November 9, 2016 at 5:09 pm #7910
What type of VFD is recommended for running large commercial type fans in HVAC applications?
I have 25 to 100HP motors coupled to supply and return fans in our office building that are aging and will need replaced in the near future.
Any help would be appreciated.
November 9, 2016 at 5:39 pm #7911
Hello Fred, many different brands of drives have the ability to run pumps or fans.
It is called a VT (Variable Torque) mode the drive is put in for running your type of application. It will allow the VFD to save energy at reduced speeds. For additional information I suggest talking to 1 of our Product managers Randy Barbret at 248-336-4591 or Dave Anderson at 248-336-4409. These guys can provide very specific information on different brands of VFDs we sell here at Galco that would be best suited for your needs.
Hope this helps and thanks for looking us up on the Galco forum.
November 10, 2016 at 10:19 am #7912
Hi I was just reading this post and wanted to know what the heck is Variable Torque?
November 10, 2016 at 10:34 am #7913
Hello Buddy and thanks for checking out our forum.
In response to your question about Variable Torque, it is a mode of motor control operation that allows an AC drive to reduce energy consumption when running at reduced speeds. Many AC drives have 2 basic modes of operation, Constant Torque and Variable Torque, and will have different Overload and Horse Power ratings based on which mode of operation you choose to run your drive in. Ok?
November 10, 2016 at 10:40 am #7914
Ok yah I’ve seen this on drive label before and always wondered why, its the same drive chassis right, so why do they have different ratings?
November 10, 2016 at 10:56 am #7915
Buddy that’s an excellent question, and I’m glad you asked.
You may have noticed on those labels that the VT rating is higher HP than the CT rating. This is because the VT drive kind of gets a break from hard work more than the CT drive does. Now I’m going to get a little technical on you. All AC drives have what is know as a volts to hertz ratio ok. They accomplish through what is called PWM (Pulse Width Modulation) technology. PWM allows a control scheme to produce a variable voltage at any motor operating frequency it wants to from a fixed voltage source (the DC Bus). So now what all drive mfg’s do is say, ok what kind of load/work are you going to do with our drive. VT loads are basically any fan or pump type application. Pretty much all other applications are CT, like machines or conveyors that need variable speed.
November 10, 2016 at 11:16 am #7916
Hello guys, just found this post and am curious myself about the differences of VT and CT. John can you tell us more about why a drive does less work and how it is able to save energy in VT mode?
November 10, 2016 at 11:19 am #7917
Yah I was wondering the same thing, how can it save energy when it has a higher HP rating?
That just doesn’t compute so to speak, lol
November 10, 2016 at 11:47 am #7918
More good questions, I love it.
Ok, first of all you need to understand the nature of a Fan or Pump load. I will reference the fan for sake of argument today, ok. We will also assume that the drive is going to go to base speed as max speed too. Between 0 and 60Hz output of the drive the voltage is going to be linear, so at 15Hz we have 25% of the rated motor voltage, at 30Hz 50% voltage, 45Hz 75% voltage to 100% volts at 60Hz for US Nema rated motors. Variable torque means at 30Hz the voltage will be below 50% because a fan does most of its work between about 70% and 100% of its rated speed. Pumps are the same way. Below 70% of rated RPM the amount of work it is doing drops off rapidly. This is how it is able to save energy at reduced speeds. The drive simply isn’t working very hard at all.
Is this better?
November 10, 2016 at 11:52 am #7919
Much better, thank you John for your detailed explanation.
November 10, 2016 at 11:55 am #7920
So am I to understand that since the drive isn’t working as hard it can be rated for higher HP?
November 10, 2016 at 11:59 am #7921
Yes Rick, that is precisely what I mean. Almost seems backwards though doesn’t it?
Another thing I didn’t mention yet was the OL (Overload) settings. A VT drive will only 110% OL for about 1 minute, and a CT drive will allow 150% for 1 minute, depending on the drive mfg, the series and its intended use. So higher HP rating means less OL for a given time limit of 1 minute.
Hope this helps you all.
January 27, 2017 at 10:57 am #8284
Hi I wanted to know what brands do you sell for HVAC applications?
January 27, 2017 at 11:05 am #8285
Hello TT, well lets see, we do have a couple brands that build drives specific for HVAC applications;
Siemens BT300 series is 1
Eaton H-MAX series is another 1
ABB makes the ACH series as another yet
They are all very good at what they do, but it is best if you speak to 1 of our product managers about your specific needs to come up with something that makes sense for you, ok?
January 27, 2017 at 11:06 am #8286
So is this all you sell is 3 brands for HVAC?
January 27, 2017 at 11:14 am #8287
No we have almost 30 different brands of drives we represent here at Galco and many different models in each brand that make for thousands of different drives we stock here. Between the drives and all the other products we rep here, we have over 2.2 million items in stock, and we ship 500-1000 of them each day.
January 27, 2017 at 11:24 am #8288
wowe dude thats alota stuff, sorry man didn’t mean to sound like I was degrading you guys but just looking for a good supplier for this kind a stuff, ok?
January 27, 2017 at 11:25 am #8289
Ok TT no problem, and thanks for asking Galco
December 23, 2017 at 5:48 am #10070
Just from a casual glance at the ASHRAE Handbook, Fundamentals it looks like R-407c may be more effective than R-410a. However, pressure/enthalpy diagrams are different which means that the existing system may have to be significantly altered. You know more about the system than I do, work through the equations and determine what needs to be changed.
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