For environmental and cost reasons, I'd like to use my AC unit less. In situations where passive cooling is not practical, I am trying to determine the most efficient way to do this. (I believe the unit is a Trane XR14 heat pump, installed 2009.)
My fiancee and I live in a brick ranch house with a brown roof, about 1,200 sq feet. We live outside Philadelphia, so during the summer it can consistently get above 90. During the day, when we are at work, I close the windows and shades and set the AC high (80 F). I keep it on when we're gone because we have two cats and a dog. I get home around 5:20 PM. At night, it will eventually get below 80 outside. At this point, I am trying to determine which is more efficient: to set the house to the expected night temperature (expecting that the cooler air will be trapped in the house and keep the AC from triggering more frequently during the night after the initial run down to, for example, 77, and taking longer to turn on the next day) or keep it at the current interior temperature (to reduce the time the AC runs at night).
A concrete example: let's say it gets to 77 outside and the house is 80. Would it use less total energy to set the AC to 77 or 80? My goal is to use the least amount of energy possible in order to lower the monthly electric bill.
Lots of people have mentioned comfort vis a vis humidity, but for the purposes of the question, I'm more concerned about cost as I'm pretty heat acclimated and I can just run a small bedside fan if it gets too gross at night.