Technicians typically measure static pressure in inches of water gauge. Calculate the cubic feet of air per minute by multiplying the average velocity pressure in feet per minute found in the above reading by the cross-sectional area of the duct in square feet. Static pressure is the amount of air pressure that can be produced by the fan in an enclosure. Insert the static pressure tip into the test port on the return side with the tip facing the airflow. In real systems, it is unlikely that a fan will be spending its operating life at these identical conditions. water). [fa icon="calendar"] Oct 25, 2019 9:00:00 AM / by Fan performance is generally measured in terms of two basic parameters. The above graph shows how characteristics may change with installation of accessories while using the MU1225S-21 fan as an example. Currently you have JavaScript disabled. The Exhaust Fan drawing below illustrates how static pressures are measured in ductwork with a manometer. Cooling Fans. In real life, examples 1) and 3) are not realistic. Once you have your total external static pressure reading measurements from your manometer, refer to the Product Data for the equipment you are servicing to determine your system CFMs. In other words, the maximum static pressure has been reached, and air flow volume drops to zero. Conditions That Affect Duct Static Dirty Coil Blower on Wrong Speed Wrong Size Duct Dirty Filter . To measure the static pressure of your unit, use a manometer to get a digital reading and test TESP, coil pressure drop, and filter pressure drop by inserting your probes into various areas of the furnace. When figuring for static pressure you use the values of, before fan and after fan. Static pressure 101 Static pressure is the amount of pressure a fan has to push and pull against to move air through a duct system. 3/8-inch hole plugs. Static Pressure (SP) Static Pressure is the resistance to airflow (friction) caused by the air moving through a pipe, duct, hose, filter, hood slots, air control dampers or louvers. For comparison, 1 pound per square inch static pressure (1 psi) is equal to 27.7 in. For a successful enclosure ventilation design, in addition to fan selection, other factors such as intake/exhaust hole size, location of holes, and placement of components, should be considered. This handout describes two methods for using airflow resistance to know or predict airflow rate: 1. The basic tools needed to measure static pressure include: Begin by identifying the spots in the ductwork where you plan to test using your pressure tips and test ports. 1.3. Airflow resistance is measured in static pressure (inches of H 2 0) and is dependent on grain type and depth. Thus, the origin of static pressure is still referred to in inches of water column as a unit of measurement. The filter causes the most significant pressure loss, while the finger guard causes little loss. Fan exiting pressure +1.18-in. Click here for instructions on how to enable JavaScript in your browser. The unit of measure for static pressure is often inches of water (in. You install test ports, take pressure measurements, record them on the invoice, and the static pressure portion of the call is complete. External Static Pressure is the measurement of all the resistance in the duct system that the fan has to work against. How are the actual air flow and static pressure requirements determined? In the graph below, we show 3 yellow lines to depict 3 different levels of impedance (A, B, and C). Let's see how this is done. How are the actual air flow and static pressure requirements determined? A larger static pressure forces the fan to consume more power to expel the same amount of air. Similar to a stepper motor's speed-torque curve, this graph is how manufacturers show the performance of their fans, and where the air flow and static pressure specifications come from. The easiest way to set the blower speed is to measure TESP (total external static pressure), cross reference the TESP to the manufacturers blower chart in the installation manual, and adjust the blower speed. This example creates a scenario where maximum air flow would occur, and we have zero static pressure. One top mistake made when measuring static pressure is to assume the condition of the blower wheel. Fan static pressure can be described in a number of ways, but in simplest terms it is the resistance pressure the fan has to blow against in order to move air in the desired direction. Static pressure is exerted equally on all sides of a duct system. Impedance is defined as resistance to air flow, and it could be in the form of electronic components, walls, or anything that impedes the path of the air flow. Let's see how this is done. Static pressure is a foundational cornerstone of air diagnostic testing, but it can be inconclusive unless you know fan airflow. Refer to the graph above with the 3 designated points 1), 2), and 3). Fan static pressure can be described in a number of ways, but in simplest terms it is the resistance pressure the fan has to blow against in order to move air in the desired direction. But there are issues that can happen if there are hardware obstructions. When air flow increases, static pressure decreases; and when static pressure increases, air flow decreases. The size of the exhaust hole is smaller than the air intake hole, which hinders air flow. Being able to measure and calculate static pressure is a basic, yet important, skill for any HVAC professional. 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