[SBE] A/C 3phase vs single phase

[Chris Hoopes]

My hypothetical questions assumes both 3 phase and single phase are available. One being 3 phase 440, or 480 with 3 hots, or 220 with 2 hots and a neutral. For years I always believed 3 phase would produce more cooling BTUs for less power bill then a single phase system. Imagine my surprise when my boss tells me that there is no difference!
Thanks for your comments.

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Chris,
 
Some of the smaller, inverter-type air conditioners are quite efficient, but they are limited in cooling capacity.  Three-phase motors are smaller and simpler in design than equivalent single-phase motors and present a more balanced load to the source.  For a relatively small cooling load, an inverter-type unit may be the way to go, but for large cooling loads where a lot of shaft power is needed three-phase machines may be the only reasonable choice.
 
Note that while there is two-phase power, it is hardly ever used these days.  Commonly found today are three-phase loads and single-phase loads.  Generally, a load connected to two line (hot) wires in a domestic or commercial system (whether or not a neutral wire is used) is single phase load and not a two-phase load.  Three-phase loads have three hot wires and, in the case of a Y-connected load, three hot wires and a neutral.
 
Regards,
 
Bob Denny

 
On 6/11/09, Chris Hoopes <hoopeschris at yahoo.com> wrote: 




It comes up every now and then that I am called upon to scope out new air conditioning systems. I always figured with both available, that 3 phase was more efficient. Less current is required to start a 3 phase motor. Smaller gauge wires, but more of them. But then the other day I was called down on this. I wondered if advancement in A/C technology had changed the fact. The way 3 phase is measured is a difficult concept, peak demand. What has been your experience? Is 3 phase cheaper to operate and cool with then a 2 phase system? Or is there no difference?

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