Explain enthalpy and its use on a psychrometric chart.

Explain enthalpy and its use on a psychrometric chart.

• A. Enthalpy is the amount of humidity in moist air.
• B. Enthalpy is the dry-bulb temperature of air.
• C. Enthalpy is the pressure-to-temperature relation of refrigerant.
• D. Enthalpy is the total heat content of moist air (sensible plus latent); differences in enthalpy indicate heat transfer and are used for calculations on the psychrometric chart.

Answer: (D)

Enthalpy is the total heat content per kilogram of moist air, including both sensible heat (related to temperature) and latent heat (related to moisture). On a psychrometric chart you don’t just track temperature and humidity separately—you use enthalpy to combine them. A common way to estimate it is h ≈ 1.006 T + w(2501 + 1.86 T), where T is the dry-bulb temperature and w is the humidity ratio. This shows how enthalpy rises with higher temperature and/or more moisture. Enthalpy is useful because the change in enthalpy between two states equals the heat transferred per kilogram of dry air. So if air is cooled and dehumidified, its enthalpy decreases; if it’s heated, enthalpy increases. On the chart, you can follow or compare lines of constant enthalpy to visualize energy changes and compute coil loads, energy efficiency, and the split between sensible and latent cooling.

Enthalpy is the total heat content per kilogram of moist air, including both sensible heat (related to temperature) and latent heat (related to moisture). On a psychrometric chart you don’t just track temperature and humidity separately—you use enthalpy to combine them. A common way to estimate it is h ≈ 1.006 T + w(2501 + 1.86 T), where T is the dry-bulb temperature and w is the humidity ratio. This shows how enthalpy rises with higher temperature and/or more moisture.

Enthalpy is useful because the change in enthalpy between two states equals the heat transferred per kilogram of dry air. So if air is cooled and dehumidified, its enthalpy decreases; if it’s heated, enthalpy increases. On the chart, you can follow or compare lines of constant enthalpy to visualize energy changes and compute coil loads, energy efficiency, and the split between sensible and latent cooling.