HEAT2 - building physics

1 Lund-Gothenburg Group for Computational building physics HEAT2 A PC-program for heat transfer in two dimensions. Manual with brief theory and examples. Version August 1, 2000 Dr. Thomas Blomberg Lund-Gothenburg Group for Computational building physics Department of building physics , Lund University building Technology Group, Massachusetts Institute of Technology 2 3 Contents 1. 7 HOW TO ALMOST AVOID READING THIS 7 INTRODUCTION TO 7 Applications .. 7 Features .. 7 Cartesian coordinates .. 8 Numerical method .. 8 8 UPDATE INFO FOR HEAT2 VERSION 10 Integrated pre-processor .. 10 Material properties .. 10 Import of climate files .. 10 Surface plot in 3D.

2 10 ABOUT THIS 10 SYSTEM 10 11 TECHNICAL 11 2. MATHEMATICAL DESCRIPTION .. 13 GOVERNING DIFFERENTIAL 13 BOUNDARY 13 INITIAL 14 FLUID 14 heat CONDUCTION COUPLED TO RADIATION IN A 15 3. NUMERICAL 17 17 COMPUTATIONAL 17 THERMAL 17 heat 19 NEW 20 CHOICE OF TIME-STEP,.. 20 ITERATIVE 20 STEADY-STATE 20 INTERNAL REGIONS CONTAINING 21 4. OVERVIEW OF INPUT .. 23 23 BOUNDARY 24 SOLVING THE STEADY-STATE 26 SOLVING A TRANSIENT 28 THE INPUT 32 NUMERICAL 33 Simple mesh generation .. 35 THERMAL 36 INITIAL 37 INTERNAL 38 INTERNAL 41 41 4 5. WORKING WITH 43 THE 43 Introduction .. 43 The tool bar.

3 43 Copying objects .. 44 Picking material .. 44 Snap to grid .. 44 Zoom 45 Scale 45 Drawing in metric or English 46 Updating the geometry .. 47 Long boundary 47 Numerical 48 Importing pictures .. 49 Pre-processor data files 49 Drawing areas with internal modifications .. 49 THE MATERIAL 51 Introduction .. 51 Saving material 54 Importing and merging other material 54 LOADING AND SAVING INPUT 54 INSERTING MESH 55 THERMAL 57 BOUNDARY 59 INITIAL 60 INTERNAL 60 Introduction .. 60 Defining internal modifications types .. 61 Note on hole with air, radiation and ventilation (type G) .. 63 Defining areas .. 64 64 Sinusoidal 65 Step-wise constant and step-wise linear function.

4 66 Import from other file 67 Example 1 - sinusoidal function with a time period of one 67 Example 2 - sinusoidal function with a time period of one day .. 68 Example 3 - step-wise constant function .. 69 Example 4 - step-wise linear function .. 69 INTERNAL 69 SOLVING THE 70 Steady-state stop 70 Successive over-relaxation used in the steady-state 71 Simulation time for transient 71 Simulation window .. 71 Screen update .. 72 Reset .. 72 73 Boundary 73 heat flows for internal modifications .. 73 Example 1 .. 73 Example 2 .. 74 Results for 77 Temperatures and heat flows at a point .. 78 CONDUCTANCES AND CAPACITIES TO 79 5 TEMP (MATLAB) TO 79 THE 80 What can be recorded?

5 83 CHANGING THE RECORD 84 84 Help .. 85 Editor design .. 85 INFO 86 86 86 Basic 87 Menu item File .. 88 Saving Printing images from Menu item Options .. 91 Viewing thermal conductivities and heat capacities ..91 Outlined materials ..93 Absolute lengths ..94 Resistance lines ..94 Menu item 95 Menu item T and 95 Better picture quality with pixel by pixel drawing heat flow magnitude ..99 heat flow Options for heat flow Printing heat flow Viewing Inverted gray-scale ..108 Showing temperatures and heat flows in cavities ..108 Menu item 109 Menu item Settings .. 110 Menu item Plot3D .. 110 6. CALCULATIONS USING PIPES.

6 113 PIPE WITH A GIVEN heat 113 Pipe approximated with a square .. 113 Pipe approximated with enclosing 113 PIPE WITH A GIVEN 113 Pipe resistance taken into account .. 114 Pipe resistance 114 7. NUMERICAL PERFORMANCE .. 115 115 8. EXAMPLES .. 117 EXAMPLE 1 - A WALL WITH A 117 117 Input using the pre-processor .. 117 Boundary conditions .. 118 Input without using the pre-processor .. 121 EXAMPLE 2 - heat LOSS FROM A HOUSE WITH A 123 123 The input mesh .. 123 Material data .. 127 Boundary conditions .. 127 The 129 6 Transient 131 Input using the pre-processor .. 135 Drawing the whole 135 Drawing parts of geometry ..137 EXAMPLE 3 - heat FLOW THROUGH A WALL WITH METAL 138 Introduction.

7 138 Pre-processor 139 Alternative input 143 Calculations for different 144 Conclusions .. 145 EXAMPLE 4 - ROOF SECTION WITH HOLLOW 146 Introduction .. 146 Geometry drawn in the pre-processor .. 146 Results for different numerical meshes .. 148 Choice of Tso and rate of convergence .. 152 Conclusions .. 153 9. RADIATION AND VENTILATION IN CAVITIES .. 155 155 INPUT 155 OUTPUT 156 NUMERICAL SOLUTION FOR THE 157 Radiation equations in temperature form .. 157 10. ANALYSIS OF WINDOW 159 159 FRAME CAVITY CALCULATION 159 DEFINING FRAME 160 EXAMPLE 1 - A PVC SHUTTER PROFILE WITH FIVE 161 EXAMPLE 2 A WINDOW 163 11. A FEW TIPS .. 171 171 NUMERICAL 171 Numerical 171 Expansive meshes.

8 171 Steady-state 171 Symmetric cases .. 171 Computational area for calculations of heat losses to the ground .. 171 Transient calculations for heat losses to the ground .. 171 Sloping 172 REFERENCES ..173 APPENDIX A. LIMITS AND RESTRICTIONS OF DATA .. 175 APPENDIX B. HOW TO ADD AND EDIT MATERIALS .. 177 APPENDIX C. INPUT DATA FILE EXAMPLE .. 181 APPENDIX D. COLOR IMAGES ..END 7 1. Introduction How to almost avoid reading this manual For a quick start read Chapter 4 Overview of input. The examples in Chapter 8 would also give a short introduction. Introduction to HEAT2 Applications HEAT2 is a PC-program for two-dimensional transient and steady-state heat conduction within objects that can be described in a rectangular grid.

9 It belongs to the latest generation of computer models from the Lund Group for Computational building physics . It is well adapted to the following applications within building physics : General heat conduction problems Analysis of thermal bridges Calculation of U-values for building construction parts Estimation of surface temperatures (surface condensation risks) Calculation of heat losses to the ground from a house Optimization of insulation fitting Analysis of floor heating systems Analysis of window frames There are also two related programs for heat conduction in three dimensions HEAT3 (Blomberg, 1998), and in cylindrical coordinates HEAT2R (Blomberg, 1994). Features 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.

10 The following list shows some features: An integrated pre-processor facilitates the input procedure, see section Material properties may easily be edited and added. Several material list are available. The default list ( ) contains about 200 common building materials. The list has over 1200 defined materials. Another file with over 200 materials (in German) from the German standard DIN (Deutsches Institut f r Normung, DIN V 4108-4) is also available. Extensive graphical capabilities: figures showing geometry, materials, numerical mesh, boundary conditions, 2D and 3D temperature and heat flow fields and isotherms may be displayed. Features: zoom, panning, rotation, color/gray-scale, high-resolution printing.