Another thing to remember is the humidity levels. During this period, dendrobiums do not need a lot of moisture. Very little water will be enough to keep their roots alive. Also keep in mind that their roots constantly need plenty of air circulation so you should place them where there is a lot of fresh air.
Remember, that is based on energy usage, not comfort-levels, which are the purpose of having an air conditioner, in my not-so-humble opinion. Fact: At night, the ideal temperature comfort range for Americans drops to 65 to 72 degrees Fahrenheit (or about 87 degrees if you are my wife).
Air conditioner units have limits to their thermostat settings. The low end of the thermostat peaks out at approximately 60 degrees Fahrenheit for most units, so if the weather outside is colder than 60 degrees Fahrenheit, opening a window to allow the outside air to cool the room is more efficient.