Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
Mandatory elements in sections ending in X.4 are always required, but other sections can be traded-off.
I think that you may be confused about the difference between the prescriptive path requirements, and mandatory requirements that have to be met if you follow the performance path for compliance. In ASHRAE 90.1-2016 § 5 (related to the envelope construction) the mandatory provisions (§5.4) do not specify mandatory U-values, but rather items related to the construction and testing of materials for the envelope. Table 5.5-X can always be a trade-off.
§ 6.4 related to the mandatory provisions for HVAC, it also does not specify mandatory EER values, but items related to minimum acceptable performance and the conditions systems should operate and be controlled. For example, if you read §6.2.2 you will find:
Projects using the Energy Cost Budget Method (see Section 11 of this standard) must comply with Section 6.4, the mandatory provisions of this section, as a portion of that compliance path.
Meaning that you cannot have, for example, a 12 SEER Air cooled AC sized to less than 65 kBTU/h. However, I have found that the minimum requirements are still pretty low compared to the equipment currently in the marker. This half ton split AC has a SEER of 17 and is fairly inexpensive.
Similar situations happen with §7 (Hot Water) and §8 (Electric power), where the mandatory requirements dictate control strategies and operation conditions.
§9 (lighting) and §10 (Misc equipment) do have hard ceilings for the power that these applications can use, but in my opinion this is the area where manufacturers are being pushed to improve technologies. In my experience, most architects would not push to have 1000 W of incandescent lighting instead of 100W of LED.
In summary, I think that there still opportunity to take a lot of trade-offs in your design, but the Code is becoming more stringent in aspects that are difficult to model accurately (like lighting control based on actual occupancy).
