Why We "Waste" Energy: The Second Law of Thermodynamics Explains--UPDATED 8/7

This is a guest post by John Schmitz. John E.J. Schmitz holds currently a senior management position in semiconductor technology research. He was awarded his Ph.D. in Chemistry in 1984 from the Catholic University of Nijmegen (Netherlands). He holds six patents in the semiconductor field and has published over 45 scientific articles and one technical book in the field of integrated circuit technology. Before, Schmitz was the Chief Operating Officer Manufacturing Technology of SEMATECH (Austin, Texas) a consortium that develops semiconductor manufacturing technology, materials, and equipment for their member chip maker companies. Schmitz has dealt with thermodynamics and entropy for 25 years on a professional level. He currently lives in a small town in Belgium with his wife, Pieternel, and his children; Lucas, Juliette, Emmeline, and Jasper.
There are many instances that we can see that in our attempts to transform energy into as much as possible usable work, we are always left with this "rest" amount of heat that we can not use anymore to generate even more work¹. Clear examples of these imperfect transformations are the coolant radiators in our cars and the cooling towers of many factories or power plants. In powerplants that use fossil fuels we can have an efficiency as poor as 50% or often even lower, meaning that only 50% of the energy enclosed in the fuel is converted into electrical power, by means of burning fuel, heat generation that leads to steam and steam that will drive then turbines and generators. 50% or less is that not a shame? Of course the question arises why that is the case?

Why can we not convert for the full 100% the energy enclosed in the fuel into utile work? Well it is here that the Second Law of thermodynamics kicks in, also known as the entropy law. But before we go deeper into this entropy law first a bit more about the First Law of thermodynamics. The First Law is nothing more than the law of conservation of energy. Energy can be present in many forms (chemical, heat, work, electrical, nuclear etc etc) and the total amount of all this energy in the universe is constant. The First Law will not object to convert a given amount of energy fully into work. Unfortunately we never observe this attractive situation. The answer why that is so can be found from an analysis of the entropy law.
What is entropy? Entropy is a concept discovered while people were answering "simple" questions such as why heat only streams from warm to cold places. Another question that came up around 1800 was caused by the growing popularity of steam engines. Steam engines can also be called heat engines because they convert heat into work. Another example of a heat engines is a car engine. Steam engines where used in England to pump water out of the coal mines, a job that was done by many workers day and night before steam engines became available. To keep the steam engine running, fuel (such as wood or coal) was burned to generate the steam. While the steam engine was gaining ground, many improvements (for instance James Watt was able to improve efficiency with about 25%) were done that increased the efficiency of the steam engines considerably. Therefore much more work could be obtained from a given amount of fuel.

While this went on there was a young French military engineer, Sadi Carnot, who asked himself the question whether there was perhaps an upper limit to this efficiency. To answer that question he carried out a careful analysis around 1825 using a simplified of a steam engine². The result of his analysis was that the upper limit of the efficiency was only determined by two factors: the temperature of the heat source (the steam) and the temperature of the heat sink (the location where the steam was condensed, for all practical matters the outside air). More precisely he found that the amount of heat, Qh, taken from the heat source at temperature , Th, is related to the amount of heat given up at the heat sink, Qc, at temperature Tc, as: Qh/Th = Qc/Tc. Although he did not coined the factor Q/T as entropy (that was done by Rudolph Clausius around 1850) he clearly laid the foundation for scientists such as Clausius who came to the conclusion that "something was missing" and was needed in addition to the First Law . That something became later the Second Law of thermodynamics.

The best possible efficiency of the steam engine was then shown by Carnot to be equal to (Th-Tc)/Th (an atmospheric steam engine efficiency is therefore limited to about (373-272)/373 = 25% efficiency).

The work of Carnot showed very clearly that in order for a heat engine to work you MUST have a heat source at high temperature and a heat sink at colder temperature and that the heat disposed at the heat sink can NEVER generate any work anymore unless you have another heat sink available at an even lower temperature. Also, from the fact that Qh/Th = Qc/Tc, it becomes clear that in an heat engine you MUST give up an amount of heat, Qc, to the cold sink no escape. That is the fundamental reason for having the efficiency of the heat engines less than 100%! We can also see now that the efficiency of heat engines will increase if we make the temperature difference between the heat source and heat sink as large as possible.

Note added on August 6th:

In the orginal post I used an example of the efficiency of a refridgerator (a heat pump) for which I used the wrong equation as was clearly pointed out in many reactions. I apologize for this problem. I have removed this part of the post since it will sent the reader in the wrong direction.


1. With work we mean here the ability to lift weights, or to to turn wheels which in turn can rotate shafts.

2. That is well known as the Carnot cycle.

Good points!

It should be noted that higher efficiencies can be realized using compressors/expanders to increase/decrease the temp of the heat sink and cold cold sink. This is done by concentrating heat using the compressor and extract much more energy than the original Carnot efficiency would allow. This compression costs energy, but you expend more to get more.

Fridges also work using the house as a cold source, and the fridge inside as a heat source. To accomplish this the heat flux storing material must be expanded such that its temperature is below that of the fridge inside, the hotter fridge then transferrs heat to the cold flux. The cold flux is then moved to a compressor, and is compressed to hotter than the house temperature, the cold flux not hot, contributes heat to the house!

It really is best to take a course on thermo, preferably an engineering one which actually deals with enthalphy and entropy of different mass streams. You will learn a great deal of practical knowledge which will save you money. (combined with engineering finance and you can do ROI/ROE for housing equipment you purchase and when is the best time to replace!)

Replacing an aging refrigerator with an Energy Star model decreases electrical consumption substantially. Maybe as much as 80 to 100 kwh per month according to my records. I also replaced the washer/dryer and dishwasher with very efficient models at the same time as the fridge replacement.

Dr. Schmitz presents a good description of the entropy problem. The beginning of his article is almost the same as that of David Goodstein in his little book, "Out of Gas" (Norton, 2004), which I happen to be reading just now. Dr. Goodstein is a physics professor at Cal Tech. Schmitz misses a minor point in not mentioning that the temperature to be used is absolute temperature, that is, degrees Kelvin in SI units, although he uses Kelvin in his calculations.

Unfortunately, he completely screws up the energy efficiency calculation for a steam engine, using the boiling point of water at atmospheric pressure as his high temperature. Steam boilers operate at a much higher temperature and pressure than this and the efficiency of a steam power plant is much above his calculated 25% Carnot value as a result. The same is also true for an automobile engine, when operated at peak efficiency, which is seldom the case for a gasoline powered vehicle.

Worse yet, his description of a refrigerator is also completely incorrect. Refrigerators (and air conditioners) operate by reversing the Carnot cycle, in a sense. They use energy from some external source to pump heat to a lower enthropic state at a higher temperature. In so doing, they "create" more enthropy than the reduction in enthropy that is produced as high temperature fluid or exhaust air. The temperature of the "exhaust" heat exchanger is above ambient temperature. As Goodstein pointed out, the thermal energy made available at the exhaust temperature compared to the temperature of the inside of the refrigerator can not then be used in another heat engine to recover the initial input of energy by the electric motor. That would be a perpetual motion device. As for the efficiency of the appliance, that could be defined as the difference between an ideal heat pump with Carnot efficiency and an actual system using some real working fluid, real pumps and real motors. The SEER rating of an air conditioner is another thing entirely.

I guess Dr. Schmitz's confusion to be expected from someone without a background in physics or mechanical engineering. Perhaps his experiences working with electrical engineers has clouded his vision. That he gets it wrong just shows how difficult it is for people to understand the energy problem, especially as so few of us have engineering or science degrees to begin with.

E. Swanson

I have to agree, at least in my limited knowledge. The refrigerator efficiency calculation seemed senseless.

I wonder if TheOilDrum could use a little more "prescreening" of articles! Sorry for criticism...

Schmitz did say an "atmospheric" steam engine, i.e., not pressurized.

And a vacuum is applied to the other side of the piston?

No vacuum involved, just compression/expansion of

Where IS that 'Theory of Everything' ?
it is !

I am presently in vocational training in HVAC/R.

RE: "atmospheric"

That is a non-rigorous term. All refrigerants have a change of state that enables them to move heat from one place to another. The change of state is dependent on temperature AND PRESSURE. PSIG a parameter of regergerants is an absolute value, atmospheric is a relative value, i.e. at about 1200 feet elevation PSIG is 14.7.

Where IS that 'Theory of Everything' ?
it is !

But why do you link to a crank science site in every sig? How do you expect anyone to take you seriously?

Am I asking an old question here or does this guy troll for this sort of nonsense every time he posts?

Am I asking an old question here or does this guy troll for this sort of nonsense every time he posts?

I quit posting much of anything that challenges
conventional wisdom cause of this attitude. History of technology is full of these kind of attitudes. I'll let time
solve this issue. Or not.

But why do you link to a crank science site in every sig? How do you expect anyone to take you seriously?


So what's the difference between this link on this issue and other over more controversial issue's ?

Don't answer, it's a rhetorical question.

To TOD Staff: Thank you for a personally
valuable site. I just hope it stays free. I will read it as much as I can. But I will keep my posting within limits of conventional thinking. I hope air conditioning
technology is conventional enough.

Where IS that 'Theory of Everything' ?
it is !

I am presently in vocational training in HVAC/R.

Try expanding your curriculum to include history of technology instead of tinfoil-hat physics. You might even get better at your job. And you would certainly be better informed about the situation we are discussing on TOD, and how we got to where we are.


The cylinder was filled with steam from a boiler (usually below it). This was condensed using a jet of water. The resultant vacuum pulled down one end of the beam, thus operating the pump attached to the other.

I found that by typing atmospheric steam engine into the Wikipedia search box and clicking intelligently. You may have heard of Wikipedia, by the way. A couple of minutes there can save a whole lot of wasted time, effort, and typing, both your own and other people's, in a forum like this. And you get to learn things instead of attracting abuse.

Would it be possible to implement an automated test of the ability to use simple online reference tools like Wikipedia as a pre-qualification for posting privileges on TOD?

In a rush, I erred - I responded to 'atmosphere' as
a adjective not a noun, since it was in quotes. I am guilty.

New sig. Heh.
in EM Theory

Would it be possible to implement an automated test of the ability to use simple online reference tools like Wikipedia as a pre-qualification for posting privileges on TOD?

I like this idea (and not just for TOD).

However, TOD has more pressing needs.  One of them is a review system which allows pieces like this to go before more eyeballs before they get posted.  TOD has people with the technical chops to catch errors like Schmitz's before publication, but Drupal doesn't allow read-only access to the publication queue for review purposes (according to SuperG, it's all or nothing).

Commenters are understood (mostly) not to be speaking for TOD.  Our articles are another matter, and I think most will agree that errors in basic science should be cause to return an article to the author for correction before the public sees it.  Drupal doesn't have the features for this sort of workflow, and from discussion behind the scenes I can tell you that the people most intimately involved don't think it will be easy.

This sort of thing may happen again.  I just want to make clear that the problem isn't the people so much as the system we have pressed into service for TOD.

Does your VocEd include a grounding in classical thermodynamics?

If you don't understand the details of the "theory of everything" you link to, do you have any business promoting it?

i am niether a scientist nor an engineer
i am totally a layperson when it comes to this. but i have read a little about thermodynamics through books like "Entropy," from jeremy rifkin etc.

my understanding:
The Nature of Energy

Energy cannot be created or destroyed. It can only change form -- From radiant energy to mechanical or electrical etc. In other words, the amount of energy in the universe is constant. There is just as much energy in the universe today as there was thirteen and a half billion years ago. The difference between now and then is that the amount of high quality energy is not the same. It has declined.

i like to think of it in terms of an hourglass with a waterwheel inside. The amount of sand in an hour glass.
Remains the same; and as the sand falls, it has the ability to spin a wheel. But you can't turn the hourglass upside down and start over again.

There is highly organized energy or high quality energy in a high state, and there is low quality diffuse energy in a low degraded state. As energy flows from a high state to a low state, it has the ability to do work. Heat always flows from hot to cold, never the reverse. Work is only done as energy flows from a high state to a low state. In the case of Industrialism, work is normally done as heat generated by burning hydrocarbons heats a turbine that generates useful electricity.

Exhaust from the tailpipe of an accelerating car, plus friction from the air and ground, equals the amount of energy burned during the trip.

Time measures rising entropy in the universe. The natural tendency is for things to fall apart through time. A highly organized system requires high quality useful energy to continue functioning. As time passes, the organized system ages and falls apart naturally. Large amounts of useful energy are required to prevent decay and eventual collapse. Human beings eat food which provides people with fuel to burn (calories) for energy and raw material to build bodies.

without actually doing the math, i'll probably never understand it like a physicist or an engineer...
but i do intend to buy the book "The Second Law of Life: Energy, Technology, and the Future of Earth As We Know It."

anyone and everyone please feel free to correct me. got to go.

Yes, applying the smell test to his refrigeration calculations downright curled my nostril hairs.

With his formula, if you take the fridge down to absolute 0 efficiency approaches 100%!!!

Pretty obviously bunk.

If the heat sink was 0°K, the efficiency would indeed be 100%.

I also have no background on physics or mechanical engineering (out of what is common to computer engineering), but would never make such mistake.

That is plain common sense (once you know about entropy) that it should be easier to create a small temperature gradient than a bigger one, as it is easier to exploit a big grandient than a smaller one.

A engineer background isn't even needed to know that. At least around here, Carnot cycles and steam machine efficiency are hight-school knowledge.

Such an ignorance from a person with that curriculum is not excusable, and TOD would be better without this article, since it makes such a gross mistake and adds so little (most discussions about wasting energy around here have very little to do with theoretical limits, but with practical ones imposed by economics or lazyness).

FYI, I cringed when I read through this post.  Unfortunately, I was not in a position to so much as comment about it publicly until today.  TOD's software doesn't allow the full list of editors and contributors to review posts before publication, and this lack of review resulted in the publication of something which should have been held for correction.

The performance of a refrigeration cycle actually increases in situations where you are trying to move heat against a relatively modest temperature gradient. So a refrigerator can in theory be more effective than a freezer, and so on. In fact, for modest temperature differentials, you can actually move significantly more heat than the amount of work you put in.

The important parameter is called Coefficient of Performance (COP), and it's defined as:

COP = Ql/W = (qty of heat removed from cold side) divided by (qty of work done by the motor)

The best possible theoretical performance occurs in the reversible case, where

COP = 1/[(Th/Tl) - 1]

In this case, we have 1/[(293/283) - 1] = 28.3

(all this is from Engineering Thermodynamics, by Cravalho and Smith)

In reality, you will never get performance this good, but you can certainly get COPs well over 1 from common appliances. That's why it can make sense to use a heat pump.

that's a good thermo book, got it stitting on my shelf.

heat pumps always make sense to use because they yield more heat than simply using the electricity for resitive heating alone.

and when trying to get heat the turbomachinery doing work (compression) adds that heat to the mix! the working fluid cools it down! So you end up with some nice numbers!

the explanation is not super bad, just pretty bad.

if there were no numbers involved it would be okay.

Please to examine constructions English posting before to on Oil drum being.

Sentences constructed in the badly sense are to the hard side of the reading spectrum unfortunately.

Is to translate difficult from Dutch or German to English sentences.

Seriously, though, I've seen hilarious bulletin boards in Dutch offices, full of postings of failed attempts by native Dutch speakers to write coherently in English. Distorted Latin vocabulary riding over distorted Germanic grammar is tough stuff. So give the guy a small break on that.

But no break on that whopper of a theory of refrigerators.

I'd suggest however, that some of the biggest "wastes" of energy are little to do with the 2nd law of thermodynamics, but rather, using energy to do "work" that has little benefit: e.g. the energy used to move a 2 tonne vehicle, when all you really need is the ability to move a 80kg person. Or the energy used to light and keep the temperature of large buildings within a tiny range, when we could work just as effectively with small amounts of light just where we really need it, and minimal amounts of heating and cooling in specific areas.


those numbers in the right hand column, one minus that number is the inefficiency!

Now consider a typical installation will spend roughly 35% of its electricity budget on lighting! Which means 3% goes to lighting at best, and 32% goes to space heating!!!

With engines think about the fact that if current efficiencies of 10-15% were magically doubled to 20-30%, one could support the SAME WEIGHT and go twice as FAR!(this isn't the relationship in reality but it's close)

or one could halve the weight, double efficiency and go 4 times as far.

weight is only as much of a problem as you make it. electric cars with regenerative breaking offer some nice things such as recapturing 80% of the energy used to accelerate that 2080kg mass and using it later, thus making it as if you are accelerating a 416kg mass.

Or people could use bicycles, or electric trains...

My point is from the point of view of what end-result we are trying to achieve: i.e. getting a person from point A to point B in a reasonable amount of time, many of easiest ways to wasting less energy have little to do with the 2nd law of thermodynamics...I don't see how I'm "wrong" in that regard. In fact, one can go further and say that the end-result isn't getting a person from point A to point B, but rather allowing the person who is currently at point A to acquire/interact with items/people at point B. In which case, actually physically transporting the person isn't always necessary. I work from home 4 days a week, and it would be a ridiculous waste of energy for me to travel 15km to work every day, when I can achieve the same result staying at home. Likewise, instead of travelling 15km to a particular shop to buy an item, I could look for a closer shop, have it delivered, or wait until I happened to be going that way anyway. Same result, but wasting far less energy.

And as far as heating & lighting goes, I don't really understand your point. I'm talking about the difference of a one or two people living or working in a large poorly-insulated, poorly-situated house, that is constantly heated/cooled and lit throughout to keep at a specific temperature 24/7, and one or two people living or working in a comfortably-sized, well-insulated and well-situated house/apartment, and only heating/cooling/lighting specific rooms when genuinely necessary. How can than not generate significant reductions in energy wastage?

Thanks for the reactions to my contribution Why We Waste Energy.
Allow me to make a few comments.
First about the efficiencies of a power plant: sure you can increase that by working at above atmospheric steam pressures that take the temperature of the heat source up. Then the Carnot cycle will give you higher efficiencies, and indeed that is what happens in practice. But fact of the matter is that also in that case the upper efficiency will still remain limited by the Carnot cycle and runs at about 50% best case.
Second my remark about refrigerators: they are big users of electricity in a normal household (see for instance http://www.nypa.gov/press/2003/030211a.htm ), that was my main point I tried to make. Certainly you can make improvements in the efficiency by compression but for safety reasons you do not want to take the exhaust temperature up too high. Thus the fact remains that there will be a relatively small temperature difference between the cold and hold spot of the refridgerator keeping the overall efficiency low of this type of devices and that leads then of course to large electricity bills…
Therefore I still think that Carnot's efficiency rule is the root cause of our "waste" of energy.

John Schmitz

You still don't have this right; the smaller the differential between the temperatures in a refrigerator, the HIGHER the efficiency of the cooling.

It is the OPPOSITE of an engine.

And yes, they do use a lot of energy anyway.

No, no, no.

To use as little electricity as possible to keep a refrigerator cold, you want the refrigerator's 'exhaust' temperature LOW, which is why they put all those radiating fins on the coils. The smaller the temperature difference, the lower the 'exhaust' temperature, the easier it is to pump the heat out of the enclosure.

The refrigerator is the automobile engine or electricity generator Carnot cycle run backwards, so the math works the other way.

For our general readers, note that the original (and incorrect) refrigerator computation actually illustrates the uselessness of low-grade heat as an energy source. You get very little high-grade energy - electricity being of the highest grade - out of it. But by the same token, you can pump a lot of low-grade heat with a fairly small amount of electricity or other high-grade energy.

In the real world, a lot of energy 'waste' is due to some combination of friction and the sheer expense or inconvenience of doing things more efficiently.

For example, steel wheels on steel rails exhibit much less friction than low-pressure rubber tires do on any surface. (BTW the theoretical minimum energy needed for any round trip is zero.) The problem is that rail systems are only economically viable in areas, such as the Randstadt, metro Paris, or Tokyo, that are crammed to bursting with people. In the vast spaces of America or Australia, you find fewer of them, and they may not run often enough to be of much use.

For another example, refrigerators can be made to use less electricity by thickening the thermal insulation. The problem is that as you thicken the insulation, you very quickly leave less and less room to store food, or else you have to rebuild the house or apartment to space for an enormous, awkward box.

And yet, going from 2 to 3 inches (5 to 7.5 cm) of insulation would help a lot without using up a lot of space... I'm amazed how thin the insulation is in older USA refrigerators. The latest ones are significantly better, but still reflect a values system that considers space far more valuable than electricity.

when will refridgerators go to airgels.


the mean free path length traversing an aerogel is huge, more heat is likely to escape from a single screw to bolt parts together than all the aerogel used to insulate the fridge.


I must again take exception to what you write. There are real world systems called Combined Cycle plants which burn natural gas or oil in a gas turbine and then use the exhaust to drive a steam cycle turbine generator. They are said to be capable of efficiencies above 58%. Siemens and General Electric sells them:


Such systems have been proposed for converting coal to electricity also, by gasifying the coal.

E. Swanson

The other posters railing at you are correct, and you are wrong.

An isentropic refrigerator with a cold-side temperature of 4°C (277 K) and a hot-side temperature of 35°C (308 K) will reject (308/277) joules for every joule of heat it takes up.  The input energy is the difference, or (31/277) J/J; the refrigerating coefficient of performance is thus 277/31 or roughly 8.9.  The greater the temperature difference, the lower the maximum coefficient of performance.  If the hot-side temperature can be lowered (say, by using the condenser to pre-heat the domestic hot water supply) the CoP can go up even further.

Another word for the "concentration of usable energy" in a carrier is its EXERGY. ( Google link )

From Wikipedia:

In thermodynamics, the exergy B of a system with respect to a reservoir is the maximum work done by the system during a transformation which brings it into equilibrium with the reservoir. ("Reservoir" in practice is the surrounding with high capacity for receiving heat). Energy that has a high convertibility potential is said to contain a high share of exergy. Electricity and mechanical work are perfectly convertible and for these forms exergy contents equals the energy content. For nuclear and fossil fuels theoretical conversion potential is close to perfect, but severely limited by available technical processes. Reversely, heat at temperature close to the reservoir has low convertibility potential, the exergy content of such heat is much lower than its energy content. Exergy analysis is used in the field of industrial ecology as a tool to both decrease the amount of exergy required for a process, and use available exergy more efficiently. The term was coined by Zoran Rant in 1956, but the concept was developed by J. Willard Gibbs in 1873. Z. Rant introduced also the concept of anergy, which is the complementary part of the (heat) energy that can not be converted into work.


anergy is also known by the true name entropy.

One way of cheating this is if the condensation temperature gives heat energy that is usefull for some industrial process like drying or heating homes or greenhouses or running absorbtion coolers. This often means giving up some of the mechanical energy extracted in a turbine to make the waste heat hotter and more usefull.

John: with regard to your fridge example I think you are using the wrong equations, the ones for heat engines, not fridges.

The first step, I think, should be to calculate the Coefficient of performance for an ideal or "Carnot limit" fridge at the temp. specified.

Using the constants you did in your example:

COP "ideal" = Tl/(Th-Tl) = 283 / 10 = 28.3
Tl = temperature low and Th = temp high in deg. Kelvin

so the best "theoretical" fridge could move 28.3 units of energy from the cold to hot sides of the unit for each unit of energy supplied from the electrical outlet at these temperatures.

Given that we need to move 40,000 joules in your example we would need to add 40,000/28.3 = 1,413 joules of energy to do the move.

1 watt hour = 3600 joules so that's: 1413 / 3600 = 0.39 watt hours.

You have specified a 350 watt cooling plant so: 0.39 / 350 * 3600 seconds in an hour = 4 seconds of run time on the motor to cool the water not one hour.

Now no real fridge can achive the Carnot limit. To qualify for the "Energy star" rating a real fridge needs to meet a COP of 3.6 or better

Such a fridge would need to run 7.8 time longer than an "ideal" fridge to cool the liter of water, or about 30 seconds, if it had a 350 watt power draw as per your example.

This does not include other losses such as through the walls of the fridge, rechilling the air inside the fridge when you opened the door etc. but these were not in your example, so I didn't worry about them

Why do we waste energy?

Because we can.

Because we must.

And perhaps intelligent life must waste all the energy it can?

[trust me, it's worth thinking about before pointing out the obvious]
Jaymax (cornucomer-doomopian)

The only worthwhile post in this thread :)

Because it's cheap and abundant. About to change, thankfully.


Why so? Having cheap and abundant energy no doubt provided a dramatic boost to the pace of technological development, and has helped improve living standards greatly. But it's also caused us to severely threaten the stability of our climate system, and made us wasteful, and somewhat lazy and complacent, both at a consumer level and at a manufacturing and innnovation level: if energy stopped being cheap 10 or 15 years ago, we could well be all driving EVs by now, for example. Nor would we be overeating as much, or constantly buying cheap consumable goods that break or go out of fashion in 5 years, and end up as landfill.

Which is not to say I don't expect to see a fair bit of hardship from dramatically increased energy prices and possible shortages, but I don't see why in the long run it cannot be for the better.


Thanks for pointing out your concerns. In my haste I did indeed mix up the formulas of a heat engine like a steam engine and a heat pump like a fridge. Appology for that.
But for both the Carnot cycle is the starting point (in different directions though) and poses an upperlimit to the efficiency that we can get, right?
We simply cannot escape Carnot principle and will always get less favorable results than the ideal reversible case.

Interesting dialog

As soon as I read this:

an efficiency as poor as 50% or often even lower

I was concerned about the logical integrity of the post, but then reading on, I gave some ground, spelling and grammar making me make allowances for use-of-language.

What I'd like to know from the critics, who understand the physics, is whether the statement

Suppose you want to cool one liter of water from 20°C to 10°C ... you have to extract ... about 40kJ. ... it will "cost" us about 1300kJ.

is fundamentally correct or not.
Jaymax (cornucomer-doomopian)

The part about 40 kJ is about right (1000 grams * 4.18J/g-K * 10K).

Per the discussion above, the amount of energy required to do the cooling is less than this, not more.

Folks, my apologies.

Various miscommunications occurred prior to the posting of this piece, the first being that I thought it had been copyedited, so I didn't read it over as I have been in and out of meetings today and haven't had time to read it over until now.

Second, as for the substance of the post, well that's already been well documented in the thread. Sorry gang.

S'okay.  The system as set up is practically built for errors like this, and it's no surprise that they happen.  That they happen when people are busy and harried should be expected.

My comment is that a technique used in Combined Heat and Power (CHP) projects is to max-fire a Heat Recovery Steam Generator, HRSG to use all of the Oxygen available in the Gas Turbine. This max-fired CHP type of power plant is 92% or 93% thermal efficiency. One example might be a 15mw gas turbine max duct fired to make 250,000 pph of steam for an industrial plant or for a University or for a large hospital etc. Between the steam and the gas turbine generator kw, total thermal efficiency is about 92%. It is possible to get slightly higher to 93% if a back pressure steam turbine is added to the process.

So many more CHP plants would greatly help . Also they avoid the very large penalty in electric transmission losses. They save perhaps the most emissions and CO2 simply be being far more efficient.

So my point is that with Peak Gas and Peak Oil, more than ever - we need to maximize efficiency first and that CHP is one excellent way to help continue to grow the economy with a fixed amount or even a decreasing amount of fuel. It is not a panasea but simply (I think) the first step to take. First use efficiency improvements starting with maximizing worldwide CHP to help manage the problem. We still must do much more and this only buys time but at least has an ROI even if 10yrs.

We have many barriers to CHP but it has really developed rapidly in Europe (especially Denmark) and amazingly in third world countries putting in new process plants, food and drug plants, paper mills, etc. This happens while USA CHP investment suffers.

>electric cars with regenerative breaking offer some nice things such as recapturing 80% of the energy used to accelerate that 2080kg mass and using it later, thus making it as if you are accelerating a 416kg mass.

There's a fallacy here. Braking has to be done at high deccelerations, at least in an emergency. The generator has a finite power rating as does the battery the energy is stored on. Now figure out the mass of the generator and the mass of the battery that stores the regenerative braking energy. How much mileage does it cost pushing that extra weight up and down hills?

I'm sure you can get 80% efficiency on the test track. I don't think you can get it in a supermarket parking lot.

In the real world of electric cars the more likely efficiency of regenerative braking for cars is 66%. The drive train efficiency is usually around 0.98, then motor efficiency is 0.92 (at beat), the energy absorbtion of the battery at very high charge/discharge rates is 0.90, then the conversion back to mechanical energy by the motor is again 0.92, with the drive train again at 0.98. Multiplying this out equals 0.66.

Better to recoup this energy then waste it in friction braking.

Trains can much better recover the kinetic energy of braking with hybrid locomotives because they have much slower acceleration, large battery packs, and higher drive train and motor efficiencies.

Last comment I want to make is that waste heat from air conditioning and refrigeration can be useful. If the heat rejected from the condensor (heat of enthalpy from phase change going from gas to liquid) is used to heat water, then energy is saved. This is possible because most condensors operate near or above boiling point of water, while most domestic potable water needs to be only 50 deg C or 135 deg F.

This system would have major natural gas or electrical energy savings for restaurants, pubs, and office buildings. But, these heat recovery devices are not built due to long time to recover capital invested in such a system. Government tax incentives in this area would save millions of tons of coal or billions of cubic feet of natural gas over the lifetime of such systems if used by all commercial and industrial users.

The worst case seems to be pumping heat out of the fridge into the house then cooling the house with a compressor air conditioner.

OK, we see the problem. Now who can supply a refrigerator that can:
1 In winter use ambient/outside air temp below 4C to cool.
2 Not heat the indoors during air conditioning conditions.

I assume a 'split system' like groceries stores use would fit the bill, but I have never seen one in a house.

I also know there are 'meat safes' and I've lived in places where I can leave the outside freezer unplugged for 5 months. But I mean something that most of civilization would like to have in their house.

A refrigerator is a type of heat pump. A heat pump may have an efficiency of 300% - for a small temperature gradient.

Need I say more?

Wouldn't that be creating energy?

A heat pump doesn't create energy it just moves it from one place to another. It's like the fuel used by a tanker truck to carry gas from a refinery to a gas station. The truck may use 100 gallons of fuel on the round trip but deliver 10,000 gallons. Refrigerants have different latent heats at different temperatures and it is this difference which the motor of a heat pump must provide.

I want to have an off grid , cool vault ,for storing seeds

Any other links ??

Build something with a large thermal mass to even out differences in the chilling rate and insulate it well. Then you can run the chilling on an intermittent power sourse such as a windmill that can power a compressor directly but it is probably cheaper to use off the shelf electrical parts.

If you have seasonal ice from cold winters you can use natural ice as a chiller and thermal mass and relie on insulation and filling up with ice once per year.

I would start with researching how to keep the humidity at the right level in the seed storage volume and how to avoid condensation to ruin your insulation. Or you could rebuild the insulation with straw and sawdust each year.

I guess the smallest reasonable solution is a common but large electrical refridgerator, filling it mostly with water as thermal mass and powering it with a small windmill.
Add more refridgerators and windmills and spare parts for redundancy and you can run it for 10-20 years. A larger cruder refridgeration systems, a simple mechanical shop and a stock of raw material and it can be run for generations.

Not using ready made parts probably becomes easier as you make the storage bigger and add more labour. And if the idea is to get a system for working thru bad years it would be better to have more labour in a company or community running the seed storage and farming in a larger scale to get produce to eat and sell and keep the seeds cultivated and renewed.

you may not need a fridge if the seed is dried correctly and stored at the correct humidity, in many cases normal "unheated basement" conditions will do fine at least up to 5 years or so storage times for many varieties.

Some good info here: