SystemIdentifier attributes

[shorowit]

Replaces the sameas attribute with retrofit_id to better clarify how the attribute is intended to be used. The attribute description is: "Use to reference the id of the matching object on the base (pre-retrofit) building where the object has not been replaced."

Adds a new shared_id attribute with the description: "Use to reference the id of the same object on another multifamily unit (e.g., a single shared boiler or common wall described in multiple multifamily units)."

[shorowit]

Some software may be using sameas even for situations where the element (e.g., HVAC system) is replaced, or for an AC/furnace->HP situation. Concerns about the "where the object has not been replaced" part of the description; should that be stricken?

Alternatives to pre_retrofit_id... base_id or upgraded_id?

Needs further discussion.

[nmerket]

🎥 Discussion in HPXML Working Group Meeting 2024-03-14

[shorowit]

Some software may be using sameas even for situations where the element (e.g., HVAC system) is replaced, or for an AC/furnace->HP situation. Concerns about the "where the object has not been replaced" part of the description; should that be stricken?

It seems like this attribute has been misunderstood/misused. Indeed, I thought the sameas attribute was supposed to be used for, e.g., a wall that has been upgraded during a retrofit, but it turns out that's not the case. It's meant to describe components that do not change during a retrofit. When something changes (either a wall upgrade or an HVAC replacement), a measure is supposed to be defined that links the before and after components. See these sections of the HPXML Implementation Guide:

• https://hpxml-guide.readthedocs.io/en/latest/software_developer/references.html#sameas
• https://hpxml-guide.readthedocs.io/en/latest/software_developer/usecases/auditupgrade.html#post-upgrade

(It's also not possible to use sameas to describe an AC/furnace->HP replacement since the HP can only refer to one pre-retrofit component.)