CYTSoft Psychrometric Chart: Step‑by‑Step Examples for Engineers

CYTSoft Psychrometric Chart: Complete Guide & How to Use ItThe psychrometric chart is an essential tool for HVAC engineers, building scientists, and anyone who works with air-conditioning, moisture control, or indoor climate design. CYTSoft’s psychrometric chart is a digital implementation that simplifies many common HVAC tasks: calculating enthalpy, humidity ratio, dew point, sensible and latent loads, and visualizing air-conditioning processes. This guide explains the chart’s elements, how to read them, and how to use CYTSoft’s features effectively with practical examples.

What a Psychrometric Chart Shows (Quick overview)

A psychrometric chart graphically represents the thermodynamic properties of moist air. Key properties plotted or derivable from the chart include:

• Dry-bulb temperature (DBT) — horizontal axis (°C or °F).
• Humidity ratio or absolute humidity (W) — vertical axis (kg water/kg dry air or lb water/lb dry air).
• Relative humidity (RH) — curved lines sweeping across the chart (0–100%).
• Wet-bulb temperature (WBT) — diagonal lines that slope upward to the left.
• Dew point temperature — points on the 100% RH curve (saturation line).
• Specific enthalpy (h) — often slanted parallel lines (kJ/kg or Btu/lb).
• Specific volume (v) — lines that indicate volume per unit mass of dry air (m³/kg or ft³/lb).

CYTSoft places these elements in an interactive interface so you can read values directly, plot process lines, and perform calculations without manual interpolation.

CYTSoft-specific features (what distinguishes it)

• Interactive plotting of state points and process lines (mixing, heating, cooling, humidification, dehumidification).
• Units toggle (°C/°F, kg/kg or lb/lb, kJ/kg or Btu/lb).
• Automatic calculation of derived properties (e.g., enthalpy, dew point, wet-bulb temperature) when state inputs are entered.
• Step-by-step process simulation (e.g., cooling with dehumidification shows sensible and latent heat splits).
• Export options for data and charts (CSV, image formats, sometimes PDF depending on version).
• Built-in templates for common HVAC tasks (mixing two air streams, coil performance, economizer sequences).

How to read a CYTSoft psychrometric chart (step-by-step)

1. Identify the units (confirm whether the chart is set to metric or imperial).
2. Locate the dry-bulb temperature along the horizontal axis for the state point.
3. From that DBT, move vertically to the humidity ratio corresponding to the point of interest. On CYTSoft you can enter DBT and RH or DBT and W and the software will place the point.
4. Read relative humidity by finding the curved RH line passing through the point. CYTSoft usually displays RH numerically on hover or in a properties pane.
5. For enthalpy, follow the slanted enthalpy line through the point — CYTSoft shows the enthalpy value directly.
6. To find dew point, follow horizontally from the state point to the saturation curve (100% RH) and read the corresponding DBT on the horizontal axis; CYTSoft can compute dew point instantly.
7. To get wet-bulb temperature, follow the wet-bulb line that passes through your point, or use the calculator feature.

Common air-conditioning processes on the chart

• Sensible heating/cooling: horizontal movement (humidity ratio constant).
• Humidification/dehumidification at constant dry-bulb: vertical movement (DBT constant).
• Adiabatic saturation/evaporative cooling: movement along a wet-bulb line (enthalpy roughly constant for ideal adiabatic processes).
• Mixing two air streams: line connecting two state points; the mixed state lies along this line at a location determined by mass flow ratio. CYTSoft can compute the exact mixed point given entering conditions and flow rates.
• Cooling with condensation: moves down and left, crossing the saturation curve; split into sensible cooling to the dew point, then latent cooling (moisture removal) along the saturation curve.

Practical examples using CYTSoft

Example 1 — Cooling and dehumidification:

• Inputs: outdoor air at 32°C DBT and 60% RH; supply target 22°C DBT and 50% RH.
• Steps in CYTSoft: place outdoor state point, place target point, draw process line. CYTSoft displays total enthalpy change, mass of water condensed per kg dry air, and sensible/latent heat splits.
• Outputs you’ll see: dew point of outdoor air, temperature at which condensation starts, and required coil capacity (kW or Btu/h) for the specified mass flow.

Example 2 — Mixing two air streams:

• Inputs: Return air at 24°C, 40% RH (flow m1) and outdoor air at 10°C, 90% RH (flow m2).
• Steps: enter both states and their flow rates; CYTSoft calculates mixed-air properties and plots the mixing line.
• Outputs: mixed DBT, RH, enthalpy, and humidity ratio.

Example 3 — Sizing an evaporative cooler (adiabatic cooling approximation):

• Inputs: outdoor DBT 35°C, RH 20%; desired supply ~25°C.
• Steps: follow wet-bulb line from outdoor point toward saturation; CYTSoft shows theoretical achievable conditions and required airflow to meet cooling load.
• Outputs: achievable supply temperature, water evaporation rate, and energy balance.

Interpreting results and common pitfalls

• Always check units before interpreting numeric outputs. A mismatch (kJ/kg vs Btu/lb) causes large numeric differences.
• Remember chart assumptions: air-water vapor mix; contaminants, particulates, and non-idealities are not modeled.
• Coil performance vs. chart: real coils have approach/deviation from ideal process lines due to heat transfer limitations; use manufacturer data where possible.
• Small plotting errors can produce large errors in calculated moisture content; rely on CYTSoft’s numeric outputs rather than visually estimating when precision matters.

Tips for accurate work with CYTSoft

• Use numeric input fields for critical calculations rather than clicking only on the chart.
• Save templates for repeated systems (AHU schedules, economizer setups).
• Calibrate unit preferences at the start of a project to avoid mixing unit systems.
• When modelling moisture-sensitive spaces (museums, labs), run sensitivity checks on outside conditions and infiltration rates.
• Export CSV results for integration with energy models or building simulation tools.

Short reference: useful formulas behind the chart

• Humidity ratio (W) from partial pressure of water vapor pw: W = 0.622 * pw / (p – pw) where p is total atmospheric pressure.

• Approximate enthalpy of moist air: h ≈ 1.006·T + W·(2501 + 1.86·T) (T in °C, h in kJ/kg of dry air).

• Dew point from vapor pressure (inverse of saturation function) — CYTSoft computes this automatically.

When to use the psychrometric chart vs. simulation tools

• Use the psychrometric chart for quick calculations, hand-checks, teaching, and showing process lines visually. CYTSoft is excellent for these tasks.
• For whole-building energy simulation, transient analysis, or systems with complex controls, use specialized dynamic simulation (EnergyPlus, TRNSYS, etc.) and treat psychrometric results as checks or inputs.

Further learning resources

• Practice with common HVAC examples: coil capacity calculations, mixing problems, and economizer strategies.
• Cross-check CYTSoft outputs with hand calculations for learning (use the formulas above).
• Study manufacturer coil performance data to connect chart results to real equipment.

The CYTSoft psychrometric chart turns a complex set of air properties into an interactive visual tool. Use numeric inputs for precision, rely on CYTSoft for derived values, and combine chart-based checks with manufacturer data or dynamic simulation for complete designs.