

IntroductionHEAT3 is a PCprogram for threedimensional transient and steadystate heat conduction. Typical applications are analyses of thermal bridges, heat transfer through corners of a window, heat loss from a house to the ground, estimation of surface temperatures for condensation risk, and fire safety design. The heat equation is solved with explicit forward finite differences. The successive overrelaxation technique is used in the steadystate case. HEAT2 and HEAT3 meet the standard requirements in EN ISO 102111 ("Thermal bridges in building construction  Heat flows and surface temperatures  Part1 General calculation methods"). This document contains three calculation cases that have been validated using HEAT2 and HEAT3. Two of them are covered in the manuals for HEAT2 and HEAT3, see page 138 (HEAT2 5.0) and page 126 (HEAT3 4.0). HEAT2 and HEAT3 confirm to the standard to be classified as a highprecision method. HEAT3 can be used for analyses of thermal bridges, heat transfer through corners of a window, heat loss from a house to the ground, to mention a few applications. One important restriction is that the problem has to be described in a parallelepipedical mesh, i.e. all boundary surfaces are parallel to one of the Cartesian coordinate planes. For a reasonably complicated case, 1015 minutes work is sufficient for an experienced user to describe the geometry, the numerical mesh, and the boundary conditions. A problem often takes less than a few minutes to solve for steadystate. HEAT3
offers high calculation speed with code optimization for Pentium 2, 3, and 4
processors. The number of numerical nodes is limited by the amount of memory
(RAM). The standard version that allows problems with one million (100·100·100)
nodes requires 64 MB RAM. A PC with 2 GB RAM gives access to more than 50
million nodes using a special version of HEAT3. The input and output can be viewed graphically (geometry, numerical mesh, boundary conditions, temperature field and heat flows). The threedimensional figure may be rotated in space, and details of particular interest can be enlarged. Heat flows and temperatures can be recorded and used for e.g. thermal response functions. HEAT3
4.0 uses the same material database as HEAT2 5.0. About 1200 materials are
available. There is also a separate list that contains 200 materials from the
German standard DIN V 41084. Material properties may easily be edited and added. The time to generate the complete input for a reasonably complicated case is less than 10 minutes after a few hours' experience of the program.

An integrated preprocessor facilitates the input procedure, see below.  
Material properties may easily be edited and added. Several material lists are available. The default list (Default.mtl) contains about 200 common building materials. The list General.mtl has over 1200 defined materials. Another file with over 200 materials (in German) from the German standard DIN (Deutsches Institut für Normung, DIN V 41084) is also available.  
Extensive graphical capabilities: figures showing geometry, materials, numerical mesh, boundary conditions, 2D and 3D temperature and heat flow fields may be displayed. Features: zoom, panning, rotation, color/grayscale, highresolution printing. Heat flows and temperatures can be recorded and shown during the simulation. Images of heat flows make it simpler to determine thermal bridges and to improve designs by optimizing the insulation at areas with large heat flows.  
The recorder may save at specified intervals (transient or steadystate) temperatures and heat flows at given points, heat flow through boundaries.  
A
simple numerical mesh generation option is available. The mesh can easily be
changed.  
Any structure consisting of adjacent or overlapping parallelepipeds with any combination of materials may be simulated.  
Boundary conditions may be a given heat flow, or an air temperature with a surface resistance. Temperatures and heat flows may vary in time by one of the following functions: sinusoidal, stepwise constant or linear (data may be imported/exported from/to programs such as Excel). Several other formats with climatic data can be imported.  
Heat sources/sinks may be specified.  
Conductances and capacities may be written to file.  
Temperature
field may be written to file and can easily be imported into other programs
such as Matlab.  
Various
formats with climatic data may be imported (TRNSYS, METEONORM, HELIOS, DOE,
TMY2  Typical Meteorological Year, SUNCODE, MATCH) for dynamic calculations 
A cadstyle preprocessor facilitates the input procedure. The following pictures shows the preprocessor and postprocessor.
A park bench drawn in the preprocessor. The top figure shows the (x,y)plane and the lower one the (x,z)plane.
The postprocessor shows a 3D view, here of the materials (top figure) and boundary conditions (lower figure).
Calculated temperature field (top) and heat flows (bottom).
Temperatures during the three first hours at a point 2 cm under the seat with a boundary condition temperature of 35 °C. Initial temperature for the bench is 20 °C. The steadystate temperature for the point is 31.45 °C.
Heat flow through the seat with a boundary condition temperature of 35 °C. Initial temperature for the bench is 20 °C. The steadystate heat flow is 49.7 W.
The following figures shows a steel beam that lies inside a wall/roof connection.
Boundary conditions.
Calculated temperature field along the steel (all other wall materials are made invisible here).
