System Performance Checks

In today's live stream, Steve Rogers (The Energy Conservatory) and Bill Spohn (TruTech Tools) join Bryan to discuss system performance checks during commissioning. This live stream has a heavy emphasis on airflow in system performance.
Some technicians cannot perform effective system performance checks because they don't know the ins and outs of their tools. These technicians fail to maximize their tools' potential by not knowing where to measure, how to measure, or what their tools can do.
Static pressure measurements are vital for system performance checks because of static pressure's relationship with airflow. Static pressure is NOT airflow; it is the force exerted in all directions in the ductwork. However, misuse of the manometer is common and leads to inaccurate airflow calculations. Technicians must understand what they must compare their static pressure measurement to. They need access to the blower chart from the manufacturer AND the specifications. Airflow should be measured BEFORE the technician checks the charge.
According to RSES, your typical A/C unit will have an airflow of 400 CFM/ton. You can expect 450 CFM/ton for a heat pump or a high sensible heat load, and you can expect 350 CFM/ton when there is lots of outdoor air coming in or when the latent heat load is high. The best way to take a measurement is to use a flow hood, vane anemometer, TrueFlow grid, or manometer and blower chart to measure the airflow and use these CFM/ton values to verify the airflow. However, these values vary with humidity, altitude, and barometric pressure.
When it comes to understanding airflow values, a good starting point is for technicians to understand how the basics of heat transfer work with airflow, especially when it comes to the intricacies of sensible and latent heat loads.
A system measurement of airflow differs from a distribution/point method of measuring airflow. Total system airflow measures the total volume going through the air handler (or furnace). You can add up the airflow of all the supply registers, but accuracy can be an issue. You also cannot account for leakage if you add up the supply registers.
External static pressure is usually measured with a diaphragm-type pressure gauge. These come in electronic or Magnehelic varieties. When it comes to the tools that measure static pressure, you must know how to use them. If the tool says that it measures a percentage of the full scale, you must account for that. If you take the measurement at face value without accounting for resolution or scale, you will get a highly inaccurate measurement. Also, due to the nature of pitot tubes, you will need to take multiple duct measurements. You can also use manometers for blower door tests to measure duct leakage, and you need a very high-quality manometer for that.
On the refrigerant side, "beer can cold" is an outdated way to measure when you have tools that can take accurate superheat and subcool readings. Superheat and subcool readings help you determine your charge and can give you some insight into the unit's efficiency.
While the refrigerant charge is important for system performance checks, technicians generally seem to have a better grasp of it than airflow.
Remember, just because an instrument gives you a value, that doesn't mean that the value is your exact measurement. Applications such as MeasureQuick also help technicians interpret their readings and collect more accurate data during performance checks.
Go to TruTech Tools (www.trutechtools.com/tec-minn...) or The Energy Conservatory (store.energyconservatory.com/...) to get your hands on a TrueFlow grid.
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschool.com/.

[@nathanhurst5155]

I really like the things you put on here. It’s all good and enjoyable. Learn a little something every time.

[@kayzin7679]

Thank u so much fo4 your sharing. Always a mere fan of u guys.🙏

[@davidwalz2283]

Can you discuss how this truflow can be used in a package system with multiple filters?

[@RJMaker]

You guys mentioned putting the TruFlow in the hands of salesman.... What is the validity of the measurement of what is in most cases dirty equipment? Does the salesman determine the cause of low total system CFM?

[@CarlosMartinez-gd9ux]

I've been out the trade for awhile, back in now and I ran across a little trouble condener starting and stopping I think it probably has to do with, oh !!! By the way it was 102 out here!!!! but unit starting and stopping I believe it has to do with high liquid pressure switch, may be dirty piston at the e-vap maybe to much refrigeration or not enough 🤔 it's a guardian 5 ton the liquid line towards the stated to freeze it's a fairly new condition I didn't have the hardware with so I was unable to repair I am going back out there (stuck) Please Advise

[@christopherborner1139]

The infinity control will tell you static and cfm. Will those measurements be wrong if you have dirty coi look s or blower wheel?

[@JayRatchets]

It can be. The static is real. The cfm displayed is a request not a reading. I had an air handler one time displaying full cfm blowing against a closed fire damper. If the static is decent however the cfm reading is pretty accurate.

[@taylerellis378]

I dont get the truflow grid. If you remove the filter to put the grid in the airflow does not include the filter correct? Then you make all your adjustments get the cfm where you want it then take the grid out and install the worst 1" filter with .6 static pdressure drop and say all is good. ?? From what I experience every day taking static pressure drops is a 1" filter no matter how good never cuts it. I only install a 2" or better filter on any of my installs. Though I must admit the existing ductwork out here is usually terrible. Rerurns are always 20% smaller than the supplies in my area. Ugg.

[@eddiegomez3628]

What do you guys mean by the word "cabinet"?

[@realestateservicessaleshea99]

👍🥃

[@publicmail2]

SYTEM

[@jsmitty4675]

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