Goal seek: Adjusting multiple airways possible or not? (Result in %)

[Fred_K]

Hello!

I would like to confirm that the Goal Seek function does indeed allow the adjustment of multiple airways, to reach a target value of one airway?

I've been playing around and when chosing Refrigeration, the result is not in kW but in %. I'm not exactly sure how to interpret this. The two airways merge into one airway and have almost identical mass flow. What I wanted to achieve is an overall value to be calculated and split between the airways.

It's working fine when selecting only one airway to be adjusted. Maybe the adjustment of multiple airways is not allowed, so I'm just checking whether this is a glitch or not.

Cheers,

Fred

 

 

 

[Martin Griffith]

Hi Fred,

The Goal Seek can be used to adjust multiple airways. 

The reason the unit changes to percentage for multiple airways is that the Goal Seek applies a multiplier to the changing parameter on the adjusting airways. Sometimes the multiple airways do not start at the same value, so the multiplier will retain the pre-existing ratio. Therefore we change the unit to percentage. If you start the 2 adjusting airways with a ratio of 2:1 in the Refrigeration property, the Goal Seek result will retain a 2:1 ratio. 

This can look a little strange when your parameter starts at zero. In these cases, the Goal Seek will guess an initial value (usually 1), so you can get some very strange percentages, as you have in your example. This is because the Goal Seek doesn't know anything about what will happen before it launches. 

I think I could improve this; if the pre-existing ratios are 1:1 then we don't have to report percentages. This should be easy to implement, we'll do it for the next version. 

[Fred_K]

I see... so that means, when adjusting two airways starting at zero (1:1 ratio), and the output of the goal seek function is 100 000 000%, then the inerpretation would be that both airways are adjusted to 1 000 000 kW (100% = 1, assumed by Ventsim)?

[Martin Griffith]

I think so. You can close the Goal Seek, keep the result and look at what the Goal Seek has actually put on the airway to verify.

One thing you can do is set the refrigeration to a non-zero value before you launch the Goal Seek, say 100kW. Then the percentage increase will be based off that starting point, and be a little more comprehensible. 

I will change it so the percentage only applies if the starting values are not equal. I'll post in this thread again when we release a version with this. 

[Martin Griffith]

In the latest patch, version 5.4.5.5, this change has been made, so that multiple adjusting airways with the same starting point, show the adjustment value in its true units. Thank you for the feedback! https://ventsim.com/download/minor-releases/