Creating and managing systems is the key to getting the Autodesk® Revit® MEP 2015 software to work for you. Systems represent the transfer of information between families. They are available for any ductwork or pipework system type you may have in your model. Electrical systems are also a part of Revit MEP and are discussed in Chapter 14, “Circuiting and Panels.”
In this chapter, you will learn to do the following:
Systems are the logical connection between elements in the model. They are the link between the air terminal, the variable air volume (VAV) box, and the air handler, and they represent an additional layer of information above the physical connections made with ducts and pipes, the engineering information. Without systems, ducts and pipes act only as connections between two points. Systems are needed to generate the bigger picture and allow you to manage the elements on a building-wide level. Systems enable you to build more than just a three-dimensional model, they enable the engineering to be included in the model as well. You can create systems to represent supply, return, and exhaust air as well as plumbing, fire-protection, and hydronic piping. You can also create new system types to represent other uses of ducts and pipes outside the predefined types included in Revit MEP 2015.
Systems also aid in the documentation of a model. Because the systems link elements, and their engineering data, across the entire model, tags and other properties can be managed quickly and accurately. One example of this is using a pipe tag that includes not only the size but also the system abbreviation and, if needed, flow rate, velocity, or friction loss within the pipe. You can even set the temperature and fluid type for your system. Tagging any piece of pipe connected to the system, in any view, immediately generates a complete and accurate annotation.
Managing systems is the easiest way to separate, say, a cold-water pipe from a hydronic pipe. If you can't separate the two, you will not be able to produce sheets showing certain systems and hiding others. As you draw a pipe or duct, Revit will automatically assign it to a system. If you are drawing pipe or ductwork from scratch, you can select the system type it will belong to from the Properties palette. If a duct system is created directly from the connectors of mechanical objects, the ducts assume the system of the host objects.
Even though the ducts are associated with a system, managing space air quantities has to be done externally. Entering all the information needed to accurately represent the mechanical systems in a building may seem like a daunting task at first, but the benefits of having all the information in one place and directly in front of the user can lead to more accurate designs. Instead of the user flipping between a building-load program and a duct-sizing chart (or wheel) and trying to keep track of which terminal box is serving which space, systems can handle all of that for the user. By feeding Revit MEP 2015 the load information, calculated internally or externally, and creating an air system for a space, the user can quickly determine the cubic feet per minute (CFM) required at each air terminal with a schedule or a custom space tag. The airflow will then be assigned to the terminal box, and the space that it is serving can appear in a schedule. One program can handle all of these tasks, which the user would have to do anyway.
Using connected systems can also improve performance for Revit. Even if systems are not being specifically set up, Revit is using systems behind the scenes to keep track of all the information in the model. You can enable or disable calculations per system type (Supply, Return, Exhaust, and so on), thus increasing the performance of the Revit model. To do this, select the Piping system from the Project Browser, right-click, and select Type Properties. All elements get assigned to their default system classification(s) (but not system types) based on the type of connector: supply air, return air, hydronic supply, and so on.
The System Browser, shown in Figure 9.1, summarizes all the systems currently in the model. If that were all that it did, it would be a useful design tool. You could keep track of all the air and water in the building and see your system totals at a glance. But the System Browser in Revit MEP 2015 takes this idea a step further; it is a live link to the components in the system as well as their parameters. You have full control to modify the airflows, equipment types, and diffuser selection, all from a single window.
You can access the System Browser from View User Interface System Browser or the F9 function key. The system browser is directly linked to the elements in the model. Elements that have yet to be assigned to a system will be shown as Unassigned. This can be seen in Figure 9.2.
In the System Browser, if you expand the system tree, you can see that when an object is selected, the corresponding item is highlighted in the drawing area. Conversely, selecting items in the System Browser highlights the objects in the drawing area, as long as the items are actually visible in that view. This is shown in Figure 9.3.
You can customize the system browser by setting up the columns it displays. The System Browser can get very large, so a second monitor is helpful. You can access the Column Settings dialog box by clicking the Column Settings button in the upper-right corner of the System Browser, which gives you an expandable list of the information that can be referenced in the model (see Figure 9.4).
Obviously, not every parameter will be filled out for every part of the system, and some of the parameters will not be useful on a day-to-day basis. The columns you choose to display depend on your personal preferences and how you model your systems. For example, Space Number and Space Name populate only if the element and space touch. If spaces are bound by the ceiling, and terminal boxes exist above the ceiling, they will not be associated with a space. You have to use the Show command to find lost terminal boxes. To do this, right-click any element in the System Browser and select Show.
Ideally, every connection on every piece of equipment would be associated with a system, and the unassigned system category would be empty. This may not be realistic on a large job or where manufacturer content is being used. You may not need to model every condensate drain, but if the manufacturer has provided a connection point for it, there will be a listing in the System Browser. If your firm decides to use the System Browser to carefully monitor the systems and elements in the model, you may want to eliminate connectors that you will not be using to keep things clean.
To remove systems you must edit the family with the connector that is not being used. For more information on equipment families, see Chapter 19, “Creating Equipment.”
Before you can jump in and start creating systems, you need to set up several things to ensure that the systems work as they should. There is nothing wrong with the default settings, but every firm is different—each has its own standards, procedures, and design requirements. Most companies have developed their own standards and endeavor to adhere to various industry standards, and these are good guidelines to follow when using a new application such as Revit MEP 2015.
The Mechanical Settings dialog box, accessed from the Manage tab's MEP Settings panel, contains some of the most critical settings for using systems in Revit 2015. This dialog box, shown in Figure 9.5, was briefly covered in Chapter 2, “Creating an Effective Project Template.” A more in-depth look is needed so you can understand how these settings affect systems in Revit 2015. All of these settings should be established in your company's project template. Changes to them should be discussed with the Revit team as well as the CAD manager, because data, visibility, and graphics can be dramatically affected by a minor change in this dialog box. Due to the specific nature of the information concerned, it is recommended that each discipline put an experienced person in charge of maintaining its own system settings.
Several settings really affect systems graphically. For example, by choosing Hidden Line, you see Inside Gap, Outside Gap, and Single Line. By default, each one of these is set to 1/16″ (1.5 mm). By changing the numeric size of each one of these parameters, you can get a different look that helps match your existing standards. We will look more closely at the Mechanical Settings dialog box separately for duct and pipe systems later in this chapter.
Before we can begin creating the system, we need to ensure that the duct and duct system settings are correct. Starting with the Mechanical Settings Dialog box we looked at earlier (Figure 9.5), expand Duct Settings and look at each section.
Now we can look at the duct type properties. You can access this from the families section of the Project Browser. Select Duct and choose any duct type, right-click, and choose Type Properties. You can create new duct types by duplicating existing ones.
In this dialog box, apart from parameters listed under the Identity Data group, there is only the Roughness value to be changed; however, from here you can also access the Routing Preferences dialog box (see Figure 9.6). With Routing Preferences, you can apply a list of each fitting you wish to be used and leave out those you do not. For example, you may wish to use flanged fittings only. You can also set the preferred junction type (Tap or Tee), although it is always a good idea to include at least one tap and one tee connection in the junction list because often you will need both. Defining the routing preferences correctly is essential to enable efficient modeling of duct systems. For standard duct types used regularly within the office, the routing preferences should be set up in the template file. See Chapter 2 for more information.
The Routing Preferences dialog box also gives you the Duct Size button to open the Mechanical Settings dialog. You can load additional duct fittings with the Load Family button.
Now let's look at the Duct Systems dialog box. Like ducts themselves, you can access the duct system type properties from the Families section of the Project Browser. You can also access them by right-clicking the system type in the System Browser. The Duct Systems dialog box (see Figure 9.7) is where you can create new systems by duplicating existing ones. You must be careful to use the correct existing system categories to begin with so you can then connect to the correct points in your families.
Duct connectors in Revit MEP allow the user to connect ductwork to a family that may represent an air terminal, fan, VAV box, air handler, or chilled beam. Duct connections can also be used as a source for boiler combustion air and flues. There are many applications of duct connections beyond a simple supply air diffuser. In this section, you will learn how to set up many kinds of systems using duct connections.
You need a good understanding of the parameters besides height and width (or radius) needed in the connectors before you can set up air systems. There are 14 parameters associated with a duct connector when its system classification is not set to Fitting. Not all of the 14 are active all the time (see Figure 9.8). The standard Supply Diffuser that comes with the Revit install can be a good place to examine connectors.
If the connector system classification is set to Fitting, the connector has only six parameters. Revit MEP has several system classifications available for duct connections that facilitate system creation and view filters within a project (see Figure 9.9).
Starting at the top, here is an explanation of each duct connector parameter shown in Figure 9.8:
Not Defined, Coefficient, and Specific Loss are the options here, and Coefficient and Specific Loss each activate another parameter. Specific Loss should be used where the loss is known from a catalog or cut sheet. The pressure loss is taken literally as the entered value for Pressure Drop.
Now that you have reviewed the parameters of the mechanical systems that exist, you will learn how to apply them in a simple exercise:
Chapter9_Dataset.rvt
file found at www.sybex.com/go/masteringrevitmep2015.Supply Diffuser - Perforated - Round Neck - Ceiling Mounted.rfa
family. Next, choose Insert Load Family, browse to where you have downloaded the family, and click Open (see Figure 9.10).
VAV_SingleDuct_4-16inch_break object styles.rfa
located at www .sybex.com/go/masteringrevitmep2015, and insert it into your model (see Figure 9.11).
Now that you have created your system, you can route your ductwork and it will take on the characteristics of the system parameters you set up. Understanding how to make mechanical systems enables you to create any duct system you may need for your design. For further instruction on how to route ductwork, refer to Chapter 10, “Mechanical Systems and Ductwork.”
You also have the ability to automatically create systems on the go as you route your ductwork/pipework. This means you don't need to create systems manually as in the previous exercise. Simply connect the supply duct to any diffuser and watch it become part of that system. But disconnecting the duct that “pushed” the system to the diffuser will not remove the diffuser from the system. Therefore, it will still be necessary to understand how to create and manage systems manually.
You can remove elements from a system using the Remove From System button when editing the system. You can also do this by right-clicking the connector symbol and selecting Remove From System. You can use either method only if the element is not physically connected to any other piece of the system (including ductwork). Once all elements have been removed from the system, the system itself will be removed from the Revit file. You can also delete the system from the System Browser. This will reset all elements in the system to Unassigned and set the ductwork to Undefined.
Mechanical piping benefits greatly from systems in Revit MEP 2015. Graphics, annotations, flow, and pressure loss can all be handled with a small amount of setup in your project template. Pipe systems also allow filters to apply to all components in the system, including the fittings. Also, the System Browser acts as a graphical pointer to the designer with regard to how objects are connected in systems; it also provides benefits in terms of how the actual systems perform.
The first of these benefits is the ability to predefine the system in which pipes (and ducts) are created, allowing layouts to be designed without the need to set up systems in the first place. This allows the designer to create hot-water (HW) and cold-water (CW) pipe runs with graphical filters already in place to display the different systems being created.
Second, this allows for different systems to be interconnected. In order to do this, you just need to specify which system you wish to use before placing each piece of pipe.
Figure 9.18 displays sanitary and vent pipe systems with the system Sanitary 2 selected. When you are working with multiple systems that are connected, a fitting, an accessory, or equipment is needed between the two pipes or ducts for the separation of the systems to work. When the system change occurs at an elbow or tee, all is good. However, when you want to change the system but continue the pipe/duct in the same direction as the original one, you need to use the Split tool to insert a coupling fitting so you can have two systems. Even though everything seems to work visually when you have multiple systems connected in such a way, it is only for graphical purposes. The reality is that the ducts/pipes will lose all the calculations such as flow, pressure drop, and so forth.
As the design progresses, systems may need to be merged with these new systemless systems. All the user has to do is connect the two systems. Figure 9.19 shows that after the two sanitary systems are joined, they effectively become one system with no further interaction required.
Parameters required for piping connectors are similar to the parameters for air systems such as Flow Factor, Calculated, Preset, Flow Direction, and so on. The available pipe system types are as follows:
There are several things to consider when setting up the components of a pipe system. You will need to define pipe types, load some fitting families, and create the necessary systems from the Project Browser by duplicating systems out of the box.
From the pipe type properties, you can assign routing preferences by size, as shown in Figure 9.20. For example, you may want to use a certain type of fitting only when routing pipes smaller than 6″ (150 mm) and another type of fitting for pipes larger than 6″ (150 mm). You may even want to choose different pipe segments (and therefore different materials) according to size, as shown in Figure 9.21. The pipe types should all reflect real-world values and the company standards and specifications. Even if you are not using Revit to size or lay out pipe automatically, not setting up the appropriate pipe types can cause headaches down the road because the Routing Preferences values still control which pipe fittings to use even if you are modeling the pipe manually. Pipe types should not be left at Standard and PVC. Those hardly cover the necessary piping systems that a building requires, and there will be fighting over what fittings should be standard and what materials should be used. Mechanical piping and plumbing piping should have their own pipe types. Even if exactly the same materials and fittings are being used, changes may arise, and splitting out pipe types late in a project will undoubtedly eat up a lot of time. This is one area of Revit MEP that enables you to have as many types as you want, so take advantage of it.
Pipe segments and sizes are set up in the Mechanical Settings dialog box, shown in Figure 9.22. All of these settings should also be determined by using company standards and specifications and created using industry standards. It may seem tedious to set up, but if the inside diameter of a 6″ (150 mm) hot-water pipe is not correct, and you are using a lot of it, your pipe volume calculations can be skewed.
Fittings should be assigned after sizes and materials for a couple of reasons. First, the connection type needs to match. A solvent-welded PVC fitting and a flanged steel fitting are vastly different. Second, the fittings need to be defined at all the available sizes for that type of pipe; if it goes down to 3/8″ (10 mm) or up to 36″ (900 mm), the fitting needs to accommodate. Fittings are specific to the type of system, which is another reason to separate pipe types for plumbing and mechanical uses.
Hydronic systems have value even if the equipment is not piped together. Terminal box reheat coils are a good example because details generally cover their final connections. By simply adding all the terminal boxes to a hydronic supply and hydronic return system, you can see the total flows for the entire model. You can use this flow summation to ensure that systems are adding up to what you expect and to compare flows between systems. That's just another way of using the benefits of systems during early design, when not everything is connected yet.
Fire-protection systems in Revit MEP are a sort of hybrid between air systems and hydronic systems. Sprinklers, from a system standpoint, are similar to air terminals. Sprinklers are designed to distribute a fluid evenly over a given area, with pressure as the driving force of distribution. In the case of fire protection, water is the fluid, and the fire pump or city connection provides the pressure.
The key to a good, manageable fire-protection system is the families. Decide what type of system you will be using, and make sure appropriate families are developed before you or other users start laying out components. Revit does have the ability to load a family in the place of another, but that tends to cause issues with system connections, pipe connections, and hosting. Sprinklers, standpipes, hose cabinets, and fire pumps may have to be created for the systems to work properly.
Pipe systems are similar to duct systems, but they do have more parameters. These can be found in the piping systems Type Properties dialog box, as shown in Figure 9.23, accessed from the Families section of the Project Browser under Piping Systems.
The parameters for pipe systems start the same as for duct systems: you have Graphic Overrides, Material, Calculations, and System Classification. Then we get some specialized values. Which values are available depends on the system category.
Fluid Type, Fluid Temperature, Fluid Dynamic Viscosity, and Fluid Density are available only in Domestic Hot Water, Domestic Cold Water, Hydronic Flow, and Hydronic Return systems:
Flow Conversion Method is available only in domestic cold and hot-water systems:
The identity data is the same as for duct systems and the Rise/Drop parameters are similar to the parameters for duct systems but include both single line and double line options and Tee Up and Tee Down options.
To fully understand systems, there is one more thing you should know about: the child-to-parent relationships they must form in order to work properly. This knowledge is especially critical when you are building families. Without understanding the child and parent and their purposes, you likely will have problems with system flow and any sort of calculations using Revit.
Figure 9.24 shows an example of a supply air system and its child and parent relationships that must be formed.
There is a pattern in the child and parent formation. The system should always start with a child (for example, an air terminal) and end with a parent (for example, an air handling unit). The child will be a connector whose flow configuration is set to Preset. A flow configuration set to Calculate will be a parent. A flow configuration set to System can be a parent or an intermediary. For example, a chilled water system with multiple chillers will need system connectors to be able to divide the flow between them, and they will still be the parent. Pumps and fans use system connectors because they will split the flow into two or more paths, each with a pump/fan, and then recombine it into the single path before it continues on to the parent.
It is not the families themselves that are the child or the parent but rather the connectors within those families. Generally, the outlet of a VAV box will be the parent to the diffusers it is supplying, but the inlet will be a child of the primary air system. A heat exchanger would have inlets and outlets of both child and parent type. This can be confusing for the user and is a good reason to make sure the Connector Description parameter is filled out.
Flow direction is also important to enable systems to function correctly. The Flow Direction parameter for the connector of a supply air diffuser should be set to In (as the air is flowing from the system into the connector), and as such the parent for that system needs to have Flow Direction set to Out. If these are not set this way, the system cannot calculate the airflows because there is not a definite direction of flow along the duct.
Mechanical engineering documents describe complex systems and design intentions. It is easy to overwhelm the person trying to understand those intentions. Revit filters offer us additional control over the visibility of certain elements in views as well as the appearance those elements will have (if you chose filters to control color and linetype). Without filters, we wouldn't be able to create sheets for the various subdisciplines—separating medical gas systems from plumbing and mechanical, for example. Filters help us create high-quality documentation as well as provide a better way to examine our design and improve the coordination of our projects.
To set up system filters, you can open any model view (plan, ceiling, elevation, section, and 3D are model views; nonmodel views are drafting views and legends) and type VG to access the Visibility/Graphic Overrides dialog box. Next, select the Filters tab and click Edit/New to open the Filters dialog box, shown in Figure 9.25. Notice that in this dialog box several filter names are in Revit by default. Remember that any changes made to filters after clicking Edit/New are global changes to the entire project, so adjusting filters should be left to the more experienced Revit users.
When you select any of the existing filters, certain categories have been selected. These are the categories for the items you want to have affected by the filter. Next, notice under Filter Rules that, by default, System Classification is selected. Because of the large number of filters typically created for a project, you should change the Filter By setting from System Classification to System Abbreviation. This helps identify and separate your systems properly.
If you try to use the default System Classification, soon you will find its limitations. The mechanical supply air system rule is set to System Classification to contain supply. This may not be a problem for small projects, but for larger ones that could have multiple supply systems, it won't work. This limitation is especially obvious when you have piping systems with numerous supply and return systems and distinguishing between all of them is critical. System Abbreviation has the necessary flexibility to allow for distinguishing hundreds of systems.
To create new system filters, the easiest method is to select an existing system filter and then click the Duplicate icon. After the system filter is duplicated, make sure the proper category elements are selected and then rename the filter rule to the name by which you want to filter.
When you are finished creating new filters or modifying existing ones, click OK to get back to the Filters tab in the Visibility/Graphic Overrides dialog box. Click Add. This brings up the filters that you have created, so select those that are needed in the current view of your project. After the filters are loaded, you can turn the filters on and off and adjust line weights, colors, and patterns, as shown in Figure 9.26. You can apply those filters to other views by opening a view, clicking the View tab on the ribbon, and then selecting Visibility/Graphics. Next, select the Filters tab.
Mastering filter options enables you to create your models with the standards that your office has developed over years of producing CAD drawings.
In order to proceed with the design, a mechanical engineer needs to create a custom air handling unit family that is not available from the manufacturer. One of the challenges is that he has to configure the duct connectors for supply, return, and outside air. What are the proper settings for those connectors?
Hint: We already mentioned the proper configuration of the supply and return air systems in this chapter. The only oddball here is the outside air. This is the same kind of decision that will have to be made when creating systems such as fuel, medical gas, and so on that do not exist as a system classification in Revit.