Magnehelic Duct Pressure Sensor

Magnehelic Duct Pressure Sensor - The Magnehelic measures duct pressure inside of ductwork. It is important, for many reasons, to know the pressure inside of ductwork. This Magnehelic measures the supply side pressure of the blower inside the air handler.

Magnehelic Duct Pressure Sensor

The static pressure in this system is actually controlled by a static pressure transducer which is directly hooked up to a DDC controller that controls a variable frequency drive based on static pressure. The static pressure transducer is a solid-state Magnehelic and works in much the same way a Magnehelic work except the transducer is digital and sends out a signal that registers the pressure it is reading. The Magnehelic pictured is simply for visual display and reading the static pressure inside the air handler. It does not send out any signals.

A technician can walk up to the air handler in a quick glance tell if everything is okay with the blower and duct system based on pressure. Pressure sensors with switches in them are also used to determine an air filter status. A differential pressure switch can be installed in an air handler with pressure probes on either side of the filter.

A differential pressure setpoint is adjusted to the switch so that when the filters load up the switch trips and send a signal to the DDC controller. This alerts the operator of the system that the filters are loaded up and need to be changed. This differential pressure switch is usually calibrated and set using a Magnehelic pressure sensor.

Magnehelic Duct Pressure Sensor

This can also be used to find problems with the air handler and ductwork system. If the pressure is too high or too low then the maintenance staff knows there is a problem with the air handler that needs to be resolved. For example, dirty air filters will cause increased pressure on one side of the filter bank and low pressure on the other side. Tools like these add to the cost of the equipment but make things so much easier for the maintenance staff. They also increase reliability.

Tools such as these allow Test and Balance technicians to balance duct systems. As noted on many pages here at High Performance HVAC, duct pressure is important and is proportional to duct size and coil sizes. It is important to precisely balance the duct system to the design of the system. Without balancing the system the efficiency will take a dive. Therefore, a Magnahelic duct pressure sensor, properly calibrated, will be instrumental in balancing a duct system.

Magnehelic Pressure Measuring | Magnehelic Duct Pressure Sensor

When you measure the pressure in ductwork you use inches of water column or “WC”. This pressure should match the engineering documents for the design of the system. This measuring parameter is deemed from manometers. A manometer is a glass tube with water inside the tube. The amount of pressure needed to move the water one inch is considered 1 WC or 1-inch water column. The Magnehelic uses the same method as a manometer except you do not need to put water in it.

When the system is commissioned by the Test and Balance technicians they insert tubes into the ductwork. The tubes are attached to a Magnahelic which measures the static pressure in inches of “water column” or “WC”. If the air handler attached to the ductwork uses a variable frequency drive the drive is manually adjusted to run the fan to maximum and then to a minimum to get a range of pressure. This data is then inputted into the control program so that precise control of static pressure can be maintained based on programmed parameters.

Magnehelic Duct Pressure Sensor – Magnehelic Duct Static Pressure

Technical Resource: Refrigeration and Air Conditioning Technology