- Only one room air node has been included for the air in the room model, which means that it is not possible to model the vertical temperature distribution in the room. This is
however expected to be small for a room with heated/cooled surfaces since there is less air movement due to convection.
- Equilibrium room air temperature calculated each time step. Therefore the storage capacity of the room air and furniture is neglected. This means that the room temperature will change instantly with solar gains and ventilated outside air and therefore the damping on the temperature fluctuations from the heat capacity is not included.
- Only one zone in the model. Therefore the influence on multiple rooms with individual heating circuits and set points cannot be included.
- Fairly simple inclusion of the air handling in the model with respect to infiltration, ventilation and venting.
In other words, the programs used in this work are modular with models for walls (including solar radiation), ceiling, floor, ventilation, room, and weather data. The single zone room model includes detailed calculation of radiation exchange between internal surfaces based on view factors, which is important when modelling floor heating, as the room is heated mainly by radiation. Walls, ceiling, floor and windows are modelled using a finite control volume method with an implicit solution scheme. Except for the two-dimensional floor construction, the models are one-dimensional. The ventilation system is a simple balanced system
optionally with heat recovery. As input, measured data or weather data from a design reference year can be used.
4.1.3 Implementation of programs
Both FHSim and TASim have been developed in Matlab Release 13 (Mathworks, 2002).
Matlab has the great advantage that it is simple to implement simulation models since many functions are predefined, especially concerning handling of matrices and plotting of results.
This is a major advantage over for instance C/C++, where neither matrix handling nor graphs are an integral part of the program. The simulation time is expected to be slightly longer than if a lower level programming language is used. However, the implementation time is much shorter using Matlab, which therefore makes it an ideal tool for research where the code is often changed.
Outer wall:
- heat transfer - heat storage
Floor with floor heating system Floor construction
- heat transfer to outdoor - heat storage
Floor heating system:
- heat added/removed in pipes - control system
Room:
- room temperature - surface temperatures - radiation between surfaces - convection between ces and room
- internal heat load - thermal comfort
Inner wall:
- heat transfer - heat storage - adiabatic centerline Window:
- solar gains - heat transfer - heat storage Outdoor:
- hourly weather data - radiation exchange with sky and ground
Air change:
- mechanical ventilation system - infiltration - venting Ceiling:
- heat transfer - heat storage
Figure 4.1 Elements used in FHSim for the dynamic simulations
4.2.1 User interface
Generally, both FHSim and TASim are “expert tools” with only one user; namely the developer. Therefore, the user interface is very simple or non-existing and typically changes to the inputs must be made directly in the source code.
However, an example of a graphical user interface, which has been developed for FHSim, is presented in this section.
A general limitation to graphical user interfaces is that they are very time consuming to develop, and consequently that changes made to the simulation model are cumbersome to include in the user interface. Therefore, this example graphical user interface is shown as an appetizer showing how the simulation program can be made available to a larger group of users. The program currently needs Matlab to run. However, it is possible to create a stand alone application based on the current implementation, which can be used on computers where Matlab has not been installed.
In the following a few main windows from the user interface has been shown to give an idea about the possibilities of an interface used in the simulation program.
Figure 4.2 shows the main window of FHSim.
Figure 4.2 Main window in FHSim showing the available main functions in the menu
Here the main functions of the programs can be accessed. These include:
- File: Loading and saving building model
- Building: Definition of geometry, building elements, windows, ventilation systems and floor with floor heating system
- Comfort data: Data for calculating the thermal comfort
- Solar calculation: Algorithms to find the solar radiation on surfaces and definition of shades
- Simulation: Definition of simulation period and main simulation window - Results: Post-processing with graphical representation of the simulation results - About: Data of the implementation and contact information.
A few of the most important windows for input and results are shown in the following.
Figure 4.3 shows the window for defining the dimensions in the room model.
Figure 4.3 Definition of the dimensions of the room zone which is used in FHSim
In this window, the size of the room and orientation, wall types, ceiling inclusion, number of windows and their position, emission factors of inside and outside surfaces and gender and position for a person in the room. The data in this window is therefore the required input for calculating the main geometrical data for the room; number of surfaces, wall and window areas, volume, view factors and data required for finding view factors of surfaces and the person in the room.
The room model, based on the geometry defined in Figure 4.3 can be drawn by pressing the
‘Draw room model’ button. This is shown in Figure 4.4 for the data given in Figure 4.3.
Figure 4.4 Graphical presentation of the room model
Figure 4.5 shows the definition window for the floor with floor heating system.
Figure 4.5 Definition of the floor and floor heating system with type of floor heating system to be modelled, dimensions and supply temperature.
In Figure 4.5 the type of floor heating system can be defined. In the upper left corner, four types of floors can be chosen; heavy and light floor heating based on two-dimensional models of a section around a pipe, a floor without floor heating and finally a two-dimensional model of the floor construction including both floor heating pipes, foundation and ground volume. In the bottom half of the window, dimensions and materials for the pre-defined floor heating types can be changed. In the upper right corner, properties of the supply temperature to the floor heating pipe can be defined.
Finally, Figure 4.6 shows the results window.
Figure 4.6 Result window showing a bar graph of the summary of the results of the main heat flows in the model as well as a tabular overview
The upper left of the result window shows a main overview of the simulation results for the main heat flows in the model. The same data are shown in the graph on the right side of the window. In the plot menu, different plots can be chosen, including different temperatures (room air, operative, and floor surface), monthly heating, ground heat loss and more. The plots can be exported and inserted in reports. Finally in the lower left corner of the window, the results can be used to create a movie-file of the temperature distribution during the entire year or for a short period of a few days. This is only active if the model results are shown for the two-dimensional simulation model of the floor construction with ground volume and foundation.