Plumbing Fixture Flow but not for IPC
Yes, the flus tank vs. flush valve was the first thing I checked.
The "International" codes only contain IP units, so that tells me everything how "International" they are 🙂
in addition every State or town can decide if they adopt them and what version and what changes they want to add. WI adopted most of the 2015 international codes, but also has a list of changes. WI didn't adopt the IPC at all. The City I'm in adopted the IFC (International fire Code) that references SOME NFPA 101 sections, but not ALL. the rest of the State doesn't use IFC. Thee also is UBC (Universal Building Code) adopted by some states... it is a mess. But IPC is adopted in large areas. So I see why Revit chose that.
I found out about the discrepancy. We use a "Hunter's Curve" developed by a Dr. Hunter based on empirical observations. Apparently for higher FU numbers. it appears IPC uses the deleted dotted line, and WI code the more accurate solid line and for up to 60FU there is an overestimation for IPC. See attached PDF.
But since the "error" is more conservative and not a problem the larger the system gets, I'm fine just using the IPC values. Better to do it slightly too large in Revit, then doing it wrong manually by hand 🙂
You may also want to check out this more recent update with some alternative suggestions:
https://thebuildingcoder.typepad.com/blog/2023/07/docs-lookup-mep-calculation-and-aps-devcon.html#6
Developer Advocacy and Support + The Building Coder + Autodesk Developer Network + ADN Open
I'm re-surrecting this since it bugs me to have the flowrate at low FU-values (50 FU and under) way too high (pipe sizing etc.)
I was hoping there is a simple txt file Revit uses and I could edit that to use the Wisconsin code data. But I can't find one.
I looked through the above linked articles but can't figure out. In addition it looks like that is a tool to be installed and I can't install software. Anything I can do is limited to editing something that I can do in windows (e.g. edit txt file).
I prefer to size pipe on velocity and like to keep pipes small (especially hot pipes) for faster response of hot water. I understand the being conservative in using IPC, but for hot water, this is not good. I can add safety factor to the overall pressure drop if needed. and since the inaccuracy is up to 50FU, this will impact the short runs from the hot water circulation to the faucet/shower. We talk about twice the assumed flowrate, so that easily increases pipes by 1-2 sizes.
This is what our code uses:
if Revit can't be forced to use our code, are there other creative and (semi) automatic workarounds? I guess I could use a higher standard velocity at low FU units. But if I use the sizing tool, it ends up selecting (with tab function) the entire system and not just some sections unless I manually select pipe sections.
Thanks for sharing. I don't think I can use any API or add-in methods. First, I'm not sophisticated enough :-). Second, our IT uses MS AppLocker to prevent any unapproved code to run. The only "unapproved" code I seem to be able to use are the nodes in Dynamo. Even approved software sometimes needs manual approval (Even Revit updates...).
I was hoping the Revit IPC method uses a table of the IPC values and it interpolates the values. And my hope was to just edit that table to meet the Wisconsin code (modified Hunter curve). but it seems it isn't as simple as finding and editing a txt file...
I don't even need alternative methods sine I only design in WI.
I found some ideas to vote on:
https://forums.autodesk.com/t5/revit-ideas/plumbing-fixture-flow-method/idi-p/11574099
https://forums.autodesk.com/t5/revit-ideas/fixture-units-on-vent-piping-system/idi-p/7975866
I also was hoping to use Revit to calculate the pressure drop for the pipes (and add the Wisconsin code required pressure drop for each fixture type in the fixture family). But with the flow being too high, this also would be too large (I like to calculate accurately first, then add safety later). On the cold side this may just yield waste in piping cost. But on hot water side, this also wastes water and energy and convenience. the thing is, my projects are smaller retrofits. So I'm below the 50FU most the time.
If I can't manipulate Revit to be correct I may use this workaround:
- use standard velocity to size pipes with high FU (~4fps)
- use higher velocity for lower FU values (5-6 fps?) - this will create a high "fake" pressure compared to my local code)
- don't add safety factors for pressure and just use the "fake" pressure for safety
EDIT: I noticed something odd about the pressure calculation. I analyzed a small system and BEFORE I added any fixture pressure drop to the fixtures, that system had ~1.6 psi pressuredrop.
I then added a pressure drop to the connector in the Family. 8 psi pre-set per our code. I expected the system pressure drop to be 9.6 psi (1.6 psi from flow + 8 psi for each fixture). But it ended up to be 15.4 psi. Editing the fixture families was the only change and each family (lavatory and WC in this case) got the same 8psi. am I mis-understanding this or is Revit doing it wrong?
I learned a few things and think I got Revit as far as I was able to. There are a lot of ideas how to make Revit "work differently", But all seem like the cure is worse than the disease. One idea is to adjust Fixture units. Obviously this won't work when you get to above 50FU. I also learned, most my fixtures require 20psi. So the pipe pressure drop is less significant. I also learned, for Tees, Revit can't calculate the pressure drop. This only works for elbows. and it also only works with a the Loss method set to "K coefficient". I assume Revit has a hard time dealing with Tees and knowing if we need the branch or through pressure drop.
I ended up laying out my pipe for a 50+ FU project. I let Revit size the pipes based on 7fps. This was fine in most cases, but not for the large pipe (close or above 50FU). For those I used 5fps. I also manually calculated the pressuredrop using the Wisconsin gpm-conversion. This gave me less pressure drop (since we assume less flow at low FU). That was expected. As expected, Revit pressure calc will be very conservatives.
I think the best method is to use Revit to size the pipes with varying velocities (higher at low FU). And in some selected situations I double-check manually for Wisconsin code. That should give me good pipe sizes while being conservative. This I think is the best short of actually "making" Revit use the Wisconsin code. It is a good idea to look into the code as you design anyway.
Edit: Also learned selective tab-selection. You click one pipe segment, then hover over a different segment and "tab". that way you select all pipes in between and can do a different sizing (different velocity) for that part.
Edit 2: I also noticed, when connecting a recirculation pipe (separate system) to the hot water pipe with a normal Tee, the system doesn't break as I feared. the hot water supply pipe calculation still works and the circulation return pipe is a different system. I totally expected I have to build a special fitting or equipment to separate them. The regular hydraulic separation tools are grayed out, though. I just wanted to point out, that Revit in this case "just works", even if I didn't expect it. This software is full of surprises.
Some new things I will implement for the next project. Our AHJ said they review based on a pressure worksheet. The way that works, it comes up with a vale "A" that is a "maximum psi / 100ft" value for the critical path. Our code has tables for different pipe material that shows the psi/100 ft based on fixture units (red-circled for flush tank systems). In my case "A" is about 4. So any pipe segment has to be sized to be at or under "A" (4 psi/100ft)
AHJ also wants me to annotate ALL segments with size and FU numbers. I assume they use that to spot-check if all pipes are sized to be under "A".
I think this is missing the part where a tiny segment technically could have higher pressure drop, and it also misses the fact that in non-critical paths I technically could have a bit smaller pipes. But I just do what they say and what code prescribes.
FWIW, with my sizing (I don't recall if I used 7fpm??) I only had to edit a few tiny segments to meet exactly what the above method requires. But this will depend a LOT on the rest of the system and available pressure (my project is just a remodel in part of the building, with all plumbing outside the project scope being existing and out of my control.
This seems to be an old method from before computers. but with Revit being imperfect outside IPC, I don't see a good way to do it in a different way than AHJ seems to request. I also don't see a good way to automate sizing in Revit. I guess using the sizing tool and 7 fpm (knowing IPC assumes higher flows than WI code), is a good start, and then I still have to manually verify and edit each segment. My project are relatively small, so this isn't too bad. I just wonder how one does it in really large projects? I assume there is standalone Plumbing software that is more flexible than Revit and also accounts for elevations, water meters etc.
And for some reason AHJ wants to see all FU and sizes on isometric views, and not on plan views or sections. I ended up creating two 3D views for each type (Water and sanitary) since it was hard to see all pipes well in a single 3D view). It is one of the things, where i just have to do as I'm told.
