Psychrometric Chart 2 Condition

Two air conditions, solved side by side, and the cooling it takes to get from one to the other. Each condition is fixed by two properties, both columns use the same pair of dropdowns, and the calculator returns dry bulb, wet bulb, dew point, relative humidity, specific volume, specific enthalpy, humidity ratio and the three pressures for each.

Sensible cooling is 1.08 × airflow × the drop in dry bulb; latent cooling is 0.68 × airflow × the drop in humidity ratio in grains per pound; total cooling is the two added. Airflow per unit capacity is the airflow divided by the total in tons, which is the CFM/ton a coil is running at. Condensate is the mass flow of dry air times the drop in humidity ratio, at 1.04 lb per pint.

Under metric units the three loads switch to kW: sensible is 1.006 × 1.202 × airflow ÷ 1000 × the dry-bulb drop and latent is 1.202 × 2454 × airflow ÷ 1000 × the drop in humidity ratio in g/kg ÷ 1000, with airflow in l/s.

The psychrometrics are the 2021 ASHRAE Fundamentals saturation-pressure correlation, over ice below freezing and over water above it, at the total pressure the shared altitude implies. Dew point and relative humidity come from the Magnus correlation and the wet bulb from Stull's approximation, so the answers are consistent with each other but not identical to a full iterative solution.

Every unit pair reads US first and metric in parentheses, following the units dropdown: 80 means 80 °F under US Units and 80 °C under Metric Units. Airflow is CFM or l/s, altitude is feet or metres, and the altitude applies to both conditions.

Picking "Temperature, DP" for the first condition pairs the dew point with a relative-humidity box that the published page never fills in: the cell is blank on the workbook and zero in the build, so that pairing returns a dew point and zeroes. It is kept because the dropdown offers it, not because it answers.

The warning appears when the entering first condition is below freezing, where the correlation is least reliable. It reads "-" otherwise.

Corrected 2026-09: below freezing the humidity ratio used to be read off the dry-bulb/wet-bulb block's own cells rather than the solved dry bulb and wet bulb, so under "RH %" it turned the percentage into a wet-bulb temperature. Entering air at 20 °F and 60% RH was published at 0.0266 lb/lb against a saturation ceiling of 0.0021 from the page's own Sat Vapor Press. row, which put a six-figure positive latent load on a coil that was heating. The humidity ratio, the specific volume, the specific enthalpy, the latent and total cooling, the CFM/ton and the condensate all move; the temperatures, the relative humidity, the three pressures and the sensible cooling do not.