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Old 08-12-18, 12:28 PM   #9
jeff5may
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Quote:
Originally Posted by oil pan 4 View Post
I'm never going to install a central A/C.
No central A/C is efficient as one that's turned off.
The big advantage is rooms where the split is off don't get heated or cooled.
Sure you can block off rooms but the system is sized to cool the whole home so when you block vents you mess with system efficiency, unless it's done on the cheap and way undersized.
I kind of like decentralized systems, that way if one fails it's not a huge household emergency.
The multi-split units suffer the same penalty. When the outdoor unit is only feeding a single zone, the energy efficiency is heavenly, as the compressor is running slow and the heat exchanger transfers heat at a super low Delta T.

As more zones come online, the compressor speeds up, and the heat exchanger has a harder time moving energy. At full capacity, the compressor is drawing full power and the outdoor HX is operating at Max Delta T. At this point, the system is running at close to the same rating as a ducted central air system.

The thing about your statement that bugs me is that the new central air systems employ variable speed compressor and zone control and expansion valve technologies that the vintage systems did not. If you're trying to keep total system initial cost low, then yes, the generalization does apply, because these technologies are sacrifices made to save money at the getgo. But modern central split units have come a long way since the 80's.
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