Why is there an inverter on an air conditioner?

I know that Jraef knows inverters as well. I work with everything from basic open loop V/Hz scalars, to closed loop, high speed vectors. Just to stick with the HVAC topic as this subject can get intense, indeed both air handler blower motors, and compressor drives are moving towards inverter control. One in which I have been begging for for 20years. It does raise the bar on potential failure modes, and nearly a guarantee that VERY few HVAC techs could ever troubleshoot one, so replacement is the recipe.

The VFD architecture for HVAC hugs the more basic side as a typical rectifier circuit, and an IGBT output stage. However, some are exploiting the benefits of back EMF for open loop vectoring, which can give feedback to actual motor speed, thus the output waveform can be modulated to optimize slip and ensure speeds are correct. It can also help do a health check on a motor via current and speed so a drive would reject a motor and lockout if predicted vs actual parameters are out of range, as in a failed motor or open line set.

Indeed these inverters can and do overspeed compressors well beyond 60hz, and this is a unique advantage in the designs, where a smaller compressor can be used, saving money! As with all VFDs, you get things like soft starting and current monitoring. But another huge benefit is reduced mechanical stresses of the old WFO methods, which cause extreme torque violence on start up.

Another unique benefit to a VFD controlled compressor is torque boost where the waveform is manipulated to optimize for torque, which cannoth othewise be achieved with just V/Hz scaling. Consider the slip of a compressor motor at 0prm, vs a smack of 60hz? That is a hard start! But with creative IGBT strategy, you can get way more acceleration torque for the motor.

What sets these HVAC inverters apart from standard industrial VFDs is actually a lack of features. They are purpose built so they blow out all the needless features like I/O and advanced parameter sets. They are proprietary! And that is sort of a turn off for me. And no question they are built to fail. Cheap caps, boards, etc. But even my refrigerator is VFD controlled. It throttles the compressor speed to snail, which only sips power. No big inrush, just nice easy starts.

Now the air handler ECM blowers are another matter because they built the VFD right into the motor so you get to buy the whole damn thing! AND they fail on the regular! I want a separate module because probably 90% of the time, those motors are not bad, but you get to pull the whole thing to find out.
 
Fastlane:

The older (1st generation ?) ECM blower motors had a "field replaceable" electronics pack, which an guy with an electronics background COULD field repair ( replace a blown thermistor and maybe a couple capacitors ). I did this a few times, as the upper board was only the power supply. The newer motors are potted, and this cant be done......... If you are talking about the older ECM's feel free to message me and I will give you the parts list...


Howard
 
That is why GFCI (Ground Fault Circuit Interrupters) problems will never be solved, they don't like VFD (Variable Frequency Drives) being used in many appliances today.
 
g-and-h_electric said:
Fastlane:

The older (1st generation ?) ECM blower motors had a "field replaceable" electronics pack, which an guy with an electronics background COULD field repair ( replace a blown thermistor and maybe a couple capacitors ). I did this a few times, as the upper board was only the power supply. The newer motors are potted, and this cant be done......... If you are talking about the older ECM's feel free to message me and I will give you the parts list...


Howard
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yeah, I've seen em but to be honest, most techs are doing good to find the right setting in their meter. PCB level repair ain't gunna happen. BUT, it severely pizzed me off that they stuff the guts and highest failure mode device in the motor! If you work on these, you will understand that just getting the damn inverter off that motor would let it live, plus making it reasonable to replace or fix.

As for standard split systems with an inverter driven compressor, they've yet to find a way to pack that in one screwjob package, but i'm sure it's coming. Hell, 20 years ago I was trying to just buy a simple, low tonnage 3P split so I could add a VFD.....Nope. Those just don't exist. I will tell you something, since most of the Copelands are 50/60hz rated anyway, that means I can walk one down there to 50 without any issue, and probably 45hz, meaning I could basically build a 2 stage system on the cheap.

And if you want to get 'real' cheap, you could just as easy step a PSC blower down with a relay. Oh the conspiracies.
 
Mostly marketing. When these things were introduced they needed a term to distinguish them from legacy units. "VFD driven" was too much to explain to consumers. So Mitsubishi and others settled on the word "inverter" to described their new tech.
 
BarryO said:
Mostly marketing. When these things were introduced they needed a term to distinguish them from legacy units. "VFD driven" was too much to explain to consumers. So Mitsubishi and others settled on the word "inverter" to described their new tech.
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That word has been used well before using them in HVAC gear. Hell, go look at the Honda EU series generators from 25 years ago. Says "inverter" right on them.
 
fastline said:
That word has been used well before using them in HVAC gear. Hell, go look at the Honda EU series generators from 25 years ago. Says "inverter" right on them.
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Yeah but those undeniably have inverters and are not variable fequency.

I don't really buy that 'inverter' is better marketing than 'VFD driven' from an *explanatory* viewpoint, but maybe it just focus-grouped better. Most consumers have no idea what either means so it comes down to vibes.

VFDs are a subset of inverters.
 
jaggedben said:
Yeah but those undeniably have inverters and are not variable fequency.

I don't really buy that 'inverter' is better marketing than 'VFD driven' from an *explanatory* viewpoint, but maybe it just focus-grouped better. Most consumers have no idea what either means so it comes down to vibes.

VFDs are a subset of inverters.
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Invert in the electric world literally means "transform DC to AC", so ALL VFDs are "inverters". Hell, if you work around them, we use the terms interchangably. Drive - inverter - VFD
 
Side note: the large hospital/research center that I retired from had over 500 VFD'S. Most drive manufacturers state the DC buss capacitors are rated for 75,000 hours we had probably close to a hundred VFD'S with over 125,000 hours. So they ran 24/7 for 15 years or more savings an incredible amount of money on power usage so am a huge fan of inverters ,drives, VFD'S even soft starters. I only wish that I would have wrote down hours , KW hours and motor ampere to figure out how much they saved as compared to a motor connected to a starter that is usually running at least with a 85% load. Heat & dirt along with loose connections are the biggest killers of drives & inverters. Only wish that drive manufacturers would use larger size wires especially on drives with three jammed in contractors behind a plate. While performing IR scans contactor area would be at least 15 to 20 degrees warmer then air conditioned space. They waited at least five years to purchase small air compressors that we kept on our PM carts. Even in clean air conditioned rooms was amazed the dust storm kicked out of VFD'S first time we blow them.out. Every VFD was blown out 1 to 4 times a year and in larger ones removed & cleaned filters on air intake fans. When contractors were performing demo.or producing dust we made them tape on 11/2" thick filter material on sir intake and replace it at least once a week. Was amazed when they retrofitted six twenty year old large boiler with VFD'S. They took an entire day on first change over where they monitored stack temperature and air samples while running boiler from 75# 's to normal 125#'s of steam pressure.
 
fastline said:
yeah, I've seen em but to be honest, most techs are doing good to find the right setting in their meter. PCB level repair ain't gunna happen. BUT, it severely pizzed me off that they stuff the guts and highest failure mode device in the motor! If you work on these, you will understand that just getting the damn inverter off that motor would let it live, plus making it reasonable to replace or fix.

As for standard split systems with an inverter driven compressor, they've yet to find a way to pack that in one screwjob package, but i'm sure it's coming. Hell, 20 years ago I was trying to just buy a simple, low tonnage 3P split so I could add a VFD.....Nope. Those just don't exist. I will tell you something, since most of the Copelands are 50/60hz rated anyway, that means I can walk one down there to 50 without any issue, and probably 45hz, meaning I could basically build a 2 stage system on the cheap.

And if you want to get 'real' cheap, you could just as easy step a PSC blower down with a relay. Oh the conspiracies.
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PSC likely less efficient than frequency driven. particularly when not running at speed corresponding to incoming frequency. But they are typically small motors to begin with and the question from owner's perspective is how fast to I recover my return on investment as the losses may be rather low. They likely less expensive to replace/repair as well.
 
garbo said:
Side note: the large hospital/research center that I retired from had over 500 VFD'S. Most drive manufacturers state the DC buss capacitors are rated for 75,000 hours we had probably close to a hundred VFD'S with over 125,000 hours. So they ran 24/7 for 15 years or more savings an incredible amount of money on power usage so am a huge fan of inverters ,drives, VFD'S even soft starters. I only wish that I would have wrote down hours , KW hours and motor ampere to figure out how much they saved as compared to a motor connected to a starter that is usually running at least with a 85% load. Heat & dirt along with loose connections are the biggest killers of drives & inverters. Only wish that drive manufacturers would use larger size wires especially on drives with three jammed in contractors behind a plate. While performing IR scans contactor area would be at least 15 to 20 degrees warmer then air conditioned space. They waited at least five years to purchase small air compressors that we kept on our PM carts. Even in clean air conditioned rooms was amazed the dust storm kicked out of VFD'S first time we blow them.out. Every VFD was blown out 1 to 4 times a year and in larger ones removed & cleaned filters on air intake fans. When contractors were performing demo.or producing dust we made them tape on 11/2" thick filter material on sir intake and replace it at least once a week. Was amazed when they retrofitted six twenty year old large boiler with VFD'S. They took an entire day on first change over where they monitored stack temperature and air samples while running boiler from 75# 's to normal 125#'s of steam pressure.
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Hi Garbo. I had similar experience but, in my case, it was based on industrial experience and mostly greater voltages up to 11k,
 
kwired said:
PSC likely less efficient than frequency driven. particularly when not running at speed corresponding to incoming frequency. But they are typically small motors to begin with and the question from owner's perspective is how fast to I recover my return on investment as the losses may be rather low. They likely less expensive to replace/repair as well.
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There isn't a significant eff boost in VFD motor loads. The eff comes from the variable capacity, and as mentioned, pushing a compressor beyond 60hz, which allows a smaller compressor to do the job. But anytime you make a volumetric refrigerant change, the airflow should be adjusted, thus ECM blowers were part of the equation. There are 2 stage systems in which the compressor has a partial bypass valve.

As mentioned, there are multiple advantages to VFD controlled systems, but that does come with additional failure points, and techs that probably won't be able to troubleshoot beyond reading the blinkies and calling the OEM.
 
fastline said:
Invert in the electric world literally means "transform DC to AC", so ALL VFDs are "inverters". Hell, if you work around them, we use the terms interchangably. Drive - inverter - VFD
Click to expand...
All VFDs can be called inverters. Not all inverters are VFDs. Like I said. So, no, not interchangeable. We solar guys installed thousands of inverters and would correctly never call them VFDs.
 
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