Author Topic: CFLs are zero sum energy users - tell me this is crap (or not?)  (Read 6506 times)

nereo

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Ever encounter a very smart person who believes something so contrary to what you think could be the truth that you are left shaking your head?  I'm not talking about religion or politics.  I mean something that seems so quantifiable, so 'common-sense' - like home energy conservation.
Here's what happened.  Keep in mind this is during the winter (key to his argument).
My boss (who's highly educated) has your typical suburban family and life, complete with all the mindless spending that often entails.  His 2500ft2 home is illuminated by CFLs, and given the size of hte house, there are a lot of them.
Over the winter I was over there and couldn't help but notice that every light in every room was on, even though no one was in most of the rooms.  Without thinking, every time I left a room I flipped the lightswitch off.  "Leave them on, leave them on!" he keep saying. 
As I was there I did a mental count - probably 25-30 bulbs all burning brightly, most of them on for 24hrs a day.
Finally I had to ask why he minded that I shut the lights off when I left a room.

His answer: "It's not that I mind you shutting them off, it's that there's just no reason to.  Later I just have to turn them back on when you leave."

Me:"um... well what about electricity?"

Him: "Common [smug look on his face] - you know better than that.  Any light is absorbed by the things around us and turns into heat.  since we're heating the house already, you don't loose any energy leaving the lights on.  It just slowly heats the room.  There's no energy loss, at all.  It's a zero sum game.  What we'd save in lighting we'd pay for by heating the house a tiny bit more."

Me: "Um... ok... well they'll still burn out faster if you leave them on 24/7"

Him: "yeah, but not for years, especially if you aren't constantly turning them on and off. Plus, the bulbs cost less than a coke! [I'm assuming he's talking convenience-store, single bottle inflated prices]"

So is he completely nuts, or can he get away with this argument?  I understand his "conservation of energy" theory but I've also calculated that he's using 8-10kw per day on lighting alone for a house where everyone is either asleep or away at school/work for the majority of each day.  Thoughts?

Jack

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #1 on: June 23, 2014, 03:57:51 PM »
His argument is correct if and only if:
  • the house needs to be heated anyway, and
  • the alternative to the CFLs would be electric resistance heating

If it is not winter, or the house is unoccupied, or the heat is supplied by any more-efficient source (e.g. a gas furnace or heat pump) then he's wasting energy and money heating with CFLs.

By the way, you should tell him that those CFLs are inefficient because they put out so much excess light compared to the amount of heat you get. He should swap them out for heatballs instead! ; )

(Or if he really wants to be efficient -- and this is a less sarcastic suggestion -- he could mine bitcoins in the winter and use the computer equipment to heat his house. I'm almost certain it's still a loser compared to gas or a heat pump, though.)

nereo

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #2 on: June 23, 2014, 04:05:31 PM »
His argument is correct if and only if:
  • the house needs to be heated anyway, and
  • the alternative to the CFLs would be electric resistance heating

If it is not winter, or the house is unoccupied, or the heat is supplied by any more-efficient source (e.g. a gas furnace or heat pump) then he's wasting energy and money heating with CFLs.

he's got a new furnace which uses heat-oil (the kind that shows up on a truck).  I can't compute how efficient heat oil is to the heat from CFLs, which was part of my consternation at figuring out his argument.  I agree his argument wouldn't work during the summer when he's not heating his house. 

RetiredAt63

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #3 on: June 23, 2014, 04:05:52 PM »
In winter I have decorative incandescent globe bulbs (6 * 40W) in my bathroom - the rest of the house is at 17-18C, and they warm the bathroom while I am having a shower.  This way the furnace does not have to heat the whole house to give me a warm environment in one room.  In the summer I change them for CFLs, I don't need a warm bathroom, I want the house to cool off at night and stay as cool as possible during the day.

But the whole house!?

deborah

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #4 on: June 23, 2014, 04:24:29 PM »
It is possible (very unlikely, but possible) that the amount of light in the house makes everyone feel warmer than they are, so he doesn't need the thermostat up as high. Even cranking the thermostat down by one degree may make enough difference.

okashira

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #5 on: June 23, 2014, 04:29:37 PM »
Mechanical engineeer here. I know a few things about energy balances and effiencies. :-D

He is 100% correct if his house is heated with electric resistance heating.

Since he has an oil heater, he is incorrect. when his heater burns the oil, approximatly 90% of it is converted to heat that enters the house.

It is true that 100% of the electricity used to power his CFL's is converted to heat, however, he needs to understand the source of that electricity.

Electricity is usually generated by burning another fossil fuel, like oil, and converting it to electricity and delivering it to his home. This is done with 35% - 59% efficiency.
Thus the total efficiency would be 35% - 55% for his CFL's.

If his local electricity has an excess of generation from Nuclear, Solar, Wind or Hydrothermal, then his CFL's may actually be a better choice.


warfreak2

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #6 on: June 23, 2014, 04:30:35 PM »
He also doesn't really understand physics. All of the light gets converted to heat eventually, but not necessarily anywhere near his house. I presume he has windows...

Generally, burning any fossil fuel in your home is a more efficient way to heat it than burning it in a power station somewhere else, converting the heat into electricity and then back into heat again. As long as you're aware that fossil fuels (including oil) are used in power stations, you don't need to use a calculator here.

taekvideo

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #7 on: June 24, 2014, 12:16:37 AM »
I use the same justification to be a bit more lax on energy conservation during the winter... like using an electric dryer and just venting inside (with a filter) instead of hanging clothes up inside... but I don't go out of my way to leave lights on or anything lol.

nereo

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #8 on: June 24, 2014, 05:05:36 AM »
I use the same justification to be a bit more lax on energy conservation during the winter... like using an electric dryer and just venting inside (with a filter) instead of hanging clothes up inside... but I don't go out of my way to leave lights on or anything lol.
just curious - how do you keep your walls from dripping with moisture when it's cold inside and you run the dryer.  I'd have thought that would result in a ton of moisture in your hose.
On a related note, i've wondered why houses in cold climates don't use some sort of heat exchanger with their dryer vents...like having a loooong uninsulated pipe that dissipates most of the heat inside before pushing cool(er) air outside.  But i'm guessing it's a combination of cost and safety (lint building up in the vent.  Hmmm..

MayDay

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #9 on: June 24, 2014, 05:26:13 AM »
This is part of why we still have all incandescent light bulbs. I hate cfl bulbs, we almost never have light bulbs on during the summer, so it's worth it to me. We will probably try out led bulbs sometime soon, though, as those get cheaper.

I hadn't thought about the efficiency of the electric generation. The transmission losses alone are huge.

Jack

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #10 on: June 24, 2014, 06:46:36 AM »
just curious - how do you keep your walls from dripping with moisture when it's cold inside and you run the dryer.  I'd have thought that would result in a ton of moisture in your hose.

I can't speak for the other guy, but in my case the forced-air furnace dries out the indoor air pretty well, plus the inside surface of the walls doesn't get cold enough to cause the moisture to condense. (The windows might get a little drippy, but that's it.)

On a related note, i've wondered why houses in cold climates don't use some sort of heat exchanger with their dryer vents...like having a loooong uninsulated pipe that dissipates most of the heat inside before pushing cool(er) air outside.  But i'm guessing it's a combination of cost and safety (lint building up in the vent.  Hmmm..

I think it's a combination of the fact that most house builders are trying to build as cheaply as possible and don't really care about energy efficiency unless it can be a selling point, and that putting a heat exchanger on the dryer vent might be below the point of diminishing returns.

dragoncar

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #11 on: June 24, 2014, 07:57:34 AM »
I admit I've used this justification for higher ( but not ridiculous) lighting levels in winter.  It may be a waste, but it's not as big as you may think.

According to this page (http://sensiblenergy.com/home-energy-efficiency-blog/cost-comparison-gas-vs-oil-vs-electricity-part-1/) it's $2.50 per therm for oil heat and $2.93 per therm for electric.  Yes some energy goes out the windows but I expect this to be minimal given incandescents are only like 1-2% lighting efficicency, glass is reflective, and many people have window treatments.

So you could say you get an 85% "discount" on lighting expenses during heating days.   That's not an excuse to light unoccupied rooms, but may affect your decision to add another reading light.

frugalnacho

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #12 on: June 24, 2014, 08:28:36 AM »
A forced air furnace doesn't dry the air out in winter, heating up cold air makes the air dry.  If it is below freezing outside, and you heat your house up to room temperature, it is going to be dry regardless of whether it's forced air or a boiler, or whatever.  That's just what happens when you heat up cold (ie dry) air.

I am confident his heating costs will be less with oil.  Not only will it be less, but it will have more direct impact.  What good does a light bulb in the back room do you?  Slightly heats up the room you're not in so that your transfer of energy to the outside can increase?

Also it seems odd that he is so fanatical about saving the time to turn the bulbs on and off, but is so cavalier about burning them out.  The best case scenario in the most ideal situation is that the heat generated by a bulb will offset an almost equal amount of oil cost ($1 to run the light will save $1 in heating oil).  All of his bulbs will not be in the best case scenario and the most ideal situation all the time, and that is a lot of light bulbs he is going to be replacing early. 

nereo

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #13 on: June 24, 2014, 07:51:19 PM »
A forced air furnace doesn't dry the air out in winter, heating up cold air makes the air dry.  If it is below freezing outside, and you heat your house up to room temperature, it is going to be dry regardless of whether it's forced air or a boiler, or whatever.  That's just what happens when you heat up cold (ie dry) air.

The comment about walls dripping with moisture wasn't from the forced air furnace, but from a dryer vent that vents inside instead of outside (like the poster mentioned he does in the winter).
Quote
Also it seems odd that he is so fanatical about saving the time to turn the bulbs on and off, but is so cavalier about burning them out.  The best case scenario in the most ideal situation is that the heat generated by a bulb will offset an almost equal amount of oil cost ($1 to run the light will save $1 in heating oil).  All of his bulbs will not be in the best case scenario and the most ideal situation all the time, and that is a lot of light bulbs he is going to be replacing early.
I totally agree that it's strange he doesn't seem to care about burned out bulbs - that's the only solid "hole" i guess I'm getting from this discussion.  Otherwise, it seems like he's "almost" right if you ignore the loss via windows and differences in energy transmission.
for the record i still think leaving lights on is a stupid thing to do, if only out of principle.

TomTX

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #14 on: June 24, 2014, 08:38:02 PM »
I admit I've used this justification for higher ( but not ridiculous) lighting levels in winter.  It may be a waste, but it's not as big as you may think.

According to this page (http://sensiblenergy.com/home-energy-efficiency-blog/cost-comparison-gas-vs-oil-vs-electricity-part-1/) it's $2.50 per therm for oil heat and $2.93 per therm for electric.  Yes some energy goes out the windows but I expect this to be minimal given incandescents are only like 1-2% lighting efficicency, glass is reflective, and many people have window treatments.

So you could say you get an 85% "discount" on lighting expenses during heating days.   That's not an excuse to light unoccupied rooms, but may affect your decision to add another reading light.

A few comments on the analysis:

Using the numbers from the blog presumes 100% efficiency.  His oil furnace/boiler is very likely 85% efficient or worse, which makes the cost equal. CFLs will be 99+% efficient - windows will be tiny losses.

If his furnace and ducting is in unconditioned space (mine is in the attic) - the reduction in heat loss by generating the heat in situ will tip the balance even more toward CFLs. Most ducts are R-6 or lower, and often leak heated air into the unconditioned space. Call it another 5-15% reduction for oil heat (if his furnace is in unconditioned space.)

The blog presumes a $3.50/gallon heating oil price. I'm seeing spot prices for the last couple years often closer to $4/gallon.

Plus, he's probably paying a delivery fee for the oil. Publicly quoted prices are generally for bulk sales, not delivered to the house.

So - it is looking quite likely to me he's right, and even saving money.

Now, I have natural gas - cheap natural gas. No reason to leave the lights on ;)

theSchmett

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #15 on: June 24, 2014, 09:52:35 PM »
So he's not wrong from a physics perspective. But what energy is used to convert light into heat? Shine visible (not IR) light on a wall, what do you get back in conversion to heat from whatever ISNT reflected back as visible light?

Is there energy used in changing visible spectrum to heat/IR? 

And yeah, just use incandescents..

Turning them on and off does reduce their life span, which is pretty long.

taekvideo

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #16 on: June 25, 2014, 02:05:09 AM »
So he's not wrong from a physics perspective. But what energy is used to convert light into heat? Shine visible (not IR) light on a wall, what do you get back in conversion to heat from whatever ISNT reflected back as visible light?

Is there energy used in changing visible spectrum to heat/IR? 

And yeah, just use incandescents..

Turning them on and off does reduce their life span, which is pretty long.

Energy can't be created or destroyed, it just moves around.  100% of the energy in the visible light will get changed to heat upon impact with surface(s) and/or air molecules.
Heat is just the motion/vibrations of atoms/molecules within a substance, and in the impact the energy from the light wave gets transferred into additional motion/vibration in the substance (heat).

I use the same justification to be a bit more lax on energy conservation during the winter... like using an electric dryer and just venting inside (with a filter) instead of hanging clothes up inside... but I don't go out of my way to leave lights on or anything lol.
just curious - how do you keep your walls from dripping with moisture when it's cold inside and you run the dryer.  I'd have thought that would result in a ton of moisture in your hose.
On a related note, i've wondered why houses in cold climates don't use some sort of heat exchanger with their dryer vents...like having a loooong uninsulated pipe that dissipates most of the heat inside before pushing cool(er) air outside.  But i'm guessing it's a combination of cost and safety (lint building up in the vent.  Hmmm..

The windows in that area fog a bit while its running, but that quickly disappears... nothing on the walls.
The winters here are really dry (my lips will literally start bleeding in a week or so without any lip balm), so the extra bit of humidity is actually nice.

warfreak2

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #17 on: June 25, 2014, 05:22:36 AM »
I don't think light loss through windows is at all negligible - if it's pitch black outside and you can see a house with the lights on... the fact that you can see their lights are on means there's plenty of light leaving through the window, and you're only seeing the small proportion of light that leaves in the direction towards you!

As I said, all light energy gets converted to heat eventually, but this could be after many thousands of reflections. If Snooker balls just kept rolling until they bounced off thousands of cushions, it would be pretty hard not to get one in the pocket. And Snooker pockets as a proportion of Snooker table perimeters are going to be much less than windows as a proportion of room surface area.


One more obvious thing that he is also missing is, what's the point in heating rooms that nobody's in?

nereo

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #18 on: June 25, 2014, 06:12:15 AM »

One more obvious thing that he is also missing is, what's the point in heating rooms that nobody's in?
Good point.  Like many suburbanites, he keeps ever part of his large house at a nice comfy uniform temperature.

frugalnacho

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #19 on: June 25, 2014, 07:50:37 AM »
[The comment about walls dripping with moisture wasn't from the forced air furnace, but from a dryer vent that vents inside instead of outside (like the poster mentioned he does in the winter).
Quote


I can't speak for the other guy, but in my case the forced-air furnace dries out the indoor air pretty well, plus the inside surface of the walls doesn't get cold enough to cause the moisture to condense. (The windows might get a little drippy, but that's it.)


I think it's a common misconception that a force-air furnace is the cause of drying out the indoor air in winter.  It's not the forced-air furnace, it's the fact that it's cold outside (meaning very low moisture in the air) and then you heat up that air inside the house (and it still has low moisture - meaning it's dry).  Any other type of heat or furnace will dry out the air an equal amount.

AlanStache

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #20 on: June 25, 2014, 08:01:28 AM »
watts are watts.

But are different devices more or less efficient at turning electrical power into heat?  Will a 60 watt old school light bulb make more heat than my desktop also using (a hypothetical) 60 watts, what about a 60 watt electric heater.  Do I get the same heat from all these for the given a 60 watt input?

Dryer heat recover: there are standards about how long an output pipe can be, distance reduces for each bend too.  Is something like 20ft, less 4' for each 90deg bend.  So I would think the geometry would get hard to fit unless things were really planed for.  Yes well past the point of diminishing returns in most all homes.

okashira

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #21 on: June 25, 2014, 09:28:34 AM »
I don't think light loss through windows is at all negligible - if it's pitch black outside and you can see a house with the lights on... the fact that you can see their lights are on means there's plenty of light leaving through the window, and you're only seeing the small proportion of light that leaves in the direction towards you!

As I said, all light energy gets converted to heat eventually, but this could be after many thousands of reflections. If Snooker balls just kept rolling until they bounced off thousands of cushions, it would be pretty hard not to get one in the pocket. And Snooker pockets as a proportion of Snooker table perimeters are going to be much less than windows as a proportion of room surface area.


One more obvious thing that he is also missing is, what's the point in heating rooms that nobody's in?

It's extremely negligible. Unless the bulb is in a room that is nothing but windows, it will be 99%.
It's simple geometry. a nearby window might only take up 2% of a bulb's spherical emission if you consider the % of (θ, φ).
Then the window itself will absorb and reflect another 70% of that.

Seriously folks, read my post above. /thread.
It may be cheaper for him to use the bulbs, but it's less efficient, unless his electricity comes from solar, nuclear, hydro, etc.
Actually even then it doesn't matter, since any excess renewable energy would be sold off if he wasn't using it (electricty can be transmitted over great distances with high efficiency.)

In the end, it would be more efficient to use that electricity to power an electric heat pump system.

Jack

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #22 on: June 25, 2014, 10:05:06 AM »
watts are watts.

But are different devices more or less efficient at turning electrical power into heat?  Will a 60 watt old school light bulb make more heat than my desktop also using (a hypothetical) 60 watts, what about a 60 watt electric heater.  Do I get the same heat from all these for the given a 60 watt input?

I think it's a question of heat vs. other forms of work.

Imagine a 60 watt incandescent light bulb inside a black box, and a 60-watt computer inside another black box. The bulb in the first box does work in the form of light, which then gets absorbed by the walls of the box and converted to heat. The computer in the second box does work in the form of mathematical computation, which the components of the computer (e.g. resistors) convert to heat which then gets conducted/convected/radiated to the walls of the box.

This raises the question: given that we agree that putting a window in the bulb box so the light can shine out would make the rest of the box heat up less, would putting a data cable into the computer box so the results of the computation could come out make the computer box heat up less? Apparently so, though it might be too small an effect to notice. (Instead, the computer receiving the data or the cable itself must heat up to compensate, I think.)

If we want to talk about "efficiency," then maybe we want to consider two more hypothetical black boxes: one containing four 15-watt CFL bulbs and the other containing a faster-but-still-60-watt computer (e.g. maybe the second box had a 486 and this box has a Pentium or something). Do the incandescent and CFL boxes, without windows, heat up the same amount? Yes, but the CFL box loses more light energy when you cut a window into it. Do the 486 and Pentium boxes heat up the same amount? Yes, but the Pentium box gives results quicker (and heats up less) when you plug a data cable into it.

I think there's also a discussion of entropy lurking around here somewhere, but I don't understand it well enough to talk about it. This article might help, though.

warfreak2

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #23 on: June 25, 2014, 10:17:47 AM »
It's extremely negligible. Unless the bulb is in a room that is nothing but windows, it will be 99%.
It's simple geometry. a nearby window might only take up 2% of a bulb's spherical emission if you consider the % of (θ, φ).
Then the window itself will absorb and reflect another 70% of that.

Seriously folks, read my post above. /thread.
Did you read my post? Light doesn't just get absorbed as soon as it hits something that isn't a window... otherwise the only light to get in your eyeballs would have to come directly from the bulb, and the rest of the room would be pitch black.

Light reflects off of every single surface in the room, like a Snooker ball that bounces in random directions and doesn't slow down. Even when it gets into your eyeballs, most of it doesn't get absorbed there. Sure, some light gets reflected back into the room by the window - and then it gets reflected back around the room, and eventually through the window again. If you follow a single photon, it could hit the window 100 times and still stay in the room - but the probability of that is negligible.

dragoncar

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #24 on: June 25, 2014, 10:19:57 AM »
So he's not wrong from a physics perspective. But what energy is used to convert light into heat? Shine visible (not IR) light on a wall, what do you get back in conversion to heat from whatever ISNT reflected back as visible light?

Is there energy used in changing visible spectrum to heat/IR? 

And yeah, just use incandescents..

Turning them on and off does reduce their life span, which is pretty long.

No, no, only 1-2% of wattage is converted into visible light.  The other 98%-99% is already heat/IR in the process.  This is called resistive heating, and is the same effect used in a toaster oven.  The "heat ball" article was particularly funny because it's true that visible light is really secondary effect in incandescents.  LED and CFL are better, but not by that much.  Just think -- if we got 100% efficient LEDs, we could replace a 100 watt incandescent with a 1 watt LED.

Anyways, 100% of visible light could go out the window, and you'd still heat the house nicely.  But of course some of that 1-2% visible light energy will be absorbed by the walls, carpet, etc.

edit: same response to other posters above.  I also did mention heating unoccupied rooms:

That's not an excuse to light unoccupied rooms, but may affect your decision to add another reading light.

The fact is, visible light just doesn't have that much energy.  If you are worried about your visible light energy escaping, draw your damn blinds at night!
« Last Edit: June 25, 2014, 10:24:19 AM by dragoncar »

okashira

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #25 on: June 25, 2014, 01:15:06 PM »
It's extremely negligible. Unless the bulb is in a room that is nothing but windows, it will be 99%.
It's simple geometry. a nearby window might only take up 2% of a bulb's spherical emission if you consider the % of (θ, φ).
Then the window itself will absorb and reflect another 70% of that.

Seriously folks, read my post above. /thread.
Did you read my post? Light doesn't just get absorbed as soon as it hits something that isn't a window... otherwise the only light to get in your eyeballs would have to come directly from the bulb, and the rest of the room would be pitch black.

Light reflects off of every single surface in the room, like a Snooker ball that bounces in random directions and doesn't slow down. Even when it gets into your eyeballs, most of it doesn't get absorbed there. Sure, some light gets reflected back into the room by the window - and then it gets reflected back around the room, and eventually through the window again. If you follow a single photon, it could hit the window 100 times and still stay in the room - but the probability of that is negligible.

Is your house made of mirrors? Have you taken Heat Transfer? (that is my book, yes those are my tabs in the side.) I have and I killed it. How about Thermo I or Thermo II?
Let's just say that reflections, absorption and transmission are a few topics that are discussed in that class. But thanks for the information.
You are right that light is reflected off the walls, let's call it 20% (actually, it is often absorbed, and re-emitted at a different energy, but let's ignore that for now.). You have to understand that the light reflected off the wall will also be reflected in a half sphere pattern. So, most of the light reflected will simply hit another wall (since the wall, like the bulb, is likely has only a very small % "view" of the window.) where it has another 80% chance of being absorbed (and converted to heat) After just a single reflection, you're already down to 4%. It will just continue like that.
I'll leave it to that... take the class and run the calcs yourself to really understand.

http://

okashira

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #26 on: June 25, 2014, 01:21:14 PM »
watts are watts.

But are different devices more or less efficient at turning electrical power into heat?  Will a 60 watt old school light bulb make more heat than my desktop also using (a hypothetical) 60 watts, what about a 60 watt electric heater.  Do I get the same heat from all these for the given a 60 watt input?

I think it's a question of heat vs. other forms of work.

Imagine a 60 watt incandescent light bulb inside a black box, and a 60-watt computer inside another black box. The bulb in the first box does work in the form of light, which then gets absorbed by the walls of the box and converted to heat. The computer in the second box does work in the form of mathematical computation, which the components of the computer (e.g. resistors) convert to heat which then gets conducted/convected/radiated to the walls of the box.

This raises the question: given that we agree that putting a window in the bulb box so the light can shine out would make the rest of the box heat up less, would putting a data cable into the computer box so the results of the computation could come out make the computer box heat up less? Apparently so, though it might be too small an effect to notice. (Instead, the computer receiving the data or the cable itself must heat up to compensate, I think.)

If we want to talk about "efficiency," then maybe we want to consider two more hypothetical black boxes: one containing four 15-watt CFL bulbs and the other containing a faster-but-still-60-watt computer (e.g. maybe the second box had a 486 and this box has a Pentium or something). Do the incandescent and CFL boxes, without windows, heat up the same amount? Yes, but the CFL box loses more light energy when you cut a window into it. Do the 486 and Pentium boxes heat up the same amount? Yes, but the Pentium box gives results quicker (and heats up less) when you plug a data cable into it.

I think there's also a discussion of entropy lurking around here somewhere, but I don't understand it well enough to talk about it. This article might help, though.

I'd say the energy equivalent of the entropy of the data coming out of the data cable would be astronomically small. Immeasurable.
That would be assuming you run a calc on the amount of data and use the current ambient temperature of the cable.


Anyway, this is the MMM forum, folks. We should be talking efficiency in terms of $$$.

If his heating oil is more expensive then the electricity in units of energy he gets, by all means use electricity, and why does he even bother to buy heating oil at all??
The correct answer is he should be using a heat pump.

okashira

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #27 on: June 25, 2014, 01:25:52 PM »
watts are watts.

But are different devices more or less efficient at turning electrical power into heat?  Will a 60 watt old school light bulb make more heat than my desktop also using (a hypothetical) 60 watts, what about a 60 watt electric heater.  Do I get the same heat from all these for the given a 60 watt input?

Dryer heat recover: there are standards about how long an output pipe can be, distance reduces for each bend too.  Is something like 20ft, less 4' for each 90deg bend.  So I would think the geometry would get hard to fit unless things were really planed for.  Yes well past the point of diminishing returns in most all homes.

Not really. They all produce the same heat per watt. Watts is a measurement of heat/time as well. (Joules / Sec)

So if you want to be heating with resistance heating (again use a damn heat pump, which will produce 200 Watts of heating for every 100 Watts of electricity.....)
Use a computer to do useful calcs such as protein folding or looking for UFO's.

dragoncar

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #28 on: June 25, 2014, 01:59:36 PM »

Use a computer to do useful calcs such as protein folding or looking for UFO's.

Back in the day (still?), bitcoin miners were probably positive EV space heaters.

Norioch

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #29 on: June 25, 2014, 02:19:49 PM »
You also need to consider the location of the heat being generated. Assume, for the sake of argument, you live in a house that needs to be heated in the winter, and only has electric heating. Usually the electric radiators will be strategically positioned along the ground to heat low air, which is near where people are likely to be and which also causes the air to rise and generate convection. In contrast, most light bulbs will likely be near the ceiling, above people's heads. Heat generated near the ceiling is more likely to be lost through the walls before actually warming the people in the house.

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #30 on: June 25, 2014, 03:55:57 PM »
You also need to consider the location of the heat being generated. Assume, for the sake of argument, you live in a house that needs to be heated in the winter, and only has electric heating. Usually the electric radiators will be strategically positioned along the ground to heat low air, which is near where people are likely to be and which also causes the air to rise and generate convection. In contrast, most light bulbs will likely be near the ceiling, above people's heads. Heat generated near the ceiling is more likely to be lost through the walls before actually warming the people in the house.

Exactly. Your lights are likely to be positioned on the ceiling, meaning you're generating heat at the ceiling. Since light bulbs have no mechanism to move the heat, it just rises up through convection, meaning the heat generated by light bulbs is essentially useless to you as a user of that heat, since you're presumably beneath the lights. Essentially, you're overheating a space that doesn't need to be heated at all. So, basically, this dude needs some face punches. (Now if his lights were inset into the floor directly below where one might presumably sit/stand/occupy space, he might have a point... so long as it's winter and you want to be heating the space). (And obviously there is a small amount of radiant heat generated, but it would be pretty much useless. Go stand outside in the winter with a 60 watt bulb turned on 10 feet away from you and tell me whether or not you can feel the radiant hear being emitted....).

dragoncar

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #31 on: June 25, 2014, 04:06:01 PM »
You also need to consider the location of the heat being generated. Assume, for the sake of argument, you live in a house that needs to be heated in the winter, and only has electric heating. Usually the electric radiators will be strategically positioned along the ground to heat low air, which is near where people are likely to be and which also causes the air to rise and generate convection. In contrast, most light bulbs will likely be near the ceiling, above people's heads. Heat generated near the ceiling is more likely to be lost through the walls before actually warming the people in the house.

Exactly. Your lights are likely to be positioned on the ceiling, meaning you're generating heat at the ceiling. Since light bulbs have no mechanism to move the heat, it just rises up through convection, meaning the heat generated by light bulbs is essentially useless to you as a user of that heat, since you're presumably beneath the lights. Essentially, you're overheating a space that doesn't need to be heated at all. So, basically, this dude needs some face punches. (Now if his lights were inset into the floor directly below where one might presumably sit/stand/occupy space, he might have a point... so long as it's winter and you want to be heating the space). (And obviously there is a small amount of radiant heat generated, but it would be pretty much useless. Go stand outside in the winter with a 60 watt bulb turned on 10 feet away from you and tell me whether or not you can feel the radiant hear being emitted....).

This is true, but the idea is the the lights offset a furnace blower.  With air blowing around, the temperature gradient won't be that bad.  If the lights weren't on, it would be cold air up there falling down into your living space!

warfreak2

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #32 on: June 25, 2014, 04:33:58 PM »
Is your house made of mirrors? Have you taken Heat Transfer? (that is my book, yes those are my tabs in the side.) I have and I killed it. How about Thermo I or Thermo II?
Let's just say that reflections, absorption and transmission are a few topics that are discussed in that class. But thanks for the information.
You are right that light is reflected off the walls, let's call it 20% (actually, it is often absorbed, and re-emitted at a different energy, but let's ignore that for now.). You have to understand that the light reflected off the wall will also be reflected in a half sphere pattern. So, most of the light reflected will simply hit another wall (since the wall, like the bulb, is likely has only a very small % "view" of the window.) where it has another 80% chance of being absorbed (and converted to heat) After just a single reflection, you're already down to 4%. It will just continue like that.
I'll leave it to that... take the class and run the calcs yourself to really understand.
Thanks for addressing my points; I did try to google for how many times a light ray is typically reflected/diffused before it's absorbed, but didn't find anything useful. I'm more familiar with it from the domain of computer graphics (where advanced raytracing programs might follow each ray of light through up to, say, 10-20 reflections, limited by available processing power) rather than thermodynamics, so I'll bow to your knowledge.

okashira

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #33 on: June 25, 2014, 04:48:02 PM »
Is your house made of mirrors? Have you taken Heat Transfer? (that is my book, yes those are my tabs in the side.) I have and I killed it. How about Thermo I or Thermo II?
Let's just say that reflections, absorption and transmission are a few topics that are discussed in that class. But thanks for the information.
You are right that light is reflected off the walls, let's call it 20% (actually, it is often absorbed, and re-emitted at a different energy, but let's ignore that for now.). You have to understand that the light reflected off the wall will also be reflected in a half sphere pattern. So, most of the light reflected will simply hit another wall (since the wall, like the bulb, is likely has only a very small % "view" of the window.) where it has another 80% chance of being absorbed (and converted to heat) After just a single reflection, you're already down to 4%. It will just continue like that.
I'll leave it to that... take the class and run the calcs yourself to really understand.
Thanks for addressing my points; I did try to google for how many times a light ray is typically reflected/diffused before it's absorbed, but didn't find anything useful. I'm more familiar with it from the domain of computer graphics (where advanced raytracing programs might follow each ray of light through up to, say, 10-20 reflections, limited by available processing power) rather than thermodynamics, so I'll bow to your knowledge.

If you want to calculate the # of times a single photon will be reflected, you cannot. You can only determine a statistical average, which is just fine for ray tracing since there are so many photons the average is what we perceive.

It has a chance of 20% of being reflected once, then 20%(20%) = 4% of being reflected twice, then 20%(4%) = 0.8% three times, and so on. This assumes a material with a 80% absorbance (20% reflectance)
So the effective number of reflections might be... ~0.23 reflections in this case.

The concept should be there in computer raytracing as well. Place a light in a room, with some body sitting somewhere in the room. Change the absorbance of the body sitting in the room, and the amount of light falling on the walls should decrease overall.

Take a look here:
http://www.ips-innovations.com/low_emissive_wall_coatings_ref.htm
chart half way down. Looks like typical white paint has a reflectance of 0.1 on average. so the average # of reflections would be ~0.11

okashira

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Re: CFLs are zero sum energy users - tell me this is crap (or not?)
« Reply #34 on: June 25, 2014, 04:50:21 PM »
You also need to consider the location of the heat being generated. Assume, for the sake of argument, you live in a house that needs to be heated in the winter, and only has electric heating. Usually the electric radiators will be strategically positioned along the ground to heat low air, which is near where people are likely to be and which also causes the air to rise and generate convection. In contrast, most light bulbs will likely be near the ceiling, above people's heads. Heat generated near the ceiling is more likely to be lost through the walls before actually warming the people in the house.

This is a good point....