What is a "VFD Dew Prevention on a Carrier Evergreen Centrifugal Chiller?
I have a 900 ton 134A Carrier Evergreen Centrifugal water cooled chiller. During a scheduled shut down at 6pm, my chiller went into a "VFD Dew prevention" alarm, which shut down my chiller and had to be manually reset. Does anyone know what a VFD Dew Pervention is and how I might prevent this from happening,Any Ideas?
Last edited by hvac399; 06-02-2010 at 08:59 PM.
The trouble is with VVFs/VFDs/invertors/motor speed controllers, the designers reinventded the wheel somewhat with parameters and terminology that didn't exist until they invented solid sate electronic speed controllers. I won't even go into the parameters of a VVF without the manual. I once had a similiar alarm condition that reffered to the dew point of the air. As it was in a panel on an outside wall in winter time, it controlled a fan on a cooling tower.
As it was wintertime, the fan didn't come on much so the invertor didn't get up to any high temps. When I got there, it had some fault code displayed, that in turn reffered to the low ambient temperature. That in turn caused it to shut down just in case condensation formed inside it and damaged it. I had to install a small watt heater in the panel and a seperate stat set at 10 deg C to control it. After that the alarm never appeared again.
But depending on the type of VVF it could have a total different meaning. Try getting hold of the manual for the VVF.
50 & 60 hz but 100's worse
The latest model evergreens have a humidity sensor to ensure condensation does not occur in the drive.