Reference for HVAC System Library

Thank you for including OpenStudio 90.1 HVAC systems in Honeybee! Where can I find reference for system assumptions, I looked for on the OpenStudio website, couldn’t find it…


I can tell you that most important assumptions about systems 1-10 are contained within Appendix G of ASHRAE 90.1 (particulary around table G3.1.1). This includes all assumptions about supply temperatures, COPs, economizer controls, etc. Anything that is not specified in Appendix G (like the size of the HVAC components) is auto-sized by default in OpenStudio/E+, using the ddy file and your HBzones.

You can buy Appendix G from here but I have personally learned much more about the systems just by opening .osm files in OpenStudio and browsing through the systems in the interface. The OpenStudio interface is really clean and organized such that I have had a much easier time understanding systems there than in other software interfaces or in complete HVAC drawings for buildings. You want to look at the ‘HVAC System’ tab and in the ‘Thermal Zones’ tab to get a full understanding of the system components using this method.

If you could be more specific about which assumptions you are trying to understand, I might be able to point you to some better resources.

Hope this helps,


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Thank you Chris I will look at the OSM files. When I’ve built 90.1-App-G models by hand the fan power is the tricky bit. The model has to be run twice. First time to obtain AHU air volumes used for fan power calculation. Calculated fan powers are entered into the model and it is re-run. I will see what the fan power assumptions are in the OSM files, since that fan power process is probably not yet included and automated.


Your specific question about the fan is helpful narrows down the topic a lot. Still, there are a number of variables related to the fan that have the words “Fan Power” in them. In particular, if you open an OSM in OPenStudio and click on a fan, you see there’s “Fan Power Minimum Flow Rate Input Method”, “Fan Power Minimum Flow Fraction” and several “Fan Power Coefficients”.

You can see on the Honeybee airDetails component that I give you the option to override many aspects of the fan like the fanEfficiency and the fanPressureRise. If you need the ability to change one of the fan power variables, just let me know and I can add it into the airDetails component.