The cost of this credit is project-specific.
Thermal Comfort Design
Complying with the thermal comfort requirements of this credit is straightforward and easy for projects planning to install an HVAC system. Added costs for this portion of the credit will be the approximately four hours of time to document credit compliance.
Thermal Comfort Control
More challenging—and project specific in nature—is to provide individual control of air temperature, air speed, radiant temperature or humidity for 50% of the individual occupant spaces, and group control for 100% of the shared multioccupant spaces and any individual occupant spaces without individual controls.
Some projects will choose an HVAC system in order to comply with this credit; others will choose an HVAC system based more on building use and occupancy and then look at credit compliance. Here are some system-specific considerations based on typical office buildings.
HVAC Considerations
A fan coil system lends itself towards credit compliance, as would fin-tube radiation with operable windows; however, single zone packaged rooftop units make this credit difficult, as will multi-zone rooftop units with VAV boxes. To make a VAV box system work, a project must use one box for every two private offices at most, which can significantly impact cost.
As an example, office buildings using VAV rooftop units with local zone VAV boxes on the interior zone or fan-powered VAV boxes with reheat coils on the perimeter zones might normally provide one interior box per 1,500–1,800 ft2 of open office, and one perimeter box per 750–900 ft2 (assuming 50–60 linear feet of perimeter wall length and maximum 15-foot-deep zone).
For perimeter zones, compliance with this credit would mean one box for every two spaces, which might be 20–30 linear feet of perimeter wall instead of 50–60 feet, which means tripling the quantity of fan-powered VAV boxes needed. Similarly, for interior areas, if the space is open office with systems furniture, 1,500–1,800 ft2 might include 18–20 people, including corridors between cubes. To comply with credit requirements, this same area would need 10 VAV boxes instead of one box.
A similar result occurs if the project uses fan coils units for space conditioning. Ceiling- mounted fan coil units serving private offices (either interior or perimeter zone) might serve 4–5 offices, and that would need to change to two offices, thereby adding potentially two more fan coils to the same building area. Wall-mounted fan coils would serve generally one office per fan coil, so costs would not change.
In any of these scenarios the cost savings due to the reduction in the capacity and size of the VAV box or fan coil, etc., is more than offset by the added costs of the additional units, with the associated connections to power, primary air duct, piping, and controls.