[TowerTalk] [Fwd: Re: Power Distribution]

[Roger (K8RI)]

On 8/8/2010 10:58 AM, jimlux wrote:
> Roger (K8RI) wrote:
>    
>> On 8/8/2010 3:00 AM, Brahmangou at aol.com wrote:
>>      
>>> Check the Seer ratings on the 3 phase eqpt vs single phase before making so
>>>    bold a statement.
>>>
>>>        
>> I think you will find that this is most likely due to equipment design
>> rather than the ability to run on 3 phase.
>> At work we only used single phase on the "small stuff".
>> 3 phase motors are just plain more efficient than single phase for the
>> same HP.  With very small motors the difference becomes less and small
>> single phase motors are cheap due to market volume.
>> "I would guess" that as 3 phase powered small airconditioners are
>> *relatively* rare here in the US compared to single phase that changes
>> in implementing new designs may lag the implementation of new designs
>> for single phase, as I can see no reason that the efficiency (seer
>> rating) of a single phase airconditioner would be better/higher than a 3
>> phase.  The seer rating is determined almost wholly by the laws of
>> thermodynamics.
>>
>>      
> not exactly..
>
> The SEER rating is determined more by how well the AC can handle varying
> loads. For a given number of joules/BTUs being pumped with a given
> temperature differential, Roger's statement is true.. you can optimize
> the size of the motor, condenser, evaporator, and expansion valve for
> that operating point and pretty much everybody is in the same boat
> (whether your electric motor is 90% or 95% efficient isn't going to make
> much difference...)
>
>
> But, when the condenser (outside) temperature (e.g. the differential
> temp) is changing, which it does, with the seasonal adjusting (the S in
> SEER), it's trickier.  Do you run the system at constant differential
> (with the evaporator running colder than normal when outside temp is
> lower) and cycle it on and of more? (that's fairly inefficient) or do
> you put in a fancy variable speed compressor (that's more efficient)..
>
>    
And some of those are major  RFI generators using PWM for speed control

73

Roger (K8RI).
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