Ladybug psychrometric chart / passive solar heating question

I am using the powerful psychrometric chart component in Ladybug, but have a question that I can’t seem to find an answer to online.

The passive solar heating strategy seems to have a mind of its own. I was using the GitHub file posted by @Chris from 2018 (

When you check Passive Solar Heating, the “comfort zone polygon” is huge, but the “strategy percent of time” reads as a small number (< 3%.). Also, it seems that when Internal Heat Gain is turned on (checked), Passive Solar Heating changes (%’s, as well as the polygon). The data seems to show this as well when viewed in a 3D comfort hours chart (the charts that show a spread of red—comfortable—over time of day for the year).

Any ideas what may be happening? Has anyone come across this before? I couldn’t attach the script here because it says i’m a new user (just created the ladybug–specific iscourse account). You can find the script here instead It is a slightly tweaked version of Chris’s file from GitHub. (psychchart component is clustered)

Thanks for any assistance you may be able to provide - this component is really awesome and is a great starting point for all projects.


Dear Martin,

I encountered a similar issue.
However, after some digging, I found an answer buried in this discussion linked below.

Basically, the small “strategy percent of time” is intended.
Quoting Chris Mackey:
"Not all hours that fall within the passive solar polygon are counted as comfortable and a given hour is only considered comfortable if it falls within the polygon AND the solar radiation for the last few hours of the EPW is enough to overcome the temperature delta between the outdoors and the building balance point. "

The thermal mass+night vent behaves in a similar way too:
The thermal mass+night vent is using a similar method to the PSH polygon in that it will only count a given hour as comfortable if there were cool enough temperatures in the previous hours to “night flush.” For this reason, even though the thermal mass polygon looks large, there are often a lot of hours inside of it that are not comfortable because the preceding hours are not cool enough.

Hope this helps!

Thank you @AdamBufacchi , I appreciate you sharing the links with me that you found. It is good to know that this wasn’t an error and is actually intended like you said.