Hello, Teeming Millions:
I am trying to convince my roommate that leaving the windows open with the air conditioning on (and set at 74!) is inefficient, thereby raising our bills.
He disagrees.
Does anyone have any hard data on a similar situation? I have tons of “energy saver” links, but nothing really solid. I’m looking for alternate angles.
Your roommate is a moron and probably not prone to being “convinced.” But here goes:
With the windows closed, the amount of work the air conditioner has to do is limited by the space of the room. Once the room gets to the set temperature, the air conditioner can cycle off until the room slowly warms back up, at which point it cycles back on for just long enough to cool the room back down.
With the windows opened, the amount of work the air conditioner has to do is limited by what temperature it is outside. If the air outside is significantly warmer than the target temperature of the thermostat, the unit could conceivably never cycle off.
Now with some things, like fluorescent bulbs, running constantly is less expensive than frequent on/off cycles. This is not the case with air conditioners. In general, every minute you can go with the unit cycled off is money you aren’t spending.
Hope this helps.
Sorry, you said you wanted hard data.
Here’s the best hard data you can get with this kind of question. Turn your air conditioner on and go watch the wheel spin on your electric meter. Then turn it off and watch.
Fast spin = more electricity = expensive.
Slow spin = less electricity = cheaper.
it depends on the outside temp. in short if the outside temp is higher or equal to the inside temp keep the window closed, if the outside temp is lower then leave the window open
A/Cs main job is not to chill the air so much as to remove moisture. If the outside air is at all slightly humid, you are wasting $$$.
The only reason to have an A/C on and the windows open is if it’s set to fan only and you’re trying to circulate air. (It’s cooler and less humid outside.)
I wouldn’t say that dehumidification was the “main job” of the air conditioner. It’s an important part of the process, true.
It all depends on the outdoor conditions. Cool, moist air can contain as much energy as warmer, dryer air. The enthalpy of 74deg, 50% relative humidity air (which is what you want in the house) is about the same as 80deg, 35% RH air and as 62deg, 100%RH air. If it is cool but humid outside, leave the windows closed. If it is warm (less than 80) but dry (less than 35%RH), leaving the windows open won’t hurt you.
An air conditioner transfers heat from inside the house to outside the house. If your windows are open, you are letting the outside heat back in.
If it’s cool enough to open the windows, just turn the AC off. If it’s an older unit, you might be able to set it to circulate and move cooler air from outside.
Thanks everyone. Unfortunately the person in question is beyond reason. All arguments fell on deaf ears.
Ever have a shouting match about thermodynamics? Wait, of course you have, this is the Straight Dope…