Air temperature – the temperature inside a building is dependant on the external temperature of the building and the U-vales of the materials used to construct the building, meaning the lower the U-vale the more effective the material is at retaining heat. This can dramatically affect human comfort as the higher the U-values used, the quicker the room will lose heat through convection. By using the U-values of materials we can calculate the total heat resistivity of a building and then create a comfortable environment in which to live.
Air velocity – another crucial factor affecting human comfort, this is the movement of air through a building. Warm air will enter a room and force the cold air downwards creating a draught, in a cold environment this draught can make a person feel even colder if the draught is colder than room temperature. In a warm environment this draught can increase heat loss through convection and help to cool someone down by increasing the rate that their sweat evaporates.
Humidity – This is the water vapour content in the air. Humans cool down mainly by sweating but in an environment with 100% humidity it is not possible for the sweat to evaporate, this is called absolute humidity. Anything below 30% humidity can feel uncomfortably dry and anything above 60% can feel uncomfortably wet or damp. Relative humidity is the ration between the amount of water vapor in the air and the amount of water vapor that can be held in the air.