[Bldg-sim] Fan Power

[RobertWichert]

Well, OK, I will bow to your expertise, but a 44% motor sounds pretty 
dismal to me, as you suggest.

Would a conservative number be 20%, air to wire?  Is so, I am looking 
for FAN efficiency.  NOT motor or drive efficiency, which are taken care 
of by the modeling software separately.

Would 50% for FAN efficiency by reasonable?

If so, this allows me to use the theoretical air BHP equation to 
calculate fan BHP at design conditions using 50% fan efficiency. This 
would be a big breakthrough for me, actually.

I do like the idea of actual testing, which is rare as hen's teeth.  
Even amp numbers are way too high.  I have had RLA that show more HP 
than the nominal motor HP.  That's gotta be wrong.

I have not seen a single ECM fan coil unit with an improved fan BHP.  
Not one.  If you got one, please share your knowledge!


Cheers from sunny California.



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







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

On 2/22/2013 6:54 PM, Graham Carter & Megan Lyall wrote:
> The data is very hard to come by, but 44% for the motor only I believe 
> is about right in those smaller motors.  35% wouldn't surprise me with 
> maybe a 60-65% direct drive blower so 20% wire-air wouldn't be out of 
> the ballpark in my opinion.  The motors are historically single phase 
> split capacitor historically and a poorer quality than a small 3 phase 
> induction motor.
>
> On a tangent, 3 phase induction motor efficiencies really drop off 
> below 1.5 HP or so.  Unless of a very high quality / HE then the part 
> load efficiency can also be very poor despite the full load efficiency 
> looking OK.  So a small 3 phase motor could have 85% full load / full 
> speed efficiency but at 25% load (say 50% speed and 50% torque) the 
> efficiency can be dramatically poorer.  We have managed to get part 
> load motor efficiency data from TECO and others in the past that go 
> down to 50% torque but at full speed (thus 50% load) so not that 
> helpful as variable speed / variable pressure systems spend time at 
> much lower loads.  The data does typically show a peak efficiency at 
> 75% load however where I2R losses have dropped but eddy current and 
> other losses haven't started to dominate the losses and thus drive 
> efficiency down which they do at lower loads.
>
> We have a large project where we have asked contractors and thus 
> suppliers to test select equipment on their test rigs to generate 
> better part load data.  We will see how we go.
>
> Fortunately with a lot of smaller equipment digital motors or 
> electrically commutated motors have lifted efficiencies dramatically 
> as they are direct drive and being digital the variable speed controls 
> are intrinsic to the motor.
>
> Getting part load efficiencies out of VSD drive suppliers we have 
> found to be like drawing blood out of a stone.  I assume that there is 
> a large fixed component of losses so at part load in % terms the VSD 
> losses could grow from 3% say to 7-10%. Don't forget your belts as 
> well if you are taking a fan manufacturer's bhp figures as they 
> typically do not include the belts - maybe 3-5% in losses if well 
> aligned and tensioned.
>
> If you have variable flow, variable pressure systems that spend a lot 
> of time at very low loads, the VSD can affect the motor efficiency at 
> lower loads.  There was an ASHRAE Transactions paper or RP from the 
> late 90's I recall that showed motor part load efficiency without a 
> VSD drive and then with and there was a difference.  If I remember 
> correctly they did the test with a SE motor but may have also done 
> with a HE motor and the HE motors are more resilient to the impacts of 
> a VSD.
>
> I guess all I am trying to say is that getting a full load design 
> point is one thing, but make sure it includes all the losses and more 
> importantly make sure you take a view on what happens at part load as 
> that is where larger modern systems operate.  Smaller systems may be 
> constant flow / constant speed but increasingly we are seeing variable 
> speed FCUs etc available on the market using ECMs.
>
> Regards,
> Graham
>
> On 23/02/2013, at 12:11 PM, Jim Dirkes wrote:
>
>> Based on Aaron's calculations, it sounds like 44% = motor efficiency 
>> x fan efficiency,  That's the net which affects energy use -- how it 
>> is composed doesn't matter too much.
>> Small motors often have terrible efficiency.  The same is true for 
>> small fans!  Put them together and it's pretty dismal.
>> *James V Dirkes II, PE, BEMP, LEED AP**
>> **www.buildingperformanceteam.com* 
>> <http://www.buildingperformanceteam.com/>*
>> **Energy Analysis, Commissioning & Training Services**
>> *1631 Acacia Drive, Grand Rapids, MI 49504USA
>> 616 450 8653
>> *From:*bldg-sim-bounces at lists.onebuilding.org 
>> <mailto:bldg-sim-bounces at lists.onebuilding.org>[mailto:bldg-sim-bounces at lists.onebuilding.org]*On 
>> Behalf Of*RobertWichert
>> *Sent:*Friday, February 22, 2013 8:07 PM
>> *To:*Aaron Smith
>> *Cc:*bldg-sim at lists.onebuilding.org 
>> <mailto:bldg-sim at lists.onebuilding.org>; Scott Blunk
>> *Subject:*Re: [Bldg-sim] Fan Power
>> A 50% efficient MOTOR cannot be correct.   50% efficient fan, yes.
>> I actually think a lot of the amps given are something akin to MCA.
>> Let's see what others say...
>>
>>
>> Robert P. Wichert P.Eng. LEED AP BD&C
>> +1 916 966 9060
>> FAX +1 916 966 9068
>>
>>
>> On Feb 22, 2013, at 1:51 PM, Aaron Smith <asmith at mreng.ca 
>> <mailto:asmith at mreng.ca>> 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
>>     <image002.jpg>
>>     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
>>     <mailto: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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