Short-Term Simulations

Overview

Figure 2-1 Short-term Scenario Buttons
Short-term Scenario Buttons
In the Short-Term Simulation Tab, you can see that there are a number of options:
  • The Restart button will return the simulation to the beginning.
  • The Start Simulation button begins the simulation
  • The Output Panel button opens up the Output panel
  • The Watch Panel button opens the Watch panel
  • Figure 2-2 Simulation Panel
    Simulation Panel
    The Simulation Controls Panel has three tabs:
  • Run Options: This allows you to set general parameters for the simulation
  • Inputs: This allows you to set specific parameters for each system component
  • Faults: This allows you to set certain faults to analyze broken systems
  • Figure 2-3a Animation Screen Navigation: Menu
    Navigation Map
    Figure 2-3b Animation Screen Navigation: Map
    Navigation Menu
    The Animation panel can show each system component. You will be able to see it in action when the simulation is running. To navigate to different system components, you can either choose them from the drop down list, or else by clicking on the component from the graphical map. Note, the overview you are presented with when Learn HVAC first starts cannot be selected from the drop down menu list, but can from the map; it is the small circle and dashed lines outside the system which turns orange when selected. Also note that from the graphical map, you cannot choose Plant system components such as the Plant, Boiler, Chiller, or Cooling Tower. In the upper right of the animation screen, you will see a small gear sprocket; hovering your cursor over this tells you if the simulation is running or not. Also, it is motionless when the simulation is not running, and will spin when the simulation is running.
    Figure 2-4 Watch and Output Panels
    Watch and Output Panel
    Now Open up both the Output Panel and the Watch Panel by clicking on the buttons to the right of the Start Simulation button, circled in red in Figure 2-4.

    If your screen is too small to view all the panels, you can resize the Watch Panel and Output Panel by clicking and dragging the lower right-hand corner. You can also move these panels and have them hover over the other panels by clicking and dragging on the top bar. You may close them at any time by clicking the "X" in the upper right corner of each panel.
    Figure 2-5 Move Panels
    Move Panels
    The Output Panel allows you to view all the variables associated with the each component in Learn HVAC. You can choose which system component you want to view by selecting it from the drop down menu. The Output panel is also associated with the image, so selecting a different system on the image will change the system selected in the Output panel. The Watch Panel allows you to choose variables you want to watch as you make changes to the simulation. We will go into this more later.

    Run Options

    Figure 2-6 Simulation Control Panel
    Simulation Controls
    In the Simulations Controls, choose the Tab Run Options. This tab allows you to set some general parameters of the simulation. Learn HVAC allows you save two different simulation runs so you can compare them later in the Analysis tab. You can choose if you want to store the results in Run 1 or Run 2 in the top menu option, Store Results As. If you run a Long-term simulation first, you can import those variables as defaults in the second menu. For now, leave it as None.
    Figure 2-7 3-story building, 5-zones
    5-zones 3-story
    This simulation building is a 5-zone, three story building. You may select which zone you want to look at and which floor based on the diagram below. Note that the images in Animation panel to the right will not change based on this selection. But the simulation results will vary.

    Finally, you can control when the simulation starts and what size of a time increment you want to view. For now, just leave these as their default values.

    Start Simulation

    Click the Start Simulation Button up on top. Notice that the animation starts playing. You can move to different HVAC systems and see how they operate. For example, go to the Cooling Coil and notice how the animation screen shows how the air particles pass through the cooling coil and are cooled down while coolant flows in and out of the coil. Surrounding the image of the cooling coil are the numerical values for many of the variables for the cooling coil. A full list of these variables and their values can be found in the Output Panel.

    Inputs

    Figure 2-8 Inputs
    inputs

    At any time, before, or during a simulation run, you may change the inputs to each component of the HVAC system. Go to the Inputs tab.

    Then, select System from the drop down menu in the Inputs tab. Also, in the menus in the Animation Panel and the Output Panel select the Cooling Coil. Change the Outside Air Dry Bulb Temperature to 20°C and change the Outside Air Relative Humidity to 35%. Notice how the input boxes which have altered values turn yellow indicating changes which have not yet been implemented. Now click the Update button and notice how the values in the Output Panel, such as the Cooling Coil Valve Position, change. Also, the rate of flow for the cooling in the animation slows down.

    Figure 2-9a User Inputted values before Updating
    inputs
    Figure 2-9b User Inputted values after Updating
    inputs

    The changes you made to the simulation might have had a broad affect throughout several of the pieces of equipment in the system, but the Output Panel only shows you the variables associated with a single piece of equipment. This is what the Watch Panel is for. By putting variables in the Watch Panel, you can track the variables of interest no matter which piece of equipment is selected in the Animation Window, Output Panel, Input Panel, or Fault Panel. To add variables to the Watch Panel from the Output Panel, simply click and drag the variable from the Output Panel to the Watch Panel. Similarly, to move variables over from the Input or Fault Tabs, grab ahold of the block symbol and drag it over to the Watch Panel.

    Now let's try adding a fault to the system.

    Figure 2-10a Watch Panel icon
    Watch panel icon
    Figure 2-10b Dragging items to the Watch Panel
    Watch panel drag
    Figure 2-10c Populated Watch Panel
    Watch Panel

    Faults

    Faults are a common occurrence in systems and can dramatically affect the indoor environmental quality of a building and/or the energy consumed by HVAC components. These can be cause either through improper installation, or just general wear on the system.

    With the Fault Panel, you can initiate common faults in a system component and see the impact each fault has on the system as a whole, and learn the warning signs to help you identify these faults in the field. If you are using Learn HVAC as part of a class, the instructor can prepare a scenario with embedded faults which will not be displayed on the Fault Panel. Otherwise, you can activate each fault yourself. Like with the Input Panel, select different system components from the drop down menu to see the different types of faults that can be created for each different component.

    Figure 2-11 Faults Panel
    Faults Panel
    Before we activate a fault, let add some variables to our watch panel so we can see what happens. In the Output Panel, go to the Cooling coil, and drag the Cooling Coil Chilled Water Entering Temperature, the Cooling Coil Valve position, the Cooling Coil Leaving Air Temperature, and the Cooling Coil Chilled Water Leaving Temperature. Next go to the Fan and add the Fan Air Flow Rate and the Fan Power. Go to the VAV Box and add the VAV Box Damper Position. Finally, go to the Heating Coil and add the Heating Coil Entering Air Temperature and the Heating Coil Leaving Air Temperature.
    Figure 2-12 Fault Panel: Heating Coil
    Heating Coil
    Now go ahead and select the Heating Coil from the list of Faults and let's simulate a Stuck Heating Coil Valve. Click the checkbox next to the name and push the slider up to 80%. Notice how the "caution tape" that appears next to the fault to alert you it is checked. Now hit update to apply the change and watch how the variables in your Watch Panel change.
    Figure 2-13 Heating Coil Fault On
    Fault on
    Notice the dramatic change in the cooling coil valve—from 36% up to 100% open and it still cant cool the air down enough to match the leaving air temperature we had from before the fault.

    Click here to go to continue on to the Long-Term Simulation Tutorial