h,x Chart · The Technician

h,x Chart Coil Measurement

Data center air handler with DX evaporator or chilled water coil, evaluated from air-side and refrigerant or water-side measurements

Sample values, replace with your own measurements

Mollier h,x chart · p = 1013 hPaHover over the chart to read a state

Coil process 1 → 2 Extension to saturation (apparatus dew point K) Evaporating temperature t₀ Saturation φ = 100 % ASHRAE envelope

1 · Air entering coil Temperature °C Rel. humidity %

2 · Air leaving coil Temperature °C Rel. humidity %

Refrigerant circuit (evaporator) Coil type

t₀ from

Pressure Input

Refrigerant Suction pressure bar Pressure reading Suction gas temp. °C, optional

3 · Steam humidifier after coil Humidifier

Boundary conditions Air pressure hPa Airflow m³/h, optional ASHRAE envelope TC 9.9, 5th edition

Air states

Quantity	1 in	2 out

Coil & cooling circuit

Assessment

Method: saturation pressure from the Magnus formula (over water, below 0 °C over ice), enthalpy h = 1.006·t + x·(2501 + 1.86·t), oblique Mollier coordinate system. Chilled water capacity Q = V·ρ·c_p·(t_return − t_supply) with properties at about 10 °C (water 4.19 kJ/kgK, ethylene glycol 30 % 3.70 kJ/kgK, propylene glycol 30 % 3.88 kJ/kgK). Refrigerant saturation temperatures (dew line) from CoolProp points every 2.5 K, interpolated, accuracy about ±0.1 K. The apparatus dew point K is where the extended process line meets the saturation curve, i.e. the effective mean surface temperature of the coil. Steam humidification follows Δh/Δx = h_steam = 2501 + 1.86·t_steam kJ/kg, i.e. almost along an isotherm (about +0.3 K at 100 °C steam); the electric power is estimated against 15 °C feed water. The dew point limits of the ASHRAE envelopes are evaluated over water, as in TC 9.9 (−12 °C DP and 8 % RH meet at about 25 °C).

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