I'm looking for guidance on how to apply tags to a typical chiller system, i.e.

2 chillers - each chiller has a series of points and then there's a points common to both i.e. there is only one chilled water entering / leaving temperature point.

Similarly the 3 cooling towers have separate fan speed / status / enable points, and common entering / leaving temperatures etc.

One of the chillers also has an HLI, and there are pumps and vsd's etc.

The Haystack documentation describes nesting a single chiller and cooling tower in a chillerPlant. It's not really clear though if the intent is to nest multiple chillers in a chillerPlant (or a chiller), multiple cooling towers in another chillerPlant (or cooling tower) and then nest these in third chillerPlant?

I've looked through the forum and there seems to be a number of posts indicating that work has/is being done to make the chiller representation more flexible but nothing that really answers my question.

David, I'm not sure there's one right way. What we have done is use a single chilledWaterPlant as the umbrella for all equipment (chillers, VFDs, pumps, cooling towers, etc.) that make up a chilled water plant. Anything at the plant level (e.g. overall entering/leaving flows and temps) can be created on the chilledWaterPlant; otherwise we create the points on specific chiller, pump, coolingTower, etc. equips. We have also used some custom (at least in Haystack 3) tags for defining chilled water loops within the plant.

You can use equipRef on an equip to nest it inside another equip; in this case I think you would use (e.g.) equipRef -> chilledWaterPlant to nest inside your chilled water plant.

Partially this is driven by understanding your use case and what rules or logic you need to enable by the tag structure. I think that question is best answered within your team.

Hey David, I can confirm that we model plants in the same way as Stephen describes in his first paragraph.

Thanks, yes it makes sense keeping things flat where possible.

More as a comment, I did run into difficulties trying to follow this guidance when there's common condenser water entering/leaving temperature points as well as entering / leaving temperature points for each chiller and cooling tower.

You cannot follow the diagram from https://project-haystack.org/doc/Chillers and place the condenser water entering/leaving temperature points on the chillerPlant since they have to reference the cooling tower or chiller ("The condenser water leaving the chiller, is the condenser water entering the cooling tower").

But if you have 3 cooling towers with leaving temperature points and a common cooling tower leaving temperature point as well you need an umbrella for the cooling towers as well as separate equip for each tower itself I guess.

As a further follow up, what I decided to do is create two new equips, a chilled water system (CHWS) and condenser water system (CDW). This allows me to add the common points (flow / temp) etc.

I made the decision that the CHWS has a convention that leaving is from the chillers to the field, entering is from the field to the chillers. And CDW has leaving from the cooling towers to the chillers and entering is the reverse.

I'm still keeping everything flat, i.e. the chillers, cooling towers, pumps, chws, cdw etc are all children of the chilled water plant.