K-12 roundtable focuses on IAQ, IEQ

HVAC systems are being upgraded at K-12 schools, with a push from COVID-19

By Consulting-Specifying Engineer March 22, 2023
Courtesy: Salas O'Brien

K-12 school insights

  • After COVID-19, many K-12 school buildings were upgraded to improve their indoor environmental quality and indoor air quality.
  • ASHRAE has guided mechanical engineers on several aspects of a K-12 school’s HVAC system.


Misty DuPré, PE, Principal, Salas O’Brien, Vista, California – Maureen McDonald, LEED AP, Director, Energy Services, Southland Industries, Garden Grove, California – Steven Mrak, PE, Vice President, Peter Basso Associates Inc., Troy, Michigan – Steve Reigh, PE, HBDP, Engineering Leader, DLR Group, Washington, D.C.


Describe a recent project in which you addressed indoor air quality issues to account for health concerns.

Maureen McDonald: A recent project that addresses IAQ issues to account for health concerns is the upgrading of HVAC and controls for Pomona Unified School District. Funded by COVID-19 relief funds and driven by the role ventilation plays in the spread of COVID-19, this project was initiated in 2021 and is slated for completion in 2024. Facing urgency to improve air quality and meet fund deadlines, the project specifically involves selecting different HVAC technologies (single-zone gas packs, single-zone split systems with gas heat, multizone air handling units, single-zone heat pumps, electric heat pumps, direct exchange split systems, mini splits, air cooled chillers and condensers, ductless split systems, cooling towers and boilers) to address different conditions at each site.

Steven Mrak: In the midst of the COVID-19 epidemic, we were approached by several public school districts that wanted our assistance in evaluating their existing building HVAC systems, regarding air filtration and ASHRAE recommended minimum air changes. Our efforts consisted of field verification, review of existing airflow balance reports and ventilation calculations. Through our efforts, these districts were made aware of specific HVAC systems and rooms throughout their buildings that did not meet current ASHRAE recommendations. They now have the ability to selectively target these spaces for improvements.

The design of the new Physical Sciences Building at Aliso Niguel High School Capistrano Unified School District incorporated exposed structural elements to highlight the engineered systems within the building. Courtesy: Salas O’Brien

What types of unique building pressurization have you designed in K-12 schools?

Steven Mrak: Building pressurization control can vary from simple gravity relief hoods to more complex variable speed relief systems that can provide makeup air accommodations for kitchens, general restroom exhaust or process exhaust. As these needs come and go in a school throughout the day, it becomes hard to define a steady state condition regarding building pressurization. To help accommodate these different scenarios, differential building pressure control can be used to vary the speed of relief fans. This uses atmospheric pressure and compares it to the pressure inside the building, controlling the speed of the relief fans to provide a consistent, usually slightly positive, differential pressure.

What unusual or infrequently specified products or systems did you use to meet challenging heating or cooling needs?

Steven Mrak: Recently we used trench heaters on a geothermal heat pump system to provide perimeter heat. A water-to-water heat pump was used to create a low temperature heating system (about 110°F) to serve in-floor radiant heat (classrooms) and in-floor trench heaters (corridors). The low water temperatures would not have provided sufficient output through more traditional finned tube radiators, plus the architectural design did not lend itself to equipment being wall mounted. The floor to ceiling glazing throughout the corridors was kept clean by using this fully floor recessed system, which even offers a solution with an integral electronically commutated motor fan for additional output.

How have you worked with HVAC system or equipment design to increase a building’s energy efficiency?

Maureen McDonald: While upgrading HVAC systems to improve ventilation and resultant IAQ, we also consider energy efficiency. Leveraging energy efficiency to reduce operating costs and greenhouse gas emissions is a significant objective of clients. Unit selection involves balancing cost, serviceability, equipment availability and energy efficiency.

The Salem Woods Elementary School HVAC system was designed by DLR Group in Monroe, Washington. This diagram shows the heat recovery air to water chiller system. Courtesy: DLR Group

What best practices should be followed to ensure an efficient HVAC system is designed for this kind of building?

Maureen McDonald: To ensure an efficient HVAC system is designed, several factors need to be considered, including the seasonal energy efficiency ratio, or SEER, temperature setpoints, humidity setpoints and duct conditions. Our projects may include duct cleaning, duct repair or replacement and sealing to ensure that the value of the efficient equipment results in the most efficient system.

What type of specialty piping, plumbing or other systems have you specified recently?

Steven Mrak: During a value engineering effort for a recent project, we were asked to evaluate a piping material substitution for a geothermal heat pump project. Instead of the specified copper or black steel piping, we evaluated a polypropylene piping solution. The piping material met the operational pressure and temperature ranges expected, provided certain inherent insulating properties and reduced labor time, all leading to a savings for the owner. Additional hangers and supports were needed for proper installation, as compared to more traditional metal piping systems.

When designing school natatoriums, what challenges have you met and how did you solve them?

Steven Mrak: A lot of our K-12 natatorium designs entail existing pool spaces that are being renovated. Standard natatorium HVAC design from the 1950s and ‘60s, which covers most of our area’s K-12 buildings, had a much different approach then today’s best practices. One challenge faced is finding pool deck area that can be converted into a low return grille. If you can’t easily carve out low return air shaft in the corners, solutions have included using adjacent storage rooms to install a return grille and ductwork or even putting the return grille in an exterior wall and routing exterior ductwork. The importance of low return is based around improving the IAQ in the natatorium. Chloramines and other chemical off-gasses are heavier than air and settle into the pool deck breathing zone.