I would guess simply cost. Air conditioning has a high energy cost, especially if your building isn't air tight, which many old buildings are not. In the UK companies can be tight fisted about air conditioning even though they could afford it; an abbey in Hungary may not have enough revenue to pay for it.

Having said that I wonder if they also have a damp issue, insects need some degree of moisture if they are eating stuff like paper.

They have electricity though right? Then they’re not too rural to have AC?

> but unless you're deeply, deeply into repetitive religious tracts of 600 years ago, most of the collection is more of a curiosity than a valuable resource to modern scholars.

It's an abbey, so they are probably into religious tracts and it has cultural and sentimental value to them. E.g. if it has a Bible from the 13th century then it's worth preserving even if it's just the usual stuff.

> I've visited that library. It's a high-ceiling architectural joy, but unless you're deeply, deeply into repetitive religious tracts of 600 years ago, most of the collection is more of a curiosity than a valuable resource to modern scholars.

You know, there are modern scholars that study that stuff, both directly and as a resource for studying other areas.

Is that validated for books? Old paper is chemically and mechanically fragile; it's not obvious that gamma/ionizing radiation is harmless to it.

Ultraviolet light is well known to be damaging,

https://www.nedcc.org/free-resources/preservation-leaflets/2... ("Protection from Light Damage")

https://www.loc.gov/preservation/care/light.html ("Limiting Light Damage")

[late edit]: And if you search the literature, gamma irradiation is known to affect the texture of certain fruits—and if you ask why, one of the studied mechanisms is that fruits' cellulose polymers—which paper is also made of!—are easily broken by gamma rays:

https://sci-hub.se/https://doi.org/10.1002/pol.1957.12026114... ("Effect of gamma-radiation on cellulose" (1957))

> "Cellulose is degraded at gamma-radiation dosages equal to or below those required for softening plant tissues such as apples, carrots, and beets. Therefore it seems probable that the degradation of this cell wall constituent is a major factor in the radiation-induced softening of plant tissues."

The effect on thin, old paper should presumably be the worst, no?

[edit]: And this paper says the lethal gamma dose for one species (different one) of pestilential beetle is 1,000 gray, or 100 krad. That's a bit higher than the threshold doses for cellulose damage, from the other paper: 34–64 krad. Stressing that I have no clue know how those numbers translate to paper integrity.

https://www.nature.com/articles/s41598-023-43739-x ("The lethal and sterile doses of gamma radiation on the museums pest, varied carpet beetle, Anthrenus verbasci (Coleoptera: Dermestidae))

or to fumigate entire building

Even among the scanned books there are tons of untranslated ones. I've collected a few that I'd like to do editions of with commentaries and translations—they're all on the same topic, which up until a few years ago nobody thought existed (in fact, someone's book on a related topic denied that these existed, because the author didn't know about them). I found them all initially through scans on Google Books.