Layered assemblies, materials, boundary conditions, calculations and results.
On this page
Interface Overview
The standalone application has three main areas:
Construction editor: The left panel contains the construction name,
exterior and interior boundary rows, physical layers, editing actions, and analysis settings.
Drawing: The right panel shows geometry, temperature, heat flux,
or humidity. Zoom, pan, and click the drawing to inspect a layer or calculated point.
Results: Calculated values appear in the results panel below the drawing;
progress, timings and warnings are written to the console.
Material Library
The material library includes supplied records and user-defined materials.
Open Settings → Material and boundary libraries, or use a layer’s
material selector. Add a custom material to define
properties like Thermal Conductivity (λ), Density (ρ), and Specific Heat Capacity (cp).
Building Constructions
The Construction Editor is where you define the geometry of your
building assembly.
Adding Layers
You can add layers to your assembly. Each layer can be:
Homogeneous: A single material slab.
Inhomogeneous: A layer with repeating thermal bridges (e.g.,
studs). You can define the stud spacing and width parametrically.
Editing and partial cavity fill
Added and duplicated layers remain selected. Reorder with Up/Down, Alt+Up/Down,
drag and drop, or Move to; Undo/Redo restores edits. The exterior and interior boundary
rows stay fixed. Stud and profile layers can specify insulation depth independently
of stud depth, filling from either face and leaving a remainder that is sealed air by default or any material you assign. Profile
layers keep a separate material for the inside of the profile.
Save writes to the current file; Save as chooses another. Unsaved work is protected
before closing or replacing a construction. Current files use format version 2;
this build continues to read legacy constructions. Run analysis explicitly after
input changes; CSV and IDF exports require a completed, current analysis.
Surface Resistances (Rsi/Rse)
Every construction requires Surface Film Resistances to account for the
thin layer of air clinging to the surface.
Rsi (Interior): Represents the resistance at the indoor surface
(convection + radiation). Standard value for walls: 0.13 m²K/W.
Rse (Exterior): Represents the resistance at the outdoor surface
(influenced by wind). Standard value for walls: 0.04 m²K/W.
KOALA automatically adds these layers to your construction stack. You do not need to
model them as material layers. Select an exterior/interior boundary row and use Edit,
Enter, or double-click to adjust temperature, humidity, and surface resistance.
Running the Solver
KOALA performs two types of thermal simulations simultaneously: a
Steady-State
Analysis and a Dynamic Analysis (ISO 13786).
Boundary Conditions
The solver calculates heat flow based on the temperature difference (ΔT) between the
indoor and outdoor environments.
Temperature: Set the Interior (e.g., 20°C) and Exterior (e.g.,
-10°C) air temperatures. The solver uses these to calculate the temperature
gradient through the assembly.
Relative Humidity (RH): Define the moisture content of the air
on both sides. This is critical for Glaser Method condensation
risk analysis.
The solver discretizes your construction into a graded 2D grid of rectangular
cells (see The Mesh) and solves the steady-state heat conduction
equation to determine the temperature at every node (see
How the Solver Works). This is crucial for identifying thermal bridges—areas where
heat
bypasses insulation (like through steel or wood studs), significantly reducing the
wall's effective performance.
Dynamic Analysis
In addition to the static U-value, KOALA computes dynamic thermal properties
according
to the ISO 13786 standard. This simulates how the wall reacts to fluctuating outdoor
temperatures over a 24-hour cycle, which is essential for understanding
thermal
mass and time lag.
Results
U-Value (Thermal Transmittance): Represents the rate of heat
transfer through the assembly. Lower values mean better insulation. KOALA
calculates
the U_Simulated, which accurately
accounts
for 2D thermal bridging effects that simple 1D calculations miss. U_Estimated uses a simple parallel path
U-Value calculation that is only valid if there is little to no lateral conducion
the the inhomogeneous layers.
Decrement Factor: How much the
exterior temperature wave is dampened before reaching the interior. Lower is
better
for stable indoor temperatures.
Time Shift (Phase Lag): The time
delay (in hours) for the peak outdoor temperature to reach the inside. A high
time
shift (e.g., 8-12 hours) can delay heat gain until night when it can be flushed
out.
Saving and recovery
Save writes the current construction; Save as selects another file. Unsaved changes are checked before opening another construction, closing or quitting. A recovery draft can restore work after an interrupted session.
Material and boundary libraries are saved separately. Existing assignments retain their own material and boundary values.
Exports
For CSV results, construction figures and EnergyPlus IDF export, see Standalone exports. The methods guide describes the mesh, steady-state heat transfer, vapour diffusion screening and dynamic estimates.
