The Museum uses a chiller/thermal storage system to both keep the building’s climate comfortable for our visitors in warmer months as well as to ensure proper humidity for the collections. The system produces ice during evening hours when demand is low and is placed in thermal storage units. Air is blown around containers with fluid chilled by that ice, which then circulates through the building during the day. As air conditioning usage is highest during mid-day, the Museum helps reduce our impact on the region’s grid system and prevent brown-outs. The Museum has a 99.4 Kilowatt photovoltaic solar array on its roof. An average residential solar array is between 2–4 Kilowatts, so the Museum’s is substantial. In fact, when the array was installed in 2002 it was the largest solar array in Illinois. You can see real-time monitoring of the solar array below, and there is an article in "Energy Seeds," a blog maintained by the Illinois Clean Energy Foundation, with additional information. The Museum also has seen energy savings of up to 40% by replacing its incandescent bulbs with fluorescent lighting, along with updating older fluorescent fixtures to newer, more energy-efficient models. LED lighting is being installed in phases as well, with the West entrance and parking lot recently converted.
When the Museum was built in 1921 there were six lightwells which provided large amounts of passive solar lighting throughout the building, but over the years these lightwells were filled in with collection storage areas (the Museum has over 26,000,000 specimens!). However, natural lighting almost exclusively lights the largest and busiest hall in the Museum, Stanley Field Hall.