[Equest-users] 90.1 Supply Fan Energy

M. Shields mshields at fstrategies.com
Wed Apr 6 15:13:53 PDT 2011


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




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