Question 474General Subjects - Assistant Engineer

The correct answer is A. The space air temperature is controlled by automatically proportioning the cold and hot air streams at the mixing unit. In a dual duct multiple zone HVAC system, the space air temperature is directly controlled by the automatic proportioning of the cold and hot air streams at the mixing unit. This allows the system to precisely blend the desired amounts of hot and cold air to achieve the target temperature in the space. The other answer choices, such as controlling the chilled water flow or steam flow, are not the primary means of directly controlling the space air temperature in this type of HVAC system. The automatic mixing of the hot and cold air streams at the mixing unit is the key mechanism for directly regulating the space temperature.