[Stoves] Energy requirement

[Nikhil Desai]

Crispin:

Do you know if that Eindhoven  list is accessible?

I don't know if my offlist reply got to Paul, or my question to Frans.

In useful energy terms, roughly 200 kJ for 1 liter water is the just the
energy to raise the temperature for that water. It doesn't say anything
about how long at that or higher/lower temperatures. So it is not very
useful.

Nor does it adjust for age/size composition of the eating club, number of
meals per day, and ambient temperatures, loss of heat from the pots.

Suppose the quantity is six liters a day and total energy input required is
200 kJ per liter per hour for two hours equivalent. That makes 1.2 MJ per
day per "family" or,rounding up for the whole year to hundreds, 0.5 GJ per
year per "family".

In my view, this is some kind of "basic" for people who do not have much
variety and quantity of food, which are limited by economic factors
including the cost of fuel and limitations on time.

I would not call it "average" by any means.

Again, look up some tables Seema Patel or someone else at GACC presented at
the 2017/8 Ethos meeting. If I remember correctly, there were computations
of useful energy, assuming some efficiencies, and the numbers varied
hugely.

Cooking is contextual. Any damned "scientific" computation is mere
shorthand for thinking or avoiding measuring everything that would
interfere with simplistic theories. Eindhoven folks, whom I never met but
read and discussed, gave us some direction on how to think.

I think that capacity to think was lost.

Nikhil

------------------------------------------------------------------------
Nikhil Desai
(US +1) 202 568 5831
*Skype: nikhildesai888*



On Wed, Oct 16, 2019 at 10:12 AM Crispin Pemberton-Pigott <
crispinpigott at outlook.com> wrote:

> Dear Paul
>
>
>
> There was a lot of work done on this matter at Eindhoven University in the
> early 80’s. They published a list of foods and the energy requirement to
> cook them.  It is not obvious but as chemical transformations take place in
> the food, the temperature drops as the reactions are endothermic. So even
> then energy is going in, they do not rise in temperature some of the time.
>
>
>
> You can take foods to be wet, so using water mass is not far wrong.
> Cabbage requires one of the greatest inputs of energy to cook.
>
>
>
> Regards
>
> Crispin
>
>
>
>
>
> *From:* Stoves <stoves-bounces at lists.bioenergylists.org> *On Behalf Of *Paul
> Arveson
> *Sent:* Wednesday, October 16, 2019 6:04
> *To:* stoves at lists.bioenergylists.org
> *Subject:* Re: [Stoves] Energy requirement
>
>
>
>
>
> Thanks for those who responded to my question, how much energy is required
> to cook a typical meal?
>
>
>
> I need more information.  The way we would calculate the basic energy
> requirement is:
>
> E = q m dT
>
>
>
> Where q = heat capacity of food
>
> m = mass of food
>
> dT = temperature change
>
>
>
> Example (in metric units):
>
> Let's assume a meal is 1 kg of water.  = m
>
> Water has a higher heat capacity than solid foods, so water is the worst
> case.
>
>
>
> It takes 4186 J to heat 1 kg of water 1 deg. C. = q
>
>
>
> Suppose we want to heat the water from 27 to 77 deg. C, or 50 deg.
> increase.  = dT
>
>
>
> So the energy required is 4186 x 50 deg. = 209,300 Joules.
>
>
>
> This is only the energy required to heat the food.   But cookers are not
> 100% efficient, since some energy goes to heat the pot, the stove parts,
> etc.  Also there is some heat loss during cooking due to conduction,
> convection and radiation.
>
>
>
> Apparently efficiency is low for most stoves, so most of the energy
> doesn’t go into cooking the food.  So the “steam cooker” was quoted by
> Frans as 1.2 MJ, which is 17% efficient (assuming he was heating 1 kg of
> water, which was not stated).   This in turn drives the fuel requirement.
>
>
>
> What then are some typical numbers for cookstove thermal efficiency?
>
>
>
> Thanks,
>
> Paul Arveson
>
>
>
>
>
>
>
>
>
>
>
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