EKS-HUM-001 / Moist-air state and psychrometric properties

Dry-bulb Temperature

干球温度

Dry-bulb temperature is the air temperature indicated by a suitable temperature sensor whose sensing surface is dry and protected from avoidable radiation and moisture effects.

Abbreviations: DB, DBT
Aliases: air dry-bulb temperature

QUANTITY, SYMBOL AND UNIT

Quantity / objectDry-bulb temperature

Symbolt_db, t

SI°Cdegree Celsius

IP°Fdegree Fahrenheit

Definition

Dry-bulb temperature is the air temperature indicated by a suitable temperature sensor whose sensing surface is dry and protected from avoidable radiation and moisture effects.

It is the temperature coordinate normally used with one or more humidity quantities to define a moist-air state. A dry-bulb value by itself says how warm the air is, not how much water vapour it contains.

Relations and distinctions

Dry bulb and wet bulb

A dry-bulb sensor measures air temperature without evaporative cooling; a wetted psychrometer sensor can cool toward a wet-bulb temperature.

Dry bulb and surface temperature

Dry bulb describes the air at the measurement location. Surface temperature belongs to a material or equipment surface and may be substantially different.

Engineering meaning

Use dry-bulb temperature with RH, dew point or humidity ratio when specifying an entering-air condition.
Record sensor position and shielding when temperature differences affect a condensation or capacity decision.

Common misconceptions

MisconceptionDry-bulb temperature determines the humidity of the air.

Accurate explanationThe same dry-bulb temperature can occur at many different water-vapour contents. A second independent moisture property is required.

Application boundaries

Radiant heat, poor airflow, self-heating and contact with a surface can bias an air-temperature reading.
Dry-bulb temperature alone does not determine dew point, moisture load or dehumidifier capacity.

Supporting sources

ASHRAE / SRC-ASHRAE-F25-CH01

ASHRAE Handbook - Fundamentals, Chapter 1: Psychrometrics ↗

2025 SI edition / Chapter 1, notation and psychrometric-chart sections, especially lines 622–633 and 800–829
Supports: Dry-bulb temperature is the ordinary air-temperature coordinate used in moist-air property relations; Dry-bulb temperature is expressed in °C in the SI chapter; Dry-bulb temperature alone does not specify the moisture state

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