Valve pressuredrop not reporting

[HVAC-Novice]

Based on the standard motorized valve family I created attached control valve. My goal is to be able to assign Cv values (or define a psi pressure drop in case of Pressure-independent valves). My goal is to be able to schedule control valves, and also include their pressuredrop in the loss report for pump sizing.

I managed to have the valve "read"  the flow of the pipe it is cut into and calculate the presuredrop (In the example screenshot based on Cv-value).

On the screenshot you see it displays the pressuredrop. but for the actual pressuredrop it shows nothing. In the family I did assign the pressuredrop to that parameter. But it doesn't seem to actually.

I'm not sure if the problem is that the two valve connectors are linked, but I tried them not being linked, only one of them assigned the flow and pressuredrop and all other combinations I could think of. I also created a mockup system with the valves between a manifold and a pump. The pipe up and downstream of the valve shows the correct flow.

i noticed that if I enter a pressure value under "Loss EMthod" and "LossMethod Settings" it will show up int he pressure loss report, but won't show up under "Pressuredrop" (in properties). I also don't seem to know how I could take advantage of that and have my parameter be that "specific loss"

[Martin__Schmid]

In order to assign based on a Cv value, that will properly assign the K value to the results in the pressure loss report, you need to modify the family and setup a formula that converts from Cv to the built in K Coefficient parameter.

http://www.eng-tips.com/viewthread.cfm?qid=88266 has a formula that may be used…

In Revit, I added a untless Cv param, and used that to calculate K Coefficient:
K Coefficient = 894 * Nominal Diameter ^ 4 / ((Cv ^ 2) * (0' 1" * 0' 1" * 0' 1" * 0' 1"))

I found this to check the results against:
http://www.flowoffluids.com/calculators/k-cv-kv-conversion.aspx

Roughly the same results… 55.6477 is close to Revit’s 55.875 … but, please do your own validation.
the variation may be due to the precision of the formula (I suspect 894 is a rounded value).

You need to make sure to have a non-0 value for Cv for each size of valve, otherwise you’ll get a rather crypic message:

Note: the default Motor Control Valve – 0.5-2in has one of its connectors mapped to the K Coefficient parameter. What I found was that was resulting in 2x the expected K coefficient and pressure drop.

I unmapped the K Coefficient property from the built-in K Coefficient parameter, and this resulted in the expected values.

Here's a video walking through the steps, and showing both the K and the Pressure Loss results in the Pressure Loss Report:  http://www.screencast.com/t/be6zSyZcDb57

In the case of assigning a PSI loss directly to the valve, you can set the instance’s Loss Method to “Specific Loss”, then use the Loss Method Settings’s Edit… window to assign a loss value.  Alternatively, you could set one of the connector's Loss Method to Specific Loss, and associate that connector's Pressure Drop property to a user defined pressure drop parameter.  Just make sure when taking this approach that the valve's instance "Loss Method' is left as not defined'. Here's a video showing both methods: http://www.screencast.com/t/qjhKRWozPeyc 

[HVAC-Novice]

I think what you describe would work for Vavles with pressure drop depending on Cv or K-values values (although it seems cumbersome and needs strict quality management ).

But I also will have pressure-independent valves. So in some cases design pressuredrop is a flat 3 psi and not based on a Cv value.

My goal was to have familytypes of valves to calculate pressuredrop based on Cv value or use the flat value in case of PICV. That I accomplished and can select the valve modelnumber (whether pressure dependent or independent) and the schedule and the parameter show the correct pressuredrop. See my above attached family.

The problem is to have that valve actually use that calculated/determined pressuredrop.

[Martin__Schmid]

There appears to be two separate limitations that prevents being able to achieve all your goals in a single family definition.

1. There is no possibility to change the Loss Method on a connector... this is a family only setting... and in your case, you want varying Loss Methods on different valves.
2.  There is no possibility to set the Loss Method type parameter to "Specific Loss" within the type.. this can only be done on an instance.

Looks like you can accomplish what you want.. but you'll need two separate families to accomplish it... one that is for "Specific Loss", and the other that is "K Coefficient".

For the Specific Loss case

make sure you set one (and only one) of the connectors to Specific Loss, then map the Pressure Drop property on the connector to your pressure drop parameter.  Make sure the other connector has loss method set to not defined.

For the k-Coefficient case

make sure you set one (and only one) of the connectors to K Coefficient, then map the K Coefficient property on the connector to your K Coefficient parameter (which, as described earlier in the thread, can be computed from Cv).  Make sure the other connector has loss method set to not defined.

Also, make sure that the Loss Method in the family's Type parameter is set to Not Defined.

Here's another video that demonstrates:  http://www.screencast.com/t/Xt0OMr1r ... it shows that by having two families defined as above,  the resulting calculated (from K or Cv) and determined pressure drops will be reported in the pressure loss report.

HTH, 

[HVAC-Novice]

Thanks so much for the effort. I actually got it to work thanks to your help. And I actually was able to combine the Cv method and the "defined loss" method in one family. What I do is create family types for each valve type. For each type I decide if the parameter that will be the pressure drop will be a fixed value, or based on Cv. 

I think the only part I really needed to change in my original family was to change the loss method parameter to "not defined".

Some things that are tricky in Revit and probably mislead me a bit:

- the hardcoded "pressuredrop" parameter won't show a value in the properties. The pressuredrop only shows up in the pressure loss report. And it seems Revit calculates an arbitrary K-value based on my fixed psi-value. So you really need to run a pressuredrop report to see if the pressuredrop is accounted for.

- When inserting the valve into the pipe ("break into") it is part of the hydronic system and will be part of the pressure loss report. But when you change the family type (like for a different pipe size), it somehow disconnects from the piping system and won't be part of the pressuredrop report (and not the piping downstream). So when inserting the valve you pretty much want to know what valve size and valve type you want or you better delete it and insert a new valve. Hmmm.. I tried again and sometimes it seems to work now when I change types. Well, just watch out for that if you change family types for an inserted valve.