[Equest-users] electric heating issues

Bishop, Bill wbishop at pathfinder-ea.com
Thu Mar 24 08:20:36 PDT 2011


Will,
 
The first thing I would do is reconsider your selection of System 6 for
the Baseline. Since you have gas boilers for preheat, I would choose
System 5. System 6 is all electric, but you say your baseline gas
consumption is high, so you are currently modeling gas boiler(s) in the
baseline. Unfortunately, if you go with System 5, your baseline reheat
will be hot water which will save cost versus your proposed design.
 
Since both your baseboards and your reheat are electric in the proposed
design, your high electric use is probably not a baseboard control issue
(provided you are not showing many unmet load hours). One thing to
consider is your preheat leaving temperature - making it higher will
favor the gas boilers and reduce the zone electric heating. I'm guessing
that the requirement for identical preheat coil control in G3.1.2.3
means that you use the same preheat leaving temperature in the baseline
and proposed models.
 
Make sure you are modeling your ventilation identically between the
baseline and proposed models, unless you have DCV.
 
Check your reports to make sure you don't have a lot of simultaneous
heating and cooling going on. Maybe you can increase the cooling supply
temperature (and convince the HVAC designer to do it) to the highest
allowable temperature that meets cooling and dehumidification loads.
 
Your baseline may have similar, or even less, heating load depending on
the proposed envelope, due to the reduced lighting load in the proposed
design. With electric baseboard and electric reheat, it will be
difficult to show much heating savings unless you have a much better
envelope or ventilation heat recovery. We should all be red-flagging
electric reheat and baseboards whenever we see them on projects.
 
Regards,
Bill
 
William Bishop, PE, BEMP, LEED(r) AP | Pathfinder Engineers & Architects
LLP
Mechanical Engineer
 
 134 South Fitzhugh Street                 Rochester, NY 14608
T: (585) 325-6004 Ext. 114                F: (585) 325-6005
wbishop at pathfinder-ea.com           www.pathfinder-ea.com
<http://www.pathfinder-ea.com/> 
P   Sustainability - the forest AND the trees. P 
________________________________

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Will
Mak
Sent: Thursday, March 24, 2011 10:31 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] electric heating issues
 
Hello all,
 
I currently modeling a project for LEED NC v2009 submission for a
corporate office building that's roughly 125,000 SF. The proposed
design's primary HVAC system are AHUs + VAVs w/Electric Reheat
supplemented with electric baseboard along hot water preheat generated
from gas boilers. This system also uses chilled water with very
efficient chillers from a DES. The baseboard is suppose to take care of
the envelope loads and the VAV electric reheat coils will take care of
the rest. Based on the size of the building, the baseline HVAC system
shall be System #6: Packaged VAV with PFP Boxes.
 
I'm pretty down the road on the models and for some reason cannot get
savings between the 2 models. The heating energy use on electrical
consumption overrides any savings attributed from lighting, site
lighting, cooling energy use, etc. Also, I know that in 90.1-2007,
preheat must be model identical on the proposed and baseline models. I
am having a hard time modeling both to be the same (inputs for preheat
capacity are the same but the energy use is different). The gas
consumption is significantly higher on the baseline model. 
 
I double checked the loads from both models and the heating/cooling
requirements are roughly the same so there's nothing wrong with the
building shell/internal load inputs. Any guidance on how to reduce the
consumption on the heating use for electrical consumption would be
great! I am confused why the baseline model wouldn't require similar, if
not more, heating requirements and isn't using more heating use for
electrical consumption. Also, guidance to ensure that the preheat is
model identical would help too!
 
Thanks!
 
Cliffnotes:
Proposed System: AHUs w/VAV Electric Reheat + Electric
Baseboard//Chilled Water from DES//Hot Water Preheat
Baseline System: Packaged VAV with PFP Boxes
Issue #1: Heating electrical consumption is super high on proposed model
despite similar loads for both models.
Issue #2: Preheat is not being model identical as required from
90.1-2007. Capacity and design inputs are same for building but baseline
building is using significantly more gas.
 
William Mak, LEED Green Associate
Mechanical Design Engineer

EPSTEIN
Architecture
Interiors
Engineering
Construction

600 West Fulton Street
Chicago, Illinois 60661-1259

D: (312) 429-8116
F: (312) 429-8800
E: wmak at epsteinglobal.com
W: www.epsteinglobal.com <http://www.epsteinglobal.com/> 

* Epstein is a firm believer in sustainability. We ask that you please
consider the environment before printing this e-mail.
 
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