[Bldg-sim] Fan Power

RobertWichert robert at wichert.org
Mon Mar 4 07:59:18 PST 2013


Thanks Aaron,

That's very helpful.  I had looked at the Johnson units before and been 
distracted by their not having obvious DX ratings, seeming to have more 
on water loops than DX loops, but they do say that they provide DX coils 
too.

Thanks again!


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







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

On 3/4/2013 7:14 AM, Aaron Smith wrote:
>
> Robert,
>
> I was looking at the engineering manual for JCI fan-coil units, 
> http://bit.ly/YPtNcH. They say "Fan Coil Units are equipped with 
> permanent split-capacitor (PSC) motors with three taps (High, Medium 
> and Low) which provides variable horsepower outputs."  So I understand 
> the "Motor HP" listed in the table below is output HP.  I'm not sure 
> why the watts were sometimes higher for higher voltages; they're 
> generally pretty consistent except for the size 20.
>
> In another table they also list the power input for various 
> configurations at ARI conditions with airflow indicated. They're 
> generally around 0.3 W/cfm which sounds good to me but that's at 0" or 
> 0.05" ESP which I think is unrealistic for a ducted system. At least 
> the airflow is indicated and they have the fan curves.
>
> Regards,
> Aaron
>
> **Aaron Smith,******//P.Eng//////
>
> /M&R Engineering///
>
> ------------------------------------------------------------------------
>
> *From:*RobertWichert [mailto:robert at wichert.org]
> *Sent:* Sunday, March 03, 2013 12:39 PM
> *To:* Aaron Smith
> *Cc:* bldg-sim at lists.onebuilding.org; 'Scott Blunk'
> *Subject:* Re: [Bldg-sim] Fan Power
>
> 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 
>> <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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