Effecient electricity use (in winter)

[padren]

I have electric heat, and this time of year it's always on. I also have two lights (florescent) a computer and two monitors that my roommate suggests I turn off more to save electricity. In the summer I'd agree, but all energy "wasted" becomes heat - light bounces around the room (a small amount escapes, but the blinds are always closed) and creates background heat, and all the electrical devices just create excess heat - and since we don't have gas for heat, electric heat is just as efficient (cost wise) when produced by lights/cpus/etc as from electric heaters, right?

 

If anything, having my lights or computer on should just lower the amount of heat the heater has to produce to maintain it's thermostat setting.

 

 

Am I wrong about the fundamentals of physics here, or do the laws of thermodynamics literally state that (in a system where heat is intentionally maintained) the sum of energy use will be the same?

 

No electric heat source can be more/less efficient than another, if heat is the desired end result. The only thing I can think of that breaks that is (A) music played loud enough to be heard outside and (B) light that is visible outside.

 

Isn't it a wash otherwise?

[lemur]

I have electric heat, and this time of year it's always on. I also have two lights (florescent) a computer and two monitors that my roommate suggests I turn off more to save electricity. In the summer I'd agree, but all energy "wasted" becomes heat - light bounces around the room (a small amount escapes, but the blinds are always closed) and creates background heat, and all the electrical devices just create excess heat - and since we don't have gas for heat, electric heat is just as efficient (cost wise) when produced by lights/cpus/etc as from electric heaters, right?

This seems logical to me, but I still intuitively wonder if a 15watt CFL bulb makes as much heat as a 15watt incandescent would. Do some frequencies get absorbed better by some colors/materials than others, e.g. your clothes and skin? Also, I would think your blinds would contain more if they were made of reflective material. If they are absorbing light, they will radiate it out the window as well, I think.

 

Also, I'm not sure how efficient electronic devices are. I wonder if a computer would emit less energy as heat because it used some for the fan, processing, etc.

 

In general, though, I think that your roommate should consider better insulation and/or alternative heating methods in addition to reducing energy usage. If your roommate wants you to turn off your devices, I think you should tell your roommate to lower the temperature on the thermostat.

[padren]

This seems logical to me, but I still intuitively wonder if a 15watt CFL bulb makes as much heat as a 15watt incandescent would. Do some frequencies get absorbed better by some colors/materials than others, e.g. your clothes and skin? Also, I would think your blinds would contain more if they were made of reflective material. If they are absorbing light, they will radiate it out the window as well, I think.

If something absorbs light, it absorbs the photons, which raises it's temperature. It may emit infrared energy due to that temperature increase, but in a closed room it'll eventually all be converted to waste heat through absorption.

Also, I'm not sure how efficient electronic devices are. I wonder if a computer would emit less energy as heat because it used some for the fan, processing, etc.

When we measure the "efficiency" of electronic devices, what we talk about is how much energy goes to the intended task, and how much is lost to unintended heat/noise/light. In a closed space, heat/noise/light all end up as heat, so while a fan, CPU, or monitor may not be highly efficient at performing the desired function, when seen as a duel-use "electronic device and heater" I am pretty sure it would be near 100% efficient.

In general, though, I think that your roommate should consider better insulation and/or alternative heating methods in addition to reducing energy usage. If your roommate wants you to turn off your devices, I think you should tell your roommate to lower the temperature on the thermostat.

I agree, I think insulation is the best way to lower electricity costs in the winter.

[lemur]

When we measure the "efficiency" of electronic devices, what we talk about is how much energy goes to the intended task, and how much is lost to unintended heat/noise/light. In a closed space, heat/noise/light all end up as heat, so while a fan, CPU, or monitor may not be highly efficient at performing the desired function, when seen as a duel-use "electronic device and heater" I am pretty sure it would be near 100% efficient.

Usually, I would think of efficiency in terms of the ability of a device to remain cooler and thus use less energy. However, if you were looking at the device as a heater, any energy devoted to functions of the device that converted energy into something other than heat could be considered waste. So when the OP's roomate asks for devices to be turned off other than the heater, the correct way to calculate the potential energy-savings of switch current from the devices to the electric heater would be measured by the amount of energy consumed by the devices converted into other expressions than heat - although I'm not sure any expression of energy would not end up as heat before leaving the room as conduction. Either way, I think you're right that no practical benefit would be gained by putting the current through an electric heater instead of a computer or other electrically powered device. I just wonder if there is any way some electricity could get converted into some expression that does not end up as heat before leaving the room.

[Mr Skeptic]

The heater is designed for heating. All the electricity will get converted to heat eventually. However, the heater might distribute it differently than electrical appliances. That might make a difference. What would make a difference for sure is if your electric heater is like an air conditioner running in reverse -- these actually draw thermal energy from outside in addition to the energy from the electricity.

[padren]

The heater is designed for heating. All the electricity will get converted to heat eventually. However, the heater might distribute it differently than electrical appliances. That might make a difference. What would make a difference for sure is if your electric heater is like an air conditioner running in reverse -- these actually draw thermal energy from outside in addition to the energy from the electricity.

 

Actually it's a baseboard heater that sits under the window, where it's coldest in the room.

 

My roommate raised the stakes: He says that the idea is ludicrous, and is almost certainly the result of misunderstanding science. He doesn't think there is any way to prove it one way or the other (without turning the whole house into a closed experiment) but if I could, I'll win $100.

 

I'm sure there's exceptions - if the heat was turned off or a window had to be cracked to lower the temperature, if it was warmer outside, if I was running an xray machine that was blasting radiation out through the walls, or radio broadcast (not sure what the wireless router uses) but the circumstances seem pretty straight forward in my case.

 

 

Any suggestions on how to "win over" my roommate?

[Mr Skeptic]

Any suggestions on how to "win over" my roommate?

 

"In this house we obey the laws of thermodynamics!" In this case the First Law of Thermodynamics, also known as conservation of energy. Energy goes in, so what happens then?

[padren]

"In this house we obey the laws of thermodynamics!" In this case the First Law of Thermodynamics, also known as conservation of energy. Energy goes in, so what happens then?

 

I'm familiar with the laws of thermodynamics, I just don't know how to break it down so my roommate will get it. For everyone that uses the laws of thermodynamics to make a valid point, there's another 10 who don't really understand them and try to use them to defend some cheesy perpetual motion machine getup. So I do get why he's skeptical, but I need to break it down simply enough to make it so clear I can win that $100 bet.

[lemur]

Maybe it would convince him if you googled the conversion from watts to btus and calculated exactly how much heat each of your appliances was generating according to its wattage. Also, you should compare the wattage of your appliances to that of your heating system. I doubt the appliances are significant in comparison with the heater.

[zapatos]

Your lights and computer add heat to your room and I think you therefore have a hot spot in the house. If that heat has not been evenly distributed around the house as Mr Skeptic pointed out, and affected the thermostat, the furnace could run to keep the location of the thermostat at the right temperature, and make your room even hotter.

 

I assume in an evenly insulated house it would not make a difference, but how is the heat loss in your room compared to the rest of the house? Do you have the same window space (relatively low R factor) per square footage of floor space as the rest of the house? If you have more windows I suppose you could be wasting heat.

[lemur]

Your body is also generating heat. And the best part about that heat is that its directly heating your body instead of having to first warm up the air. You can increase the feels-like temperature of the air by exercising. I have biked for an hour at 32F and sat for 2 hours with an inside temperature of 40F with just a sweater and light jacket without feeling cold. After that, more heat or warmer clothing is required. I know this diverts from the thread topic some, but I think it's important to remember that your body is emitting heat just like any other appliance in the room; more than most actually. Invite people over for a dance party and you can probably shut down your heater completely.

Edited February 25, 2011 by lemur

[Mr Skeptic]

I'm familiar with the laws of thermodynamics, I just don't know how to break it down so my roommate will get it. For everyone that uses the laws of thermodynamics to make a valid point, there's another 10 who don't really understand them and try to use them to defend some cheesy perpetual motion machine getup. So I do get why he's skeptical, but I need to break it down simply enough to make it so clear I can win that $100 bet.

 

Combine that with showing him how the various appliances always generate heat.

 

Hm, come to think of it, depending on the resistance of the appliance, perhaps a slightly different proportion of the energy ends up heating cables outside the house? Anyone know what sort of effects, say, a transformer with no load might have? In particular, the sort of current it draws and its resistance?

[CaptainPanic]

I have electric heat, and this time of year it's always on. I also have two lights (florescent) a computer and two monitors that my roommate suggests I turn off more to save electricity. In the summer I'd agree, but all energy "wasted" becomes heat - light bounces around the room (a small amount escapes, but the blinds are always closed) and creates background heat, and all the electrical devices just create excess heat - and since we don't have gas for heat, electric heat is just as efficient (cost wise) when produced by lights/cpus/etc as from electric heaters, right?

You're absolutely right.

 

If you stand outside your house, and you cannot see any light from inside, then you can safely assume that all that light was absorbed and converted to heat.

All other appliances create heat directly. Unless your heater is a heat-pump (reverse airconditioner), your heater and any other appliance will create exactly the same amount of heat per kWh of electricity. Both have 100% efficiency in creating heat.

 

The only difference is that visible light is absorbed by different objects than the infrared... so other things get slightly warmer because of the visible light... but it is safe to assume that this effect is negligible.

 

You can test this by getting a small heater and a lightbulb of exactly the same power, and preferably of the same weight... Place both in a separate box which is completely closed (i.e. lets no light out). If the boxes are relatively heavy compared to the heater nad lightbulb (i.e. it takes a little while to heat up), then you will notice that both boxes heat up at the same speed.

You can then later replace the lightbulb by a fluorescent light (which is more efficient at making light) of the same power, and check again. It should have the same outcome.

Edited February 25, 2011 by CaptainPanic