Dry-bulb temperature (DBT) is defined as?

• A. The temperature of air indicated by an ordinary thermometer shielded from solar and long wave radiation.
• B. The temperature of water in the cooling system.
• C. The dew-point temperature.
• D. The wet-bulb temperature.

Answer: (A)

Dry-bulb temperature is the air’s actual temperature as read by a standard thermometer placed in still air and shielded from radiant heat, such as direct sun and other long-wave heat sources. This reading represents the thermal energy of the air itself, without the influence of moisture effects or evaporative cooling.

That’s why the description of an ordinary thermometer shielded from solar and long-wave radiation is the correct definition. It distinguishes the air temperature from other related measures: the temperature of water in a cooling system is a fluid-temperature reading, not the air temperature; the dew-point temperature refers to the temperature at which air becomes saturated with moisture; and the wet-bulb temperature involves evaporative cooling of a wetted bulb and is typically lower than the dry-bulb temperature under most conditions.

Understanding dry-bulb temperature is foundational for analyzing indoor air conditions because, when paired with humidity-related properties (like humidity ratio or relative humidity), it helps determine comfort, heat loads, and other psychrometric calculations used in building commissioning.