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Posted by Bipolar Bear on August 24, 2008, 2:25 am
Gorsh I sure bet strormy will be proud of you.
> Hi,
> I fail to see how inverter heat-pumps can be more efficient than fixed-
> speed ones.
> I guess this boils down to another question: a heat-pump probably has
> a speed where its efficiency is maximum. Hopefully this is where fixed-
> speed heat-pumps are set to operate. Is that right?
> If so, when the inverter varies the speed, it moves away from the
> optimum, and efficiency goes down.
> It would seem to me, from a pure COP view point, and if my assumptions
> are correct, that a fixed-speed heat-pump would have the maximum
> efficiency. Now, comfort is also important, and off-on maximum heating
> a not as nice as sustained, adapted, heating.
> But this is not what is advertised. All vendors claim that COP is
> better with an inverter, even though i assume there are lossses in the
> current-inverting circuitry. How can that be? The only way I can see
> that this would be true is if the COP increases as compressor speed
> decreases, but I was never able to find any information about that.
> And also -this is presumably linked- why do smaller heap-pumps have a
> better COP than larger capacity ones?
> Does anyone know the answer to this mystery?
> Thanks you for your lights, Chris
When a system cycles on and off the average EER is not the rated EER.
So a unit that may have a lower EER and does less cycling can actually
have a higher average EER. Than the unit that cycles more often.
Andy
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> I fail to see how inverter heat-pumps can be more efficient than fixed-
> speed ones.
> I guess this boils down to another question: a heat-pump probably has
> a speed where its efficiency is maximum. Hopefully this is where fixed-
> speed heat-pumps are set to operate. Is that right?
> If so, when the inverter varies the speed, it moves away from the
> optimum, and efficiency goes down.
> It would seem to me, from a pure COP view point, and if my assumptions
> are correct, that a fixed-speed heat-pump would have the maximum
> efficiency. Now, comfort is also important, and off-on maximum heating
> a not as nice as sustained, adapted, heating.
> But this is not what is advertised. All vendors claim that COP is
> better with an inverter, even though i assume there are lossses in the
> current-inverting circuitry. How can that be? The only way I can see
> that this would be true is if the COP increases as compressor speed
> decreases, but I was never able to find any information about that.
> And also -this is presumably linked- why do smaller heap-pumps have a
> better COP than larger capacity ones?
> Does anyone know the answer to this mystery?
> Thanks you for your lights, Chris