Add cooling demand

[ekatef]

Changes proposed in this Pull Request

The PR adds implementation of cooling demand similarly as it's done for heating

Checklist

• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Unit tests for new features were added (if applicable).
• Newly introduced dependencies are added to environment.yaml, environment_docs.yaml and setup.py (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the MIT license.

[lkstrp]

Looks good to me if we don't touch general things, but method wise I would like to ping someone who is more into atlite.

[ekatef]

Looks good to me if we don't touch general things, but method wise I would like to ping someone who is more into atlite.

Thanks for the quick response and coordination @lkstrp! 😄

[fneum]

LGTM! One thing you could clarify is how the 23°C default threshold was chosen, but it's a very minor comment.

[ekatef]

LGTM! One thing you could clarify is how the 23°C default threshold was chosen, but it's a very minor comment.

@fneum thanks a lot for looking into that! Have added a short comment on that to the docstring.

Adding a bit more details here to facilitate tracking the things, as a default threshold can be quite important, especially for the regions where the warm season temperatures are around the threshold.

Currently, there is no globally-accepted standard for CDD definitions. For US, EIA recommends 65F = 18.3C, while for Europe the official definitions are more liberal, like 22C by UK Met Office and by Umweltbundesamt, and 24C by European Commission.