the element so it averaged around 190F.

The reason boiling is used as a benchmark is because it's a very obvious constant.  Simmering can have a pretty wide range of temperature depending on the container and intensity.  A rolling boil is always 212F at sea level, and consistent at any altitude.  For pasta a 10 degree difference won't matter if you're testing it along the way.  When you're trying to get perfect soft boiled or poached eggs, 10 degrees could make a difference.  As long as you're consistent you'll be fine simmering, you've just got to practice with it.
« Last Edit: November 15, 2016, 10:04:56 AM by ooeei »

With This Herring

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Re: Are we wasting energy boiling water?
« Reply #16 on: November 15, 2016, 12:04:25 PM »
*snip*
But, no matter how many BTUs the stove burner makes, the water will NOT get hotter than 212F.  All heat energy added  to the water at that point is used to change the water into steam, ie. boil it.
*snip*
Remember, water never goes above  212F.
*snip*

This is not true, and it can get you into trouble if you have never heard of the phenomenon.  Water (and other liquids) can be superheated under certain circumstances, which leads them to explode when disturbed.  These circumstances can be created in households by accident, especially when using a microwave.  It is not hugely common, but it can happen.

Prairie Stash

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Re: Are we wasting energy boiling water?
« Reply #17 on: November 16, 2016, 11:23:20 AM »
So, to cook with a lb / pint of water, it requires 140 BTU's to bring the water from 72F to 212F - of water (this is important).
When all of the pound of water has been vaporized to steam, the stove will have added 970 BTU's to that pound of water to turn the 212F water into 212F steam.
My question:  Would it be more frugal  / efficient to use a thermometer instead of boiling the water?
Its an interesting thought experiment, thanks for sharing.
Using your numbers it takes 1110 BTU to make a pint of water disappear into steam. I cook with electric at $0.14/kwh, which is 3412 btu (google), so it would cost me $0.045, or less than a nickel to boil off the water.

You're better off putting a lid on the pot and turning down the temperature, try it at home and you'll notice it keeps a rolling boil at a much lower heat setting. Its not the steam that is running up the electrical, its the release of the heat from the pot itself. All the heat applied to the pot needs to be either absorbed into the water or dissipated, the goal is to stop the release of heat or to reduce the required amount of heat. The best option is also the simplest - use a lid.

We do a fair bit of water bath canning in the fall. I've never considered the cost of the steam, its just a habit to put the lid on to keep the heat in.
« Last Edit: November 16, 2016, 11:31:58 AM by Prairie Stash »

ohsnap

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Re: Are we wasting energy boiling water?
« Reply #18 on: November 16, 2016, 02:42:20 PM »
instead of hard boiling eggs, I steam them.  I use a steamer basket and heat less than an inch of water rather than an entire pot full of water.  Once the water is boiling, I can turn the heat down quite low and still maintain steam to cook the eggs.  Works wonderfully!

I do this, too!  I started doing it because I read that it would make the eggs easier to peel, and it does.  But I hadn't thought about the energy savings, too.

Here's another idea to save on boiling-water-energy:  Once your spaghetti comes to a boil, turn the burner off and cover the pot.  You can read about it here:  http://www.thekitchn.com/does-cooking-pa-158205

Spork

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Re: Are we wasting energy boiling water?
« Reply #19 on: November 16, 2016, 03:44:04 PM »
You can reduce the wasted heat by using a lid and also by adjusting the burner to the size of the pot.  If the flame is too high for a small pot, most of the heat will go around the pot, not towards the actual food.

This is actually indicative of a badly designed burner.  Most burners today are round.  The reason is they are marketed with "Now with 25,000 BTUs!"  If they had well designed burners, they wouldn't NEED 25,000 BTUs.  Daisy burners and cloverleaf burners will put a lot more heat into the pan than a simple round burner.

Spork, I love that you spend so much time invested in your Chambers. The only reason I've noticed is that I, too, have a Chambers and think it is just the best thing ever. Only mine's a model D with the "plane of flame" burners. Glorious and so good a temperature modulation!


It is a sickness.

Bumperpuff

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Re: Are we wasting energy boiling water?
« Reply #20 on: November 16, 2016, 06:13:01 PM »
Depending on what you cook, you may want to consider buying a pressure cooker.  The increased heat and pressure greatly decrease cooking times, and once the contents are under pressure, you can keep the burner pretty low.  I imagine you could get further efficiency by making an insulating bag for your pressure cooker.

Also, pressure cookers just rock.
http://www.seriouseats.com/2016/10/why-pressure-cookers-are-better-than-slow-cookers.html
http://www.seriouseats.com/2015/09/pressure-cooker-recipes.html