[Bldg-sim] Fan Power
RobertWichert
robert at wichert.org
Mon Feb 25 08:39:35 PST 2013
Yes, good ideas, Jim, but I am disappointed in your 2,000 CFM fan with
40% static efficiency. That's scary.
We use Aspen fan coils, and I don't know if they have fan curves. I'll
ask. They are most likely smaller though, so even more scary.
Robert Wichert P.Eng. LEED AP BD&C
+1 916 966 9060
FAX +1 916 966 9068
===============================================
On 2/25/2013 3:51 AM, Jim Dirkes wrote:
>
> Why don't you see if you can get fan curves for some small fans --
> they'll show fan efficiency.
>
> p.s., I think 50% for the fan is darn good for most rooftop equipment;
> anything smaller will almost certainly be worse. I did some modeling
> for a manufacturer a while back who used ~2,000 cfm backward inclined
> fans -- 40% static efficiency
>
> *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] *On Behalf Of
> *RobertWichert
> *Sent:* Sunday, February 24, 2013 10:03 PM
> *To:* bldg-sim at lists.onebuilding.org
> *Subject:* Re: [Bldg-sim] Fan Power
>
> 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
>
> ===============================================
>
> _______________________________________________
> Bldg-sim mailing list
> http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org
> To unsubscribe from this mailing list send a blank message
> toBLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG
> <mailto:BLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG>
>
>
>
>
> _______________________________________________
>
> Bldg-sim mailing list
>
> http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org
>
> To unsubscribe from this mailing list send a blank message toBLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG <mailto:BLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20130225/44230ad5/attachment-0002.htm>
More information about the Bldg-sim
mailing list