Minimum flow set points for VAV and fan powered terminals

ASHRAE 90.1-2019

G3.1.3.13 Minimum volume set points for VAV reheat boxes shall be 30% of zone peak airflow, the minimum outdoor airflow rate, or the airflow rate required to comply with applicable codes or accreditation standards, whichever is larger.

G3.1.3.14 Minimum volume set points for fan-powered boxes shall be equal to 30% of peak design primary airflow rate or the rate required to meet the minimum outdoor air ventilation requirement, whichever is larger.

Code Requirement Interpretation

These requirements aim to determine the minimum damper position of standard VAV and parallel PIU air terminals. The position is based on either the minimum outdoor air requirement or 30% of the peak zone/primary airflow.

Implementation

For each terminal, the zone outdoor airflow is calculated and the minimum damper position is determined by taking the largest of the 0.3 or the zone outdoor airflow divided by the maximum terminal airflow (or primary airflow for parallel PIU terminals). The determination is initiated in air_loop_hvac_apply_minimum_vav_damper_positions and the calculation and assignment is done in air_terminal_single_duct_vav_reheat_apply_minimum_damper_position and air_terminal_single_duct_parallel_piu_reheat_apply_minimum_primary_airflow_fraction.

Key Ruby Methods

Existing