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Mollier Diagram

Enthalpy Guidelines (h) Absolute Humidity Lines (x) Saturation Line (100% RH)

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Custom Pair State Point Setup

Property 1

°C

Property 2

Property 1

°C

Property 2

Property 1

°C

Property 2

Point Delta Process Analyzer

Cooling & Dehumidification

Start Point (Point A)

End Point (Point B)

Δ Dry-Bulb Temp

-23 °C

Δ Humidity Ratio

-0.01315 kg/kg

Δ Enthalpy

-57.24 kJ/kg

Δ Rel. Humidity

+35 %

Thermodynamic State Data Summary

Property Name	Symbol	Unit	State 1 (Outdoor Air)	State 2 (Coil Leaving)	State 3 (Supply / Mixed)
Dry-Bulb Temperature	T_db	°C	35	12	22
Wet-Bulb Temperature	T_wb	°C	28.17	11.55	15.43
Dew Point Temperature	T_dp	°C	26.07	11.22	11.11
Relative Humidity	RH	%	60 %	95 %	50 %
Humidity Ratio	W	kg/kg	0.02144	0.00829	0.00822
Specific Enthalpy	h	kJ/kg	90.23	32.99	43.04
Specific Volume	v	m³/kg	0.903	0.819	0.847
Vapor Partial Pressure	p_v	kPa	3.377	1.332	1.322

Engineering Guide to Mollier Diagram (h-x) Analysis

DIN 4107 European Standards, Oblique Enthalpy Axes & Real-World HVAC Equipment

Switch to Psychrometric View

1. Principles of the Mollier (h-x) Coordinate System

Developed by German physicist Richard Mollier in 1923, the Mollier h-x diagram is the standard thermodynamic representation for moist air across European mechanical engineering (DIN 4107, VDI 4672). Unlike the rectangular Carrier psychrometric chart, the Mollier diagram uses an oblique coordinate transformation where lines of constant enthalpy (h) slope downward so the 0°C dry-bulb isotherm lies strictly horizontal.

Specific Enthalpy (h)

Oblique diagonal grid lines (kJ/kg or Btu/lb).

Absolute Humidity (x)

Vertical grid lines (kg water/kg dry air or grains/lb).

Isotherms (θ)

Dry-bulb lines with positive slope in unsaturated zone.

Saturation Line (φ=100%)

Boundary separating clear moist air from the supersaturated fog region.

Wet Thermometer (θ_v)

Equilibrium wet-bulb temperature along saturation curve.

Process Gradient (Δh/Δx)

Enthalpy direction vector determining coil / steam process angle.

2. Enthalpy Gradient (Δh/Δx) & Sensible Heat Ratio (SHR)

On a Mollier diagram, process lines follow the direction of the enthalpy-to-moisture gradient (Δh/Δx). In HVAC coil design, this directly correlates to the Sensible Heat Ratio (SHR):

Δh/Δx = (h₂ - h₁) / (x₂ - x₁) [kJ / kg moisture]

SHR = Q_sensible / Q_total = (c_pa · Δθ) / Δh_total

High SHR (0.85 – 1.0)

High sensible heat load with minimal moisture exchange (e.g. Data Centers, Switch Rooms, Dry Climates).

Comfort Range SHR (0.70 – 0.80)

Combined sensible transmission/solar loads and human metabolic moisture generation (Commercial Offices, Classrooms).

Low SHR (0.50 – 0.65)

Intensive latent dehumidification demands (Indoor Aquatic Centers, Hot Yoga, Commercial Kitchens).

3. Mollier Air Conditioning Process Vectors & Real Equipment Examples

Sensible Heating (Upward along vertical x line: Δθ > 0, Δx = 0)

Air is heated at constant absolute moisture content. The state point moves upward across isotherms while relative humidity φ drops.

Real Devices: Electric finned duct heaters, hydronic heating coils (central boiler loops), gas-fired warm air furnaces, perimeter convection radiators.

Sensible Cooling (Downward along vertical x line: Δθ < 0, Δx = 0)

Heat removed without moisture condensation. The cooling coil surface remains above the entering air dew point (θ_coil > θ_dp).

Real Devices: Chilled ceiling radiant panels, sensible air-to-air plate heat recovery units, dry chilled water coils in warm return air paths.

Cooling & Dehumidification (Down & Left: Δθ < 0, Δx < 0)

Air passes across a cold coil below the entering dew point (θ_coil < θ_dp). Moisture condenses out as water while enthalpy and temperature decrease.

Real Devices: Direct Expansion (DX) evaporator coils in rooftop units (RTU), chilled water AHU cooling coils (6°C supply / 12°C return), computer room air handlers (CRAH).

Heating & Humidification / Steam Injection (Up & Right: Δθ > 0, Δx > 0)

Simultaneous heat and water vapor injection. On a Mollier diagram, steam humidification follows a steep upward gradient corresponding to steam enthalpy (h_steam ≈ 2680 kJ/kg).

Real Devices: Electrode boiler steam humidifiers, gas-fired steam dispersion manifolds, pressurized boiler steam injection nozzles in AHU supply ducts.

Evaporative Cooling / Adiabatic Humidification (Parallel to h lines: Δh ≈ 0)

Water evaporates into the air without net heat exchange. State point moves down and to the right parallel to constant enthalpy (h) guidelines toward the saturation line.

Real Devices: Direct evaporative wet media pads (swamp coolers), open cooling towers, high-pressure water fogging nozzles, adiabatic air washers.

Chemical Desiccant Dehumidification (Δθ > 0, Δx < 0)

Adsorption of moisture by hygroscopic media releasing heat of sorption. Air temperature rises while moisture content drops to ultra-low dew points (-40°C).

Real Devices: Rotary desiccant wheels (silica gel / zeolite rotors in lithium battery dry rooms, pharmaceutical tablet coating suites).

4. Mollier Diagram vs. Carrier Psychrometric Chart

Switch to Psychrometric View

While the American Carrier Psychrometric Chart plots dry-bulb temperature along the horizontal axis and humidity ratio vertically, the European Mollier Diagram (h-x) aligns absolute moisture on the vertical grid lines and tilts the enthalpy axis obliquely. This enables direct geometric construction of steam addition lines and mixing vectors without needing oblique auxiliary protractor scales.