Ireland's only dedicated building services engineering journal
Ireland's only dedicated building services engineering journal

Detailed MEP Design Part 1 – Mechanical Services

Traditional design involves taking some of the information produced during the concept stage as was outlined in the previous article. This may be in the form of developing building systems around a naturally-ventilated scheme, or a more heavily serviced mechanical ventilation or air conditioning scheme.The various components must be sized, selected, assembled into systems, scheduled and specified to produce pricing documentation.

The move towards building information modelling means that engineers need to carry out specific tasks at a much earlier stage in the design process. This includes listing components that will be needed for the project such as air conditioning units, tanks, pumps, boilers, fans, valves, radiators, etc so that the component families for these items can be either sourced directly from vendors, BIM resource websites or created in-house.

Figure 1: Typical chilled beam modelled in BIM format.
Figure 2: Typical coarse/medium detail of valve.

The optimum scenario would obviously involve sourcing families from vendors but, at this stage in the evolution of BIM in Ireland, there are only a select number of vendors who have produced their products in a BIM format. In-house component families can be created based on manufacturers product data sheets and these will more than serve the required purpose as all relevant information relating to mechanical performance, electrical input and technical specification can be edited to suit specific requirements. See Figure 1.

Figure 3: Typical fine detail valve.

One of the most onerous tasks, which inevitably becomes something of a work in progress in most cases, is the editing of 3D families to incorporate 2D symbols that are visible when 2D drawings are being produced. This is done in the form of drawing a 2D symbol, either directlyor as an annotation symbol, into a 3Dcomponent and creating weak reference that is visible in a coarse or medium detail view on a 2D drawing sheet. The detailed 3D component view will only be visible with the view setting at fine detail level. This ensures that the standard of 2D drawings produced from the 3D model is consistent with the quality and presentation of 2D drawings produced using software such as AutoCAD or similar 2D drawing software. See Figures 2 & 3.

Designing domestic water services and drainage systems in Revit MEP is facilitated through use of demand units or “fixture units” within sanitary fittings. WCs, wash-hand basins, showers, etc are typically created within the architectural model. Individual component families can be edited to include the drainage and water service connections. See Figure 4.

Figure 4: Typical WC family with plumbing connections.

One of the issues that is not present within Revit MEP in its latest versions is a hot water return system. This is overcome through the duplication of pipework systems and modification of the calculation setting to none. This will effectively prevent the hot water return system from being overridden by either the cold water or hot water system and allow designers to specify the pipe sizes manually. This is not ideal but is a temporary solution while software designers develop a means of sizing hot water return systems automatically. See Figure 5.

Figure 5: Modifying the pipe system calculation setting.
Figure 6: Creating a piping system group.

The creation of pipework systems can either be done manually or through Revit MEP. Using Revit MEP, groups of appliances can be linked together to create local systems, or all appliances can be grouped together to create a whole building system. See Figures 6 & 7.

Figure 7: Automatically generating pipework layout.

At this stage there are still inherent difficulties associated with using the automatic method of creating pipework systems. In order to efficiently ensure the system is designed as accurately as required, and that the actual layout of the pipework system will avoid clashes, the manual method of “drawing” pipework into the model along desired routes and connecting to the sanitary appliances and system components is preferable.

Much of the same techniques used to develop the pipework models for domestic water services and drainage pipework systems can be applied to hydronic systems such as heating and chilled water.

Experience thus far has taught me that it is easier to develop the pipework system from start to finish, i.e. boiler to radiator, and then add piping components such as valves. The same is true for ductwork systems and this will minimize the number of times components such as valves, balancing dampers, fire dampers, etc are re-entered during the iterative process of identifying routes and risers.

The design calculation software within Revit MEP for performing heating and cooling load calculations is more developed than that for the water service systems. Revit MEP can carry out steady state heating and cooling load calculations based on user-specified building design conditions, either based on building or space type.

The ability to interlink the building design conditions for individual spaces within the model allows design checks to be carried out more efficiently and also ensures that the environmental performance criteria required are satisfied. Several variables can be selected from a list of predetermined options to create a schedule. See Figure 8.

Figure 8: Typical space heating design schedule.

Schedules such as these can be manipulated to sort by level, space name, space number, system, etc with automatically- calculated subtotals. This offers improved efficiency in developing the overall design and can create a more robust design filing system. Updates and progress revisions of the building design can be revised and will automatically revise once schedules such as this have been created.

Once the design has been completed, the ability to automatically schedule components within the MEP model saves time in manually counting, selecting and scheduling these components. Any number of components can be scheduled by reference, level, model, output and input properties, costs or material. This greatly enhances the ability to accurately quantify the tender design and reduces the cost risk for contractors who are able to use this design format. See Figure 9.

Figure 9: Typical MEP component schedule.

The evolution of building services design engineering tools is happening apace and we are starting to see the fruits that have been in use in the industrial and maritime sectors for many years. While the benefits to engineers and ultimately clients are obvious, there is considerable time required to set up company standards, family libraries and project templates, and to discover the various nuances of using the software.

While this is initially a steep learning curve, the fastest way to learn is to get training from a certified training provider and look to identify pilot projects as well as personnel who will use the software. This is fundamentally a design engineering tool and the mistake of believing this is simply a CAD drawing tool should be avoided.

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