Static Mistakes - Short #232 · HVAC School - For Techs, By Techs summary

Key takeaways

Static pressure is not airflow; static pressure measurements are crucial for HVAC diagnostics.
Gas furnaces and heat pumps have different static pressure rating considerations, which can impact system performance.
Dirty components can mislead technicians regarding system performance as they can cause total external static pressure to drop.
Lower static pressure at the blower results in better system operation, including reduced energy consumption.

Summary

Understanding Static Pressure Measurement

Brian emphasizes the importance of measuring static pressure in HVAC systems. The episode highlights that static pressure is fundamentally different from CFM (Cubic Feet per Minute) and velocity pressure. It is characterized as 'balloon pressure' that requires containment, meaning it cannot exist without ducts, filters, or other obstructions to create pressure. Brian recommends starting to measure total external static pressure as an initial approach to understanding system performance.

Common Mistakes in Static Pressure Measurements

Brian identifies several common mistakes technicians make when measuring static pressure. He notes that gas furnaces and heat pumps have different static pressure ratings due to their design; static pressure in gas furnaces is rated for the equipment outside the coil, while it is included in the rating of heat pumps. A key takeaway here is that the highest static pressure will always be found at the blower, and technicians need to measure at this point for accurate diagnostics.

Impacts of Dirty Components on Static Pressure

The podcast discusses how dirty components like coils and blower wheels can significantly alter static pressure readings, often leading to misdiagnoses. For example, if a coil is clogged, measuring static pressure drop across that coil can indicate the issue. Moreover, the podcast explains that when components are dirty, total external static pressure may drop, misleading technicians into thinking the system is functioning well when it isn't. Brian stresses the importance of understanding how cleanliness affects static pressure and, ultimately, system performance.

Ideal Static Pressure Conditions

Brian closes with insights on optimizing static pressure for energy efficiency. He notes that lower static pressure is generally better for reducing amp draw and improving airflow. Properly selected registers, grilles, filters, and system design can contribute to maintaining low static pressure. Emphasis is put on understanding airflow first and using appropriate measuring techniques to diagnose any potential problems within the system accurately.

Show notes

In this short podcast episode, Bryan covers some common mistakes when measuring static pressure. Static pressure is balloon pressure, not CFM or velocity pressure, but it can be an airflow indicator. The best way to start learning about static pressure is to start measuring total external static pressure.

Gas furnaces and heat pumps are different; static pressure is rated at the furnace in the former (not the cased coil, which is additional), and the static pressure includes the coil in a heat pump. The highest static pressure will always be at the blower, but restrictions on either side of the blower will raise static pressure on both sides of the blower.

Dirty components can drop the total external static pressure, which is a common point of confusion that can lead to misdiagnosis. You'll want to determine static pressure at the blower and across components. If you want to determine if a cased evaporator coil is clogged, you can measure the static pressure drop across the coil (by measuring below and above the coil) and compare it to the manufacturer's specifications. Dirty blower wheels can also cause problems, as they don't move much air in the first place.

Lower static pressure at the blower is the best for amp draw and airflow, and our system designs and accessories can support low static pressure. Dialing in airflow, putting your probes in the right positions when you measure static pressure, proper register and grille selection, and minimally restrictive filters all go a long way.

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Static Mistakes - Short #232