What is the difference between summer air conditioning and winter air conditioning?

The conditioning of air is basically a tranferance of heat. In the summer time you remove heat from the air, in the winter you add heat to the air. Also in the summer an air conditioning unit removes moisture from the air allowing moisture to evaporate quickly from your skin and give you that crisp cold feeling. A dry space feels a lot cooler than a humid space at the same temperature. Heating dries the air. Making it a good idea to have a humidifier added to the heating system to provide the opposite effect in winter. Humid air holds heat longer than dry air and will not evaporate moisture on your skin and make you feel cold.