[Bldg-sim] Fan Power

RobertWichert robert at wichert.org
Sun Mar 3 08:39:24 PST 2013


This data is way better than I can get, Aaron.  I don't know the CFMs 
these fans move, but for me it is normal to see the smallest H.P. for 
the smallest 1.5 / 2 ton fan coil at 1/5 H.P.  Seeing something lower 
than that would be a godsend.  Who made these fans and how much air do 
they move? Typically the fan coil manufacturers that I work with don't 
bother giving fan H.P. (listed on your chart as Motor H.P.?) but rather 
jump right to the motor nominal H.P. which is always higher.

But I agree with you regarding amps.  Typically the amps are much higher 
than the corresponding H.P. for unknown reasons.  Startup current?  
Perhaps...

I also note that your data has higher watts at higher voltages in some 
cases, for unknown reasons, along with "peak" watts at 208/230 in other 
cases.  I can't explain that.

Thanks for sending this, but if you can identify the manufacturer and 
the product, I would be very grateful.


Cheers!


Robert Wichert P.Eng. LEED AP BD&C
+1 916 966 9060
FAX +1 916 966 9068







===============================================

On 2/22/2013 1:51 PM, Aaron Smith wrote:
>
> Robert,
>
> I've also run into problems obtaining combined (fan and motor) 
> efficiency and input power, mostly with terminal units such as heat 
> pumps and fan coil units but also with individual fans.  What I've 
> often done is used the watts listed in their electrical tables. For 
> example, below if you take their size 20 at high fan speed, they 
> classify the motor HP at 1/30HP or 25W (output power).  I've taken the 
> subsequent columns to mean input power so the watts at 115V is then 
> 57W which would make the motor is 44% efficient and that seems 
> reasonable to me.  The listed amps don't necessarily equate to the 
> same wattages, they are usually higher so my only theory is that this 
> is the starting amps.
>
> I'd be interested in finding out what other have to say.  I have tried 
> talking to some local equipment reps without any luck.
>
> Aaron
>
> Aaron Smith, P.Eng
>
> M&R Engineering
>
> -----Original Message-----
> From: RobertWichert [mailto:robert at wichert.org]
> Sent: Friday, February 22, 2013 12:25 PM
> To: bldg-sim at lists.onebuilding.org; Scott Blunk
> Subject: [Bldg-sim] Fan Power
>
> This is a DOE-2 question, I think, but I am applying it to EnergyPro.  I
>
> am asking here in the hopes that some will have a more in-depth
>
> knowledge of DOE-2 and how it relates to fan power.  I am also hoping
>
> that some here will be able to reflect on the theory and application of
>
> fan power and energy as it relates to actual systems and modeling.
>
> When inputting indoor fan power, I have used many sources for the fan
>
> power.  I sometimes use the motor nameplate, which I believe is too high
>
> in every case.
>
> I also sometimes use FLA or RLA, which I also do not believe are
>
> accurate, but sometimes give more realistic numbers.
>
> Some manufacturers give fan BHP at design conditions, which I find to be
>
> very helpful, but not everybody is that helpful.
>
> It has been suggested that I calculate the fan BHP using the theoretical
>
> formula *** Fan BHP = (cfm x static press "w.c.) / (6356 x fan
>
> efficiency) *** and then use a conservative fan efficiency (maybe 50%)
>
> for a good number.  This gives a much lower value than the other
>
> methods, and I am trying to see if there is anything wrong with this
>
> approach.
>
> As I understand the usage, indoor fan power is divided by motor and
>
> drive efficiency to come up with fan energy. So the fan BHP is the
>
> starting point.  Having this too high drives up fan energy, sometimes
>
> dramatically, and can influence the proposed case quite a bit if there
>
> are lots of fans, even small fans.
>
> Any thoughts on this approach would be very much appreciated.
>
> -- 
>
> Robert Wichert P.Eng. LEED AP BD&C
>
> +1 916 966 9060
>
> FAX +1 916 966 9068
>
> ===============================================
>

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