Simulation¶
Running a Simulation¶
The model must be initialised before a simulation is run for the first time. To do this, click on the “initialise” button. If there is a problem a message box will appear. The most common error is “mass flow imbalance” which means that the inlets and outlets are not balanced and their flows should be checked and corrected.
Once the Initialization is complete, click on the “play” button to start the pre-conditioning. The pre-conditioning will continue until Ambiens finds a stable solution.
Viewing the Results¶
During pre-conditioning and simulation, each cell will be colour coded dependant on where it fall’s in a parameter’s range. The parameter’s ranges are displayed on the right hand side of the section. If a cell’s value is greater than those shown in the range it will be white. If it is less, it will be black.
The parameter displayed in each cell by Ambiens can be selected from the “display” drop down list. The options are:
Dry Bulb Temperature: this is the default value. It is measured in degrees centigrade.
Speed: the air speed in the cell. This is measured in metres per second.
Relative Humidity: this value is displayed as a percentage.
Mean Radiant: this value is in degrees centigrade. Selecting this option, will start the radiant calculations, if they have not been done already.
Resultant: this value is in degrees centigrade. Selecting this option, will start the radiant calculations, if they have not been done already.
PPD: this is the percentage of people dissatisfied. This value is displayed as a percentage. Selecting this option will start the radiant calculations, if they have not been done already.
The radiant calculations can be stopped by pressing the “esc” button. It is advisable to select mean radiant, resultant and PPD when the simulation is paused as at other times it slows the simulation down as it will do the radiant calculations for every moment.
Clicking on a cell will make Ambiens display that point’s temperature, air speed, relative humidity and heat gain.
Calculation Settings¶
Refresh rate: the interval between updating the results being displayed. The value is measured in seconds.
Velocity Scale Factor: the size of the arrows used to display air velocity. The arrow will show how far the air has moved in a user-defined number of seconds. The velocity scale factor is that number of seconds.
Temperature Range Upper: the upper limit of all the temperature ranges. The value is in degrees centigrade. If a cell’s value is greater than this, it will display in white.
Temperature Range Lower: the lower limit of all the temperature ranges. The value is in degrees centigrade. If a cell’s value is lower than this, it will display in black.
Temperature Range Upper: the upper limit of all the speed ranges. The value is in metres per second. If a cell’s value is greater than this, it will display in white.
Temperature Range Lower: the lower limit of all the speed ranges. The value is in metres per second. If a cell’s value is lower than this, it will display in black.
Temperature Range Upper: the upper limit of all the percentage ranges. If a cell’s value is greater than this, it will display in white.
Temperature Range Lower: the lower limit of all the percentage ranges. If a cell’s value is lower than this, it will display in black.
Changing Parameter¶
To change the geometry or boundary conditions of a section after viewing the results, click on the “stop” button.
The following parameters can be changed and the simulation can continue with the changes taken into account:
Segment Temperature: this is set for inlets and walls
Sensible gain: this is set for gain regions
Latent gain: this is set for gain regions
Radiant proportion: this is set for gain regions
External Wall: this is set in the domain parameters dialog box
Clothing Value: : this is set in the domain parameters dialog box
Metabolic Rate: this is set in the domain parameters dialog box
Once changes have been made, click on the pause button to return to the result view. Then click the “play” button to watch the effect of the changes over a period of time.
Altering the geometry or any of the following parameters will stop the simulation and it will have to be re-started by clicking on the “initialize” button:
Start temperature: this is set in the domain parameters dialog box
Relative Humidity: this is set for inlets
Air Velocity: this is set for inlets and outlets
Target: this is set for segments and gains connected to a thermostat
Lag: this is set for segments and gains connected to a thermostat
Type: this is set for thermostats
Temperature Range Upper: this is set for thermostats
Temperature Range Lower: this is set for thermostats
Recording Videos¶
A video (AVI) file of a dynamic simulation can be made by clicking on the “record” button when viewing results. Click on the button will bring up the “windows save” dialog box where the user can specify the name and path of the video file.
The recording will start when the “play” button is pressed. To pause it, click on the pause button or the stop button. Clicking on the stop button will allow the user to change some of the parameters such as surface temperature. Once the changes have been made the pause button can be pressed to run the user to the display view. Clicking on play will re-start the dynamic simulation and the recording. The recording can be stopped by clicking on the “record” button again.
The video file can be opened in a program that can play AVI files, including Windows media player.
Thermostats¶
The behaviour of an inlet, surface or gain region can be controlled by linking it to a thermostat.
To create a thermostat, click on the “add thermostat” button and then left click on a cell to place it there. To link a surface, inlet or gain to a thermostat, click on the “select” button, click on the thermostat, hold down the left mouse button, move the pointer to the gain, inlet or surface and then release the mouse button. A line will automatically be drawn between the thermostat and the edge of the gain, inlet or surface. Multiple gains, inlets and surfaces can be linked to the same thermostat. A section can contain multiple thermostats.
The thermostat works by changing the temperature of a wall/inlet or the amount of gain in a region in an attempt to control the dry bulb temperature of the cell the thermostat is placed in. Both the thermostat and the gain/surface it is linked to need to be set up with the correct values. Double clicking on a thermostat while the “select” button is depressed brings up a dialog box with the following parameters:
Type: Select either “proportional” or “on/off control” from the drop down list.
Temperature Range Upper: when the thermostat’s cell’s temperature is this value or greater, the wall/inlet/gain it is linked to will use its initial value. This value is in degrees centigrade.
Temperature Range Lower: when the thermostat’s cell’s temperature is this value or lower, the wall/inlet/gain it is linked to will use its target value. This value is in degrees centigrade.
The behaviour of the wall/inlet/gain when the thermostat’s cell’s temperature is between the temperature range values depend on whether “proportional” or “on/off control” was selected. If proportional control was selected then the wall/inlet/gain will use a value which changes proportionally between initial value and target value as the thermostat’s cell’s temperature moves from lower to upper limit of the temperature range. If “on/off control” was selected, the wall/inlet/gain will use target value until the thermostat’s cell’s temperature reaches the upper limit, at which it will use the initial value until the thermostat’s cell’s temperature drops below the lower range value.
Double clicking on a wall linked to a thermostat, while the “select” button is depressed will bring up a dialog box which has the following parameters linked to the thermostat control.
Temperature: the surface temperature that will be used at the start of the simulation i.e. it is the initial value. When the thermostat’s cells temperature is greater or equal to its upper range temperature then this is the value the surface temperature will aim to be. It is in degrees centigrade.
Target: when the thermostat’s cell’s temperature is equal or lower than the temperature lower range this is the value the surface temperature will aim to be. The value is in degrees centigrade.
Lag: the time in minutes in takes to get from the initial value to the target value and vice-versa.
Double clicking on an inlet linked to a thermostat, while the “select” button is depressed will bring up a dialog box which has the following parameters linked to thermostat control.
Temperature: the temperature of the air entering through the inlet that will be used at the start of the simulation i.e. it is the initial value. When the thermostat’s cells temperature is greater or equal to its upper range temperature then this is the value the inlet air temperature will be. It is in degrees centigrade.
Target: when the thermostat’s cell’s temperature is equal or lower than the temperature lower range this is the value the inlet air temperature will be. The value is in degrees centigrade.
Double clicking on a gain linked to a thermostat, while the “select” button is depressed will bring up a dialog box which has the following parameters linked to thermostat control.
Sensible gain: when the thermostat’s cell’s temperature is equal or lower than the temperature lower range this is the value the region’s sensible gain will aim to be. The value is W. In the case of a gain region, the sensible gain can be considered the target value and the initial value is always zero.
Lag: the time in minutes in takes to get from the initial value to the target value and vice-versa.
Changing any of the parameters related to thermostats will stop any on-going simulation. A new simulation must be started by clicking the “initialize” button and then the “play” button.