The sweep helped the Storm (10-17, 6-12 Iowa Conference) earn a split in the series after dropping two games to the Beavers (14-14, 6-10) on Saturday.
Pennings (3-3) surrendered just seven hits to Buena Vista in the opener en-route to the complete-game win. After allowing two runs in the fourth, he went on to retire 9 of the next 12 batters.
The Simpson offense got to starter Scott Harris early, taking advantage of three walks to score three runs in the first inning. Blake Heitmeier drew a free pass with the bases loaded and Ethan Hale drove in two on a single to give Pennings an early cushion.
Buena Vista tied the game on an Alex Davis single in the fourth, but Tyler Crandell drove in what would be the winning run with a single in the fifth.
Crandell finished with three hits and Barr – who went 7-for-8 in the doubleheader – went 3-for-3.
Harris (1-2) struggled to find the strike zone, walking five and allowing four runs – all earned – in the loss.
A big fourth inning by Simpson proved to be the difference in the nightcap.
With the game tied 2-2, Simpson scored eight runs off seven hits and an error to pull away in the deicing frame. Crandell had two hits in the inning alone, leading things off with a double and chipping in with a run-scoring single.
Barr and Brett Crable had four hits apiece and Taylor Neff (1-0) held Buena Vista to one hit in 3 2/3 innings of relief for the Storm. Neff entered with the bases loaded and Simpson leading 12-6 in the sixth, but induced an inning-ending 4-6-3 double play to escape the threat.
Adam Bernstrof (2-1) got roughed up for eight runs off six hits in the loss.
Simpson hosts conference co-leader Coe in a four-game set Friday-Saturday, April 26-27. The Kohawks (20-7, 14-2) swept Loras over the weekend.