Question 216General Subjects - 1st Asst/Chief

A) The space air temperature is controlled by automatically proportioning the cold and hot air streams at the mixing unit. This is the correct answer. In a dual duct multiple zone HVAC system, the space air temperature is controlled by automatically mixing the cold and hot air streams at the mixing unit. The system senses the space temperature and adjusts the proportions of cold and hot air to maintain the desired temperature in the conditioned space. The other options are incorrect because they do not accurately describe how the space temperature is directly controlled in this type of HVAC system. Options B, C, and D involve controlling the temperature through the preheat, cooling, or reheat coils, respectively, rather than the direct mixing of the air streams.