You need to make new materials for HVAC elements (red, green, yellow..) plus one transparent material for everything else. I took glass material as a reference, made a copy, adjusted the transparency a little, and then tinted it red. All the real materials can be as they are modelled and as they are going to be for real. This is going to be just a temporary overdrive which we will switch off later while doing renders, construction drawings and details etc.
Adjust the overdrive rules so that HVAC elements are overdriven with respective colors, for example you can order all elements in one layer to be opaque yellow or opaque green, and so on. Last you order all other elements exept HVAC elements in your project to be transparent red. Or maybe just transparent white, whatever suites you.
There are a lot of criterias to use when overdriving the graphics, it's not just layers. For all other elements I can use for example renovation status (new) as a filter
User interface is a little bit cumbersome I think, but it is a powerfull feature. Very handy to do checks for the model. It could well be used as a poor mans visual collision detection.
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