High Performance Sequences of Operation for HVAC Systems

Abstract

This addendum revises the way the variable-speed series fan is controlled.

Currently, the speed tracks the primary airflow.

This revision maps the fan airflow set point from a minimum equal to the larger of the ventilation minimum and the primary airflow minimum up to the cooling maximum.

The intent is to help ensure that the fan airflow exceeds the primary airflow so that no primary air exits the induction port into the return air plenum, recognizing that the actual fan airflow and actual primary airflow can vary from set point.

Note that this will only be effective if the ventilation minimum is larger than the primary airflow minimum, as it will be if the designer is taking advantage of the indirect ventilation capability of the recirculated return air from other zones.

If the ventilation minimum is the same as the primary airflow, the sequence is effectively the same as the current sequence.

Note: In this addendum, changes to the current standard are indicated in the text by underlining (for additions) and (for deletions) unless the instructions specifically mention some other means of indicating the changes