[Equest-users] 90.1 Supply Fan Energy

[Paul Diglio]

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
 

_______________________________________________
Equest-users mailing list
http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org
To unsubscribe from this mailing list send  a blank message to 
EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG



-- 
Carol Gardner PE



-- 
Carol Gardner PE

_______________________________________________
Equest-users mailing list
http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org
To unsubscribe from this mailing list send  a blank message to 
EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG



-- 
Carol Gardner PE
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20110406/88591eaa/attachment-0002.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/png
Size: 1189 bytes
Desc: not available
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20110406/88591eaa/attachment-0002.png>