What is the difference between HAVC load calculation from Heating and Cooling load option and System Analysis Option?

[utech.udara]

I have noticed there are two options for cooling load calculation in Revit.

• One is from Heating and Cooling Loads in Reports and Schedules tab 
• Second Option is by running HVAC load calculation in Energy Optimization > Systems Analysis 

Check the Image Below.

I input space and zone data and analyzed through both ways for same model. Yet it get values as peak cooling load with a drastic difference. 

Does anyone know the reason for that and why there are two options for same purpose?

 

[robert.klempau]

Hello @utech.udara ,

I have a few links for you that might help you.

How to use System Analysis in Revit

Systems Analysis

See also the topic: Best Practices for Systems Analysis

Heating and Cooling Loads Analysis

[utech.udara]

Hi, 

Thank you for quick reply.  I have already gone through links you have provided.  But still i doubt about two different results from two methods.

[Kevin.Lawson.PE · Accepted solution]

The difference is that the Heating and Cooling Loads Tool uses a Radiant Time Series Method (RTSM) calculation engine to calculate loads and the Systems Analysis load calculation tool uses a Heat Balance Method (HBM) calculation engine provided by EnergyPlus.

The RTSM typically calculates slightly more conservatively (the load calculated is higher than the true load imposed in real world conditions) while the HBM is typically more accurate, but may underestimate loads.

The RTSM calculates loads component by component, so you can see the load coming from the window, roof, internal, ect. The HBM only calculates one number for the load and you can't see which component is driving the load.  EnergyPlus attempts to break that number back out into components, but does a poor job.  For example, you may see a huge interzone load going between floors, even though that's impossible because both floors are at the same temperature setpoint. This isn't because the load is wrong, it's because the HBM doesn't lend itself to reporting.

The RTSM is what most engineers are used to looking at.  It's what Trane Trace 700 uses.

As of now, it seems like the Heating and Cooling Loads tool will not be available in version 2022 onward, which is a shame because with Trane Trace 700 going offline there will not be a lot of RTSM engines available anymore.

[utech.udara]

Thank you very much for the explanation. 

I also noticed same variation in output but couldn't find the reason behind. Your explanation helped me to understand the senario.

Thanks

[HVAC-Novice]

Actually in T700 you can set it to use the HB method and it will give you analysis results that break out the components.

I think T3D (uses energy plus) only does HB, but I don't know I recall correctly. but i asked their support some time since it doesn't have an option to select the method anymore. 

[sdcartmell]

You can reactivate the legacy Heating and Cooling Loads tool by editing your revit.ini file:

About the Revit.ini file:
https://help.autodesk.com/view/RVT/2023/ENU/?guid=GUID-FE24D0A5-4603-41A5-BACB-4122993AFA6A

Misc settings in the Revit.ini file (including turning on the H&C Loads Analysis):
https://help.autodesk.com/view/RVT/2024/ENU/?guid=GUID-B01A6B07-4FF2-4115-8B61-1274FAF9CC91

The helpful tip that led me to this discovery (thanks Autodesk help docs!)
https://help.autodesk.com/view/RVT/2024/ENU/?guid=GUID-2DD2759D-3E3A-4AE7-BB37-0DF53981591E