Michaud Cooley Erickson project profile: Bell Museum of Natural History
Engineering firm: Michaud Cooley Erickson
2019 MEP Giants rank: 73
Project: Bell Museum of Natural History
Location: St. Paul, MN, U.S.
Building type: Educational facility, office building
Project type: New construction
Engineering services: Automation, controls; electrical, power; energy, sustainability; fire, life safety; HVAC, mechanical; lighting; plumbing, piping
Project timeline: December 2015 to January 2018
MEP/FP budget: $588,000
As with any project, the Bell Museum had a list of unique challenges that the MCE team faced throughout the project. Specifically, selecting the mechanical heating, ventilation and air conditioning (HVAC) system takes careful consideration. Chilled Beams, Variable Refrigerant Flow (VRF), Geothermal and Dedicated Outdoor Air Systems (DOAS) systems were modeled and compared to a more conventional Variable Air Volume (VAV) system with low temperature baseboard radiation heating. One of the challenges for the mechanical system was to provide comfortable conditioning and ventilation with 10 staff people in the building during nonbusiness hours, up to 350 people during large events and everything in between.
The final mechanical system selection includes two large interconnected air handling units. Each air handling unit includes two direct drive fans with Variable Frequency Drives (VFD’s). To provide the ability to reduce the airflow down to 25% of maximum through fan shutdown and even lower using the VFD’s, resulting in significant energy savings.
Ventilation air to the building is provided through a DOAS system, which includes an energy recovery wheel. During low cooling load conditions, the entire building can be conditioned with this air handling unit alone. When space cooling loads exceed the capacity of the DOAS system, the air handling units are ramped up to meet the demand. The DOAS system and conditioning air units share common distribution ductwork downstream of the zone control VAV boxes.
Chilled water for the air handling units is provided through air cooled chillers, which include heat recovery. The heat recovery provides dehumidification control through the DOAS unit in the summer when the exhibit design conditions are 74°F and 50% RH maximum. The separate cooling loop uses chilled water in the summer and a heat rejection coil in the DOAS unit during the offseason, which uses the outdoor air to cool the loop, which the added benefit of using the rejected heat to preheat the DOAS outdoor air.
The heating system for the building is condensing boilers operating between 140°F and 110°F. This provides a boiler operating efficiency of about 92%. The heating water serves fin tube radiation, radiant panels and heating coils installed in parallel fan powered VAV boxes. Because the ventilation air to the spaces is provided through the DOAS, the primary air through the parallel fan powered VAV boxes can be shut off before the heating coil is activated, resulting in zero reheat.
The main challenge of the power aspect was determining generator power requirements for critical equipment for the exhibits, including getting the correct amount of power to all the lighting components of the Bell Museum. Lighting obstacles came with controlling sound carried by heat sinks in the planetarium and concealing light fixtures, so the focus remains on the exhibit. Proper lighting design was key on the interior to bring the exhibits to life, but also on the exterior and throughout the site to showcase the building.