Bishara

A typical mechanical system for many commercial office buildings includes package rooftop DX unit with zone VAV reheat. The IDF and MDF rooms are designed with dedicated DX split units for backup and after hours operation; with a VAV unit as the primary source of cooling during occupied hours.

The challenge with the VAV being the primary is it’s impact on the roof top unit discharge air temperature and pressure setpoints through trim and response logic. Due to the IDF/MDF VAV constant cooling demand, the roof top unit will not reset it’s temperature and pressure as optimum as it should.

Here’s my thought for a compromise. Design the VAV maximum cooling airflow using the highest discharge air temperature available to the trim and response logic, and prevent such VAV from broadcasting a vote into the trim and response.

This provides the ability to utilize roof top unit economizer in cooling IDF/MDF rooms during occupied hours