The ACC contract currently includes 2-3 ND games per season. ND NBC contract includes their 7 home games. That leaves a few games that are not currently included in either contract. Also ESPN is now getting 28 more conference games instead of non-conference foes. Hopefully there was some negotiation.
Also as easy as this was to work out with ND. What are the odds this is part of a bigger agreement between ND and the ACC. Pooling of funds with ND's NBC contract actually takes about $1M away from every ACC team. Would they do this deal without some assurances of long term payoff?
Answered my own question. Even if every ACC team played their non-conference game at home that is still only 84 games instead of 98 televised by ESPN. ND also loses 1 game as ND can only play 6 at home. My guess is the only reason the TV providers agreed is because NBC gets Clemson vs ND and ESPN gets more conference games to make up the difference in total broadcast.