Ways to Program a Run Status for the VFD on an HVAC System

The entire team here at AirReps, which now includes the Control Products Group division, is dedicated to helping customers and partners with all of their HVAC needs, 24/7. That’s why when we had a customer reach out with an issue on their HVAC system with the VFD, we thought it might be pertinent to not only assist him with his issue, but also, to create a blog post that others could look to in order to rectify issues with their HVAC system as well.  

The question that has prompted our blog post today is fairly simple, but incredibly important when it comes to ensuring that your VFD is running properly. 

“Is there ever a time where the VFD status can say the pump is on, but the pump actually isn’t running? Whether from a burnt-out motor or any other reason. Will the VFD always recognize that the pump has failed?”  

This truly is a great question, and the answer contains imperative information for anyone with a VFD as an integral part of their HVAC system.  

To truly answer this question, we must go back to before the VFD even existed. Back in the old days, long before VFDs, customers would sometimes rely on Current Sensing Relays, often referred to as CSRs, in order to verify that amps were actually flowing through the motor wires. The CSR status gave us an indication that the motor was pulling amps and likely rotating, and to this day, many savvy users still add these CSRs to VFDs to show status.  

However, while in many cases helpful, these CSRs do need some adjustment. To ensure proper operation, you want them to go high when the motor is pulling a real load, and not necessarily show a run status in the event that the motor throws the belt or is otherwise operating under no-load conditions. The little screw pots inside the device can be finnicky, and they come in different sizes depending on amps that you need to read. 

Which leads to the question, can we just use the VFD programmable relay outputs to tell us the same thing? The answer is MAYBE, but there are several options that depend on your specific sequence.  

Below is a summary of the options, however, there are many, and I’m sure as soon as this article has been published, I will likely think of more options!  

Option 1: This option to check the VFD on an HVAC system is typically default from the factory. Set one of the relay outputs 5-40 to “[5] Running”.   This tells you that the drive has a start signal and is trying to run the motor.  

Advantage:  This is easy and it’s the default setting on most drives. This application is very user friendly, as it’s easy for many to understand, and best of all, it usually works. If a motor phase was lost or if the system had experienced a ground fault the VFD, the system would trip, and the status would drop. 

Disadvantage: In this application, there is no guarantee that any motor is connected, just that we are asking the VFD to run and it thinks it is running.  That is, if the motor throws the belts or is physically disconnected, you wouldn’t necessarily know. 

Option 2: Set relay output 5-40 to “[6] Running/no warning”.  This version is a slightly more advanced variety of option 1, as it just adds the information that we don’t currently have any VFD warnings, such as high temp or current warnings.  

Option 3: Set relay output 5-40 to “[8] run on reference/no warning”.  Even more information here, now the VFD has reached the commanded speed with no warnings.  If the speed is within 5% of the setpoint then the relay goes high. 

Option 4: Set relay output 5-40 to “[14] above current, high”.  Then adjust 4-51 to a current value that is slightly below the current at minimum speed.  

Advantages: This is now an electronic version of the current sensing relay, the VFD relay will only show a status when the current goes above the typical draw that you see above the motor minimum speed.  The motor is probably working and turning a load here. 

Disadvantages: The display will read “current high,” which might put some owners on high alert if done unexpectedly.  It doesn’t actually show as a warning, rather a message on the bottom of the display.  

Option 5: Utilize options one, two, or three, and in addition to those functions, add programing the “broken belt detection” sequence that is built into the VFD.  This will give you a “broken belt” warning, or trip if the amps are below a preset limit when the drive is running. 

Option 6: If you have completed any of the above options and read the actual motor current value over BACnet, then it will show up as AV5 and reads in amps. If the motor has amps and there are no other alarms reading, that is probably the best that can be done to see if the motor is doing work here. 

An important note to consider – on VFDs with bypass, if you are running in bypass due to a (hopefully) very rare failure in the VFD – how do we get the motor status? Since this is a rare and temporary emergency operating condition, you may not necessarily need a motor status here. If you manually switched it into that condition, and it is running full speed – if you really need a motor status here at the EMCS – you will probably need a CSR to tell you if the motor is spinning.  

As always, this blog post is meant to be helpful in operating your HVAC system, but this guide is not the end all be all in addressing issues with accessing your VFD. If you’re still having issues, or you’re not quite sure if your system is running properly, give our team a call. Whether you need a quick fix or it’s time to upgrade your entire system, someone on our team here at AirReps can assist!  

Using the jog mode on Danfoss VFDs

Recently, we had an interesting inquiry from a customer about having a VFD go to a preset speed from a single input. In this case, that would pre-empt the speed the drive is being commanded to in normal circumstances.  

For example, when an exhaust fan ramps up typically by building pressure, while it really should go to full speed on a local command from a fire panel or other gas sensor.  

In the example above, the VFD is utilizing jog mode, which can also be used in cases where the system has a single input that you want to use to start the motor AND go to a preset speed, with no other speed reference required.  

What sets jog mode apart? This setting is different than other modes, such as fire mode, which simply ignores all alarms, and runs the VFD until it burns up. Sometimes, the sequence doesn’t need that, and so you can adjust to something a little simpler, such as jog mode. While jog mode still monitors the safeties and alarms from the VFD, plus, it will trip if limits are exceeded. 

Once the drive has been started and is running smoothly, typical s/s signal on term 12/18 and speed ref on 53/55, users can add the “jog” signal to terminal 29, when utilizing the example share in this blog post. However, on some new drives terminal 29 may be defaulted to “jog” already, so make sure to take a look at your system to find what your VFD requires specifically.  

Here are some additional steps to setting your VFD to jog mode:  

Set 3-11 “jog speed” to the speed you want the vfd to run 

Set 5-13 terminal 29 to [14] “jog” 

At that point, a contact closure between 12/29 will put the drive into jog mode and run at the jog speed.  

While we hope this is helpful, please feel free to reach out if you’re still stuck putting your VFD into jog mode, or if these steps didn’t work for your specific VFD system. Our AirReps team is always here and ready to help you with all things HVAC.  

Danfoss Warning 34 Fieldbus Fault

Using your VFD should bring ease to your life, but we all know how difficult it can be when equipment is not functioning properly. Recently, we had an inquiry about Warning 34 on the Danfoss VFD, so we thought it would be the perfect topic for a blog post. Plus, we love a chance to make the customer experience easier while reassuring you with good news.  

And that good news is – while it may be stressful – Warning 34 on a Danfoss VFD won’t hurt anything in your overall system. While there are a few reasons why you might be greeted with this warning, in most cases, it will come up during the startup process, if the VFS has a communications option card, such as BACnet, but no communications are connected.  

After a couple of minutes without that communication, you will most likely see a “Fieldbus Fault W34,” or a communication failure on the card. While we understand this can be highly frustrating, it has no actual impact on the operation of the VFD unit. However, we understand that even with this in mind, you likely want the warning to go away as quickly as possible. So, we have put together a list of the top three steps you can take to reach a solution and get rid of the warning.

First, start with the simplest option. Connect to communication! Connect to the BACnet communication with some BACnet traffic.  

If that doesn’t help rectify the issue, power off the VFD and remove the card in order to restart the drive. This should prompt the VFD to show that there has been an “option change,” which should clear the alarm. This works well in cases where you do not and do not plan to use the card.  

If this option isn’t right for you, change function to 8-02, “control source,” from Option A to none. This way, the VFD won’t be looking for the control communications for the card, which means the warning will no longer come up on your VFD. 

The intention behind warning 34 is that if your VFD ever lost communications on the card, the system could trigger certain events. Events such as stop/full speed/pre-set speed, all things you might want your VFD to do if communications went down and control was lost. Having these measures in mind, plus ways to rectify them when they aren’t working as planned can help you to ensure that your VFD is running as smoothly and efficiently as possible. 

As always, if these steps don’t garnish the results you’re looking for, or if you’re having other issues with your VFD, please feel free to reach out to our team of HVAC experts here at AirReps today!  

 

 

Danfoss Proof of Motor Operation

In this technical HVAC blog post, our VFD expert, Tom Mahrer provides the step-by-step process needed to provide a “Proof of Operation” via the VFD Relay to show that the motor is operating with a desired range of motor Amperage. The goal of this process is to generate a drive alarm if the remote disconnect at the fan is opened, and the solution is setting up current monitoring programming and applying it to a relay output.

To begin, our team used the Comparators function in the Smart Logic menu to compare drive motor current to a fixed value.  We can then use a Logic Rule to combine both Comparators together and apply them to a Relay Output when the drive is commanded to run.

  • Using the Main Menu, scroll down to the 13-** Smart Logic menu 
  • Select 13-1* Comparators 
  • Select Comparators 0
    • Set 13-10 Comparator Operand to [4] Motor Current
    • Set 13-11 Comparator Operator to [0] < Less than
    • Set 13-12 Comparator Value to the high current limit.  This was set to 19.
  • Now select back and then select setup Comparators 1 
    • Set 13-10 Comparator Operand to [4] Motor Current 
    • Set 13-11 Comparator Operator to [2] > Greater than 
    • Set 13-12 Comparator Value to the low current limit.  This was set to 1. 
  • Now go back to the 13-** Smart Logic menu and select 13-4* Logic Rules 
    • Select Logic Rules 0 
    • Set 13-40 Logic Rule Boolean 1 to [22] Comparator 0 
    • Set 13-41 Logic Rule Operator 1 to [1] AND 
    • Set 13-42 Logic Rule Boolean 2 to [23] Comparator 1 
    • Set 13-43 Logic Rule Operator 2 to [1] AND 
    • Set 13-44 Logic Rule Boolean to [33] Digital Input 18 
  • Now go to the 5-** Digital In/Out menu 
  • Select 5-4* Relays 
  • Select Relay 2  
    • Set 5-40 Function Relay to [70] Logic Rule 0 

 Relay output 2 will now close when the motor current is above 1 Amp and Below 19 Amps, and the drive is commanded to run.  During operation if the motor current draw falls below 1 Amp or increases past 19 Amps the Relay 2 will open.  

As always, please reach out to AirReps at [email protected] with any further questions or issues with your HVAC system today!  

Danfoss VFD Fire Mode

In the majority of our blog posts, we give tips, tricks, and guidelines that allow users to test them out on their own before having to go through the hassle of making a call in order to keep their HVAC system running smoothly. In this case, we give these tips with the express warning that before you try any of them out, you give our team, or your go-to HVAC experts a call.  

The Danfoss VFD has the ability to program an input a “fire mode,” meaning that the drive will ramp up and continue to run, regardless of any alarms.  

While some people like to refer to this as the “run until destruct mode,” and for good reason, today, we will be operating under the true name of “fire mode.”  

This setting is more frequently used for circumstances such as stairwell pressurization fans, where you don’t want too much pressure, as this would keep the stairwell doors from opening, but enough pressure to keep the fresh air flowing into the stairwell so that people can evacuate.  

In cases like this, you would want your VFD to ignore all of the internal alarms to keep the air flow going as long as possible in cases where it’s life or death.  

As you can imagine there are some risks to this. In many cases, the risk is that during routine testing of this feature, the VFD could be forced to exceed the programmed safeties and cause equipment damage, so please use caution here, and always consult with an HVAC expert!  The manufacturer can’t warranty a VFD that has been overloaded or damaged by fire mode testing.   

However, here we have some of the points that are useful when running these types of tests, or when setting your VFD up with this mode.  


24-09 Fire Mode Alarm Handling 

Set this point to [2] “trip at all alarms-test” during setup and testing, this will keep you from damaging the VFD or motor during testing 

Change to [0] “trip and reset at critical alarms” ONLY when you are ready to arm the system for tenants 


5-11 Digital Input 19 (or pick any available input) 

Set to [37] “fire mode”, a contact closure on this input puts the vfd into fire mode 


24-00 Fire Mode Function 

Set to [1] “Enabled” 


24-05 Fire Mode Preset Reference 

Set this to the value that you want the fan to run—usually the balancer will tell you this value based on pressure measurements from the stairwell 

You can also set a reference to come from an analog signal, call us to help set this up. 

As we mentioned above, this blog outlines a very important, but potentially damaging mode for a VFD. Please call us before testing or programming your VFD to ensure that your system isn’t poorly impacted. Our team of AirReps HVAC experts are always here to help!  

VFD sizing and NEC

When working with your VFD, the motor, of course, is a vital piece of the puzzle in making sure that your system is running smoothly. Often times, we have clients and partners ask us about VFD sizing in terms of the motors. 

In general, when it comes to the Danfoss VFDs, motors are sized to ensure that the VFD system has the ability to slightly exceed the max amp values, as show in the NEC Table 430-150. That NEC 430-150 table tells us a great deal of information, but the most important when it comes to motor sizing can be found in the excerpt below.  

  • The MAXIMUM amps that are allowed for a given HP motor (see 7.6amps for a 5hp/460v motor).  Most modern high-efficiency motors will be less than this max value by 10-30%. 
  • Low RPM motors may need MORE amps then specified on this table— the table is for standard 1800rpm motors.  If you remember your high school physics (heh!),  HP = Torque x RPM.  Since the RPM is lower, you need more torque to get the same HP.  To get more torque you need more amps from the VFD.  We see low RPM motors sometimes on direct-drive fans.  Verify the motor FLA on low rpm motors before ordering.  
  • Multi-motor applications may need to bump up one VFD size to accommodate the amps— To drive two 5hp/460v motors needs 7.6a + 7.6a = 15.2amps max.  If you look at the 10hp/460v value in the table, it is only 14amps max.  In this example we may need a 15hp VFD to run those two 5hp motors. 

In summary, while many in the industry frequently turn to this table for budgeting, it’s important to remember that users should also always utilize the Motor FLA from the data plate to ensure that the VFD is sized appropriately. It’s so important that it bears repeating, always use the Motor FLA to verify that the VFD is the correct size. It’s incredibly important in ensuring that your VFD system can run smoothly, effectively, and safely.  

 

As always, if you’re struggling to get the correct measurements or fit, or if you’re just not confident in your findings, reach out to our team for further assistance. Team AirReps is here for all of your HVAC system and HVAC design needs, and our experts are always ready to help!  

Viewing the status on Danfoss VFD inputs

Recently, our Control Products Group team had an inquiry from a customer who was asking how to view the status of the inputs on a Danfoss VFD, as they couldn’t quite figure out when the VFD system was on or off. While this may seem confusing at first, here at AirReps, we’re experts in HVAC, so of course we have advice on an easier way to check the status of your VFD system by utilizing the display.

First, head over to your HVAC system to your VFD and navigate to parameter 16-60, Digital Input. As a reminder, the display on the Danfoss VFD is binary, showing the status of all the inputs at that moment. Zero means the input is “off” and a one means that the input is “on”.

In order to decipher which digit corresponds to which input, we suggest you take a look at the chart below from the programming guide for the Danfoss VFD.

As a note, when utilizing this chart, input 18 is typically used for the start/stop. According to the chart, input 18 is “Bit 5”, and you count from the right starting with “Bit 0.” In summary, input 18 is going to be the sixth zero, for more help, see the picture below.

Here at AirReps, we know that these simple issues can cause major stress and frustration when not working properly. If you need any further assistance, please feel free to reach out to our team of experts today!

VFD HVAC issue and assistance – Jumpy Analog Inputs, Plus Input 53 Speed Reference Filtering

Here at AirReps, our Control Products Group division has an incredible legacy of creating blog posts to directly help customers and partners. This particular issue was impacting a customer named Ryan who was looking at his VFD one morning when he noticed an issue he had never seen before. When he reached out to our team, we were happy to help.

Ryan reported to the Control Products Group team that while looking at his VFD, he noticed that the analog input from the building control system looked “jumpy,” which obviously, doesn’t look too good!

Before we jump into this specific issue, for those who may not be aware, the most untilized definition of a Variable Frequency Drive in the HVAC industry would describe it as an electrical device, used as a fan accessory, to increase and decrease the rotations per minute, or RPM, of an alternating current, or AC, motor.

While seeing the analog input looking “jumpy” may seem like cause for alarm, this isn’t completely uncommon. This is something our team here at AirReps notices from time to time. In these cases, when looking at the VFD, we occasionally see that the 0-10v signal from the EMCS is moving around constantly by fractions of a volt. Again, while this may seem like cause for alarm when it comes to your VFD system, it truly doesn’t do any damage to your system, and won’t hurt anything long term either.

A VFD isn’t like a damper actuator, where hunting will wear it out. So, while it may be a bit annoying, the VFD isn’t harmed by this issue. However, in this case, our customer didn’t enjoy seeing the display constantly changing between “running on reference” and “ramping” like it didn’t make a setpoint. As mentioned above, we’ve seen this before, so we know that while it may not harm the system, it is something that customers would rather not have to deal with, with systems new or old.

While no one may know where these tiny voltage changes come from, we can help you to smooth them out, so your VFD input is back to running smoothly. Simply change the default filtering in parameters 6-16 from .001s to around 1s or so. Remember, if you set the filtering too high, it will slow down the VFD response to reference actual changes, so make sure to follow these instructions carefully. This should help to smooth out those little bumps and help to get your VFD system running perfectly again.

If you’re still struggling with your VFD system, or if you’re looking for even more help when it comes to your HVAC system, reach out to us here at AirReps! We’re happy to help, or to get started on your custom HVAC design today.