As a child, were you ever told something like “turn the light off when you leave a room! It’ll save energy”?.
That’s not always true.
If you live in Boston and it’s January, chances are you’re using some kind of heating device to keep your house at a constant, livable temperature. Chances are you’re also using light bulbs to keep your your house at a livable level of illumination. Now, every Watt-hour the light bulb, computer, stereo, TV or gas stove is burning is a Watt-hour your heating device won’t have to spend to keep the room at said livable temperature. Hence turning the life off is not saving any energy (ok except for the few photons that will go out the window)
On the other hand, if you live in Phoenix and it’s July, chances are you’re using A/C to keep your house at a constant, livable temperature (I’ve been there, literally). Things are now very different. Every Watt-hour spent by your light bulb, computer, stereo, TV or gas stove requires your A/C to spend energy to keep the room at a constant temperature. From what I read, the coefficient of performance (energy taken out the room over electrical energy to do so) of an A/C is somewhere around 2 to 3. So in the best case scenario, a Watt-hour burnt by your light bulb costs you 1.33 Watt-Hour of electrical energy.
In conclusion: if you’re heating your house up, leaving an appliance on doesn’t cost any energy. On the other hand if you cooling your place down, leaving an appliance on costs you even more than the appliance itself and those “energy-saving” light bulbs are even more beneficial than advertised!
Thanks for visiting my blog, and for your comment. I learned something!
marguerite
http://lamarguerite.wordpress.com
This is only try if your heating device operates at the same or less efficiency as the device that was creating the heat. If is a very high efficiency unit then it will save you money to turn off the lights and equipment.
Charles, thanks for the feedback. However, I’m not convinced (yet).
Thinking in terms of energy balance, if the house is kept at a constant temperature, the power going out, Pout has to be constant (for constant outside temperature).
The power going in the house is Pin=Pin,heater+Pin,lights+Pin,others-appliances.
For the house’s temperature to remain constant, Pin has to be equal to Pout. Therefore, if one reduces Pin,lights by buying efficient bulbs, the average Pin,heater has to increase (i.e over time the thermostat will kick in more often). Similarly, if you use more appliances, the thermostat will kick-in less often.
This will remain true until you have so many appliances and inefficient bulbs that they will be enough to heat up your house to a temperature greater than the temperature the thermostat is set at. In this case, there is a true loss of energy because the house is now at a higher temperature than desired.
Am I missing something ?
ML