Inside the System

Interconnecting Panels and Transformers

Connecting 208/120 volt panels to 480/277 volt panels requires the use of a transformer.  Once the panels and transformers in the distribution system are all connected, loads from the low voltage panels feed through the transformers to the high voltage panels, giving the ability to compute and tabulate the total connected load in the distribution system.

Connecting panels to one another, or to transformers, is concptually similar to circuiting Devices.  You select the component you want to connect, create the power circuit, then specify the equipment that feeds the selected equipment to complete the connection.

Click here for a brief demonstration video.  The basic steps are:

1. Place Panels using appropriate types

2. Set Panel Name and Distribution System for each panel (LA for 208/120, and HA for 480/277).

3. Place transformer

4. Set Primary (480/277) and Secondary Distribution System (208/120) on transformer.

5. Set the transformer name (shown as Panel Name) to T-LA

6. Tag the equipment (optional)

7. Circuit low voltage (208/120) panel LA to Transformer T-LA - note changes in System Browser showing relationship.

8. Circuit the transformer T-LA to the high voltage (480/277) panel HA.

9. Modify the rating of the circuit on HA feeding T-LA:

 

Note: breaker is rated 125% for continuous load, and is rounded up to next standard breaker size.  Standard breaker sizes are: 15, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 800, 1000, 1200

10.  Modify the rating of the circuit on HA feeding T-LA:

 

Note different manufacturers provide different standard panel ratings.  Generally, they are 60A, 100A, 125A, 200A, 225A, 400A, 600A, 800A, 1000A, 1200A

Cheers-
Martin Schmid, P.E.
MEP Customer Success Engineer

A Case for Type Parameters

The concept of Type parameters vs. Instance parameters seems to put many users' minds into a spin.  Instead of trying to describe what the difference is, I'm going to provide a scenario where Type parameters should be used instead of Instance parameters.  Perhaps by providing a concrete example, one will be more readily able to discern when to use one over the other.

I came across a Revit project file recently.  Some things weren't jiving for me in trying to diagnose an issue, so I put together a quick schedule, and found this:

 

If you have a keen eye, you're asking yourself, how can multiple "Fixture Types" be associated with the same Family and Type (i.e, the Corp_Recessed : 277V Recess)? 

Upon further inspection of this particular Family, I found the following:

 

The issue is simply that the method used in this project to 'type' the fixture will easily lead to inconsistencies.  The Instance parameters, indicated by (default), introduce a lot of uncertainty into the model. 

Take for example the following instances in the model:

 

I.e., what is to keep someone from adjusting the length of an "A1" fixture to be 8' long instead of 4'?  What is to keep someone from adjusting the geometry of an "A4" fixture to appear like a 2x4, or even a 4x4 (instead of the apparently intended 2x2), or adjust the height too?  Or... what is to keep one from mis-'Fixture Typing' a "A1" as an "A9"? 

Even the Load in this family is an instance parameter... I don't think anyone would want to rely on someone to enter the proper load at each instance of all of these fixtures.  For this one type containing 514 total instances, that is over 2500 opportunities for error (514 x 5 params each: length, width, height, load, fixture type).  Using Type parameters for these properties avoids all such problems and will lead to a much more consistent model. 

Take for example (referring to the schedule above) fixture type "E1" - is this fixture supposed to be Wall mounted or Ceiling mounted?  120v or 277v?  If it makes a difference in the model number that needs to be ordered, it could be a change order waiting to happen.

To summarize:  each fixture type (corresponding to a manufacturer's model number) of a lighting fixture should be uniquely identified - this is nothing new.  However, the execution of how you do this can make your documentation much more consistent if applying the proper techniques in your modeling application.  In Revit - this means make sure you have a separate Fixture Type for each Type of fixture.  If you use the 'Type Mark' parameter built-into the software, Revit will even warn you if you in-advertently duplicate a value!

Cheers-
Martin Schmid, PE
MEP Customer Success Engineer

 

Revit MEP - Hydronic Piping Calculations

We've done duct, electrical, heating and cooling loads... Well piping must be next. Please let us know how well the attached document explains the calculations that are taking place in Revit MEP.

Download MEP_Hydronic_Piping

Thanks!

jason

Revit MEP - Heating and Cooling Load Calculations

The next entry in the series of Revit MEP Calculations is the Heating and Cooling load calculations. Please let us know if there is additional information that you would like to see, if you feel that there is anything wrong, or if there is information that needs to be explained better.

Download RME_Calc_Heating_Cooling

Thanks

jason

Revit MEP Electrical Calculations

As a follow up to the Duct calculations post a couple weeks ago, we are now asking for some feedback on some of the electrical calculations that we do in Revit MEP.

Attached is a draft PDF version of some information on how we do these calculations. We would appreciate any information that you can provide on what information in the attached document is helpful as well as any information that you think might be missing.

You can download the file at: Download Revit_MEP_electrical_calculations

thanks!

jason

Revit MEP Duct Sizing - Feedback Please!

The Revit MEP User Assistance team (the group responsible for help and tutorials) has been working hard to document some of the calculation methods that are used in Revit MEP. We are going to be posting some of the information that they are working on in a “pre-release” state to try and get feedback on how they can better meet your needs.

The first of these reviews will be on how duct sizing in Revit MEP works, with additional sections to follow as we get them completed. Any / all comments are welcome about the information we provide in the attached files.

If the contents of these documents don’t apply to you, please don’t feel like you need to review them (i.e. I’m the electrical person, I don’t want to review duct sizing stuff!!!), but if you know someone who might be interested please let them know. The more feedback we get the better we can make the documentation.

Download RME_Calc_Duct_Sizing

I’ll start; just to document some of the things we know, as these are in a “pre-release” state…

·        Page ii is blank

·        On Page 2 there are images missing in the Graph Labels after Friction and Velocity (a total of 4 images)

·        On Page 4 the Duct Sizing Examples section is blank

·        On Page 5 the index is blank

·        Page 6 is entirely blank

Thanks for your feedback!

jason

Pipe Fitting and Drop Sizes

The world of small diameter pipe when working in model based software is very different from the world working with 2D lines, arcs, and circles.

In Revit's 'Fine' Detail Level, elements are shown 'actual size'.  I.e., a 1" pipe valve or rise/drop symbol is representative of the actual size of that element in the 'real world'.

In Revit's Coarse and Medium Detail level views, these elements are 'scaled' to the settings defined in Mechanical Settings... these settings are demonstrated below.

This image shows what settings control the display of the piping elements.

This video demonstrates the Rise Drop Annotation Size Setting

This video demonstrates the Pipe Fitting Annotation Size Setting

Linked DWG in Mechanical and Electrical Views no Longer Halftone in 2010

In prior releases of Revit, linked  DWG files were displayed as halftone in Mechanical and Electrical views.  In 2010, this is no longer the case.  If you WANT the linked .dwg to be halftone:

1. Edit the Visibility/Graphics overrides for the view
2. Click the Imported Categories tab
3. Check the Halftone box for the particular DWG.

This recently came up in the Revit MEP discussions forum:  http://discussion.autodesk.com/forums/thread.jspa?threadID=728971&tstart=0

Heating and Cooling Loads in Autodesk Revit MEP 2010: Building Service Type

If you’ve been calculating heating and cooling loads in Revit MEP 2010, you may have wondered how the new Building Service parameter affects the analysis.

Heating and cooling load calculations are affected by variables that are extrapolated from the Building Service type. The most important variable is the Calculation Type, which is set to either Constant Volume, Variable Air Volume, or Radiant.

 

Most of the building service types are Constant Air Volume or Radiant (almost the same). The Variable Air Volume types include the acronym “VAV” in their naming convention. 

There are also smaller characteristics determined by the service type, such as whether Use Reheat or the Fan Configuration (Blow Through or Draw Through) is used. These inputs help determine some of the zone-specific loads.  Currently all of the service types use draw-through as the fan configuration.

 

The following table indicates the Building Service type variables that affect the heating/cooling load calculations.

 

Building Service Type Variables

Building Service Type	Calculation Type				Fan Configuration
	Constant Air Volume	Variable Air Volume	Radiant	Use Reheat	Blow Through	Draw Through
Central Heating: Radiators			x			x
Central Heating: Convectors			x			x
Central Heating:  Radiant Floor			x			x
Central Heating:  Hot Water	x					x
Other Room Heater	x					x
Radiant Heater – Flue			x			x
Radiant Heater – No Flue			x			x
Radiant Heater – Multi-burner			x			x
Forced Convection Heater – Flue	x					x
Forced Convection Heater – No Flue	x					x
VAV – Single Duct		x				x
VAV – Dual Duct		x				x
VAV – Indoor Packaged Cabinet		x				x
VAV – Terminal Reheat		x		x		x
Fan Coil System	x					x
Induction System	x					x
Constant Volume – Fixed OA	x					x
Constant Volume – Variable OA	x					x
Constant Volume – Terminal Reheat	x			x		x
Multi-zone – Hot Deck / Cold Deck	x					x
Constant Volume – Dual Duct	x					x
Radiant Cooled Ceilings			x			x
Active Chilled Beams			x			x
Water Loop Heat Pump	x					x
Variable Refrigerant Flow	x					x
Split System(s) with Natural Ventilation	x					x
Split System(s) with Mechanical Ventilation	x					x
Split System(s) with Mechanical Ventilation with Cooling	x					x

Information in this post provided by Dylan Reid, Martin Schmid and Michael Lavoie

Create ANY Pipe System in Revit MEP

YES.. it is true - it is possible to create ANY pipe system in Revit MEP - that is, you can name a pipe system whatever you want (O2, NO, N, G, Wilma, etc...), and use View FIlters to show/hide as desired.  Refer to the Video below to find out how. Once you start the video, you may want to right click, and selct Zoom > Full Screen.

Create Any Pipe System

Note, for this to work as demonstrated, you must have Revit MEP 2009 with the Web Update 3 Service Pack.

Martin Schmid, P.E.
MEP Customer Success Engineer
Autodesk, Inc.