[Equest-users] FW: Number of systems required by 90.1?

[George Hu]

It seems odd to me that 90.1-2007 requires the baseline building to have one system per floor (system types 5, 6, 7 & 8).

These are all VAV systems, where you have individual VAV boxes responding to different thermal zones. Why would different

number of AHU’s in this case make a difference in heating and cooling energy consumption?

In terms of fan energy, however, different number of AHU’s may make a difference. This is because 90.1 regulates

the fan brake horsepower, which is depending on the size of the fan (Table G3.1.2.9, <20,000 cfm or >20,000 cfm).

For the same sized  building, assuming the total supply airflow being roughly the same independent of the number of 

AHU’s used, each individual fan’s brake house power would be different depending on its fan size, this may lead to 

different total fan energy consumption when you add all individual fan energy up. For this reason, I would argue, it makes

more sense to keep the same number of AHU’s in the baseline case as in the proposed design, for you would then be comparing

“apple to apple”, because the fan sizes in the proposed design would be “comparable” to those in the baseline case.

 

George Hu, PE, LEED AP

President

AWE | Air Water Energy Engineers, Inc.

781.652.8688

www.awe-e.com

 

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bill Talbert
Sent: Wednesday, December 10, 2008 1:01 PM
To: James Hansen; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] FW: Number of systems required by 90.1?

 

James,

90.1-2004 addendum u includes the 'one system per floor' wording for systems 5 thru 8, but floors can be grouped when the thermal blocks are similar. For LEED, it is optional to use addenda. 90.1-2007 adopts the same wording.

Regards,

Bill 

 

 

Bill Talbert, PE, LEED® AP
Mechanical Systems

Phone: (608) 441-6677
E-mail: btalbert at aeieng.com

Affiliated Engineers Inc.
5802 Research Park Blvd.
Madison, WI. 53719
Tel. (608) 238-2616
Fax. (608) 238-2614


>>> "James Hansen" <JHANSEN at ghtltd.com> 12/10/2008 11:45 AM >>>

Thanks for your response Richard.

 

Can anyone confirm whether ASHRAE 90.1-2007 specifically says that your Baseline model MUST have a system per floor?

 

I can’t seem to find it in 2004, or the user’s manual, or in the LEED-NC reference guide.

 

GHT Limited
James Hansen, PE, LEED AP

Senior Associate

1010 N. Glebe Rd, Suite 200

Arlington, VA  22201-4749

703-338-5754 (Cell)

703-243-1200 (Office)

703-276-1376 (Fax)

 <http://www.ghtltd.com/> www.ghtltd.com

 

From: Richard Ellison [mailto:REllison at southlandind.com] 
Sent: Wednesday, December 10, 2008 11:53 AM
To: James Hansen
Subject: RE: [Equest-users] Number of systems required by 90.1?

 

I interpret ASHRAE to suggest one should use 5 AHUs for just the reason you mentioned.  They are different because of different exposures.  One has slab and one has roof.  The external load would be different as would the return plenum temperatures.  One might be able to group floors 2-5 energy wise but I recall reading, perhaps in 2007 where they specifically meant on per floor for the baseline.  I always have at least one AHU per floor in my baseline models.  Using only one AHU would be cheating a bit.  This would be the same logic that says one must zone rooms with different occupancies or schedules separately.

 

RICHARD ELLISON 
Energy Engineer 

Southland Industries

22340 Dresden Street, Suite 177

Dulles, VA 20166

Office: 703.834.5570

Direct: 703. 834.2438

Fax: 703.834.5572

 

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of James Hansen
Sent: Wednesday, December 10, 2008 11:40 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Number of systems required by 90.1?

 

I’m working on a model of a 5-story building – my Proposed system is floor-by-floor chilled water AHUs connected to a water-cooled chiller central plan.  Airside is shutoff VAV boxes with hot water reheat.

 

For the size of the building, the baseline model is almost identical.  It is System 7 – Packaged rooftop VAV system with reheat boxes, chilled water, hot water boilers.

 

My question is whether or not the Baseline model has to have a single system for the building, or should it have 5 separate RTUs (doesn’t really make any sense) since my proposed building has 5 systems?

 

I’m pretty sure the answer is that the Baseline should just have one packaged RTU for the building, but it actually makes a big difference on energy use.  By breaking the systems down into one-per-floor, as is the case with the proposed model, I end up saving a LOT of energy, possibly because the 1st floor is slab-on-grade, and the 5th floor has a roof. 

 

Just wanted to make sure I have the correct number of “systems” for the Baseline model.

 

Thanks!

 

GHT Limited
James Hansen, PE, LEED AP

Senior Associate

1010 N. Glebe Rd, Suite 200

Arlington, VA  22201-4749

703-338-5754 (Cell)

703-243-1200 (Office)

703-276-1376 (Fax)

 <http://www.ghtltd.com/> www.ghtltd.com

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