Engineering notes
AHU filter differential-pressure sensors: range and tapping
Choose a filter ΔP sensor: pascal range, tappings before and after the filter, signal into the DDC.
A dirty filter the BMS cannot see
AHUs have coarse and bag filters. Differential pressure rises as they load. Without a sensor the shift changes on a calendar, or when airflow is already weak. With a sensor on the wrong range (0–2500 Pa while a clean filter is 80 Pa) the software number barely moves.
Read the AHU sheet: clean ΔP and the dirty alarm. Offices are usually a few hundred pascal. Pick a range about 1.5–2 times the dirty threshold. One sensor per filter bank — do not share one device across two AHUs. HVAC parts