[rovolo]

I understand electrical and plumbing, but why does the HVAC need to be bigger/smaller?

[deltarholamda]

HVAC has to account for the BTUs produced by all equipment. An office might have one or two refrigerators per floor, maybe a dishwasher. Apartments will have one in every apartment. Ditto for ovens, dryers. Even computers and TVs.

[ArchitectAnon]

Offices have a lot more people per m² all of them using computer equipment continuously for 7hrs/day so in my experience they tend to have considerably higher cooling loads. I know from experience that a typical high rise office building in London, UK will have no heating requirement for most of the year; it is in cooling mode most of the time.

[MrLeap]

Just conjecturing, but I assume an apartment contains more ovens than an office.

Would probably make it take more cooling?

[Ekaros]

They also contain lot less people. Average person generates 70-100W at rest. Add that to what ever screens, computers, extra lighting. And it is not that big difference in load.