Comment Re:I rarely find offices cold enough (Score 1) 388
The proof that turning it off over the weekend will save money is this. Imagine that they turned it off for some arbitrarily long time (say a century). Would that save money? Of course. How about for half a century. Et cetera. You have to pay to cool it back down again and that offsets some of the savings of letting the temperature rise. The question really is where the break-even point comes in. If you let the temperature rise back to ambient and then immediately cool down to desired temperature, that should be an approximately break-even time. Anything longer and you are ahead. Anything shorter and well you really haven't turned it off!
This is incorrect.
The rate at which heat enters a building from warmer outside air is proportional to the difference between the temperatures. If there's a five-degree difference half as much heat energy per unit of time enters the building than if there's a ten-degree difference. The amount of heat that must be removed Monday morning is the integral of that heat flow function. If you keep the office cool all weekend, you keep the interior/exterior temperature differential large and the heat flow high. If you allow the interior to warm up then the differential decreases and heat flow decreases. Less heat in means less to pump out.
This effect is maximized in the scenario you describe, where interior temperature rises to match exterior temperature, because when the temperatures are the same heat transfer ceases, but it's useful even if the difference never falls to zero. Actually, it's even better when the temperature differential goes negative and heat starts naturally flowing out of the building (e.g. interior temperature rises during the day and exterior temperature falls enough at night to be below the elevated interior temperature). Heat that flows out naturally is heat you don't have to remove. Smart buildings should be able to improve this effect by facilitating beneficial heat transfer (e.g. opening windows or pumping exterior air through the building) and impeding undesired heat transfer (e.g. insulation, keeping doors and windows closed).