Facing the challenges of mixed-use buildings: HVAC
Fulfilling the demands of a mixed-use facility can be challenging, considering the structure’s diverse components. Here, professionals with experience on such projects share advice and explain how to end up with positive results for specialty buildings and HVAC systems.
Dave Crutchfield, PE, LEED AP Principal, RMF Engineering, Charleston, S.C.
Julianne Laue, PE, LEED AP BD+C, BEMP, Senior Energy Engineer, Center for Energy Performance, M.A. Mortenson Co., Minneapolis
Robert Nixdorf, PE, LEED AP, Vice President, WSP | Parsons Brinckerhoff, San Francisco
Rodney V. Oathout, PE, LEED AP, Energy + Engineering Leader, Principal, DLR Group, Overland Park, Kan.
CSE: Have you specified distinctive HVAC systems on any specialty projects? What unusual or infrequently specified products or systems did you use to meet challenging HVAC needs?
Laue: I have been seeing an increased interest in displacement-ventilation systems for theaters, auditoriums, large stadiums, and arenas. Overhead mixing air distribution can be noisy and hard to achieve control in large-volume spaces. With displacement ventilation and air being supplied in the occupied zone of the spaces, better thermal control and better acoustical control can be achieved.
Crutchfield: Using rotational air units, which have cooled factory floors for years, we have been able to effectively cool large sporting spaces at an economical cost. These units have the ability to pump out air in long distances, which enables us to cool the entire field and allows us to place these units out of the way of game space.
CSE: What unique HVAC requirements do such projects have that you wouldn't encounter in other projects?
Oathout: Sports venues commonly have large variations in occupancy and environmental requirements. The HVAC requirements for hockey games are very different as compared with a monster truck race or an empty arena. Arena operators will tell you that this example is probable in just one week's event calendar. The HVAC systems must be scalable and designed to achieve the many environmental requirements of the venue.
Laue: Due to the overall volume of the spaces and the density of the occupants, HVAC system design is complicated by large quantities of ventilation air, humidification, de-humidification, smoke management, and the intermittent and varying use of the facility. Arenas may need to be designed for a basketball game one day, hockey the next, and then maybe a monster truck rally or rodeo soon after. Each scenario requires different controls and setpoints, which mean specialty controls and flexible HVAC design.
Nixdorf: Unique HVAC requirements include exhaust systems for specialty areas, such as welding, painting, or carpentry shops. Indirect conditioning of the public concourses is common, along with pre-balancing the seating bowl air-distribution grilles prior to installation. Some additional requirements include high ventilation and exhaust rates for specialty areas, such as locker and training rooms. In many cases, vehicle-access areas are typical, requiring additional carbon monoxide detection and added exhaust. A challenge specific to operable-roof facilities is designing a system and heating/cooling strategy to provide comfort and efficiency, whether the roof is open or closed, and under various weather conditions.
Crutchfield: These projects tend to have a more diverse load profile. For example, they can go from completely empty to full of active professional/collegiate athletes in a matter of minutes. We design them so that they can transition from completely cooled, closed buildings with controlled HVAC to an open-air environment, in which the coaching staff opens the walls or windows to allow outside air to heat or cool the facility.
CSE: When retrofitting existing buildings, what challenges have you faced, and how have you overcome them?
Laue: Existing buildings—especially historic buildings—were not designed for forced-air systems, and many were not designed for cooling. Forced air requires ductwork that may not fit well in the existing floor-to-floor heights, and this limits HVAC system selection and increases design coordination between architects and mechanical engineers. Moisture control in buildings that were not designed for air conditioning can also provide challenges that need to be overcome.
Oathout: There are many challenges that arise when retrofitting an existing building. However, there are two factors that commonly surface. First, the changes in building code requirements regularly impact HVAC design. A more interesting challenge is the evolution of the public perception of an acceptable indoor environment. More than ever, engineers need to ask specific questions of the stakeholder on environmental requirements and tolerance for variation.