There are several key differences in the goals and intentions behind the design and functionality of a residential Heating and A/C method versus a commercial method in a big building with lots of people inside at any given moment. Although the basic logic and engineering from a housing method is simply expanded upon and supplemented in larger systems, there are several key factors that make designing commercial Heating and A/Cs much more complicated. The main one is you building occupancy. Even if you have a family of four, unless you all live in a tiny cupboard sized apartment, the body heat of your family typically isn’t having a considerable effect on your Heating and A/C performance, regardless of whether or not all of your are at home or none of you are. But in big buildings, like superstores where hundreds of people are coming and going hour by hour, indoor occupancy levels have a considerable effect on that building’s AC performance. A small residential unit is working against outdoor temperatures. It is typically going to have a harder time running at 12pm under full sunshine versus at 12am in pitch blackness no matter how many people are in the house. But this isn’t typically the case with something like a big department store or an outlet mall. You have to consider air leakage, customer level peak times, heat exhaust from machinery, and any number of other variables in commercial settings. You don’t want your building to be so sizzling hot that customers are sweaty and angry but you don’t want to see them shivering either. It’s about finding the balance between the numerous things and maintaining that balance as much as possible.