What makes them so different in the first place?
Most heat pumps are either on full blast, (sucking up as much electricity as they need to operate on max power) or they’re off. Off is actually a “standby mode”, until the next time they try and burn a hole in your electric budget. Mini splits don’t take that approach at all…
Mini splits use what we call “inverter drive technology”. The basic explanation of the inverter drive is simply this. They operate less like an on/off switch, and more like a volume knob than can be in any position within their range. They can run at 100% capacity, 25% capacity, or anything in between. Some models can even exceed their rating, and run at 110%. They use built in sensors and control boards along with some specialized software to “decide” the most cost effective way to operate. They don’t “slam” on at full capacity, rather they’ll take their time ramping up to whatever capacity they need at the moment.
They can decide to reduce or increase outdoor fan speeds to build more or reduce liquid line pressure as needed. They can make decisions based off of their sensor readings that allows them to do the job with the lowest electrical usage possible.
What's the upside to the inverter drive?
Mini splits (ductless systems) are extremely energy efficient. Their ability to ramp up to capacity is a huge energy saver alone. With standard heat pumps, it’s common to see them pull 80 or 90 amps during start-up, then fall back down to 12 or 13 amps during normal usage. This really matters because amps are part of how you calculate your kilowatt hours, which is what you’re paying for on your electric bill. Multiply that by the 60 or 70 times a day that your heat pump cycles on, and you’ve got yourself a hefty power bill!
The inverter technology inside of a mini split will never have that excessive amperage during initial “start-up” because they slowly ramp up to capacity. They also usually operate far below their maximum output. So not only are they able to skip that “start-up surge”, they use reduced power during normal operations.
Another huge power saver is their ability to make heat well below what a standard heat pump can do. Standard heat pumps lose efficiency as the outdoor temperature drops. When it gets to be around 30 or 35 degrees outside, they’ve completely lost the ability to heat your home, so they use back up heat. (You’ve probably seen the “aux heat” setting on your thermostat, and this is the back-up heat.) For most systems, this is electric heat strips… These heat strips use a massive load of power to operate, so even if you only had a day or two that was well below freezing, it’s possible to see your electric bill double for the whole month! Mini splits can make heat pump heat at 100% efficiency all the way down to -5 degrees outside! In fact, they can still heat your space far below the -25 degree mark before they’ve lost enough efficiency to need the back-up heat! For the North Alabama market, it would be an extremely rare moment for an inverter drive not to be providing all the heat you need.
Did you hear that? Of course not! Mini splits are exceedingly quiet. In fact, almost every customer that has ever been present for the initial start-up has asked “is it on”. The virtual silence makes them a great option when you need a quiet space.
The technology inside of these things is leading the way in terms of sipping power. It’s so good, inverter tech is making its way over to the ducted system, and barring some “disruptive new gadget”, I’m confident that all new air conditioners will be using inverters sooner rather than later.
There are lots more advantages, but this is already going to be a long read, so we’ll leave it here for now.
It can't all be good, can it?
Like most anything else, there are some trade-offs to get all these goodies. First up is cost. Ton for ton, inverter systems cost a good bot more than standard heat pumps. In addition to the up-front cost, the maintenance cost is generally higher as well.
The complexity can be a problem. There are a whole lot of different manufacturers, and finding the information you need for troubleshooting can be next to impossible for too many brands. For example, you may show a fault code that isn’t listed in the manual, and unless you can get their tech support on the phone, an “on the spot” diagnosis is out of the question. Even worse, service request voicemails and emails just might go unanswered… It’s just a fact of life with most things; increased complexity means decreased dependability – at least, for a while until the developers figure out a way to make it better and better. There’s no way to avoid the complexity, but the brands with lack-luster support can be sidestepped by asking your HVAC professional what manufacturers provide great service after the sale.
They almost always use flare fittings for refrigerant line connections, and the flares frequently leak! It certainly improves your odds if you use a torque wrench, and approved flaring tools, but even then, leaks are a reality for a great many “properly made” flare fittings. Lately, I’ve started using a gasket made specifically to solve this problem, but the jury is still out on this one…
So what's the verdict?
Mini splits definitely have their place. Attic rooms over garages, newly enclosed sunrooms, small work shops and garages are all places where a mini split just might be the best option, but I believe in managing expectations. Mini splits check a lot of boxes, and solve a lot of problems – So long as you know what you’re getting into, I’m happy to install one for you. Just reach out anytime!