Year Round
All Year, Whole Year, Throughout The Year
adverb, noun
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.
ねんじゅう
This is a jukugo word, which usually means on'yomi readings for 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 ぢ is very rare it just switches to じ and you end up with じゅう. That's called rendaku.
この町のそらは、年中どんよりしています。
The sky in this town is overcast all year.
トーフグのしゃいんは、二十四じかん年中むきゅうではたらいている。
Tofugu employees work twenty four seven, year round.
この国では一年中雨が降るんだが、妻もまた年中その文句を言うんだ。
It rains year round in this country and my wife complains about it year round as well.