The MEP (Mechanical/Electrical/Plumbing) Modeler was a new extension to ArchiCAD® 13. Architectural practices and architectural departments of A/E firms using ArchiCAD can use MEP Modeler to create, edit or import 3D MEP networks (ductwork, piping and cable trays) and coordinate them with the ArchiCAD Virtual Building™. http://www.graphisoft.com/products/mep-modeler/
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One of the basic methods of creating the desired mechanical systems is by placing individual duct, pipe or trays MEP elements one at a time. With this method, connections are built up one-by-one and element positions are adjusted individually at the time of placement. This is a very flexible "LEGO®" type workflow where you have full control over the type, allocation and parameters of placed elements.