System Airflow Measurement w/ TEC TrueFlow
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Steve Rogers and Chris Hughes with The Energy Conservatory (TEC) talk to the Kalos techs about airflow measurements. They also explain how to use the TrueFlow grid and app to help with commissioning.
Airflow is important because we need it to be accurate to charge refrigerant properly, it’s crucial to homeowner comfort, and it can affect system efficiency.
When the airflow is too low, less heat can be absorbed in the evaporator coil, which drops the pressure in the coil and decreases the refrigerant density. The compressor can’t move as much refrigerant if the airflow is too low. You won’t get proper air mixing, which makes it difficult for air to circulate comfortably for the customer.
If the airflow is too high, the efficiency is good, but you can also get noisy ducts, reduce dehumidification, and run high suction pressure. High airflow is also uncomfortable for a lot of people, as they don’t want to feel air blowing on them forcefully.
The TrueFlow app has four workflows: system airflow & static pressure, system airflow, blower fan airflow grade per ANSI/ACCA/RESNET Standard 310, and pressure gauge. Most A/C technicians can meet their needs by selecting system airflow & static pressure because you will get both of those critical values on the diagnostic screen. The system airflow is a fast workflow, but you won’t get the thorough breakdown you’d normally get on the first option. The RESNET 310 Standard is mostly for inspectors to check the target airflow. Finally, the pressure gauge allows you to take and record static pressure readings.
You can connect the pressure gauge and TrueFlow plate to your mobile phone via Bluetooth. Then, you choose if you’re dealing with an air handler or furnace. You then select the airflow orientation and enter the cooling capacity, air filter location, and cooling climate. After you input the relevant information, you’ll receive a set of test instructions. During the test, your tools take 100 readings and give you an average value on the TrueFlow app.
The TrueFlow grid replaces the filter during testing and takes readings where the filter normally is. It measures the airflow by taking a measurement similar to a duct traverse. With the filter in place, our test measured 563 CFM. A lot of math happens on the back end; the TrueFlow grid and app use a correction factor to predict what the CFM would have been with the filter in place.
The diagnostic screen shows whether you have good, okay, or bad airflow and static pressure, and it shows potential problem areas that it has identified with the A/C system. It also shows the return static pressure drop and the supply static pressure. In our case, we had a very high supply static pressure. Overall, both airflow and static pressure were okay, with the former being a bit low and the latter being a bit high.
In some cases, the static pressure and airflow issues may occur due to poor duct design. In our case, the TrueFlow app recommended checking to see if the supply duct is undersized, collapsed, or restricted.
If a homeowner wants a copy of the results, we can send them the results and send pictures of the equipment through the TrueFlow app. The app automatically generates a PDF that you can send to the customer.
The TrueFlow grid comes with an adapter plate that can help the grid fit in oddly sized systems. TEC has also been considering custom sizing options. However, when selecting a TrueFlow grid, the most important thing is that it measures the total airflow through the grid. The TrueFlow grid works regardless of the equipment’s cleanliness, but TEC doesn’t recommend doing static pressure tests with dirty equipment.
In our second test on a different set of equipment, the TrueFlow grid picked up 687 CFM. Overall, the airflow and static pressure were both in the optimal range. However, if we wanted to improve a little bit, we could have addressed the somewhat high supply static pressure.
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