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What are "Initial Design" and "Design" in the summary report when running Coincident sizing?

asked 2024-04-02 02:47:11 -0500

Keigo's avatar

updated 2024-04-02 07:35:09 -0500

When we run simulation with Coincident sizing, the html summary report shows Initial Design Capacity/Flow Rate/Power Consumption, etc. and Design Capacity/Flow Rate/Power Consumption, etc. I can't find clear explanation of these Initial Design values and Design values in I/O Reference and Engineering Reference. Does anyone know what they mean?

I guess that Initial Design values are intermediate products during Coincident sizing and Design values are the final results of Coincident sizing which are used in annual simulation.

However, I often get weird results. As an example, I show you the chiller sizing results of NonCoincident sizing and Coincident sizing with 5ZoneVAV-Pri-SecLoop.idf (V23-2-0) below.

image description

The chiller capacity is

Initial Design Capacity in Coincident sizing < Design Capacity in NonCoinsident sizing << Design Capacity in Coincident sizing.

Due to the nature of Coincident sizing, it cannot be greater than NonCoincident sizing. I think Coincident sizing in EnergyPlus has many bugs and is unusable. Hopefully the bugs will be fixed at some point. As a first step, I want to know what Initial Design and Design mean.

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answered 2024-04-02 11:17:18 -0500

updated 2024-04-02 11:18:19 -0500

I found some information in the EnergyPlus documentation. First, there is the Plant Coincident Sizing Algorithm:

A special report is issued to the eio file that provides details for the Coincident sizing option. Coincident plant sizing adjustments using HVAC Sizing Simulations run a sizing algorithm at the end of each Sizing Pass. The following report provides details on the calculations and observations from monitoring the previous Sizing Pass.

And then more specifically, the Input Field Description:

This field shows the field description/variable with units. When using HVAC Sizing Simulation for advanced sizing methods, there are two versions of the report for each component that might be affected. With HVAC Sizing Simulation, there is a first size value reported, which is the result of the Ideal Loads Sizing Simulation, and there is the final value after all the Sizing Passes have completed. This input field description will have “Initial” prepended to the description to indicate that this is the first size, the same report without “Initial” is the final size. Note that with HVAC Sizing Simulation, these reports will occur much later in the simulation and hence appear further down in the .eio file.

This is documentation for the EIO output file but surely applies to the html outputs too.

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Thank you for your answer! I haven't checked Output Details and Examples.

My guess was correct, and plant coincident sizing definitely has bugs.

Keigo's avatar Keigo  ( 2024-04-02 19:48:34 -0500 )edit

For what it's worth, there's at least one known issue for non-coincident sizing.

shorowit's avatar shorowit  ( 2024-04-02 21:44:52 -0500 )edit

That issue is about air flow rate (air-side), isn't it? I always have an unreasonable result in plant coincident sizing (water-side) rather than air-side...

Keigo's avatar Keigo  ( 2024-04-02 22:08:24 -0500 )edit

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Asked: 2024-04-02 02:47:11 -0500

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Last updated: Apr 02