EQS Air

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EQS Air is the psychrometric chart for HVAC work on the iPhone, the iPad and the Mac. It gives the state of moist air from any two of its properties, at any elevation; it draws the points on a chart you can touch, mixes two air streams, and gives the loads of a coil, a heater or a humidifier.

Write to us: [email protected]. We answer within one working day. Please say which device and which version (Settings → About EQS Air).

How do I…

Give a state from what I measured?

In Points, choose the pair you know (dry bulb and relative humidity, dry bulb and wet bulb, dew point and relative humidity, enthalpy and relative humidity, and seven more) and type the two values. The other six properties follow at once.

Move a point on the chart?

Touch the point and drag it; on a Mac, drag it with the mouse. Its values follow, and so does every mixture and process that uses it. Tap an empty place on the chart to read the air there, then “+ Point here” to keep it.

Mix two air streams?

Points → “+ Mixture”, then choose the two points and their airflows. The mixed point moves when either stream moves. If the mixture would be above saturation, EQS Air shows the saturated state and the water that stays as fog.

Get the load of a coil, a heater or a humidifier?

Processes → “+ Process”, from one point to another, with the airflow at the start. You get the total, sensible and latent load, the sensible heat ratio and the water removed or added (in IP units also in tons).

Work in °F, psia and Btu/lb?

Tap SI/IP at the top, or Settings → Units. Everything is stored in SI, so switching back and forth never changes a value.

Account for my site's elevation?

Settings → Site elevation. The atmospheric pressure follows the standard atmosphere and every state and chart line uses it.

Put my results in a report or a spreadsheet?

Settings → “Copy as a table”, then paste into Numbers, Excel, a note or an e-mail.

The equations

Moist air as a mixture of ideal gases by the equations of the ASHRAE Handbook — Fundamentals (2017), chapter 1: saturation over water and ice by Hyland and Wexler, the thermodynamic wet bulb, the dew (frost) point, and the standard atmosphere for the pressure. Checked against CoolProp's humid-air model within a few tenths of a per cent from −20 °C to 50 °C, sea level and 1500 m.

Requirements

iPhone and iPad with iOS 16 or later; Mac with macOS 12 or later. One purchase covers all three.