[Equest-users] electric heating issues

[Will Mak]

I thought the heating system only referred to the heating source itself? (not including preheat fuel source??)

 

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/> 

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

 

From: Rob Hudson [mailto:rdh4176 at gmail.com] 
Sent: Thursday, March 24, 2011 12:23 PM
To: Will Mak
Cc: Bishop, Bill; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] electric heating issues

 

as per the baseline system discussion, i would use System 5.  If you read the 90.1 manual, it says if you use a fossil/electric hybrid heating system to implement System 5 in the baseline.

 

 

Rob

 

 

On Thu, Mar 24, 2011 at 12:14 PM, Will Mak <wmak at epsteinglobal.com> wrote:

See comments below, thanks!

 

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 <tel:%28312%29%20429-8116> 
F: (312) 429-8800 <tel:%28312%29%20429-8800> 

E: wmak at epsteinglobal.com
W: www.epsteinglobal.com <http://www.epsteinglobal.com/> 

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

 

From: Bishop, Bill [mailto:wbishop at pathfinder-ea.com] 
Sent: Thursday, March 24, 2011 10:21 AM
To: Will Mak; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] electric heating issues

 

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.

 

Yes, I am modeling the gas boilers in the baseline purely for preheating. So you are saying that because I am modeling gas boilers (even though they are just for preheat), I technically can run with System #5 for my baseline model?

 

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.

 

I currently have both models at minimum leaving temperatures for preheat of 60F (which is the design preheat leaving air temp). You would think that because the preheat is pumping out 60F air to the VAV boxes, you would see similar zone heating requirements. However, the proposed design's zone heating is much higher. Could it possibly be the parallel fan powered boxes that help the baseline model that much?

 

Make sure you are modeling your ventilation identically between the baseline and proposed models, unless you have DCV.

 

Yup, I have the same OA cfms for both models

 

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.

 

Currently, I have the cooling supply temp at 52.5 F. This was because the design engineer wanted to take advantage of the efficiency of the chillers on the project for cooling energy savings. Perhaps this could be the issue? The cooling temperature is too low that it triggers the reheat/baseboard to kick on all the time??

 

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.

 

So you are saying that electric heat/reheat is bad for 90.1 PRM??

 

Thanks for the response!

 

Regards,

Bill

 

William Bishop, PE, BEMP, LEED® AP | Pathfinder Engineers & Architects LLP

Mechanical Engineer

 

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T: (585) 325-6004 <tel:%28585%29%20325-6004>  Ext. 114                F: (585) 325-6005 <tel:%28585%29%20325-6005> 

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 <tel:%28312%29%20429-8116> 
F: (312) 429-8800 <tel:%28312%29%20429-8800> 

E: wmak at epsteinglobal.com
W: www.epsteinglobal.com <http://www.epsteinglobal.com/> 

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

 


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