Units in Formulas

[Dean Camlin]

I'll apologize in advance if this has already been discussed, but I searched & couldn't find it:

I'm working on the design of a day care building. In Maryland, each classroom is required to have a minimum of 35 net sq.ft. per child. Net area is calculated as not including fixed obstructions or hard-to-move equipment, such as drinking fountains or refrigerators. Recent interpretations have also deducted the floor space taken up by door swings. The number of children each classroom is designed for is fixed, as determined by the number of staff planned to take care of them.

I would like to be able to schedule the net floor area in each of my classrooms, by entering integer values for each of the obstructions present and using a formula which deducts the areas of each obstruction from the room area that Revit calculates. But Revit returns an error message: "Inconsistent Units." Has anyone been successful doing this?

[The Sweg]

I think I know what you mean. I did this with calculating the tons of gravel we needed by using the area of the basement concrete slab. I believe what it means by 'Inconsistant Units', is that if you are working with area, everything in your formula has to be an area parameter. You can't mix a length or weight parameter with area and so forth. I don't believe you could use an integer and area parameters together in the same formula. You would have to generate area values for the door swings, tables, etc. (possibly with shared parameters using formulas within each family) then use those area figures in your scheduling formula. HTH

[cosmickingpin]

I think you would need to add two fields. One for you integer input value (number of deductions), then another for the actual deduction number (or deduction coefficient)- each could be calculated differently per room. then a third field where you include the formula [gross area-(number of deductions X deduction value)]. I am by no means the formula expert though. I think this is what you are asking. i think the problem is in your fields type. the units you have selected for each field you may need to play with that to get it right and it may be counter- intuitive.


I'll apologize in advance if this has already been discussed, but I searched & couldn't find it:

I'm working on the design of a day care building. In Maryland, each classroom is required to have a minimum of 35 net sq.ft. per child. Net area is calculated as not including fixed obstructions or hard-to-move equipment, such as drinking fountains or refrigerators. Recent interpretations have also deducted the floor space taken up by door swings. The number of children each classroom is designed for is fixed, as determined by the number of staff planned to take care of them.

I would like to be able to schedule the net floor area in each of my classrooms, by entering integer values for each of the obstructions present and using a formula which deducts the areas of each obstruction from the room area that Revit calculates. But Revit returns an error message: "Inconsistent Units." Has anyone been successful doing this?

[Tom Dorner]

The inconsistent unit error can be resolved by dividing length or area by one unit of the length or area. i.e. (10SF/1SF)*6 will give a result of 60 without any units.

Another approach to consider is using area plans to calculate out the classroom loads. You could define an area plan style called class loads and then draw or pick lines over the classroom areas going around the things you are allowed to deduct from the space. If you have different types of space a key schedule can be developed and a master occupancy schedule produced.

HTH

Tom

[Dean Camlin]

. . . I don't believe you could use an integer and area parameters together in the same formula. You would have to generate area values for the door swings, tables, etc. (possibly with shared parameters using formulas within each family) then use those area figures in your scheduling formula. HTH

Yes, this is exactly what I was trying to do: simply count the number of obstructions in each room, multiply them by the area they take up, then deduct that from the total floor area to obtain the net result. But Revit apparently won't allow a mixing of integers and area units in the same formula. I'm not sure why.


Another approach to consider is using area plans to calculate out the classroom loads. You could define an area plan style called class loads and then draw or pick lines over the classroom areas going around the things you are allowed to deduct from the space.

This is much too laborious and "counter-Revit" for me. I might as well subtract everything by hand.

[LRaiz]

The solution is simpler than you may think. When you use an integer in your formula Revit indeed does not know how to interpret it. Let's say your integer parameter is named FooInt and you write netarea = area - FooInt. Revit will give you an error because it has no way of knowing if FooInt counts square meters, square feet or acres. So fix the problem by simply telling to Revit how implied unit of FooInt counting. For example netarea = area - FooInt * 1SF

[Dean Camlin]

The solution is simpler than you may think. When you use an integer in your formula Revit indeed does not know how to interpret it. Let's say your integer parameter is named FooInt and you write netarea = area - FooInt. Revit will give you an error because it has no way of knowing if FooInt counts square meters, square feet or acres. So fix the problem by simply telling to Revit how implied unit of FooInt counting. For example netarea = area - FooInt * 1SF
Thanks, Leonid, but I tried what you're suggesting & it still returns that error message. As an example, in the following formula, Area is a value calculated and scheduled by Revit; No. of Doors is an integer plugged into my room schedule; 7SF is the area of each door:
Net Area = Area - (No. of Doors * 7SF)
This, according to Revit, contains inconsistent units--whether or not I include the SF. I don't understand why.

[LRaiz]

Dean,
I just tried it myself and did not encounter any problem. Attached is a 8.1 project file that I made in 5 min of testing. See if you can resolve you difficulties using this example as a guide.

[Tom Dorner]

Dean,

Make sure that your calculated value of "Net Area" has the parameter type of 'area' as Leonid has done in his example file.

Tom

[Dean Camlin]

Thanks for all the help, folks. I did finally get it to work. I had not realized that I had to set the units type as the "Calculated Value" is initially made; if I forget to do that, I cannot go back and edit the Calculated Value to change the units (as you can see, it's "greyed out").

[JamesVan]

Thanks for all the help, folks. I did finally get it to work. I had not realized that I had to set the units type as the "Calculated Value" is initially made; if I forget to do that, I cannot go back and edit the Calculated Value to change the units (as you can see, it's "greyed out").Dean, can't you just delete the calculated value and make a new one? You won't lose any data.

[Dean Camlin]

Dean, can't you just delete the calculated value and make a new one? You won't lose any data.
Thanks James. That's exactly what I ended up doing.

Now it turns out that the franchisor for the day care won't allow my classroom doors to swing out into the corridor (they're concerned that children in the hallway might get hit by the doors). So all of those door swings must be deducted from the net classroom area. But with my functioning room area schedule, it'll be a snap to recalculate the effect of all of those doors!

[James.Lupton]

Leonid

Is there a list available of the unit types which Revit recognizes or is there a way to add units.

Engineering calculations involve a wider range of units and different preferences in how these are displayed.

A typical calculation which we would find useful to add into a schedule may be bearing pressure under a foundation. We typically use kN/m^2 however some people may use kPa (kilo pascals) or Map (mega pascals)

How would we define a parameter for support load in kN and then divide the base load by the base area (in square metres) then display the results in kPa (1kPa = 1kN/m^2)

initially it would seem that a formula for force divided by area was incompatible units however, this is not the case are the resultant is pressure which is measured in different units.

In the past we have used software called MathCad which allowed units to be defined by reference to other units (e.g. MPa = 1000 x kPa)

the results of any calculation could then be displayed in any units simply by adding the output units to the end of the calculation. (e.g. BaseReaction/BaseArea Map)

A list of units recognized by Revit would be useful as would a means of defining how to convert to other types of units.