Arkansas HVACR NewsMagazine May 2022

HVACR NewsMagazine May 2022

Tech News

There's a better than good chance the airflow is wrong and has been since day one.

Knowing the supply and return duct pressure drop can be useful as well. It's not unheard of for vents to be closed, return grilles blocked, internal liners to collapse, or flex duct to get smashed or even disconnected. A static pressure reading of the ducts referenced to the pressure drops when commissioned can quickly tell you if there are any discrepancies. Better yet, it tells you what actions to take.

Benchmarking

The airflow is set. Now what? Take it to the next level; benchmark your pressure drops. The pressure drops across the return duct, air filter, indoor coil, and supply duct can be valuable pieces of information when servicing the equipment in the future. Imagine knowing exactly what the pressure drop across the coil was when commissioned 7 years ago. In a typical arrangement of the evaporator coil on top of a furnace, a visual inspection of the coil for cleanliness can be difficult. Knowing the original pressure drop can save time diagnosing and justify taking further action. TESP by itself will not give you this information, only that there is an issue somewhere in the supply air side of the system. (It is recommended to record the dry and wet pressure drops across the coil, they will be different.) The same applies to the air filter. I typically install 5" media filters on our installations. On a furnace, I aim for a .10" pressure drop across the filter when new. Air handlers can typically handle a higher pressure drop across the filter (because the coil is included in the TESP rating) but at the cost of filter efficiency. Generally, these filters are good for 6-12 months. Knowing the before and after pressure drop of the filter in this system will help you determine how frequently it needs to be changed.

Does benchmarking lengthen the time it

takes to commission the system? Yes. Does it give you the information necessary to quickly and accurately diagnose airside issues during future servicing? Yes, it does. In reality, once you