Case Studies – Temporary Climate Solutions

High temperatures challenge Radisson Blu hotel construction

For decades, Radisson Blu has been well-known as a luxury hotel brand in Europe and Asia. To bring the brand to the US in a big way, Radisson located its flagship property at the Mall of America in Minneapolis - the largest retail mall in the country.

Construction was witnessed by thousands of prospective customers every day, providing Mortenson with a constant aesthetic challenge: minimize the messy reality of construction, and don’t damage the finished exterior of this high-fashion, luxury building.


Building a five-star, 500-room flagship hotel for Radisson Blu on a tight schedule was tough enough. But in 2012, Mother Nature also gave Mortenson Construction her hottest on-record summer to add to the challenge of tight temperature and humidity specifications for the installation of cabinetry and millwork.

Neil Cooper, Project Superintendent for Mortenson, faced the further problem of keeping the interior of the high-rise tower both dry and cool during millwork installation. “We had to maintain the humidity below 40% and the temperature below 78 degrees Fahrenheit (°F) at all times, but our weather was much hotter than expected for a Minneapolis summer,” said Cooper. In addition, we were unable to circulate the air-conditioned air. The building's exterior finishes were at risk from the extra ductwork needed for return air, which would have had to hang off the side of the building compromising the exterior finishes during wind and rainstorms. “We needed a solution that would maintain conditions even though we had to blow all our conditioned air out of the building several times every hour.”


John Pfeffer, Business Development Manager for Polygon, recommended using multiple high-capacity HCU units, delivering 6,000 to 8,000 CFM each to the corridors of every floor as millwork installation progressed up the building. He explains that “our HCU equipment combines cooling and desiccant dehumidification in a single compact package, which reduces the amount of space needed for equipment,” said Pfeffer.

The small equipment size allowed Mortenson to place all the systems on rooftops out of sight of spectators. The location on the hidden rooftop, made possible by the compact but powerful HCU design, was also helpful. “It was a tight fit, which is not ideal” explains John Pfeffer, “but placing the equipment on the roofs of the lower parts of the building let us run all the condensate to roof drains. Placing units at each floor could have meant high volumes of condensate flowing down and possibly staining the exterior walls, which was out of the question for this flagship luxury hotel.”

Additionally, the HCU provides cool air even when the outdoors is far hotter and more humid than expected. Historically in Minneapolis, extreme air conditioning design conditions have been assumed to be 91°F and 94 grains per lb. But during the summer of 2012, the outdoor air was regularly above 98°F with humidity of over 127 grains.

Mortenson’s warranty of the building’s HVAC system also benefited from the control of temperature and humidity provided by Polygon’s portable equipment. In some projects, a building’s new cooling equipment is used to provide a modest amount of cooling during the installation of millwork. But as John Pfeffer explains, “starting the building’s systems during construction puts the manufacturer’s warranty at risk. Permanent AC systems optimized for energy are not designed or built for the large cooling loads of semi-open construction, and certainly not designed for the normal dust and debris of a construction site. Our portable equipment allowed complete control of humidity as well as temperature, without any need to risk the warranty of the high-end cooling equipment installed in the building.”

As Neil Cooper notes, “the Polygon units kept the rooms below 78°F and the humidity at or below 40%. Our tight millwork specification was maintained even without cool air recirculation, and our installation schedule stayed on track despite record-breaking heat.”



Because each project is unique and demands various things, flexibility is essential. Aesthetics and scheduling were crucial aspects in this Radisson Blu case that needed to be preserved, which is exactly what was done. The hotel was successfully built on a tight schedule with a tough spec during summer with record-breaking temperatures and humidity.

Reducing Energy Costs

Using our system to purge the building’s air with fresh air several times each hour for months, the ultimate quality of the building’s indoor air improved. Purging rids the building of any volatile organic vapors that might be emitted during construction. Consequently, such long-term “building flush out” qualifies for extra credit under the standards established by the LEED® program of the U.S. Green Building Council.

For more information on Construction Drying solutions from Polygon, please click here.

Mortenson kept environmental conditions in-spec, in spite of record-breaking heat.

"Our tight millwork specification was maintained even without cool air recirculation, and our installation schedule stayed on track despite record-breaking heat.”

Neil Cooper, Project Superintendent at Mortenson