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🏢 Application

Psychrometric Properties

Atm. Pressure--
Dry Bulb Temp--
Wet Bulb Temp--
Dew Point--
Relative Humidity--
Humidity Ratio W--
Specific Volume--
Air Density--
Saturation Pressure--
Vapour Pressure--
Specific Enthalpy (h)--
COMFORT / APPLICATION STATUS
Formulae (ASHRAE 2009): p = 101.325×(1−0.0065z/288.15)^5.255 | pₛ = Wexler-Hyland | W = 0.621945×pᵥ/(p−pᵥ) | h = 1.006T + W×(2501+1.86T) | v = 0.287058×(T+273.15)×(1+1.6078W)/p | ρ = (1+W)/v | Twb: ASHRAE thermodynamic (Stull 2011 init) | Tdp: ARM (Alduchov & Eskridge 1996)

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Calculate cooling, heating, humidification & dehumidification loads for a given air flow.

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📊 Psychrometric Chart — Current State Point

State point auto-updates from Tab 1 inputs. Comfort zone shown in green.

Educational Reference

📚 Psychrometrics — Complete Guide

A comprehensive reference for students and engineers covering all key terms, how to read the psychrometric chart, and how to use every feature of this calculator.

🔬 What is Psychrometrics?
Psychrometrics is the branch of engineering science studying the physical and thermodynamic properties of moist air — a mixture of dry air and water vapour. Understanding moist air is fundamental to HVAC engineering, building science, meteorology, industrial drying, food processing, and pharmaceutical manufacturing.

Governing standard

This calculator is based on ASHRAE Fundamentals 2009, using the Wexler-Hyland saturation pressure equations, ARM dew point coefficients, and ASHRAE thermodynamic wet bulb definition.
🧩 Core Terms
Dry Bulb Temperature
Tdb
°C (SI) · °F (Imperial)
Standard air temperature measured by a thermometer shielded from radiation and moisture. The horizontal axis of the psychrometric chart.
Relative Humidity
RH
% (ratio × 100)
Ratio of actual water vapour pressure to saturation pressure at the same temperature. RH = 100% means fully saturated air.
RH = (pᵥ / pₛ) × 100 %
Humidity Ratio
W
kg/kg dry air
Mass of water vapour per unit mass of dry air. Absolute moisture measure — does not change during sensible heating/cooling.
W = 0.621945 × pᵥ / (p − pᵥ)
Dew Point
Tdp
°C · °F
Temperature at which air must be cooled before condensation begins. Surfaces cooler than dew point collect moisture.
ARM (Alduchov & Eskridge 1996): a=17.625, b=243.04
Wet Bulb Temperature
Twb
°C · °F
Temperature of a wet-wick thermometer in airflow. Always ≤ dry bulb. Equals dry bulb only at 100% RH. Solved via ASHRAE thermodynamic Newton-Raphson iteration.
Specific Enthalpy
h
kJ/kg · BTU/lb
Total energy content of moist air per kg of dry air. Used directly in HVAC load calculations: Q = ṁ × |h₂ − h₁| kW.
h = 1.006·T + W·(2501 + 1.86·T) kJ/kg