Mini Split COP?

[Mikesolar]

Originally Posted by jeff5may

MN,

I see your point about COP at sub-zero temps. With air-source units, there's no escaping the cliff at or around 20 degF. Either the unit loses heating capacity at slowly declining power draw or you increase power draw to maintain capacity. No two ways about it.

It looks to me like Mitsu fielded too many complaints from customers about their units not producing "hot" air in frigid outdoor conditions. With the hyper heat models, they went the way Hallowell did, increasing mass flow at the expense of COP. When outdoor temps take a dive, they "over-rev" the compressor to keep up first, then do something proprietary and secret with the multi-split units("hyper-rev" compressor? Flooded evap? Suction line hx? AUX heat? Anyone...anyone??) when it gets really cold. So now Joe Dirt or Joe Six-pack can't complain about Mr. Slim not keeping their trailers warm during the winter. They might pay 200 dollars a month more for that heat, but guess what? The dag nabbin thing does what it should when it's freezin outside.

Fuju and Panyo have chosen to try to maximize COP at the expense of sub-zero capacity. With larger outdoor coils and inverter compressors, they may over-rev a little, but not enough to injure efficiency. At Rob's -20 temps, they may only put out 1/3 of rated capacity, albeit at decent COP. To meet this condition, expect to spend double on an oversized unit that would then run at reduced capacity in milder weather at near water-source efficiency.

Either way, which unit to go with depends on the end goal. For a 225 sqft room, a 12k hyperheat or 15k rls2 would meet the need at -20f. For around 2000 dollars max.

Interesting that no manufacturer is immune to issues but the one that seems to have the most problems (according to my European fridgie friends) is Daikin so I will steer clear of them.