Calculating Baseline Fan Power and CFM?

The energy modeling software should be capable of autosizing the Baseline fan CFM given a 20 deg. supply air Delta T. Some software can also calculate the Baseline fan power allowance given the applicable pressure drop adjustments. If not you can use our calculator.

Hi Tyler, we predominantly use your calculator for calculating the baseline fan power. We input out the static pressure in energyplus software by taking a ratio of baseline fan power from calculator to design airflow rate in the floor(from peak cooling load simulation), which is whole multiplied by the fan total efficiency(generally taken as 60%). Does that meet the LEED requirements as baseline fan power in model ought to be less than the fan power allowance.

Or, is it suggested to keep everything autosized in the model and let it compute the total energy consumption. 

Appreciate your advise and sorry to reopen this thread.

The Baseline model should always be auto-sized, but you will need to define the fan power based on the calculated allowance unless the software has a built-in 90.1 Appendix G fan power calculation. My understanding is that EnergyPlus now has a W/cfm input, which would be more straightforward than your static pressure and efficiency approach. If not I would recommend verfying the resulting fan power against the Baseline fan power calculator. 

Hi Tyler, we are using design builder energy plus simulation engine but it never takes the pressure drop adjustments into account while incorporating the input details. However, the resulting fan power is always less than the calculated allowance from your calculator. So, we can't really decide what is supposed to be the correct final figure.

I would recommend reaching out to the DesignBuilder support team since this seems to be a software-specific question. 

Hello Anurag. Within the DesignBuilder help you can find an ASHRAE 90.1 modelling guide (DesignBuilder LEED and ASHRAE 90.1 Appendix G User Guide) which includes inside the Appendix B tips to adjust the allowed fan power for the Baseline systems (in few words, you only have to calculate the pressure drop which results in the desired fan power).

https://designbuilder.co.uk/helpv7.3/#HelpTutorials.htm?TocPath=Support%2520%252BTutorials%257C_____1

Even one step beyond, if you have licence for the Scripting Module and scripting skills, inside the EPNet library you can find scripts to automate Baseline fan power and other ASHRAE 90.1 calculations.

Namespace EpNet.LEED | EpNet

Hi Manuel,

Thank you so much for your helpful response and the reference to the Appendix B tips and scripting options in the EPNet library.

I was particularly interested in the scripting route you mentioned for automating Baseline fan power and other ASHRAE 90.1 calculations.

• Do you have any tutorial, documentation, or example scripts that could help a beginner learn how to use the Scripting Module in this context?

• Is there any community forum, GitHub repository, or knowledge base where users share such scripts or approaches for LEED modeling automation?

Also, are there any best practices or common pitfalls to keep in mind when trying to match the baseline fan power using pressure drop adjustments manually or via scripting?