Ashrae Fitting Database
Teodolinda Mattson
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Featuring pictorial outlines of each fitting, this database is useful to design engineers dealing with a variety of duct fittings. For any given fitting, enter the flow rate and fitting information and obtain loss coefficient data and associated pressure loss. The product includes table data for supply, exhaust, and common (supply/return) duct functions. Fittings may be saved into a project file, which is easily navigated and can be stored and transferred.
The database interface features fully available input, output, calculations, and table data properties; and easily viewable calculations that update in real time.
Purchasers receive a one-year subscription for cloud-based access to the ASHRAE Duct Fitting Database ver. 6.00.05.
ASHRAE Duct Fitting Database (DFDB) for the iPhone, iPod touch, and iPad allows you to perform pressure loss calculations for ASHRAE duct fittings in both I-P and SI units. Use this mobile app in the field for quick duct pressure loss calculations. The inputs can be adjusted by touch, and installation is automatic. Purchase this product from iTunes for $9.99 Learn More
Standard 120-2017 --Method of Testing the Determine Flow Resistance of HVAC Ducts and Fittings
ASHRAE Standard 120 establishes uniform methods of laboratory testing of HVAC ducts and fittings to determine their resistance to airflow.
The Duct Size Calculator is a quick reference tool for approximating duct sizes and equivalent sizes of sheet metal duct versus flexible duct. It includes sizing for metal ducts, and for flexible duct when compressed at 4%, 15%, and 30% straight line compression. The Duct Size Calculator is the result of collaboration between ASHRAE TC 5.2, Duct Design, and the Air Distribution Institute. Learn more
ASHRAE Duct Fitting Database, this database, includes loss coefficient tables for more than 200 round, rectangular, and flat oval duct fittings. Featuring pictorial outlines of each fitting, DFDB is useful to design engineers dealing with a variety of duct fittings. For any given fitting, the user may enter the flow rate and fitting information and obtain loss coefficient data and associated pressure loss.
This is a problem with all kind of fittings. In this example of a round elbow, it uses mitered elbows, which has higher pressuredrop. As an optimist i say this isn't too bad since it is more conservative. But the fact the 90 defaults to have a lower pressuredrop than the 30 fitting doesn't make sense. Even if i don't know a value is correct, seeing something illogical like that makes me nervous. Also the fact that it is zero at unusual angles isn't good, but knowing it I can adjust to that.
I opened the family but did not see a way to set the type of fittings it uses and the connectors are type "fitting". Since I use Revit to get at least a reasonable number, I like to resolve this or at least improve. Here my questions and ideas and I wonder if someone has ideas:
I started manipulating the elbow duct fitting and replaced the connectors with regular global/bidirectional connectors and assigned a pressuredrop. So far I have to manually enter the pressuredrop, but it seems to work in a system, and also works with auto-route.
Next step I will have it calculate the pressuredrop based on the SMACNA/ASHRAE loss coefficients. I need to find an approximation that changes the coefficient based on the angle parameter. But it looks like it could be done to calculate pressuredrop based on actual flow (and a velocity that derives the velocity pressure).
I also saw ASHRAE has different coefficients based on duct size, while SMACNA has one coefficient. I guess that can be implemented somehow. At least to a point that it makes more sense than what Revit does oob.
Then in the project, set all the Loss Method for all of the fittings to "Specific Loss" (you can do this with a Dyanamo script or using a duct fitting schedule). After all this, the built in pressure drop calculator will work fine.
The tricky part is that some fittings have two different loss coefficient tables. A booted tee, for instance, has a different pressure drop if it's diverging (like on a supply system) or converging (like on and exhaust system). You can either build two different families and remember to use the right family, or you can add a Converging/Diverging check box which changes which loss coefficient table is used. My goal is for the Ripple plugin is to keep track of connector flow directions in the background and automatically set your converging/diverging setting.
In the project it still is set to ASHRAE. But if I try out and set the pressuredrop to 1", the system pressuredrop raises by 1" and that branch becomes the critical path. Obviously this isn't a validation of my family yet....but tying the pressuredrop value to the duct connector seems to override whatever the project does with fittings. (Don't quote me on that.....:-)
But I created a duct fitting schedule and included ALL available parameters, but I can't see one that looks like it is setting the calculation method. which parameter do yo mean to set the "loss method"? I came across similar advice in a different thread, but seem to not be able to see such parameter in a schedule.
As for other fittings, I will look into each one I use if they behave OK oob, or if they need adjustment. Elbows seem to be the most urgent since a duct system has many elbows compared to other fittings. I saw for tabs Revit uses a different fitting that is less efficient than mine. but I'm less concerned about that since that likely just gives me a tiny bit too much pressure drop and would be conservative. Maybe i will, but i wasn't planning to re-create all the fittings.
The Loss Method isn't schedulable, but you can create a schedule of all of the duct fittings, select them all in the schedule, then click your Default 3D View and you will have all of the duct fittings in the project selected, you can then change the loss method of all of them to Specific Loss in one click as opposed to having it done fitting by fitting.
Either would work, but once you've gone through all of the work to calculate the K factor, the pressure drop is just one more calculation and it allows you to tag the fittings with the pressure drop, which is nice.
then click your Default 3D View and you will have all of the duct fittings in the project selected, you can then change the loss method of all of them to Specific Loss in one click as opposed to having it done fitting by fitting
My fit is a bit different and i ignored the values below 30. I usually correct the fit equation so that all relevant values are like the measured value, or a bit higher. but I think this is reasonably close either way.
But I discovered one problem. Revit adds its own pressure drop to what I calculate. That shows in the properties and also in the pressure drop report and the system inspector. In the below screenshot I set it to specific loss = 0 and the oob parameter "Pressured Drop" shows my calculated value (0.0106 in htis case). if i set the specific loss to 1 in-wg, the Pressure Drop goes to 1.0106 and so on. Same if I set it to ASHRAE fitting, then the "Pressure Drop" will be what the ASHRAE fitting calculates plus my calculated value. The only solution would be to select all the fittings and set the Loss method to specific at 0. That obviously is inconvenient, I and has the danger the user doesn't do that or doesn't remember to do that again after adding fittings.
Another practical idea would be to just leave these fittings that have some sort of pressure drop alone and only manipulate fittings that have no Revit pressuredrop set already. Those obviously are the most dangerous ones since they make Revit underestimate the pressure drop. I agree with iansavage that we want conservative design values, and not necessarily the absolute correct values.
I wish Revit would either fix the fittings and make them all be correct, or at least would allow us to override them. But they chose to set it up with partially wrong calculations AND prevent us from overriding them (at least not easily).
I noticed another oddity. I used the SMACNA fittings since i onw the SMACNA HVAC System Design guide. thsoe C-values seem to be higher than the ASHRAE values. I don't have the ASHRAE fitting database or design guide, so i rely on what Google shows me and what is in the pressure report. but for gored and die-stamped fittings, the SMACNA values seem to be higher by a bit. Did anyone else notice that or have an explanation? The engineer in me would use the higher (SMACNA) values. but this drives me even more to use my own calcs.
I'm entertaining the idea to buy the ASHRAE database, but it seems to be a subscription. and since I would prefer to use the higher values, it wouldn't be much use to me anyway compared to the SMACNA values.
For the fittings where ASHRAE adjusts the C-factor based on diameter, it looks like SMACNA data are equal to what ASHRAE has for 8"-10" duct size. For larger ducts, the ASHRAE factor gets smaller. So SMACNA will be more conservative for larger ducts.
I tried to "flush out" the default ASHRAE fitting setting in the fitting family. I took the family, converted it to a mechanical family, saved it. then converted it back to a duct fitting. but it still "remembered" the ASHRAE options it had assigned. When I create a duct-fitting from scratch (from generic template, then convert to duct fitting), the ASHRAE options are blank and I ASSUMME it would then not use an ASHRAE value, but only use my calculated value.
Does anybody know how for a new fitting the ASHRAE options get assigned to begin with? Or how to "reset" the fitting family so it forgets that? I think if I could do that, the fitting could work the way I want without me having to manually disabling the ASHRAE option in the project. Maybe dynamo? (I'm a total noob in dynamo)
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