[Equest-users] 90.1 Supply Fan Energy

[Carol Gardner]

The reason someone "thinks OA might cause a problem" is because of the way
that someone thinks it was entered. It sounds like it was entered using
outside-air-flow, and I may be wrong because Michael hasn't really said.
Using Outside-Air-Flow overrides any values eQUEST might otherwise
calculate, and I would suggest that might make a difference. If OA Flow-Per
was used instead, that's the one I use, it gives eQUEST the flexibility to
calculate the OA cfm itself. To my mind, that a good use of an energy model
that is not only interactive but uses 8760 hours of weather data.

Any other thoughts on this?

On Wed, Apr 6, 2011 at 4:07 PM, Paul Diglio <paul.diglio at sbcglobal.net>wrote:

> Michael:
>
> The kW/CFM you used seems reasonable.
>
> I don't know if you are using a CV or VAV system, but lets assume VAV.
> 90.1-2007 G3.1.2.9 shows the formula CFMs *.0013+A for baseline BHP.  A is
> calculated per Section 6.5.3.1.1.  Using Table 6.5.3.1.1A VAV, we have the
> formula BHP<= CFMs*0013+A.  The footnote defines A=sum of (PD*CFMd/4131).
> So assuming you have a fully ducted return, the PD is .5 which should be
> multiplied by (CFMd/4131).  If there are various pressure drops throughout
> the system we need to estimate the CFM flow at each pressure drop.
>
> As an example, let's take a 20,000 CFM VAV system with 18,000 CFM of return
> air through a ducted return.
>
> A = (.5*(18000/4131) = 2.178
>
> BHP =20000*.0013+2.178 = 28.17
>
> pFan= 28.17*.746/ Fan Motor Efficiency.  Note that since we need kW not
> watts per CFM the 746 becomes .746.  That is probably the reason you
> generated a large kW number. Per Table 10.8 a 30 HP baseline motor needs to
> be 91% efficient.
>
> The formula now becomes pFan =28.17*.746/.91 = 23.09 kW.  Our kW per CFM is
> .0011.
>
> If I am modeling a proposed project with a defined supply and return CFM, I
> would expect that the baseline would be approximately the same.  The CFM/Ft2
> required varies greatly between building and systems.  In the real world I
> see 1.2 or so CFM/Ft2 much, much more than I see .5 CFM/Ft2. Check your
> CFM/Ton to see if you are in the ballpark.
>
> I don't know why someone would think that outside air would cause a
> problem.  Air is air.  Too much outside air would raise energy costs though.
>
> Paul Diglio
>
> ------------------------------
> *From:* M. Shields <mshields at fstrategies.com>
> *To:* Paul Diglio <paul.diglio at sbcglobal.net>; Carol Gardner <
> cmg750 at gmail.com>
>
> *Cc:* equest-users at lists.onebuilding.org
> *Sent:* Wed, April 6, 2011 6:13:53 PM
> *Subject:* RE: [Equest-users] 90.1 Supply Fan Energy
>
> I’ll try OA as a per person number instead of a per space number and see
> what happens.  kW/CFM varied by space between ~ .0007 and .001, and when I
> look at the SV-A reports the Fan Demand (kW) matches what I calculated using
> 90.1.
>
>
>
> I found G3.1.2.9 could possibly be interpreted a couple different ways (for
> example the denominator include X BHP instead of the whole fraction), but
> the only one which produced a reasonable bhp for to me was .  I guess this
> could have been where I messed up but all the other possibilities generated
> kW numbers which didn’t make sense (quite large or negative).
>
>
>
>
>
>
>
> *From:* Paul Diglio [mailto:paul.diglio at sbcglobal.net]
> *Sent:* Wednesday, April 06, 2011 5:51 PM
> *To:* Carol Gardner; M. Shields
> *Cc:* equest-users at lists.onebuilding.org
> *Subject:* Re: [Equest-users] 90.1 Supply Fan Energy
>
>
>
> Michael:
>
> Just out of curiosity, what did you calculate for the kW/CFM?
>
> I have modeled buildings where the ventilation fans use much more energy
> than the heating and cooling energy combined.
>
> Paul Diglio
>
>
>
>
> ------------------------------
>
> *From:* Carol Gardner <cmg750 at gmail.com>
> *To:* M. Shields <mshields at fstrategies.com>
> *Cc:* equest-users at lists.onebuilding.org
> *Sent:* Wed, April 6, 2011 5:46:30 PM
> *Subject:* Re: [Equest-users] 90.1 Supply Fan Energy
>
> Yes, that is correct and obviously there isn't a large number in there. The
> default is 0.5 cfm/sf. I really think it's your outdoor air. Try changing it
> to cfm/person.
>
> On Wed, Apr 6, 2011 at 1:47 PM, M. Shields <mshields at fstrategies.com>
> wrote:
>
> Do you mean under the Systems->Fans->Flow Parameters Min Flow cfm/ft2?  I
> left this blank thinking that equest would then size the flow rate based on
> my design parameters for supply air temp and zone temp as Appendix G
> requires, is that incorrect?
>
>
>
> *From:* Carol Gardner [mailto:cmg750 at gmail.com]
> *Sent:* Wednesday, April 06, 2011 4:04 PM
>
>
> *To:* M. Shields
> *Cc:* equest-users at lists.onebuilding.org
> *Subject:* Re: [Equest-users] 90.1 Supply Fan Energy
>
>
>
> Under the HVAC systems tab, go to the Air Flow screen and look for the
> field labeled cfm/sf. It usually defaults to 0.5 cfm/sf, something I've been
> going on about a bit lately on this listserv. A better number is 1 or so,
> usually but it depends on building type, exposure, etc. For you, make sure
> it is not too large. I suspect, however, that this is not where your problem
> is. I suspect you have accidentally entered too much OA. I suggest you go
> back and simply put in the Standard 62 cfm/person rate and call it good. I
> have never specified it as a cfm rate but that sounds like not such a good
> idea for energy modeling. See if that helps.
>
> On Wed, Apr 6, 2011 at 12:57 PM, M. Shields <mshields at fstrategies.com>
> wrote:
>
> I looked at the ACH based on the SV-A system CFM and the volume of the zone
> and it does seem high (2-5 ACH), but I let equest calculate the system CFM
> for me.
>
>
>
> I have one system per zone so I specified OA in the zone tab as a overall
> CFM rate based on the 62.1 calculations I did.
>
>
>
> *From:* Carol Gardner [mailto:cmg750 at gmail.com]
> *Sent:* Wednesday, April 06, 2011 3:37 PM
> *To:* M. Shields
> *Cc:* equest-users at lists.onebuilding.org
> *Subject:* Re: [Equest-users] 90.1 Supply Fan Energy
>
>
>
> Check your cfm/sf number in your systems, that would definitely cause this
> if it's set too high. Also what field are you using for your OA ventilaton?
>
> Carol
>
> On Wed, Apr 6, 2011 at 12:22 PM, M. Shields <mshields at fstrategies.com>
> wrote:
>
> Hi all,
>
>
>
> I am in the process of breaking out the fan energy from my HVAC system per
> ASHRAE 2004 G3.1.2.1, following G3.1.2.9.  The amount of energy coming from
> my fans seems massive and I’m not sure if that is typical, or if I’ve messed
> something up.  I started by setting the temperature difference of 20 degrees
> between supply and desired temp (55/75 cooling and 90/70 for heating) and
> specified 62.1-2004 ventilation for outside air.  I then ran equest and used
> the SV-A reports to get supply CFM for each system.  From that number I then
> used Table G3.1.2.9 to get BHP for each system, which I then converted to kW
> using the formula in ASHRAE.  I then took that number and divided by CFM to
> get kw/CFM and entered this number on the system->fan tab.  When I go to the
> SV-A report the system kW is exactly what I calculated it to be, but the
> energy required for my ventilation fans is about the same as my heating and
> cooling load combined, which seems outrageous.
>
>
>
> Is this typical?  Have I entered it In the wrong way? I would think fan
> consumption would typically be a fraction of the actually heating and
> cooling energy.  Thanks for any thoughts.
>
>
>
> ____________________________
> Michael Shields
> Facility Strategies Group, LLC
>
> 1012 Market Street, Suite 307
>
> Fort Mill, SC 29708
>
> Phone: 803-493-4507
>
> Fax: 803-548-2511
> Email: mshields at fstrategies.com
>
>
>
>
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>
> --
> Carol Gardner PE
>
>
>
>
> --
> Carol Gardner PE
>
>
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> Carol Gardner PE
>



-- 
Carol Gardner PE
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