power requirement for a minisplit system
Last Post 02 Aug 2016 05:20 PM by jonr. 5 Replies.
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arborvetUser is Offline
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01 Aug 2016 02:23 PM
my electric company wants FLA or LRA values for the electric motors on our proposed minisplit system. we haven't chosen the exact units yet, probably Fujitsu or Mitsubishi so I am looking for some reasonable response to their inquiry. our house will be a 1500 sq ft single floor , half with a 10' ceiling the other half 8', about 15 to 20% window surface, r40 walls and r60 roof (dense pack cellulose). there will be a full walk out basement with spare bedroom, den, and guest bath. Any general numbers including power draw for the HRV.
thanks Craig
Dana1User is Offline
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01 Aug 2016 06:15 PM
An HRV draws next to nuthin' less than half an amp of 110-120VAC.

Even if you went all nuts on it with a 3 ton multi-split with four mini-duct cassettes you'd be drawing less than 20 amps FLA or RLA on 220-240VAC circuit. For a clue, look at the max power draw and circuit breaker recommendations on the submittal sheets.  You're more likely to be in the 1.5-2 tons of multi-split (or separate mini-split) and if you use wall coils instead of mini-duct cassettes it'll pull even less current.  With right-sized modulating inverter drive DC motors throughout ductless you'll be WELL under the current ratings of typical low efficiency split capacitor motors on the average oversized traditional AC.

arborvetUser is Offline
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02 Aug 2016 08:02 AM
I forwarded the spec sheet you sent to Eversource, they still are questioning the LRA locked roller amperage for our minisplit system ? thanks for your help
jonrUser is Offline
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02 Aug 2016 12:13 PM
Dana's 20A is a good number for 3 tons of inverter driven AC. Non-inverter units would be much higher.
Dana1User is Offline
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02 Aug 2016 03:11 PM
Inverter driven DC motors don't draw higher amperage when the rotor is locked. Split capacitor AC motors, which can draw multiples of the normal operating current if the motor is seized and will often draw more than 2x the normal operating current while spinning up, which is why they need/want that information. But higher current with the motor locked simply doesn't/can't happen with DC motors powered by an inverter. Simply asking the question belies a certain amount of ignorance on their part about the nature of this type of equipment. The question presumes the HVAC system has AC motors driving the blowers & compressors.

Even with ALL compressor and blower motors locked the multi-split I pointed you to won't quite pull 20A, but it might pull 17-18A.
jonrUser is Offline
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02 Aug 2016 05:20 PM
4.5-6x are common LRA to RLA ratios for a non-inverter AC.
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