# What’s different about an “HVAC” drive?



## MDShunk (Jan 7, 2007)

Firmware. 

The ones I've seen specifically marketed as HVAC drives have modified firmware that make setup easier and more sensible for HVAC installs, has many parameters factory defaulted to better suit and HVAC application, and gets rid of the 10,000 other parameters you'll never need. Many have some of the analog I/O preconfigured for common process signals they're likely to follow in an HVAC application. Some will have the comm card preinstalled for LON or BACnet and such if you're going that route. 

There's nothing an "HVAC drive" is going to do for you that the bog-standard version of that same drive won't do, but it will be a lot easier with the preconfigured HVAC version. Myself, I don't much like drives with custom firmware and stick to stock standard catalog items. I'm in an environment where ready spares are important, and if I need a 2hp drive, I want to use that same 2hp drive wherever I please and not have to worry about custom firmware.


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## SpaceMonkey (Sep 19, 2018)

Thanks. Debating on either getting an AB or an ABB Hvac drive for a supply fan. Having trouble finding an ABB distributor, but I have a source for AB right in town. 


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## gpop (May 14, 2018)

We got sent a abb hvac drive by mistake. The software parameters are diffrent to the point it was unusable for what we required.


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## MDShunk (Jan 7, 2007)

SpaceMonkey said:


> Thanks. Debating on either getting an AB or an ABB Hvac drive for a supply fan. Having trouble finding an ABB distributor, but I have a source for AB right in town.
> 
> 
> Sent from my iPhone using Tapatalk


They're both fine brands, but I'd say there's value in harmonizing the drive brand with what you have deployed at that location already for more expeditious future MRO. Either that, or a brand that your techs are most familiar with. If it's from any major brand, it won't suck, but I just see the benefit of using what you have already or what you know the best.


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## JRaef (Mar 23, 2009)

Drives designated as “HVAC” are almost always exclusively only rated as Variable Torque loads. The difference is in the VFDs capacity to deliver overload current. Because a VT machine, ie a centrifugal pump of fan, cannot be overloaded if designed properly, there is no need for the VFD to need the ability to deliver overload current, unless there is a problem in which case you WANT to shut down. So you will see the OL capacity in a VAriabke Torque /Normsl Duty rated drives is significantly lower than that of a Constant Torque / Heavy Duty rated drive. So VT is typically rated for 110% overload for 30 seconds, 150% for 1 or 2 seconds, CT rated drives are typically rated at 150% for 1 minute, 200% for 3 seconds. That allows a CT / HD rated drive to make the motor deliver maximum torque for short bursts, VT /ND drives cannot accomplish that, but if used for centrifugal machines, should never be asked to.


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## SpaceMonkey (Sep 19, 2018)

JRaef said:


> Drives designated as “HVAC” are almost always exclusively only rated as Variable Torque loads. The difference is in the VFDs capacity to deliver overload current. Because a VT machine, ie a centrifugal pump of fan, cannot be overloaded if designed properly, there is no need for the VFD to need the ability to deliver overload current, unless there is a problem in which case you WANT to shut down. So you will see the OL capacity in a VAriabke Torque /Normsl Duty rated drives is significantly lower than that of a Constant Torque / Heavy Duty rated drive. So VT is typically rated for 110% overload for 30 seconds, 150% for 1 or 2 seconds, CT rated drives are typically rated at 150% for 1 minute, 200% for 3 seconds. That allows a CT / HD rated drive to make the motor deliver maximum torque for short bursts, VT /ND drives cannot accomplish that, but if used for centrifugal machines, should never be asked to.


Thanks for the response!

So would a small powerflex (4M family), be an okay choice for an air handler supply fan? Not sure it thats considered a CT/HD drive. I do know that it is not marketed specifically for HVAC.


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## paulengr (Oct 8, 2017)

Fans and pumps have torque basically proportional to the square of speed so yeah extreme variable torque. The are also nonregeneratjve applications so a simple diode front end suffices. Control is uncritical so V/Hz is just fine.

The 4M was made super cheap to compete with the Altivar 16 at the time, another dirt cheap drive. It was discontinued due to high failure rates (lots of warranty claims). The 40 was a lot better. The 4M is V/Hz only, no comms, diode front end, almost no filtering, very weak processor, pure PWM instead of space vector output, no internal protection. Total crap compared to even a current model KB Electronics but when you could get a 1 HP drive for $100 with the octagon logo what's not to love?

Current HVAC drives simplify the settings with application profiles. They often have minimal filtering because it's a very price sensitive market (noisy). Now that vector control is almost free you see vector or pseudo-vector control to decrease voltage at low loads to reduce power consumption by effectively reducing V/Hz tendency to overflux even in HVAC drives.

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## lmicky (Dec 3, 2018)

simple explanation: its all about your load characteristic e.g. a fan or pump load will have 'square' caracteristic i.e. at full speed you have full load, at half speed you have 1/4 load ect...

It all depends which type of load you will supply...


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## JRaef (Mar 23, 2009)

SpaceMonkey said:


> Thanks for the response!
> 
> So would a small powerflex (4M family), be an okay choice for an air handler supply fan? Not sure it thats considered a CT/HD drive. I do know that it is not marketed specifically for HVAC.


Below 10HP most drives are always CT rated, there is not enough savings going to VT ratings to worry about at that size. That is true for almost all brands of drive. The PF4M is a CT rated drive.




pauleng said:


> The 4M was made super cheap to compete with the Altivar 16 at the time, another dirt cheap drive. It was discontinued due to high failure rates (lots of warranty claims). The 40 was a lot better. The 4M is V/Hz only, no comms, diode front end, almost no filtering, very weak processor, pure PWM instead of space vector output, no internal protection. Total crap compared to even a current model KB Electronics but when you could get a 1 HP drive for $100 with the octagon logo what's not to love?


Almost everything in this paragraph is not true. The PowerFlex 4 preceded the Altivar 16 drives by about 2 years and is the most widely used component class drive in the world. The 4M is the CURRENT version only because the plain PF4 is now more expensive than the PowerFlex 523 drive and is not Vector capable. Even so, none of the PowerFlex small drives have been discontinued. What A-B does is make older versions that have been replaced with newer ones "unpalatable" by making them more expensive than the new versions. But if you still want a PF4 or 40 as a replacement, they are still in production.


They are keeping the PF4M in play as a current product because it is the lowest cost drive A-B offers, for people who just want a "shaft turner" and because it has what's called "feed-through" wiring, meaning line in the top, load out the bottom, something that has gone away in most small drive designs now. For small machinery OEMs that can't change their panel designs, this is still desirable. It does have communications built-in (Modbus RTU) and you can add comm cards for just about any other protocol on the market. It does have internal protection features, but yes, it is intended to be a low cost drive in a very small package, so it doesn't have a lot of features. If you want features, use the PF520 series.


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## Switched (Dec 23, 2012)

priyankagupta said:


> HVAC deal with heating during winter and cooling during summer also when the outside temperature is cool it will allow the cool air to enter the room making it to function as a ventilation device.​
> HVAC products are supposed to maintain comfort through out the year irrespective of temperature outside that is if your using a HVAC unit and set the room temp for 24C the HVAC unit will do the following.
> TO MAINTAIN 24C FOR 365 DAYS.​
> *From Nov to March* As its winter the HVAC system. Will work on heating mode There by if outside the temp is 5 or 6 degree the HVAC system will keep the room warm at 24C.​
> ...


AWESOME!

But what happens in July, August, September, and October? Do you just open the windows and run around in underwear to save money on the HVAC bill?

I think the government should pay for my HVAC bill, I tried to pay with my EBT card but they wouldn't accept it. I don't understand, because the place I bought my Mercedes S500 from takes it. 

What's your thought on that?


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## SpaceMonkey (Sep 19, 2018)

I must’ve cued in some hvac spambots or something haha


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## splatz (May 23, 2015)

From @MDShunk's reply above.



MDShunk said:


> They're both fine brands, but I'd say there's value in harmonizing the drive brand with what you have deployed at that location already for more expeditious future MRO. Either that, or a brand that your techs are most familiar with. If it's from any major brand, it won't suck, but I just see the benefit of using what you have already or what you know the best.





priyankagupta said:


> They're both fine brands, yet I'd state there's an incentive in orchestrating the drive mark with what you have conveyed at that area as of now for progressively quick future MRO. Either that, or a brand that your specialists are most acquainted with. On the off chance that it's from any significant brand, it won't suck, however I simply observe the advantage of utilizing what you have as of now or what you know the best.


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## Mr. Lacarno (Jan 2, 2019)

I see now... This MDShunk guy is an Indian spammer!


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## splatz (May 23, 2015)

Mr. Lacarno said:


> I see now... This MDShunk guy is an Indian spammer!


I KNEW IT! I had a funny feeling about him. 

I give credit though, investing what 30 - 40 years in the trade to develop a sleeper cell is some real spammer commitment.


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