Defining the difference between System and Equipment

[corymosiman12]

To me, I'm not sure I understand why all *_Systems are a subclass of an Equipment. The distinction is somewhat arbitrary. A system to me is something made up of a bunch of interacting components, but often times what people refer to as a piece of equipment (AHU) is a system in a sense, it is just contained to a smaller physical location.

I'm not sure I know of a good solution, I just think maybe it needs some consideration, focusing on answering some questions:

• Is a system a logical grouping of individual equipment intended to achieve a similar purpose / have similar functions?
• Should a system be a distinct type of equipment, or do these run parallel to one another?
• At what point does a system break down into an equipment, and vice versa? I wouldn't consider a Coil as a specific system, but I could see somebody making the case of a Fan and Motor assembly being defined as a system, even more so for an AHU (built up of fans, coils, filters, etc.), and even more so for an AHU and Terminal_Unit combination.

Apologies if there has already been discussion / justification to this.

[gtfierro]

Can you point to where you're seeing System classes as subclasses of Equipment? They should have been separated out into their own hierarchy as of the 1.1.0 release. Other ontologies such as SAREF adopt a much more generic approach to describing these kinds of things: an HVAC system would be a System just as an AHU or a VAV would be. In Brick we draw a distinction between the discrete, "packaged" assets that one might buy (e.g. an AHU) vs the system that one would assemble from a set of components (e.g. an HVAC system or chilled water system).

Is a system a logical grouping of individual equipment intended to achieve a similar purpose / have similar functions?

Our definition for a System is : "A System is a combination of equipment and auxiliary devices (e.g., controls, accessories, interconnecting means, and termi­nal elements) by which energy is transformed so it performs a specific function such as HVAC, service water heating, or lighting. (ASHRAE Dictionary)."

Should a system be a distinct type of equipment, or do these run parallel to one another?

I'm not quite sure what you mean by "run parallel": are you asking whether the concepts are disjoint or orthogonal?

At what point does a system break down into an equipment, and vice versa? I wouldn't consider a Coil as a specific system, but I could see somebody making the case of a Fan and Motor assembly being defined as a system, even more so for an AHU (built up of fans, coils, filters, etc.), and even more so for an AHU and Terminal_Unit combination.

A coil would probably be part of a couple systems, e.g. Hot Water System and the HVAC system. A Fan/Motor assembly and AHU or AHU/TerminalUnit could also be systems as well but it is my feeling that this is somewhat of an arbitrary distinction as well. Personally, I like the idea of the Systems representing as much of the "whole" as possible --- not just the AHU, TerminalUnit but the Boiler, Chiller etc --- Equipment are modelled discretely, but you can always "drill down" through the hasPart relationship. That will likely remain true regardless if the entities are modelled as equipment or systems.

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One note: I just noticed website documentation hasn't been updated yet, hence the possible confusion. I plan on getting that fixed today, so take a look later this afternoon.

[gtfierro]

Website should be updated by PR BrickSchema/brick-website#84 when that gets merged

[corymosiman12]

Ok - those things make sense to me - thanks for the clarification, Gabe. I have mainly just been looking at the website definitions, so that is probably true for the confusion. I will wait for that PR to go through and will check back in a day.

[gtfierro]

Website should be updated now!