From what I could see in related posts, "40 equivalent full-load hours per week" are plainly interpreted as 40 working hours and without any connection to thermal load and I am not sure why is that and what does the above exception actually means. Detailed explanation would be much appreciated to understand this as I couldn't find any definition on that in 90.1.
To give a proper context to as why I am confused: I have a retail core and shell project where the space is predominantly used as Retail-Sales (shops) with working hours Mon-Sun 10:00-22:00 with System 7 as baseline system per each floor, and then there is an office section and cinema theater with different working hours (Office | Mon-Fri 08:00-16:00; Cinema | Mon-Sun 15:00-01:00). Now, both of these space type schedules differ significantly from the main building use according to the already given interpretation where the exception is 40 working hours per week and that I should use separate System 3 for the baseline HVAC system. I assume I got this right, but I would still like to know why "40 equivalent full-load hours per week" is interpreted as 40 work hours per week. Also, the whole second sentence of exception b is not clear enough, not just the equivalent hours. Thank you!