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Thread: Adding a Pressure Drop calculation to a family

  1. #1
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    May 12, 2016
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    Question Adding a Pressure Drop calculation to a family

    Hello guys,

    I am trying to solve a calculation in the fan coil family I created. In this situation we are using a Daikin fan coil "FWM". The manufacturer doesn't provide a Revit family file but I was able to model it from the .dwg drawings. Now I want to add flow and pressure drop calculations from the table provided by the manufacturer.

    The reason why I want to use calculations is that we will probably have different flows and I want to save time by not editing the flow in the family every time. I want the family to calculate the pressure drop and the flow from the system flow it is connected to.

    I already know the equation for the relation between the flow and the pressure drop. Is there an option to connect them with parameters in the family?

  2. #2
    Forum Addict josephpeel's Avatar
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    May 3, 2012
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    In the family you need to have a Duct Connector with the Flow Condition set to Calculated. This will get the flow from the connected duct system.
    Next to the Flow parameter in the connector properties there is a small grey button, click on it and create a new parameter and link it to the connector flow (Call something different to Flow, like 'Air Flow'. You cant use the built in flow parameter directly in formulas and creating parameters with the same names as built in parameters can cause problems..).
    Loss Method should be set to Preset. Then you can also create and link a parameter for Pressure Drop in the same way.
    Now go to Family Types where you can edit your formulas for the different parameters.

  3. #3
    Join Date
    February 16, 2012
    Perth, Australia
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    For the Pressure:

    I have done this for diffusers/ grilles but not for coils, it should be the same though. If the manufacturer has given you a table of pressure drop vs flow you can use Excel to plot a trendline and get a formula (usually a quadratic equation shows a good correlation). You can then use this formula to find out your flow from the velocity of air across the coil, however you need to remember to make everything unitless before putting it in the equation then adding the units back into your pressure value.

    Your other option is to go back to first principles and try to work out the pressure that way - good luck!

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