Installing VFD's inside a sealed air handling unit electrical control panel. Rooftop AHU was engineered and built with motor contactors for supply and return fan motors. Energy management company comes along and puts 2 new VFD's in place of existing contactors. VFD's rated at 113 degrees farenheit at 3300 feet elevation. AHU units are located at a site that is 6500 feet. Not concerned about operating temperatures in the cold Winters of Colorado. Wondering how these VFD's will operate on a hot day when outside temperatures reach above 90 degrees. Not sure how to derate equipment temperature rating based on a higher elevation. Common sense tells me this installation could create future reliability problems with the new VFD's. Energy management company disagrees. Are my concerns justified? BTW-AHJ still waiting on equipment info before passing installation.
VFD installations
- Thread starter dshurt
- Start date
- Status
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: VFD installations
Yes your concerns are valid. The installation violated NEC section 110.3(B).
Suggest contacting the mfg of the VFD and see what the effect is on operating above the rated elevation.
Temp may be a factor as well.
If the energy management company feels its acceptable, ask for an extended warranty
Yes your concerns are valid. The installation violated NEC section 110.3(B).
Suggest contacting the mfg of the VFD and see what the effect is on operating above the rated elevation.
Temp may be a factor as well.
If the energy management company feels its acceptable, ask for an extended warranty
tony_psuee
Senior Member
- Location
- PA/MD
Re: VFD installations
I agree with Tom, contact the VFD people. In my experience they will most likely derate the VFD output. Since VFD's are current limited devices if the energy management company did not take this into account it could require going to a larger VFD. Per the NEC 2005, 430.122 the conductors supplying the VFD must be sized per the rated input of it, not the motor requirements. So up sizing the VFD could have a ripple effect.
Tony
I agree with Tom, contact the VFD people. In my experience they will most likely derate the VFD output. Since VFD's are current limited devices if the energy management company did not take this into account it could require going to a larger VFD. Per the NEC 2005, 430.122 the conductors supplying the VFD must be sized per the rated input of it, not the motor requirements. So up sizing the VFD could have a ripple effect.
Tony
justdavemamm
Senior Member
- Location
- Rochester NY
Re: VFD installations
Has anyone done any heat dissipation calcs for the enclosure for the warm weather? Ask the energy management company for them.
You should be concerned. Most drives are rated somewhere close to 32 deg. F minimum temperature, you might have to install heater / thermostat to keep them warm when not turning the load.
Has anyone done any heat dissipation calcs for the enclosure for the warm weather? Ask the energy management company for them.
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