Running fan motors at over 50Hz?




Subject to the only alteration to the ventilation system being alteration of the fan speed within its designed perameters:
Volume varies directly as speed. Pressure varies as the square of the speed. Power varies as the cube of the speed.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Krankie wrote:

Doesn't it get a bit more complicated than that? I thought the shape of the fan blades affected the performance curve significantly.
Chris
--
Chris J Dixon Nottingham UK
snipped-for-privacy@cdixon.me.uk
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 21/11/2015 09:20, Chris J Dixon wrote:

As you imply, I had believed power was between a square and cube of speed, much like air resistance of moving objects like cars.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Are you suggesting that fixed fan blades morph to a different shape in use? I am aware that attack angle of some duct type propellor aerofoil fan blades can be changed (whilst in motion? - not sure). This type of fan usually has a characteristic curve for each attack angle. Different centrifugal fan types (forward curve, backward curve, paddle blade,etc., and configurations inbetween) have impellor profiles suitable for its proposed use and each has its own unique characteristic curve but all still obey the fan laws.
My statement referred to the effect of speed change only without any other change to the installed system. I am not suggesting that an upward speed change beyond the fan design parameters and/or system parameters is desirable or safe.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 18 Nov 2015 21:11:25 +0000, gremlin_95 wrote:

As others have pointed out, there might be a cooling issue at very low speeds but in this case, the torque demanded by the fan will drop considerably compared to the max torque at full speed (which should be comfortably within the motor's maximum torque rating anyway - current demand correlates very closely to torque loading).
Presumably the variable frequency inverter is a purpose made speed controller in which case the output voltage will also vary in direct proportion to the frequency. Provided that the torque stays below the motor's maximum limit when run at the highest speed setting (highest frequency and applied voltage from the speed controller) there shouldn't be any problem assuming you don't take the upper frequency/voltage to an extreme, risking insulation failure of the motor windings.
I'd get the contractor to confirm that the 'inverter' is actually a speed controller with the characteristics I've just described. If the output voltage varies in direct proportion to the frequency then you're "good to go".
If, when you appraise your 'consultant' of the speed controller, he still rejects the specification with no further justification as to this decision, sack him and get a qualified consultant who *does* understand the basics of frequency/voltage converter speed control.
--
Johnny B Good

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.