I am puzzled at the fact that split systems are not more common in the US. They have all the advantages of central AC without requiring expensive and inefficient duct work, and are great for zoning. I have seen them in commercial installations, but in that case they have a single evaporator for each compressor. One of the big advantages of a good split system is that you can have two or three evaporators for each compressor.
The only "split-systems" I'm familiar with are relatively small. That is to say, they are typically aimed at installing a single evaporator in each small room of a fairly small room complex, and are severely limited in both the total number of cubic feet which can be cooled, and the distance the evaporator can be from the compressor. Each evaporator is only capable of cooling one room.
However, if by "split system" you are simply referring to something different from a Window Unit, where the Compressor and evaporator are in a single chassis, then that is the "norm" in the US for any kind of "installed" or "whole house" (or commercial) cooling system.'
A typical commercial installation, like in an apartment house, for example, is more likely to be a "chilled water" installation, where a central "chiller" chills the water which is in turn piped to the individual in-room "evaporators, which may or may not include fans. These systems are typically switched between hot water and chilled water on a seasonal basis. Which is why Warm Spring days tend have no cooling available, and cool Fall days no heat!
Residential systems typically use a "Freon" (whatever it's called now) gas instead of water.
The primary advantage to a high-velocity system is that it does NOT require expensive ductwork. Because of the number of these 4-inch ducts per room, and the significantly higher air-flow, the issue of efficiency is "different." "Efficiency" is a multi-headed monster. Generally speaking, "efficiency" equates to the ability to cool any given area more than it does to the cost of any system. [i.e. an undersized unit of any kind simply can not cool an area even if it costs less both to install and run.]
Based on the little bit I know about Japanese (don't know about European versions) split-systems, their "efficiency" is significantly lower than that of any US-style "central" system where the evaporator and compressor are independent of the distribution system. That is to say, one needs significantly more compressor capacity to cool any given area as that area (volume) increases in size.
Probably the biggest reason why Japanese style split systems are not popular in the US is the simple fact that they require an unobstructed location in the room -- either fairly high on the wall above furniture, or on a wall by themselves. This requirement tends to integrate quite poorly with most US housing and decorating tastes. These kinds of cultural differences are quite similar to why Asians and Europeans like watching TV on Cell Phones and hand-held games while most Americans prefer to watch TV on as big a screen as they can afford. Instant Messaging adoption is much the same issue ... Americans have far more networked computers with 9 to 17 inch screens than they have cell-phones.
T.T.F.N. William H. Magill [EMAIL PROTECTED] [EMAIL PROTECTED] [EMAIL PROTECTED] [EMAIL PROTECTED]
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