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asked 2015-07-14 12:26:19 -0500

hugopft's avatar

updated 2015-07-14 13:49:33 -0500

I am modeling a building to submit to LEED certification and I have a concern regard to the baseline HVAC system and the increment of 15% applied to the Equipment Capacity.

First, regarding to the baseline HVAC system, I am using two chillers and fan coils to met the thermal load of the proposed model. Considering that my building has three floors, I choose the system 4, as presented in the picture below.

To represent this system in EnergyPlus, I set the following system in OpenStudio (Packaged Rooftop Heat Pump).

Is it the right representation of the system 4 (appendix G- Table G.3.1.1B)?

Second, Should I Set the 15 % for both models, baseline and proposed model, or only apply this coeficient for the baseline model.

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I have a couple of questions about your baseline HVAC choice. There are a few details you didn't add to your question which are important when choosing the baseline system. 1. What fuel are you using for the heating in your design case, if you are using any fossil fuels at all? Then you can not use system 4, it would be system 3. 2. What is the total floor area of your building? If it is more than 2,300 sqm then even if it has 3 floors it would be system 5 or 6. Otherwise the system set up looks ok.

Annie Marston's avatar Annie Marston  ( 2015-07-14 14:11:04 -0500 )edit

I am using eletricity and the the total area of the building is 2732 m².

hugopft's avatar hugopft  ( 2015-07-14 20:08:58 -0500 )edit

In that case I think you should be using system 6, system 4 is for buildings less than 2 300 sqm. System 6 uses 1 AHU VAV system per floor with PFP boxes in each zone.

Annie Marston's avatar Annie Marston  ( 2015-07-15 07:10:47 -0500 )edit

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answered 2015-07-14 13:34:16 -0500

I can say that the system templates in OpenStudio are designed to follow the ASHRAE Appendix G system types. It is no coincidence that the names you see in the OpenStudio UI match the names used in Appendix G (Packaged Rooftop Heat Pump for example). I can't reliably answer the second part and in fact the main reason we have not overtly called the templates out as ASHRAE system types is that the templates will not precisely follow all of the rules appendix G spells out in terms of sizes, fan efficiency etc.

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Thank you very much!

hugopft's avatar hugopft  ( 2015-07-14 21:22:12 -0500 )edit

answered 2015-07-14 13:48:21 -0500

To answer your second question, Section G3.1.2.2 of ASHRAE Standard 90.1-2007 is where the 15% number comes from and says:

G3.1.2.2 Equipment Capacities. The equipment capacities for the baseline building design shall be based on sizing runs for each orientation (per Table G3.1, No. 5a) and shall be oversized by 15% for cooling and 25% for heating, i.e., the ratio between the capacities used in the annual simulations and the capacities determined by the sizing runs shall be 1.15 for cooling and 1.25 for heating.

So this applies to the baseline only. The proposed design should use the actual capacities for the design.

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Thank you very much.

hugopft's avatar hugopft  ( 2015-07-14 21:21:48 -0500 )edit

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Asked: 2015-07-14 12:26:19 -0500

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Last updated: Jul 14 '15