[Bldg-sim] Existing building HVAC modeling

James Hansen JHANSEN at ghtltd.com
Sun Sep 6 12:47:57 PDT 2009


Karen, this seems to contradict your earlier statement.  Or more likely,
I'm just not comprehending it.

 

As Cam pointed out, the user's manual says that when an existing system
exists, as in an existing building that is being built out for a tenant,
the HVAC system in the baseline may match the proposed.  This makes
sense to me, and it was how I understood the modeling requirements.

 

However, it doesn't go into more depth than this, and neither do the
CIRs, if there are modifications to the existing plant to increase
efficiency, but that do NOT alter the system type.

 

As another example:

 

LEED building, 10-stories, existing water-cooled chilled water plant
serving dual duct terminals.

 

The manuals and CIRs basically say:

 

For modified areas/systems: The Proposed Building Performance is
calculated as per design. The Baseline Building Performance is
calculated as per ASHRAE 90.1-2004 Appendix G requirements

For areas/systems not modified: Both the Proposed and the Baseline
Building Performance must be modeled as per the existing conditions.

 

This is straight out of a CIR ruling dated 2/9/09.

 

But what if we took our example building, and made a minor change to,
say, the AHUs (as part the LEED project, we installed VFDs to replace a
pressure bypass configuration).

 

Is this "modifying" the existing systems enough so that we would then
have to model the Baseline HVAC system per the App G requirements
(System 7 or 8) in lieu of modeling the baseline HVAC system as the
existing system (dual duct system)?  Or could we just bring the AHUs up
to App G requirements (temperatures, VFD, fan HP sizing, etc), and leave
the chilled water plant and air distribution system as it currently
exists since we aren't modifying those?

 

Thanks for any clarification.

 

This is particularly important for this project because the Client does
not have sufficient funds to upgrade the chilled water plant, so all
existing equipment is to remain.  If I have to bring the Baseline HVAC
system completely to App G standards, that's a huge penalty since the
proposed building chillers are older.

 

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)

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

From: Cam Fitzgerald [mailto:cam at energyopportunities.com] 
Sent: Friday, September 04, 2009 4:14 PM
To: 'Karen Walkerman'; James Hansen
Cc: bldg-sim at lists.onebuilding.org
Subject: RE: [Bldg-sim] Existing building HVAC modeling

 

See ASHRAE 90.1-2004 User's Manual, page G-21...HVAC Systems #1

 

"A complete HCVAC system exists...In a case like this, the proposed
building and baseline building models are the same and based on the
existing HVAC system."

 

Hope this helps.

 

Cam S. Fitzgerald, PE, LEED AP

 

Energy Opportunities, LLC

a 7group company

phone:  (717) 292-2636 x11

fax:  (717) 292-0585

e-mail:  fitzgerald at sevengroup.com

 

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Karen
Walkerman
Sent: Friday, September 04, 2009 12:07 PM
To: James Hansen
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Existing building HVAC modeling

 

>From table G3.1:

"The HVAC system(s) in the baseline building design shall be of the type
and
description specified in G3.1.1, shall meet the general HVAC system
requirements specified in G3.1.2, and shall meet any system-specific
requirements in G3.1.3 that are applicable to the baseline HVAC system
type(s)."

the only time the existing building properties are used are for the
building envelope.

--
Karen

On Fri, Sep 4, 2009 at 9:50 AM, James Hansen <JHANSEN at ghtltd.com> wrote:

Thanks for the response Seth.  The entire building is undergoing a
renovation (new windows, insulation, lighting)...and I'm going to keep
the existing HVAC system in the EXISTING portion of the building for my
baseline model.  I just don't know how to treat the NEW portion of my
building in the baseline model.  The plant is interconnected, so Item No
2 in Table G3.1 doesn't apply.  I want to include the existing building
in the model (and I have to).

 

Any other advice on how to properly set up the baseline HVAC system for
a new portion of an existing building if the proposed chilled water
plant is being expanded to accommodate new load but the existing airside
systems in the existing building are NOT being touched?

 

Common sense would say that my baseline building also has a new App G
chiller to accommodate new load and the new airside systems are shutoff
boxes....but if there is a chance that the new portion of the building
is treated as a standalone 15,000 square foot addition, packaged RTUs
may make the proposed system even more efficient.

 

Paul, thanks for the email...I'm going to look thru CIRs and see what I
can find.  Can't wait for LEED v3.0 where this convenient Option goes
away.

 

Thanks again,

 

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)

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

From: Seth P. Spangler [mailto:sspangle at rmf.com] 

Sent: Friday, September 04, 2009 9:23 AM

To: James Hansen; bldg-sim at lists.onebuilding.org
Subject: RE: [Bldg-sim] Existing building HVAC modeling

 

James,

 

If you are only adding an additional floor - and are not renovating any
portion of the existing 1st-4th floors then I would model the 5th floor
as if it was a new building by itself according to App. G guidelines.
See Table G 3.1 item no. 2 in 90.1-2004

 

 

If the entire building is undergoing a renovation but the existing HVAC
systems are existing to remain then the building would be modeled to
reflect the existing system types and capacities. Refer to the LEED
manual for these guidelines.

 

Hope this helps.

 

Seth Spangler, LEED(r) AP 

Project Engineer

 

RMF Engineering, Inc 

Ph: (843) 971-9639 ext:1497

Fax: (843) 971-9641 

sspangle at rmf.com

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of James
Hansen
Sent: Friday, September 04, 2009 9:07 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Existing building HVAC modeling

 

I'm modeling a building for LEED EAc1 compliance, and was wondering how
you are supposed to model existing building HVAC systems if you are
adding square footage to the building.

 

Let's assume you have a 4-story building with a 2-chiller HVAC plant and
dual temp boxes.  If you were to add a 5th floor to the building, what
would your baseline model look like?  I know that the 1st four floors
would use the existing HVAC system, but would your new 5th floor be
treated as a new 15,000 square foot area with packaged RTUs, or would
you add a new chiller to the existing HVAC chilled water plant, and have
that chiller meet all the requirements of App G, and have shutoff VAV
boxes for the 5th floor in lieu of dual temp boxes? 

 

For reference, under our proposed design, we are doing just that:
adding a frictionless chiller to the plant to make up the extra load.

 

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)

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

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