Fan Efficiency???
Fan Efficiency???
(OP)
A colleague just told me that a contractor changed out some fans on a couple of cooling towers at our facility. He said that the amp draw dropped from 40 to 18 and asked if we might be able to calculate energy savings. Supposedly the blades are of a new design, with a honeycomb structure.
My first impression is that there are too many variables at play (power factor, speed, air pressure, humidity, etc.). Can the mass of a blade make that much difference?
My first impression is that there are too many variables at play (power factor, speed, air pressure, humidity, etc.). Can the mass of a blade make that much difference?





RE: Fan Efficiency???
Are you sure you got the same blade geometry? Is it possible to measure air velocity versus previous?
Goober Dave
RE: Fan Efficiency???
That big a drop in amps can probably only come with a big drop in the air moved.
RE: Fan Efficiency???
(a) The existing fan is so highly inefficient !
(b) The new fan is running at lower speed ? VFD ?
HVAC68
RE: Fan Efficiency???
The mass of the blades would affect transient energy consumption, if the blades speed changed a lot, but again I doubt this much.
There are real world scenarios you could imagine, most of which involving a VFD, but I lean towards the contractor cleaning the tower fill at the same time as replacing the fan blades.
RE: Fan Efficiency???
ht
RE: Fan Efficiency???
Was the fan-change part of a complete overhaul of the coolingtowers?
Maybe the coils/fins were changed or cleaned and this resulted in less resistance, lowering the power of the fan.
As for the energy-saving: calculate fan-power from the measured amps and then have an educated guess of the number of hours the fans run annually. Multiply and you have kWh.
RE: Fan Efficiency???
In general, less resistance results in more air flow which in turn increases fan amps.
RE: Fan Efficiency???
http://www.hvacknoxville.org Repair Services.
RE: Fan Efficiency???
Link is to an old presentation online with the various curves.
RE: Fan Efficiency???
(1) strap a power logger to the MCC fan feed and measure actual consumption,
(2) if your electrical vault has a power quality analyzer (Power Logic panel, for example), then go in afterhours when all the systems are off and the cleaners are gone, find the power meter and record the kW, go to the DDC and turn on the fan, and return to the panel to take the kW reading. Multiply the kW by the hours of operation and you have your kWh,
(3) multiply the new Amps x Volts = Watts x hours = kWh as a ballpark estimate.