Some buildings, such as retail malls and speculative office buildings, are typically built in phases. For example, the core mechanical system may be installed with the base building while the ductwork and terminal units are installed later as part of tenant improvements. A similar situation can occur with the lighting system or other energy-related features of the building.
There are frequently spaces within a building where the temperature control is not required for oc-cupant comfort but is required to maintain a minimum space temperature for equipment protection. This may require cooling-only or heating-only systems depending on the space needs. Some spaces are heating only to protect against freezing. Other spaces are cooling only to offset high internal heat gain associated with process loads. While these heating-only or cooling-only systems are permitted, they require special consideration when using the Performance Rating Method.
In either of these situations, for the purpose of calculating the proposed building performance rating, the rule is simple: heating or cooling systems that do not exist or that are not yet designed or recorded in the construction documents are assumed to be of the same type that is used in the baseline with characteristics that minimally comply with the applicable mandatory provisions and prescriptive requirements from Standard 90.1 Chapter 6.
- In cases where the space use classification is not known, the default as-sumption is to classify it as office space.
For heated-only storage buildings, and for thermal zones designed with heating systems in the proposed building serving storage rooms, stairwells, vestibules, electrical/mechanical rooms, and restrooms not exhausting or transferring air from mechanically cooled thermal zones in the proposed design (Standard 90.1-2019 G3.1.1 exception e) the baseline HVAC system is a heating and ventilating system with no cooling. For these applications only, cooling is not modeled for the proposed design.