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Wednesday, July 25, 2012

Revit - Computing Per Phase Demand Loads

Source/Link: 
BIM Inside the System

An update in Revit 2013 Update Release 1 makes this functionality possible... before attempting to replicate this on your own, please download and install the update.

For Revit MEP 2013, you can download here.

For Revit 2013 (part of the Design Suite), you can download here.

Near the end of this post, I suggested that it would be possible to compute the per-phase demand load by computing the ratio of Total Estimated Demand Current / Total Connected Current, then multiplying by each phase's current.  Lets take a look at the built-in parameters and how they are used to compute the Connected Current in two different ways, then how to find the demand ratio for each method, and then finally, how to apply that ratio to the per-phase currents.

 Per Phase Loads

(click image to enlarge)

In the attached image, if you based your panel sizing only on the Total Est Demand, you may resolve that a 200A panel and feeder is sufficient.  However, by seeing the load per phase, you may determine that the rating may need to be at least 230A.  Of course, balancing your panel will have an effect on ther per-phase loads. 

Dot-1Panel Totals

Total Connected

This is a built-in parameter.

This is the total sum of all connected loads (VA)

 

Total Estimated Demand

This is a built-in parameter.

This is the sum of all loads after demand factors have been applied (VA)

 

Total Connected Current

This is a built-in parameter.

In the case of a 3-phase panel, this is computed as:

Total Connected / (Line-to-Line Voltage * sqrt(3))

 

Average 3-ph Connected Current

This is a Calculated Value in the schedule.

(Current Phase A + Current Phase B + Current Phase C) / 3

 

Total Estimated Demand Current

This is a built-in parameter.

In the case of a 3-phase panel, this is computed internally as:

Total Estimated Demand / (Line-to-Line Voltage * sqrt(3))

 

Dot-2Demand Ratios

Demand To Total Ratio

This is a Calculated Value in the schedule.

Total Estimated Demand Current / Total Connected Current

 

Demand To Average Ratio

This is a Calculated Value in the schedule.

((Current Phase A + Current Phase B + Current Phase C) / 3) / Total Connected Current

 

Dot-3Per Phase Demand Loads

These are computed for each phase, replacing X with A, B, and C.

Demand phase load based on Demand To Total Ratio

These are Calculated Values in the schedule.

Current Phase X * (Total Estimated Demand Current / Total Connected Current)

 

Demand phase load based on Demand To Average Ratio

These are Calculated Values in the schedule.

Current Phase X * (Total Estimated Demand Current / ((Current Phase A + Current Phase B + Current Phase C) / (3)))

 



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