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).
A temperature of 18 Â°C indoors corresponds to an outside temperature of about 15.5 Â°C. If the air temperature outside is 1 Â°C below 15.5 Â°C, then heating is required to maintain a temperature of about 18 Â°C. If the outside temperature is 1 Â°C below the average temperature it is accounted as 1 degree-day. The sum of the degree days over periods such as a month or an entire heating season is used in calculating the amount of heating required for a building. Degree Days are also used to estimate air conditioning usage during the warm season.