Designing efficient K-12 schools: HVAC

In a digital age, children across the U.S. are more technologically advanced than ever—and they require educational facilities that can keep up. Here, engineers with experience working on K-12 schools share views on HVAC.



MEP Rountable Respondents

Maxwell Chien, PE, LEED AP BD+C, Associate, Kohler Ronan, New York City
Chuck Dale-Derks, PE, LEED AP, Principal, McClure Engineering, St. Louis
Evan J. Hammersmith, PE, LEED AP BD+C, CGD, Associate, Mechanical, Karpinski Engineering, Cleveland
Michael Lentz, PE, CPD, HFDP, Director of Operations, Baltimore Office, Setty, Baltimore
Rodney Oathout, PE, LEED AP, CEM, Principal | Energy + Engineering Leader, DLR Group, Overland Park, Kan.
Michael Rader, PE, CEM, Vice President and Chief Operating Officer, Barton Associates Inc., York, Pa.

CSE: In your experience, what unique HVAC requirements do K-12 school buildings have that you wouldn’t encounter in other buildings?

Michael Lentz: One unique aspect of K-12 buildings is the wide variety of program requirements encountered. The program for each school is different and brings about unique challenges. Each individual school program defines different HVAC systems. For example, a school with an arts and humanities focus requires a much different type of HVAC system than a school that focuses on the sciences.

Hammersmith: K-12 schools have a number of unique conditions when compared with other commercial buildings. In schools, students migrate in groups to different areas of the building throughout the day and year. The HVAC system needs to be able to operate efficiently and react quickly to the changing loads to maintain comfort. In competition gyms, the HVAC system has to support hundreds of people during a sporting event, as well as a couple dozen students during gym class. Lastly, the HVAC system needs to be able to maintain humidity levels in spite of the exterior doors being propped open every morning and afternoon.

Rader: The variable occupancy of the K-12 building presents challenges in maintaining both temperature and humidity control. Some facilities are essentially vacant during summer months while others are fully occupied. Understanding how an owner will use their facility is critical in designing a system that will meet their needs.

Chien: Typical K-12 school buildings require many different HVAC systems that are typically designed for restaurants, theaters, laboratories, and fitness centers, as a school typically requires all those functions. Gymnasiums and locker rooms are provided with 100% outdoor air units with energy recovery, while special exhaust systems with kilns and science fume hoods are designed for art and science classrooms. Kitchens and prep areas require grease removal and fire suppression. And lastly, smoke control and pressurization life safety systems are required at schools with large spaces and/or are considered high-rises.

Oathout: We continue to stress the importance of the human element on building performance. Equipment and system designs have become more complicated to achieve the code, energy performance, and sustainability requirements of a project. Engineers need to fill the information gap with their owners by staying involved with projects after completion to ensure the stakeholders understand the design intent and maximize the performance of the facility.

CSE: What unique or innovative HVAC systems have you specified on such facilities? What unusual or infrequently specified products or systems did you use to meet challenging HVAC needs?

Lentz: The most innovative HVAC systems that we see in K-12 schools are those that employ variable refrigerant flow (VRF) or geothermal well systems.

Chien: We have used many different HVAC systems to provide thermal comfort to classrooms, including the use of a dedicated outdoor-air system (DOAS) along with a VRF system to provide a smaller footprint and better comfort for the occupants. We also have designed classrooms with an active four-pipe chilled-beam system to provide both heating and cooling. In this example, the classrooms are required to have inoperable windows and the fresh air must be extremely dry. By passing the air through two enthalpy wheels and a cooling coil to make sure water condensation does not occur in the space, a successful end result was achieved.

Rader: We recently renovated an existing elementary school. However, the renovations did not extend to the building envelope outside of window replacement. The owner wanted to achieve LEED Silver certification and take advantage of available increased state reimbursement that is associated with high-performance buildings. This put a lot of emphasis on the HVAC system design to achieve the desired building energy performance. We looked at the building and HVAC system in a holistic manner and tried to incorporate elements of the building structure to support the HVAC system. This resulted in specifying a transpired wall to allow preheating of outdoor air in the winter and convective cooling of exterior walls in the summer. Additionally, we incorporated a thermal chimney in a tall-volume space to take advantage of natural stratification within the space. When outdoor conditions are suitable, the HVAC system can be turned off in the space, which can then be conditioned using 100% outdoor air without any mechanical cooling or fan energy. These two strategies helped us in achieving increased energy performance and ultimately LEED Silver certification.

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