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Psychrometrics

3 tools in the Building Systems area.

Psychrometric Calculator

The full state of moist air from its dry-bulb temperature and one other property (relative humidity, wet-bulb temperature, dew point or humidity ratio) at the pressure of the entered altitude: humidity ratio, relative humidity, wet-bulb and dew-point temperatures, enthalpy, specific volume, density, vapor pressure and the saturation values, by the ASHRAE perfect-gas relations with the Hyland and Wexler saturation pressure. The state is drawn on a psychrometric chart with the saturation curve and the relative-humidity lines. Temperatures are entered as plain numbers in °F (USCS) or °C (SI).

2 worked examples reproduced, listed on the tool page.

Mixing and Coil Process

The two processes that make up an air handler: adiabatic mixing of a return-air stream with an outdoor-air stream, and the coil that takes the mixture to its leaving state. The mixed state follows from the mass-weighted humidity ratios and enthalpies; the coil load is the enthalpy change times the dry-air mass flow, split into sensible and latent parts with the sensible heat ratio and the condensate rate for a cooling coil (or the sensible heating load for a heating coil, whose leaving humidity ratio equals the entering one). The states are drawn on a psychrometric chart. Temperatures are plain numbers in °F (USCS) or °C (SI).

Humidification Water

Water or steam needed to take an airflow from its entering state to a target humidity, by the two ways it is done: steam injection, which adds moisture at nearly constant dry bulb and needs the steam's enthalpy as heat, and adiabatic (evaporative or atomizing) humidification, which adds moisture along a line of constant wet bulb and cools the air as it does. For the target relative humidity the tool gives the leaving state of each method, the water mass rate and its volume per hour, the steam heat, and the reheat an adiabatic humidifier needs to restore the dry bulb; dehumidification by a cooling coil is the same balance run the other way. Temperatures are plain numbers in °F (USCS) or °C (SI).

Other Building Systems sections

HVAC Loads · Ducts and Airflow · HVAC Equipment · Ventilation and Air Quality · Energy · Plumbing · Fire Protection · Lighting and Electrical · Controls and Commissioning · Codes and Compliance