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Thermodynamics of home heating

This isn't a real research post, but my friends/colleagues thought I was wrong when I explained this to them so I want to see what others think.

I live in a condo and my apartment is heated by electric baseboard units (call this heating electricity). Like everyone else I also use electricity to accomplish domestic tasks such as lighting, cooking and refrigeration (call this working electricity).

I argue that the inefficiency with which I use working-electricity processes in my home is irrelevant to my electricity consumption because all the electricity used by these processes ultimately becomes heat. This applies not only to 'wasted' energy such as the heat put out by light bulbs, but to the work I'm using the electricity for, such as the light itself. That's because work becomes heat; for example light becomes heat when it is absorbed by the surfaces it hits. Thus every watt of electricity I use for cooking or lighting sooner or later becomes heat, and as such proportionately reduces the amount of electricity I need to send directly to the heaters. In effect I'm getting my working electricity for free.

The argument doesn't apply to working energy that gets lost as light out the windows or sound through the walls or hot water down the drain. And maybe not to the energy equivalent of the information I'm transmitting to Blogger with this post, though I suspect that is somewhere between infinitesimal and nonexistent. But it applies to everything that happens in the apartment.

The argument also doesn't apply when the weather is warm enough that any heating needed is less than the heat produced by working electricity. And if the weather ever got hot enough that I used electricity for cooling, I'd be paying double for the energy wasted by my working electricity - e.g. once to run the computer and once to run the air conditioner to get rid of the heat.

And it wouldn't completely apply in winter if I was able to use natural gas or a similarly cheap energy source for heating. But, given that I'm stuck with expensive electrical heating, I console myself with the thought that all the rest of my electricity is free.

So, blogosphere, do you agree?

13 comments:

  1. This is well explained but there are details that need to be disclosed.
    Like, does the heating electricity only heat to a defined temperature?

    If the heating electricity turns off at a certain point (ex 22ºC), then the working electricity might contribute to that heating process.

    So, instead of only the heating electricity warming up the apartment, you'd have the contribution of the working electricity. Anyhow, energy goes into cooking and into you after cooking, so it's not totally free electricity, but you're getting two products for your penny, heat and work while cooking, for example.

    Put lightly, your working electricity is relatively cheaper because it helps with the heating while getting the work done.

    It's mostly a question of defining a system and then checking where the heat is being produced, accumulated and consumed

    You didn't present the discordant argument of your colleagues. I'm curious to read their opinion.

    ReplyDelete
  2. "all the electricity used by these processes ultimately becomes heat"

    This statement appears correct for processes that "completely" convert over a relatively short period of time. For example, the heating of water by an electrical stove. The energy not lost as heat during the heating process, is what raises the temperature of the water (~ the work) and consequently produces a thermal potential. By the time you have finished your meal, the water will have cooled down close to room temperature - thus the input energy is "fully" converted into heat; unless of course, you create an open system by draining your pasta and vegetables in the sink.

    But keep in mind, there may exist appliances that transform part of the work into non-thermal potentials, such as mechanical, chemical, electrical, elastical, etc. And these may not decay within the lifetime of your apartment.

    The above mentioned potentials are reversible. However, what happens to the work in irreversible processes? I'm not sure of this, but it seems that these just gobble up energy, without necessarily increasing order! For example, heating an egg or mixing via a blender. At the moment that doesn't make sense to me. Maybe http://www.biophysics.org/education/cramer.pdf will help.



    "the inefficiency with which I use working-electricity processes in my home is irrelevant to my electricity consumption"

    If you do indeed adjust your heating accordingly, I believe you are correct. I don't think this is such a great advantage, however, as most of your appliances' heat loss is relatively small. Accidentally leaving a window open for a few minutes may cancel out all your "gains". But in principle I think you are correct.

    ReplyDelete
  3. "The above mentioned potentials are reversible."

    Here I use the term reversible in the conventional sense. For example, a battery is "reversible", while in fact it's not completely reversible in the thermodynamic sense.

    The potentials I'm speaking off are intermediates. They are part of the transduction of energy and contain "ordered" or "useful" energy.

    ReplyDelete
  4. I would say you're correct to first order. I can think of three ways that your assumptions can brake down though.

    One is that if you're cooking (or especially baking) in the kitchen the temperature will probably exceed the temperature set on your thermostat the rate at which heat flows out of your house will be higher than if you had not cooked (since the rate of flow of heat depends on the temperature difference between inside and out).

    The second way is related but probably a smaller effect. To illustrate the point, imagine an extreme case where you had, say, a big old-fashioned TV right next to a window. If it locally heated the air around the window to a temperature higher than that set on the thermostat, you would also be wasting energy in that case.

    The last way is that you might only want to have parts of the house heated at certain times (e.g. the bedroom at night). In that case, if the computer was heating the air in another room where the main heat is turned off, that would also be wasted energy.

    ReplyDelete
  5. I could have agreed with you even more simply if I could have understood better what was your fundamental question -or not.

    But even without that, as I point out to my dear husband every time he farts in our bed and then pretends to be doing so to generate some heat, the fortuitous generation of heat by your appliances may be produced at very unwanted places. For example, while cooking a very energy-demanding dish you may be liberating thousands of kilowatts of heat in the direct environment of your kitchen but this may not be the best place to do so, as during that moment your hungry guests will be freezing while waiting for your dinner.

    It is not unusual in my home and in the freezing winter to open the windows to cool down the scorching kitchen while having guests in the living room comfortably discussing in from of a heat-warming fireplace: the whole problem is in the very uneven distribution of the precious heat in our homes.

    A while ago, while hiking in the countryside with an industrial architect friend of mine, we came across an electric power station that was liberating in the atmosphere huge plumes of steam from its cooling towers. Excess heat. I asked him, "as an industrial architect, couldn't you design something to do with this heat, let's say, grow plants in greenhouses during the winter?". His answer was: "this is like asking people to fart in the right place".

    ReplyDelete
  6. Ricardo Vidal wrote:

    "Put lightly, your working electricity is relatively cheaper because it helps with the heating while getting the work done."

    I hope you see how light your comment is: what if you are in the middle of the summer and you need to cool it down?

    Therefore and according to your logic: whatever gain you may do in winter, you waste it in summer.

    You talk about "defining a system". Well, have at least that into account!

    ReplyDelete
  7. Kinetics also matter here since you are usually heating the room while you are in it (when you usually are using the other technology as well). If the electric heaters are well placed then they are designed to quickly give you the feeling of warmth. The heat in the lights for example may be in places where they will not quickly heat the room (or where currents carry them to a room that you are not using). Also if the lights are next to the windows, heat is radiating out of the room. Initially then much of the heat would not be heating the room. The electric heater generated heat obviously would soon radiate out as well, but the current would give you the feeling of a warmer room. As others have noted, during periods where you don't want to heat your room but use the the equipment/lamps

    ReplyDelete
  8. Valerie,

    The post is relative to winter, hence the heating electricity. If it were summer oriented, we would be talking about a different scenario, right? :)

    We all seem to agree with the post to a certain extent. There are easy breaking points in the logic at hand, like sebastian has said.

    ReplyDelete
  9. If more people learned "to fart in the right place" - or, indirectly increase efficiency via multi-step processes much akin to those found in nature - this world would be more sustainable. Sadly, cost effective solutions are slow in their development.

    But, just reading the original post before publishing a comment would satisfy me for now...

    ReplyDelete
  10. Ricardo

    "The post is relative to winter"

    Sorry, but that is not obvious at all.

    Read the original post once more very carefully, word by word, in search of any clue that would limit the proposed theory only to a winter situation, please.

    It is just question of "heating", but "cooling" is just the same bloody thing, if you haven't yet realized: to heat somewhere you must cool somewhere else, and to cool a place, you must deliver the heat to another place.

    Simple, very elementary physics.

    You should then fully agree with me: wouldn't the world be an extraordinarily better place if nobody ever farted in the wrong place?

    Unfortunately that doesn't seems to ever be going to happen systematically, I am afraid...

    ReplyDelete
  11. Valerie,

    My bad. I read something about "if it were warmer" and knowing that Rosie is in BC, Canada... I assumed the Winter temperatures.

    I can't see where my thermodynamics went wrong because I totally agree with you.

    And by the way... the flatulence part was just brilliant! :)

    Cheers,
    Ricardo

    ReplyDelete
  12. Valerie said:

    "to heat somewhere you must cool somewhere else, and to cool a place, you must deliver the heat to another place.

    Simple, very elementary physics."

    That's not true. Energy is conserved, but heat is not so there doesn't need to be a balance as you describe. What cools down when I light a match?

    ReplyDelete
  13. Sorry it's taken me a while to respond to these comments; I've been drowning in teaching responsibilities.

    Valerie, I did point out that the argument doesn't apply in weather so warm that I don't need heating (in Vancouver we call that summer).

    Bob and Valerie, in response to your concerns about heat not being evenly distributed, I could use a fan to mix the air. The electricity this consumed would move air molecules, ultimately producing heat.

    Sebastian, I'm not sure about the energy that goes into denaturing egg proteins. The denatured proteins are actually in a more random configuration - the heat just helps them get over a hill - so they may contain less energy than before they were cooked. Same for most other cooking - it's increasing the entropy of the food.

    Rosie

    ReplyDelete

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