Interesting. The energy (heat), removed from your food, needs to go somewhere and typically that somewhere is heat - which is pretty inefficient.
An efficient refrigerator would produce no output heat, it would use the ‘heat in the food’ to go towards motion - ie: driving the pump. Something I’ve been pondering for quite some time.
The part used to turn the motor eventually winds up as heat. The motor doesn’t gain kinetic energy indefinitely. Friction produces heat.
Consider your vacuum cleaner. Some of the power is dissipated as waste heat in the motor windings, the rest goes toward moving the air. Now you’ve got a mass of air with kinetic energy exiting the vacuum cleaner. That air goes whooshing out into the room, where it mixes with the stagnant air. Viscous dissipation means that this kinetic energy eventually gets transformed into heat.
Refrigerator? Some waste heat from the motor. The rest of the electrical power gets inserted into the refrigerant, compressing it and warming it up (due to adiabatic compression). Then the compressed, warm refrigerant goes to a condenser coil (that warm radiator-lookin’ thing on the back of the fridge), where it dumps heat to your room and condenses into a liquid. Then the cool, now-liquid refrigerant goes through an orifice into the low-pressure evaporator coil, where it evaporates, cooling your freezer compartment. Finally, it goes back out to the compressor to repeat the cycle. Bottom line is, ultimately all of the electrical energy your fridge draws from the wall gets dumped into your kitchen as heat, either from the motor windings or from the condensor coil, no matter how efficient or inefficient it is; the inefficient ones just draw more power and dump more heat.
It is true that waste heat from appliances will reduce wintertime furnace load (note that they will also increase summertime cooling load). This will reduce your furnace operating cost, but the much-higher cost of electrical energy (as compared to natural gas or fuel oil) means your overall power bill will be higher.
Leaving electrical appliances turned on unnecessarily does waste energy. The waste is in the heat going up the chimney of the power plant (steam-cycle power plants are probably around 50% efficient at generating electrical power), and in the resistive heating of the power lines used to transmit electricity to your home.
I’ve heard (no cite, sorry) that the overall efficiency of the electrical system, from a lump of coal at the power plant to electrons in your house - is something like 25 percent. So when they burn coal and release 100 BTU’s of energy, you can expect to receive only 25 BTU’s at your house, and 75 BTU’s gets pissed away up the smokestack and along the lines.
Contrast this with your home’s furnace. Recent high efficiency models cool the flue gas down so much that they generate a considerable amount of condensate to be dealth with; these furnaces typically have efficiencies in excess of 90 percent. So when your furnace burns natural gas and releases 100 BTU’s of energy, you can expect to receive 90 BTU’s as warm air in your house, and only 10 BTU’s going out your chimney as lukewarm flue gas.
So, yes, leaving electrical appliances on for no reason other than to heat your home is quite wasteful from an energy standpoint; as you might expect, you’ll also notice it on your monthly bill.
Yeah, that would work great, if not for the second law of thermodynamics.
About 10 years ago, I was talking to someone from the Electrical Engineering dept from a polytechnic in NZ. They were using off the shelf truck parts (turbocharger and alternator) to build a natural gas fueled unit that delivered 10kW electrical power and 10kW heat. It has taken a long time, but you can now buy such a unit for home fitting in the UK - the trouble is that reversible meters and co-generation is a no-no as far as the UK power companies are concerned. If the govt forces the power companies to play ball and sets the co-payment levels at a suitable value, I would look at the investment. Lower line losses, the gas infrastructure is in place, and lower CO[sub]2[/sub] emissions.
Si
I feel that way around here in the south regarding lights in the winter. Many houses here just have electric funaces.
Heating house wise, there aint a toots thermodynamic difference between a electric furnace and a light bulb.
So when its chilly and I am in a room here in the winter, crank up the lights baby because heat is heat, I prefer a little more in the room I am in or frequent, and I can take the edge of the winter gloom and darkness.
In that scenario, one could either consider the light or heat “free”.
It should also be noted, by the way, that even though almost all heaters (which includes appliances intended for other purposes) have an efficiency of 100% at generating heat, an electric heat pump can actually be said to have an efficiency of greater than 100%. This works by spending some energy from the power company to pump some energy from the heat of the outside air (and even in the dead of winter, there’s some heat there) into the house, and then making sure that all of the “waste heat” also ends up inside the house. So even if gas lines are impractical for your house, there are always more efficient options available than light bulbs or computers.
We actually use the heat off of our computers to our advantage. Our computers sit in a spare bedroom that we use as an office. In the winter, the section of our house with the bedrooms is kept in the mid 50s. By keeping the door into the office shut, the computers and other hardware kept that room probably 15 degrees warmer. Since we are both geeks, and spend lots of time in there, that made the room more comfortable, without having to raise the temperature in all the adjoining bedrooms.
So yes, if you can set things up correctly, the heat off of appliances can be free heat to the house, and also allow for reduced heating in the areas you aren’t using.
I suspect the most dramatic application of this theory is baking in the winter. If you choose to prepare food using your oven, the residual heat will warm the kitchen and perhaps let you turn the thermostat down. The oven’s not as efficient as your furnace, but as you’re already using the appliance’s energy to produce something useful (say, cookies or a roast), the heat gained is a bonus.
Obviously, essentially all the electricity used in the home (ignoring outside lighting) is converted into heat. The main problem is that the kitchen gets a disproportionate share of it (stove and fridge, mainly) so it winds up nice and cozy, but that doesn’t do much for the rest of the house. Incidentally, about 70% of the home heating in Quebec is electric. I have “bi-energy” which means electric until the temperature drops below -12 (about +10 F) and then I burn oil. For this, I get a 20% discount on electricity until that -12 is reached and then pay about triple the regular cost. All this came about because environmentalists succeeded in blocking a contract for Quebec to sell its excess hydro-electric power to NY State and City, saying, “No, we will conseve instead”!!
Unless all your lights are on the floor there is still some wasted energy because more of the heat is up near the ceiling.
Is there some facet of this I am not thinking of that makes this NOT retarded?
Isnt hydro generally a use it or loose it proposition?
So they are encouraging you to burn fossil fuels when it gets really cold ? :rolleyes:
Yes. This policy conserves the fossil fuels which would otherwise have been use to warm homes on moderately cold days by incentivizing that method of heating over fossil fuels. Of course, when it gets really cold, customers will still have to turn on their fossil-fuel heat, but it will conserve some fossil fuel use in private homes.
Now, how much fossil-fuel use that sold electricity could have displaced at fossil-fuel powered plants in the United States probably isn’t something globally minded environmentalists would want to think about without feeling stupid.
THATS the part I am wondering about.
The environmentalists were upset becuse Hydro-Quebec was going to build more dams and New Yokers would start to conserve power. The dams were built anyway.
The basic tradeoff is that Quebec’s power needs peak in winter and New York’s in summer.
The term “Coefficient of Performance” is the proper one; if you use the term efficiency, lesser intellects’ heads will explode as they try and fail to reconcile thermodynamic efficiency with a less stringent one (it’s really just defining the system and realizing that a heat pump is open).
Speaking from experience.
This idea – running a not-particularly-efficient generator and using the waste heat for building heat, thereby getting the electricity for almost ‘free’ – is called cogeneration, and is used a lot for large installations (campuses or factories).
My thermostat is right above my stove so I leave it set where it is but the heat comes on less. The rest of the house suffers!
If you can’t stand the cold, get into the kitchen, eh?