The Aqua tower is an 82 story high-rise building located in downtown Chicago designed by Studio Gang. The mixed use structure holds a hotel (3-17), residential apartments (18-53), condos (53-81) and retail space. Each floor covers approximately 16,000 sq ft (1,500 m2) which totals to 2 million sq ft. The project is LEED certified on the most basic level.
The distinctive balconies that cantilever between 2-12 ft not only give the building its organic character but also act as a passive system providing shading and reducing heat gain during the cooling season. However, as concrete is a good conductor of heat, some residents report that heat radiation from the building during the winter. The design team have investigated adding thermal breaks between the interior and exterior of concrete slabs but was proven to be to difficult to effectively achieve as every floorplan is unique, but in terms of overall energy use the heat loss in winter is surpassed by savings made by reduction of air cooling during the summer due to cantilever, glazing and natural ventilation. Moreover, Studio Gang tackles the heat island effect by an 80,000-square-foot planted garden on the tower’s park located on top of the base that hold the tower.
While visiting the Aqua Tower we were first introduced to the chief engineer named Armin. He explained the general HVAC system before taking us on a tour of the mechanical rooms, control rooms and the roof of the building. He explained that the building was originally intended to be all condominiums but because construction occurred when the recession of 2008 happened the program was changed to be part hotel and apartments as well but parts of the HVAC system remained how the original plans were for only condos. The building is legally split into three different owners: the Radisson Blu Hotel, the condominium associate (Armin worked mainly for) and the apartments. He was the chief building engineer from the beginning of construction 10 years ago so he knew the building from inside-out.
Before going on tour we asked about the locations of the chiller and boiler rooms and he explained that there was no chiller room because they purchase all of their chilled water from a company called Enwave located on Jackson and Franklin and is piped in from a nearby generation plant. He said that they spend $320,000 a year for chilled water so they are looking to join the construction costs of a chiller being built in a nearby new construction to utilize it from them instead at a cheaper cost. Looking online at Enwave’s website I found that they provide chilled water for many other buildings in downtown, as seen in the image below.
We began the tour by going into the boiler room that was located on the 2nd floor. There were 4 very large boilers around 15 feet tall. He explained how the building has a 4 pipe system that allows the occupants to have heat and AC year round in contrast with a 2 pipe system that the heat kicks when the balance point temperature is reached and remains on until the temperature changes were AC would only be on for the entire building. Having control year-round of either AC or heat is an additional benefit that the building provides to its residents and occupants.
Armin explained that the HVAC system was air and water because the water pipes were pumped into the spaces and with a VAV system each individual unit had control on the amount of water that would flor through the coiled fans. This system has more potential for leakage compared to an all air system, but the risk for the more leakage is in all water systems.
I asked Armin if and how the building was divided into zones and he explained to me that overall the building was split into the three zones for the hotel (floors 3-17), the apartments (floors 18-52) and the Condos (floors 53-81) but there was also overlap because of the initial design changes explained previously. The HVAC water (both chilled and heated) was pumped vertically throughout the building with intermediate pressure controls and heat exchangers every so often.