[ldolse]

HTML is zipped up when added to Calibre because an html ebook can contain many files -css, images, etc. Callibre's library only stores a single file per format, hence the requirement for zipping html ebooks.

If you don't want your files which were originally single file html to be split when you convert them to epub then change your epub output settings to not split on page breaks and change the max split file size to a few megabytes. Note epub files generated in this manner won't have much compatibility with many ebook reading devices, but they will be more or less the same as your original html - i.e. single flow. You can unzip the epub the same way you unzipped the zip file.

Your first post was asking for suggestions - you did not even indicate you were aware of epub reading software in that post - apologies if you took offense at suggesting the use of such software...

Short of that I don't have anything else helpful to suggest, except I don't think Calibre can do exactly what you want right now, it would be a feature request, which you're welcome to get involved to implement.