Background: This project is using underfloor air distribution (UFAD) as the main HVAC system. Passive floor-mounted swirl-type diffusers (manually operated by the occupants for interior "cooling-only" zones. They will not be controlled via thermostats. The perimeter zones will be served by UFAD fan powered units (with electric heat for heating) and will be controlled via space mounted thermostats. The prerequisite requires compliance with ASHRAE 90.1-2004, section 6.4. Section 6.4.3.1.1 states: "The supply of heating and cooling energy to each zone shall be individually controlled by thermostatic controls responding to temperature within the zone". Question: Does the use of passive floor mounted diffusers in the UFAD system and controlled as described above meet the requirements of ASHRAE 90.1-2004, section 6.4.3.1.1 and this prerequisite?
The project team is requesting clarification regarding the requirement for zone-specific thermostat controls in order to meet the requirements of section 6.4.3.1.1 of ASHRAE 90.1-2004 for EAp2. The interior spaces of the project receive cooling air through in-floor swirl-diffusers that are occupant controlled, but there is no zone-specific thermostat control. In this case, the design meets the intent of the ASHRAE 90.1 requirement. Ultimately the temperatures in these spaces are maintained in a similar approach to a VAV box, by regulating air flow. The occupants control this airflow based on personal comfort levels, and are effectively the controls system (similar to operable windows in a naturally ventilated and cooled space). Provided that the system meets the rest of the requirements of section 6.4 (especially 6.4.3.2.1-Automatic shut-down), and thus does not supply unneeded cold air during unoccupied hours, the design appears to meet the intent of ASHRAE 90.1 and LEED-NC 2.2- EAp2. Applicable Internationally.