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!