Does the Inverter Type Split AC Energy Efficiently?

It is not just room temperature but humidity that needs to be low. So once the room temperature is acquired, a normal system would cycle off, with no control of humidity. In this system keeping the operation at maximum can lead to evaporator freeze up, if a humidistat is used to keep it operating, as well the dry bulb temperature may be too cold for human comfort. With this old technology, the capacity was sized so on the warmest day, it would operate at 100% with no cycling. So it was not oversized. With the inverter technology the system can be oversized, allowing fast room cool down, and then slow the compressor and fans to reduce humidity.

To understand the answer to this question we have to understand that the basic function of a variable speed drive (VSD/VFD) is to control the flow of energy from the mains to the process.

Energy is supplied to the process through the motor shaft. Two physical quantities describe the state of the shaft: torque and speed. To control the flow of energy we must therefore, ultimately, control these quantities. In practice, either one of them is controlled and we speak of "torque control" or "speed control". When the VSD/VFD operates in torque control mode, the speed is determined by the load.

Likewise, when operated in speed control, the torque is determined by the load. Initially, DC motors were used as VSDs/VFDs because they could easily achieve the required speed and torque without the need for sophisticated electronics. However, the evolution of AC variable speed drive technology has been driven partly by the desire to emulate the excellent performance of the DC motor, such as fast torque response and speed accuracy, while using rugged, inexpensive and maintenance free AC motors.

I had one of those AC units some years ago. I bought it to replace a 12K BTU window unit that I had been using in my bedroom because I thought it would be quieter and was supposedly about 40% more energy efficient.

The new one was rated for the same 12K BTU capacity but to be honest in real life daily use it was useless. Sure it used 40% less power but it also didn't keep up worth crap and the compressor ran constantly whereas the old one would reach its set point and shut down.

The old uint drew about 12 amps with no PF correction and the new one drew about 9 with PF correction but couldn't keep up despite being supposedly the same capacity rating.

Anyway now the 25 year old unit, I bought at an auction for $2, is back in place and the $240 fancy high efficiency one went out with the scrap about 2 years after I bought it because the compressor locked up.

TCMTECH:

You don't recall if there was a brand name on the scrapped unit?

Price seems low for an AC with inverter, but then you seem to be a good scrounger.

Current going rate for a 12KBTU mini split with inverter is $700, and it's Air-Con brand (eBay), says it meets AHRI compliance testing.

My bigger worry is the inverter electronics located in the condensing unit, I don't see any conformal coating on the PWB, (both on an air-con and Mitsubishi) and the boards are not sealed inside any hermetic enclosure. I can see a failure waiting to happen.

Sorry dont recall. A buddy of mine does surplus and salvage buying and came a cross a number of them new in the box so he sold me one. Supposedly high end units with a $600 -$800 retail price but as I said compared to a old unit of identical ratings I was not impressed.

I also had a cheapo 12K BTU unit from walmart that I was less than impressed with as well. The compressor lasted just fine but the blower motor locked up and the whole unit was designed to be non serviceable even by my capabilities. After two or three summers All the internal plastic was so dry rotted that with the slightest touch it just crumbled into powder.

As yourself why:-

"A buddy of mine does surplus and salvage buying and came a cross a number of them new in the box so he sold me one."

They are unlikely to be top quality under such circumstances......even if you paid less than half price....

For me, I am personally convinced that full and proper house insulation, modern windows etc., is the way to go. We have not switched on our AC since having the work done in 2008......I don't even know why I keep it!!!

In a warmer climate than Germany, the same work and a small efficient AC would do it at a far lower energy cost per year, though the house insulation was not cheap, but it does run VERY quiet too!!!

Its a bit like comparing a roundabout and a traffic light junction. The RA costs about the same as the TL to install, but the running costs are minimal and it works in a power cut too......there are many other plus points, but not needed to be mentioned here...

Energy will never get cheaper......most likely more expensive, even if fusion eventually works.....one day!

I'm not sure how smoke staining on the box it was in from the warehouse fire salvage job they got them from would affect the unit that was inside?

The boxes they were in never even got hot enough to affect the vinyl stickers and ID tags (no shrinking or peeling) on them so I really have doubts they were affected by heat damage being inside styrofoam packing inside plastic wrap inside a cardboard box.

You missed the point I was trying to make, I think it was possibly a crap design in the first place....good ones don't stay on a shelf very long...

Do you remember the make and type?

Could it have been a Chinese fake copy for example?

I don't recall exactly . I would say it was either German made or a Scandinavian name that sounded German to me.

Either way I can't name a single person I have ever met who replaced a good working old style AC unit with a new high efficiency one of supposed equal ratings and found that they gained anything from it.

As I have had a fully insulated house since 2008 (partially since 1995, which proved to me how effective it was), I never have such problems anymore, it is quiet, uses no power anymore (some by installation!!) and works when the mains (if it ever did fail here!) drops.....

It works in winter and summer.

High initial cost, but seen over 20 odd years, as energy prices increase and increase, I feel I have already got my money back.

Also TOTALLY silent!! (as I said before!!)

I cannot recommend anything else, even if it is so hot that where you live that some A/C is still needed, you will still reduce your cycling and your power bills, not forgetting repair costs....the hot part of the summer will be drastically shortened for you....

Maybe one of these units you mentioned (don't like) would then be more than enough....just a thought as I don't know how well your house, windows and doors are working/insulated relative to warm weather....I changed all mine out as well for some really secure ones that are also insulated....I also added automated roof windows. Totally great, but not cheap here!

I halved my heating an hot water bills over the year, in comparison to what I was paying in 1986!!! If you take into account the loss in value in the German currency, its even more!! It actually appears to be less than half the value/Cost, so I am basically paying less than a quarter of my 1986 bills.....value wise...

Just a thought!!

My A/C tends to short cycle on mild days. A VFD would allow the unit to run at lower capacity to better match the load on mild days. I'm not sure about compressors, but on centrifugal pumps the power required changes by the cube of the RPM change i.e.: at 3600 RPM the power required would be 8HP, but at 1800RPM the power required would be 1HP.

Modern A/C units typically have multi-speed blower motors that are thermister controlled for humidity subjugation....A unit that operates 24/7 is not efficient....a range operated control allows the unit to cycle on and off to reduce running time which, besides lowering the heat load(ie; insulation etc.) is the only way to go....

I have had a long exposure to AC. One of the first I worked in was the only AC in a town in the 30's that had Summer temps in the 110F's. I helped my dad with it in the 50's and it was a strange beast. It was not Freon. I moved back in the 90's due to a work transfer. When new owners of the building decided to replace the AC in the late 90's the AC contractor who got the job had done some work for me on projects. He asked a lot about the system, but I really didn't know much about it other than it did not have Freon in it. Before he removed the system, he took a sample of the gas and proved it to be some form of hydrocarbon. He looked at the system and determined that it had variable speed DC motors that mechanically responded to the pressure at a measuring point in the system. Each evaporator had it own thermostat that would shut down or throttle coolant flow to that evaporator if the cooling point were reached. It was a very quiet unit. The new unit took more power, was noisier, and never was quite as good as the old one. (It was a variable speed unit.) But they got an energy rebate because they installed a new one.

I have worked as a Vendor on the electrical portion of power for Carrier and remember when they started putting electronic variable speed drives on their large commercial units. The comparison in energy usage was dramatic. The difference between a commercial unit is that you have many locations where the coolant going to evaporators can be throttled or stopped completely to respond to local needs. The compressors needs to be able to supply coolant to the evaporators all operating in parallel or with only one in operation. A variable speed/torque compressor is ideal and it works well and can save energy.

Come along and think about a window AC. One compressor, one evaporator. You can see why the saving are not as great, but I will agree that some savings could be had. Add to that the fact that these are commodity items and everyone is looking at the lowest possible purchase price. One would expect the cheapest unit to not have much advantage over a standard on/off AC. I have spent a lot of nights in motels and some units are very good. The variable speed lets the compressor and fan run all the time, quietly keeping a stable temperature. Then there are the on/off cycling units that keep you up all night, alternately being too hot or too cold. Basically you get what you pay for. Good units are available, that save energy, and they are not necessarily the most expensive. But they are definitely not the cheapest. The research is difficult. I have only one house AC. It is a 5K unit which uses so little power that I made a mount to put it in the window of a pickup camper and am able to run it off the battery and inverter. We have only used it in the home once when there was smoke from a forest fire in our back yard. The area we live in now rarely gets above 80 degrees and the house usually stays 76-78F during the day. The cost? I got it for $5 at a garage sale.

Variable speed compressors can save money on energy, but the cost of a good one must be calculated as return on investment and a decision made. Cheap AC's are just that. Poor quality and iffy savings.