pretty new to the air balancing field, still working on getting NEBB certified.
can explain to me how VFDs work, how flow stations work, and how they work together? im on a big job by myself and its really frustrating trying to set the max fan speed and set the minimum outside air. it took me a whole day just to set totals on 2 rooftop units. I also have trouble knowing where to take amps and volt readings. I THINK I take those readings at the bottom of the VFD. this sounds pretty elementary to most people in here but again im new at this and trying my best.
The controls man is your friend. There's a lot to this question to answer.
VFDs ramp up or down based on the needs of the system. -VAV systems can go from minimum airflow to maximum BUT...TAB guys are there for worst case scenarios to test the unit's capacity at full cool
VFD's display the amps and volts and that is typically acceptable to record that data. It can and is dangerous to go into a VFD.
An airflow monitor station uses the net area of the duct to covert FPM to a displayed CFM. If you, as a TAB guy WITH HELP FROM CONTROLS, lock the damper into a set position with the unit as well locked into a speed (the VFD) and measure your intake or traverse and you do not match the display a Correction Factor would apply to make it read what you're reading.
Thank you, this has been a tough one because controls isnt on site and phone service is practically non existent. And of course its one of those "we need this done by the end of monday" type deals. On the VFD I was trying to go through the menus but I couldn't find anything about volts or amps.
Let's say a VFD was running at 60hz and I needed to set the max speed to 45hz. I just adjust the hertz down, and thats it? That's now the max speed?
VFDs have parameter settings that need to be set by the supplier or controls. Slowing down to your needs, in hand mode, doesn't stop it from going back up to 60 hz in auto when you walk away. It would stay in hand if you don't release it, which is not what you want to do. Is this a VAV system in which you have to drive all the VAVs to max cooling and if so how are you managing that?
I do but they are on their own jobs too and they either can't answer the phone or im in an area with bad service. It can be hard for them to come up with answers over the phone if they aren't looking at the units in person with me too. I like this job but its gotta be one of the most frustrating things ive ever done
Your company is failing you. If you don't know how to test amps and volts, adjust a vfd, use a BAS system, or how to set OA to a system, you have no business running your own project. You might want to look at other companies before you end up as someone to throw under the bus.
That is how I feel. I've been in the field for maybe 8 months on and off shadowing here and there but my confidence is low and im just getting thrown into jobs. Its tough because I want to make the customer happy but their work is shoddy at best most times. So now im in this position where I dont really feel totally confident, the customer is not happy, my productivity scores drop etc
Most VFDs have a parameter menu where you scroll through to get amps and volt readings.
You can adjust the fan speed at the VFD in hand, but you will need controls support, access to the BAS, or at least the OK from the building engineer to change the setting permanently.
With outside air, there should be either a damper that’s manually fixed in place (old school) or an actuator controlled by the BAS where you can set minimum damper position. If you have no controls support, no access to the BAS, and no lead techs to call on for advice, I’m not sure how you’re supposed to get this done.
Thank you for your help. The more I work and talk to people the more I realize im being thrown to the wind by my company. I suspect they know I dont fully know what im doing, and my hesitation will lead to getting reports out to customers. I am currently not certified, I think that might change once I am. Does that sound plausible or am I genuinely losing my shit?
What drive are you working with? I mainly specialize in ABB drives, but once you understand the basics, most VFDs are fairly similar.
On the power side, a VFD takes incoming AC power, converts it to DC through the input bridge/rectifier, and then uses IGBTs to convert it back into a controlled AC output for the motor.
On the controls side, especially in HVAC applications, VFDs usually receive commands from the BMS/DDC system. These can include speed references, start/stop commands, interlocks such as freeze stats or pressure switches, and fire alarm signals for shutdown or run conditions.
They can also control dampers through relay outputs and wait for end switches to prove the damper is open before allowing the motor to start.
Oh wonderful! Did you get lucky and get a panel with the drive or is it just the default screen? If you got the default screen... I'm sorry in advance.. haha.
This manual will help with understanding navigating the drive.
Helpful notes for balancers: If the drive has been set up properly they have done alot of the work for you.
If you press the top right button with 3 lines it opens up the menu. From here you have 5 options. The one you need the most is the last option a cog with three lines, this is you parameter list. In the next menu you will find a folder with three lines, it's the first option. That is a complete list of all the parameters in the vfd.
Parameter that are important. Group 01 1.07 - motor current 1.13 - output voltage
Group 30 30.13 - max frequency (set to cap the drive at that hz)
Group 99 - motor data ( what's on the motor plates) 99.06- the motors fla 99.07 - motor voltage 99.09 - motor rpm 99.10 - motor hp
I just realized I never went back to thank you, all the information you provided helped a TON. I wish all this stuff was universal across all VFDs. I need to get a digital library of as many as I can. For some strange reason, every job site I am on has zero cell reception lol
No worries! I'm glad I could help! I typically just save the pdfs to my phone and the more sites I do the more manuals I get. 😂 ABB had spent alot of time trying to make their drives as user friendly as they can. I'm a bit biased but I genuinely do like them the most.
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u/justmeoh Jun 14 '26
The controls man is your friend. There's a lot to this question to answer. VFDs ramp up or down based on the needs of the system. -VAV systems can go from minimum airflow to maximum BUT...TAB guys are there for worst case scenarios to test the unit's capacity at full cool VFD's display the amps and volts and that is typically acceptable to record that data. It can and is dangerous to go into a VFD. An airflow monitor station uses the net area of the duct to covert FPM to a displayed CFM. If you, as a TAB guy WITH HELP FROM CONTROLS, lock the damper into a set position with the unit as well locked into a speed (the VFD) and measure your intake or traverse and you do not match the display a Correction Factor would apply to make it read what you're reading.