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Old 08-01-18, 09:56 AM   #12
jeff5may
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On the opposite side of your question, the actual variable speed compressor in nearly all of the "novelty" outdoor unit is going to operate like a super size computer fan. Permanent magnet rotor and multiple phase stator. Depending on how the manufacturer designed the compressor, it may or may not have a 3 phase rotor and stator. This is very important, because a generic 3 phase motor drive might not work. More phases equates to more precise control and maybe higher efficiency, and these smallish capacity variable speed units are uncommon by nature. As such, the designs are all over the place.

Above the 2 ton rating, most of the units are built with 3 phase drives, and as capacity increases the permanent magnet design becomes much less implemented. At a certain point the novelty goes away.

The smaller DC units are pretty much all designed for use with a battery bank in mind, so the drives use multiples of 12 volts. Controls are built for mobile ac or refrigerating duties. The PV residential twist exists, but in general all of these smallish DC units are super uncommon (residential heat pump or mobile commercial refrigeration plus DC power equals single digits parts per million products offered). Not converting source power from DC to AC back to DC has a definite efficiency advantage, but the 120/220 VAC controls are way more common in general.

As to the nature of the units you're looking into, read this article:
https://coolautomation.com/wiki/vrv-or-vrf/
There are more topics in the blog section that will give you lots of quick tidbits to wrap your head around.

Recently the manufacturers have been making 2 stage compressors for the top efficiency outdoor units with variable capacity. They're designed for Sub-Zero temps outside and btu maintenance inside and/or heavenly performance ratings during less demanding conditions. Nearly all of the units are able to run or bypass the second stage of compression on the fly. They can be reduced to 10 percent of the rated output and increased to around 150 percent, so they're very versatile. Naturally these units are the opposite of cheap.

Last edited by jeff5may; 08-01-18 at 10:50 AM..
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