The sky in this town is dull all year.
Tofugu employees work twenty four seven, year round.
It rains year round in this country and my wife complains about it year round as well.
The year middle sounds like it should be something like "the middle of the year," but it's not. Think of something that happens in the middle of the year and then all other parts of the year. It's just referring to everything within this year, which is how we get year round.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well. 中 does have a strange reading, though, which is じゅう. This is basically just ちゅう changing to ぢゅう, but since nobody uses ぢ it just switches to じ and you end up with じゅう. That's called rendaku.