Psychrometric Chart HVAC
Walk an air handler through its psychrometric processes — mix outdoor and return air, then cool, heat, and humidify. Pick a stage with the pills, edit its parameters in the panel, or drag OA and RA on the chart. The supply-air state and all intermediate points follow.
Air handler
Outdoor air entering the air handler. Drag this dot on the chart, or edit values here.
Air returning from the conditioned space. Drag this dot on the chart, or edit values here.
Mass-weighted mix of OA and RA. The mixed point falls on the straight line between OA and RA on the chart, at the OA% fraction of the way from RA to OA.
Coil leaving condition. Must be at or below entering DB; humidity ratio can't increase across a cooling coil.
Sensible heating only — humidity ratio is unchanged across the coil. Leaving DB must be at or above entering DB.
Adiabatic (constant wet-bulb) humidification — an evaporative pad or wetted media. Adds moisture; dry-bulb drops a little. Leaving RH must be at or above entering RH.
Supply air is the leaving state of the last enabled stage in the chain. Full property table at right.
Chart
Heavy green = saturation. Light curves rising right = constant RH; light dashed = constant wet-bulb. Process segments are colored: gray = mixing, blue = cooling / dehumidification, orange = heating, green dashed = adiabatic humidification.
Stages
| DB °F | gr/lb | RH % | h Btu/lb |
|---|
OA — Outdoor air
Properties are per pound of dry air, computed internally from the ASHRAE Fundamentals (Chapter 1) IP equations and converted to your selected display units. RH is taken as the partial-pressure ratio (the usual approximation). Mixing is a mass-weighted enthalpy / humidity-ratio combination. Adiabatic humidification holds wet-bulb constant. Coil capacities use AHU airflow and inlet specific volume: Q = ṁ·Δh with ṁ = CFM·60/vin; Qsens = ṁ·(0.240 + 0.444·Win)·ΔT. For building feel and quick design-day state-point checks — not a substitute for a calibrated load-study tool.