Understanding BHP and HP
Understanding BHP and HP
(OP)
I am in the process of reviewing a shop drawing for an AHU. I have received the attached cut sheet from the manufacture.
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When I look at this cut sheet it seems like the motor size they have specified is too small. I took the BHP (4.89) and divided it by the motor efficiency (87.5%) to get a HP (5.6). So to mee a 7.5 HP motor should have been specified NOT a 5 HP motor.
Am I missing something?
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When I look at this cut sheet it seems like the motor size they have specified is too small. I took the BHP (4.89) and divided it by the motor efficiency (87.5%) to get a HP (5.6). So to mee a 7.5 HP motor should have been specified NOT a 5 HP motor.
Am I missing something?





RE: Understanding BHP and HP
What did the drawings or specs specify for motor size?
RE: Understanding BHP and HP
RE: Understanding BHP and HP
RE: Understanding BHP and HP
RE: Understanding BHP and HP
You are correct this is an output for a York unit and it was selected using software. The supplier told me that there is a service factor on the motor which allows you to run above 5 HP. Would there be any issues of burning out the motor or tripping if you are continuously operating above 5 HP (like at 5.6 HP).
This is the unit that we had used to create the specs/dwgs. Unfortunetly the motor size was not looked at carefully at the time.
RE: Understanding BHP and HP
That was one theory that I had; that the motor HP listed in the shop drawing (5 HP) was the acutal motor output. The inefficiencies would only change the full load amps. ie. a more efficient motor would lower the full load amps and a less efficient motor would raise the full load amps. But both motor regardless of efficiency would output 5 HP thus satisfying the 4.89 HP requirements.
RE: Understanding BHP and HP
I would have a 7.5 Hp motor in that application.
We pay a premium price per kWh here, the additional cost of going something above a 'standard efficiency industrial motor' like York is offering to a Premium Efficiency motor like a Baldor Super E, pays for itself fast under a year but like I said, we pay well over 30 cents here a kWh.
May not be the case in your area perhaps electricity is cheap.
The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install
RE: Understanding BHP and HP
Now you didn't ask this question, but you stated it was a FC fan but make sure you are in a satisfactory area of the curve if it is indeed a FC fan.
RE: Understanding BHP and HP
RE: Understanding BHP and HP
RE: Understanding BHP and HP
The service factor is intended for transient events, not constant operation.
RE: Understanding BHP and HP
RE: Understanding BHP and HP
RE: Understanding BHP and HP
The way we build has a far greater impact on our comfort, energy consumption and IAQ, than any HVAC system we install