Businesses work on indoor air quality for returning workers MARK ZDECHLIK, Minnesota Public Radio News May 30, 2021 FacebookTwitterEmail ST. PAUL, Minn. (AP) — Building ventilation systems bring in lots of outdoor air, but they aren’t designed to rely exclusively on fresh air. Instead, it’s a balancing act: filtering and conditioning inside air while replacing some of it with outside air. Fine-tuning it all is the challenge facing many businesses, including Twin Cities software company LuminFire. Its space is ultra-modern and open plan — couches and bistro tables abound, while cubicles are scarce. But CEO Tim Cimbura says the welcoming space has been largely empty because of the pandemic. Most LuminFire employees have been working from home. Cimbura wants them back, in person, crafting ways to help companies increase efficiency.