I m modeling a 52 floor building and 2 detached retails buildings,The proposes system are chilled water system with FCU except : 1-8 floors core and shell ( m0re than 78000 sqft) 2- G+2floors retails core and shell (around 20,000 sqft) floors 3-G+1 floors shops core and shell (around 10,000 sqft) as per ASHRAE 90.1-2007 table G.3.1.1.A the basline & proposed systems should be : 1- Packaged VAV DX 2-PSZ-AC 3-PSZ-AC my question is what shall I do if the cooling load of these spaces are considered in the chiller load and tap points are provided in the design? shall i model them as per ASHRAE and deduct the load from the chillers..But that will not be proposed design? what to do?

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Jean Marais

b.i.g. Bechtold DesignBuilder Expert

LEEDuser Basic Member

581 thumbs up

Wed, 06/27/2012 - 09:20

For the C&S spaces you mentioned (1,2&3): Model the baseline as per ashrae (ignore tap points). Model the proposed for these spaces just like the baseline (ignore tap points). Think of it as if the tap points are not used and you have an extra system(s) taking care of the cooling. This is according to the standard. This is irritating because your chiller will be running at a very low part load where the efficiency is rubbish. Any thoughts, Marcus?

Tarek Dalati

Sustainbility manager

CRHI

LEEDuser Basic Member

70 thumbs up

Wed, 06/27/2012 - 09:29

Jean, I just noticed that ,As per AHSRAE table G.3.1.1a if I have non-residential more than 5 floors i can use system 8 ( because ihave boilers) but what about the retails? can i say that all part of my non residential? or i have to use system 4? and Jean I am simulating the retails because they are fed from the chillers and boilers if I am going to model them using DX system what is the use of modeling them i can pretend that only my tower is under certification and not these 2 detached retails buildings. What do you think?

Jean Marais

b.i.g. Bechtold DesignBuilder Expert

LEEDuser Basic Member

581 thumbs up

Wed, 06/27/2012 - 09:42

Now you're talking about the LEED Project Boundry. Everything in the LEED Project Boundry must be simulated (except non-building shading like trees, or reflective natural features like lakes). As the project boundry effects all credits in the leed rating system, this is not an easy answere. Also, if spaces inside the same building are part of that buildings normal functioning (i.e. needed to funtion, like a parking garage) then it must be included in the leed project boundry. This is according to my current state of knowlege and is my interpretation...in no way sacrasanct.

Tarek Dalati

Sustainbility manager

CRHI

LEEDuser Basic Member

70 thumbs up

Wed, 06/27/2012 - 09:49

ok so for the office will use system 4 what about the retails?

Jean Marais

b.i.g. Bechtold DesignBuilder Expert

LEEDuser Basic Member

581 thumbs up

Wed, 06/27/2012 - 10:07

Your retail [2- G+2floors retails core and shell (around 20,000 sqft) floors] is (Non-Res) and (3 Floors or less) and (<2300 m² ) system 3 ---PSZ-AC (DX fossil fuel furnace), unless your proposed building boiler is "Electric and Other"

Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Wed, 06/27/2012 - 13:54

Going back to the original question. Model the Proposed as designed, almost always. The Proposed HVAC system does not really matter, just the heating fuel. Model the whole Baseline according to Table G3.1.1A. Secondary systems in the Baseline can be modeled if any of the exceptions in G3.1.1 apply. So in your case the 52 story building sounds like a system 8 and the two smaller buildings system 3 or 4. To complicate things further since there are three buildings this could probably use the district energy guidance. Jean is correct that the shell spaces should be modeled the same as the Baseline if the systems in those spaces have not been designed according to Table G3.1-10 Proposed.

Tarek Dalati

Sustainbility manager

CRHI

LEEDuser Basic Member

70 thumbs up

Wed, 06/27/2012 - 13:57

I forgot to mention that 46 floors are residential so I will use system 2 for them the 8 floors offices I will use system 8 retails I will use system 4. so in the proposed design I will enter the chiller capacity as it it but without taking into consideration the retails because they are modeled as baseline now DX system AM i correct?

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