Choosing a calculation tool comes down to two questions a feature list never answers: what exactly does it compute, and where does it stop. Both are below, along with the standards behind the numbers and the formats you can hand over. Step-by-step instructions are a separate document, the user manual.
What kind of tool this is
PsychroView is a steady-state psychrometric calculator with an interactive chart. You define an air state, chain air-treatment processes onto it, and the application solves each step, draws it in the Mollier h-x or Carrier chart, and reports the energy and mass flows involved.
The unit of work is a chain: outdoor air enters at one end, passes through heat recovery, a heating coil, a humidifier and whatever else the design calls for, and arrives at the space. Every node carries a full set of state variables — dry-bulb temperature, humidity ratio, [relative humidity](/glossary/relative- humidity/), enthalpy, dew point, wet-bulb temperature, specific volume and density.
“Steady-state” is the word that decides most comparisons. The application solves design conditions, not a year of operation, and it solves air, not the building around it. Loads are an input to the calculation, never an output of it.
Air-treatment processes
Thirteen processes are available. Each one takes the outlet state of the previous node as its inlet, so a chain of any length stays consistent.
| Process | What it computes | Principal input |
|---|---|---|
| Air point | The starting state of a chain, from any valid pair of state variables | two of , , , , , |
| Air heating | Sensible heating at constant humidity ratio, and the coil duty | outlet temperature or capacity |
| Air cooling with condensation | Cooling with dehumidification, the apparatus dew point (ADP), the bypass factor (BF), condensate rate and the sensible heat ratio (SHR) | outlet state, or capacity, or coolant temperatures |
| Heat recovery (HRV) | Sensible — and for enthalpy wheels also latent — transfer between extract and supply air, with the exchanger efficiency | efficiency, or outlet temperature |
| Adiabatic cooling | Evaporative cooling along a line of constant enthalpy, with saturation efficiency | saturation efficiency or outlet state |
| Heat load | Internal sensible gains from people, lighting and equipment, applied at constant humidity ratio | heat input [kW] |
| Heat loss | Dry sensible loss through the envelope, with a warning if the outlet falls below the inlet dew point | capacity [kW] |
| Air humidification | Water (adiabatic), wet steam or saturated steam, including the water or steam flow rate | outlet humidity or water/steam rate |
| Humidity load | Moisture released into the space, applied at constant temperature | moisture production [g/h] |
| Sorption dehumidification | Desiccant drying — moisture removed without condensation, with the temperature rise that accompanies it | outlet humidity ratio |
| Mixing of 2 streams | The resulting state of two air streams combined, weighted by mass flow | flow rates and both inlet states |
| Mixing of 3 streams | The same for three streams | flow rates and three inlet states |
| Flow split | Splitting one stream into two branches that can then be treated separately | split ratio or branch flow rate |
Mixing and split work as a pair, which is what makes recirculation possible: split the return air, mix part of it back into the outdoor air, and treat the result.
Room balance solvers
Three of the process cards contain deterministic solvers. They work backwards from the state you want in the space to the supply state and the equipment duty needed to reach it, with no manual iteration.
- Space load solver (cooling). From the target band for the space, the heat gain (either total or split into sensible and latent), the moisture production, the permitted supply- to-space ΔT and the coolant temperature range, it derives the required supply state, the coolant span /, the cooling duty, the condensate, the SHR and any reheat needed.
- Room balance solver (heating). From the heat loss, the moisture production and the target band, it derives the supply state, the heater duty and any humidification needed, including the steam or water flow rate.
- Heat and humidify. From a target temperature and relative humidity, it derives the heater duty, the steam rate and the intermediate state after heating.
When the input is physically impossible — saturation exceeded, flow rate too low, a coolant that cannot reach the required apparatus dew point — the solver says so in words and suggests what to change, rather than returning a number that looks valid.
Design climate data
Outdoor design conditions can be taken from published datasets rather than typed in by hand. Winter and summer conditions are available at several severity levels, with the coincident humidity or enthalpy wherever the source provides it.
| Source | Coverage |
|---|---|
| DWD CDC | Germany, design temperature by the DIN/TS 12831-1 method, two climate periods |
| GeoSphere | Austria, NAT-13 plus summer percentiles |
| Location search | Worldwide, via Open-Meteo geocoding; percentiles from JRC PVGIS TMY or the ERA5 1994–2023 reanalysis |
| German postcode | Conditions of the nearest DWD station |
| EPW file | Your own EnergyPlus Weather file — conditions derived from 8,760 hourly values |
| Your own data | JSON or CSV import, validated with a preview and stored with your account |
Locations can be compared side by side, which is the practical way to check how much a design depends on the site rather than on the equipment.
The chart
The chart is the working surface, not an illustration generated at the end.
Both conventions are available: the Mollier h-x chart used across continental Europe and the Carrier T-x chart familiar from ASHRAE practice. It is the same data with the axes exchanged. Barometric pressure is set explicitly, so calculations at altitude are correct rather than approximated at sea level. Chart range, working zones, auxiliary lines for SHR and dh/dx, the legend, the info panel and a dark mode are all configurable, and points can be dragged directly in the chart with the calculation following the cursor.
Outputs
| Format | Content |
|---|---|
| Multi-page A4: project header and chart, summary table, per-process detail tables | |
| PNG | High-resolution bitmap of the chart |
| SVG | Vector chart, editable in Inkscape or Illustrator |
| DXF | CAD line work for AutoCAD or BricsCAD |
| XLSX (beta) | Numerical data for all processes, plus the chart as an image |
| DOCX (beta) | Formatted document with chart and process tables |
| HTML (beta) | Stand-alone page with the chart and tables embedded |
| Clipboard | Chart or summary table, for pasting into an email |
| Animation (beta) | WebM or GIF of the points appearing one by one, for teaching |
Blank, unmarked charts for printing are available separately on the downloads page, including a DXF for CAD.
Calculation core and standards
The psychrometric core implements Chapter 1 of the ASHRAE Handbook — Fundamentals 2021, including the real-gas enhancement factor, with saturation pressure from the Hyland- Wexler correlations. Every quantity has been compared numerically against the ASHRAE reference tables across the HVAC temperature range; the measured deviations are published on the ASHRAE conformance page.
The constants and correlations used in Czech technical literature are available as an alternative, for work that has to match a national convention rather than ASHRAE.
How it runs
The application is an online psychrometric chart: it runs in the browser, on desktop and on mobile, with no installation and no licence management. Calculations can be started without an account; an account adds saved projects, your own climate data and share links. A project can be published as a read-only link, or embedded in another page as a widget. The interface is fully localized into English, German, French, Czech and Slovak, and switches between SI and I-P units.
What PsychroView does not do
This list decides fit more often than the feature list above it does.
- It does not simulate a year of operation. Calculations are steady-state design points. There is no hourly simulation, no energy consumption over a season and no part-load behaviour.
- It does not compute building loads. Heat gain, heat loss and moisture production are inputs you supply, from your own load calculation or from a dedicated tool. The application applies them to the air; it does not derive them from geometry, construction or occupancy.
- It does not size ductwork. Pressure drop is tracked for the components you place in a unit, but there is no duct network design, no fan curve matching and no hydraulic calculation.
- It does not select equipment from manufacturer catalogues. It gives you the duty and the state points; choosing a specific coil or unit is a separate step.
- It is not a CFD tool. Air distribution, velocity fields and comfort mapping inside a space are out of scope.
In development
Several modules are built but not yet released: the Builder for assembling an air handling unit visually, Autopilot for deriving a process sequence automatically, a Sankey diagram of energy flows, WBGT heat stress, a toolbox of quick calculators, and PMV/PPD thermal comfort analysis to ISO 7730, ASHRAE 55 and EN 16798-1. They appear in the interface marked as in development, so you can see what is coming without mistaking it for a finished feature.