ESP – External Static Pressure –
The resistance that the fan has to overcome in the duct system is measured by the external static pressure. Examples include filters, grilles, air conditioner coils, and ducting. This is the result of adding the positive pressure of the appliance blower and the negative suction pressure at discharge.
The external static pressure and the motor’s CFM are directly correlated. The is produced with greater ESPs. Higher CFM is associated with lower ESP. There is too much resistance in the system, according to a high ESP reading. This may be brought on by clogged dampers, filthy evaporator coils, dirty filters, obstructed supply or return grilles, or inadequate duct size. CFM can be calculated if you know ESP.
In HVAC, the phrase “static pressure” is frequently used. Junior engineers and homeowners alike frequently lack a basic understanding of static pressure. Static pressure is essential to HVAC systems’ operation, thus I felt a thorough explanation was required.
Static pressure in HVAC refers to the fan strength required to provide the necessary airflow. Static losses occur in ductwork components such air filters, return air grilles, and flexible ducts. Therefore, in order to provide the necessary airflow, a fan has to have enough static pressure to counteract the static loss.
Many consumers frequently experience issues with their HVAC system’s inadequate airflow. Inadequate fan static pressure might occasionally be the cause. Therefore, it’s critical to comprehend HVAC static pressure.
HVAC Static Pressure Basics
Depending on its design and airflow capacity, blowers, exhaust fans, air conditioners, and other fans all have a specific amount of static pressure.
A fan’s capacity to produce airflow is closely correlated with its static pressure. The airflow subjected to the fan’s full capacity increases with increasing static pressure.
On the other hand, the fan might not even be able to provide the airflow as specified on its nameplate or specification sheet if the fan static pressure is insufficient.
A fan’s airflow rate is always accompanied by a static pressure reading. For example, the fan model below has an airflow rate of 875 cfm at medium fan speed settings with external static pressure of 0.3 in wc
Fan Static Pressure It is crucial to consider static pressure when choosing a fan. A fan needs sufficient static pressure to overcome the total static loss, which is the sum of the static losses of all the ductwork components, in order to produce the necessary airflow.
The overall static loss influences how much airflow a fan can provide. The airflow supply will be low if the overall static loss is underestimated.
