RV Y APRENDIZAJES SIGNIFICATIVOS
3.5 RESULTADOS
PDMS Database Hierarchy
Although this guide is about the design of HVAC ducting networks, in practice you will usually route your ductwork with reference to predefined design items such as the framework, floors and ceilings of a building. You will therefore learn how these other items are defined in PDMS as well as learning how to route sequences of HVAC components and ducting within them.
In this chapter, you will:
• learn how PDMS stores design data
• see how the design model can be viewed and manipulated.
How PDMS stores design data
All PDMS data is stored in the form of a hierarchy. A PDMS Design database has:
• A top level, World (usually represented by the symbolic name /*)
• Two principal administrative sublevels, Site and Zone.
The names used to identify database levels below Zone depend on the specific engineering discipline for which the data is used. For HVAC design data, the lower administrative levels (and their PDMS abbreviations) are:
• HVAC (HVAC)
• Branch (BRAN).
Each HVAC can represent any portion of the overall ducting network.
Each Branch within an HVAC represents a single sequence of components running between two, and only two, points:
• Branch Head
• Branch Tail.
The data which defines the physical design of the individual HVAC components is held below Branch level.
To represent the parts of the building within which you will route your ductwork, you use an administrative level below Zone; Structure (STRU) level.
The physical design of each part of the building is represented by a set of basic 3D shapes known as Primitives, held below Structure level:
• Primitives are used to represent physical items
• Negative Primitives are used to represent holes through items.
During the exercise, you will use rectangular BOX primitives for ducting, and negative boxes, NBOX primitives, where HVAC ducting is to pass through the walls.
Together, these hierarchic levels give the following overall format:
PDMS design data definitions
All data is represented in the database (DB) as follows:
• Each identifiable item of data is known as a PDMS element.
• Each element has a number of associated pieces of information which, together, completely define its properties. These are known as its attributes.
Every element is identified within the database structure by an automatically- allocated reference number and, optionally, by a user-specified name.
Additional items of information about an element which can be stored as attribute settings include the:
• Element type
• Element physical dimensions and technical specifications
• Element physical location and orientation in the design model
• Element connectivity.
Some attribute settings must be defined by you when you create a new element, others will be defined automatically by PDMS.
• When you are modifying a database (for example, when you are creating new elements or changing the settings of their attributes), you can consider yourself to be positioned at a specific point within the hierarchy. The element at this location
is called the current element (usually abbreviated to CE).
In many cases, commands which you give for modifying the attributes of an element will assume that the changes are to be applied to the current element unless you specify otherwise, so you must understand this concept and always 4-2 HVAC Design Using VANTAGE PDMS Version 11.6 be aware of your current position in the database hierarchy. The Design Explorer displays this information continuously.
• The vertical link between two elements on adjacent levels of the database hierarchy is defined as an owner-member relationship. The element on the upper level is the owner of those elements directly linked below it. The lower level elements are members of their owning element. Each element can have many members, but it can have only one owner.
You can navigate from any element to any other, thereby changing the current element, by following the owner-member links up and down the hierarchy.
Exploring the HVAC database hierarchy
The Design Explorer holds the design element hierarchies currently present in the HVAC multiple databases. This hierarchy is collapsed by default.
Exercise continues:
In the Design Explorer, expand the elements in the HVAC database, and navigate up and down the hierarchy by clicking on the various elements. You can see that there is already:
• A Site (HVACSITE) that owns
• A Zone (HVACZONE) that owns
• A number of Structures, each of which is the owner of one or more Boxes.
Together these elements represent the building that will hold your HVAC ducting network.
Note: If you or other users have accessed this database before, the list may also contain other elements.
• Click on HVACZONE in the Design Explorer.
• In the 3D View tool bar, click on the Limits CE button. This adjusts the scale of the view automatically such that it corresponds to a volume the right size to hold the chosen element(s); in this case, the Zone.
• To set an isometric view direction, position the cursor in the 3D View window and hold down the right-hand mouse button to display the pop-up menu. Select Isometric>Iso 3 from it.
• If the graphical view background color is not already black, select View>Settings>Black Background from the 3D View menu.
Using the draw list
To view the Draw List, select the option Display>Draw List from the main menu bar.
You specify which elements of your design you wish to display, by adding them to or removing them from the draw list.
The sample database associated with this exercise represents the whole of a simple building. To route your ducting network, you need to be able to see the floors, walls, columns and beams of this building, but not the roof. You will display the required structures in different colours.
Exercise continues:
Select Display>Draw List from the main menu bar. You should see the Draw List come up in a separate floating window. If you wish, you can dock this window.
• Make sure that in the Design Explorer you have expanded HVACZONE to display the structures below it.
• Pick the HVACFLOOR Structure from the design element hierarchy, right-click the mouse and select 3D View>Add. This adds HVACFLOOR to the Draw List:
Alternatively, you can click the right or left mouse-button and drag-and-drop the element into the 3D View.
• On the Draw List, click on the HVACFLOOR element. You can now use the controls in the Draw List to set the colour from the popup palette. Make the floor Black.
• Now pick the HVACWALLS Structure from the design element hierarchy and add it to the draw list in the same way. Set the colour of the walls to aquamarine.
• Use the same method to add:
HVACCOLS (columns) in green HVACBEAMS in blue.
Do not add HVACROOF at this stage.
Your building now looks like this:
• Observe the effect of selecting different view directions from the Look and Isometric menu options provided by the 3D View shortcut menu. Revert to Iso>3 when you have finished.
Saving the current design and leaving your design session:
Even though you have not yet made any changes to the design database, this is a suitable point at which to demonstrate how to store the current design at any stage of a PDMS Design session and how to record your screen layout so that you can start your next design session in exactly the same state that you ended the current one.
It is good practice regularly to save your work. This avoids the need to start all over again in the event of loss of work due to an unforeseen interruption, such as a power failure.
Exercise continues:
• Update the database to store changes to the design model so far by clicking on, or selecting Design>Save Work.
• You should also save your current screen layout and display settings, so that next time you use the application you can easily pick up your design as it stands. Do this by selecting Display>Save>Forms & Display.
• You can now leave PDMS and return to the operating system. Do this by selecting Design>Exit.
Ordinarily, if you had made any changes since your last Save Work operation, an alert form would ask whether you want to save those changes; this time, you are just asked to confirm that you want to leave PDMS.
• Click OK.
Routing a Sequence of HVAC Components In this chapter you will learn:
• More about how the design data is stored and accessed in PDMS;
• How to route an HVAC network between the grilles in the building walls;
• How to position a selection of HVAC components within the ducting runs.
HVAC component representation in the catalogue
Each HVAC component is represented in the PDMS catalogue by the following types of data:
• Physical shape
• Variables.
HVAC physical shape
The physical shape of a component is defined by a set of geometric primitives.
So that a component can be manipulated and linked to adjacent HVAC items, all principal points needed to define the component position, orientation and connectivity are identified by uniquely-numbered tags.
These tags, which have both position and direction, are called p-points:
• Each p-point is identified by a number of the format P0, P1, P2 and so on.
• P0 always represents the components origin position.
The principal inlet and outlet points are also identified as arrive (PA) and leave (PL). P1 is the same point as arrive, and P2 is the same point as p-leave. The reason for this is that the logical flow statement is not true for HVAC (only Piping flow).
HVAC variables
The settings of all variables needed to distinguish a component from others with the same geometry and p-point sets are defined by parameters. The values of these are defined to suit the specific design requirements.
For example, a rectangular three-way component (or branch connector) might be represented in the PDMS catalogue as follows:
• The two curved duct sections form the component geometry set
• The four p-points form its point set
• P-point, P3, enables you to control the direction of the branch connection arm when you incorporate the component into your design.
The dimensions of the component, and other constructional details, are represented in the catalogue by parameters whose values are set to suit the design requirements.
Restoring your PDMS session and starting the HVAC application You can now go back into PDMS Design.
Exercise continues:
Note: It is assumed from now on that you know how to use the OK, Apply, Cancel and Dismiss buttons on forms, so they will not always be mentioned in the rest of the exercise.
Restart PDMS and enter the Design module as you did at the start of the exercise, but this time set the Load from button on the PDMS Login form to User’s Binary.
When loading is complete, your screen should look the same as it did when you saved the layout in the previous chapter.
(If you intend to continue from where you finish at the end of any PDMS session, it is always quicker to use the Display>Save>Forms & Display option so that you can reload the binary files in this way, rather than to reload the applications from their source macros each time you use the Design module. You can revert to the most recently saved layout at any time by selecting Display>Restore>Forms & Display)
So far, you have been working in PDMS Design’s General application mode, where the menus and facilities available are common to all engineering design disciplines. You can now start the HVAC-specific application, which tailors the functionality of the PDMS Design module to suit the explicit needs of the HVAC designer.
Change from the General application to the HVAC application, by selecting Design>HVAC Designer.
The menu bar for the General application is replaced by that for the HVAC application. The menu bars for both applications look very similar, but the latter gives you access to options with specific relevance to creating and manipulating HVAC components.