Many factors help us determine what mechanical systems are best for a project Owner. The decision depends on their building type and what it will be used for, as well as their financial and operational priorities.
For K-12 schools, there are unique considerations we must often take into account when choosing HVAC and other building systems. These include programming and class offerings (think science labs, art studios with kilns, FACS rooms, etc.), athletic programs and gym usage, and traffic and student migration throughout the building. Not to mention, schools go through dramatic shifts in usage throughout the year, with summer and other extended breaks.
There are a variety of tools and strategies we use to build the appropriate system for each school. Let’s take a look at one example.
Kesling Campus | LaPorte Community School Corporation (LPCSC) | LaPorte, IN
LPCSC consolidated fifth through eighth grade students across the district into one location—Kesling Campus, a combined intermediate and middle school.
On the campus, we renovated an existing middle school building and built a new addition. The new and old structures were connected, with multiple shared spaces. The HVAC and other building systems needed to support that new flow and function. We also had to determine what of the existing equipment in the original building to keep or replace.
Our engineering team utilized several tools to evaluate various system options, including energy modeling software and our own building system matrix rating system. These tools help us weigh system performance, cost, and other factors so we can make the best recommendations to the Owner.
For Kesling Campus, we evaluated the following types of HVAC systems:
- Variable Refrigerant Flow (VRF) with a Dedicated Outdoor Air System (DOAS)
- Chilled Beam with a DOAS
- Dual Duct Variable Air Volume (VAV) System with a DOAS
- Fan Coil System with a DOAS
- Ground Source Heat Pump (GSHP) System with a DOAS
- Energy Recovery Vertical Unit Ventilator (ERVUV) System
We created an energy model that represented the school building. We accounted for typical weather conditions in LaPorte, as well as Indiana standards for lighting levels, envelope performance, and other operating parameters. Then, we factored in occupancy volume and schedules—how many people would typically be using the spaces, and when?
We simulated each system within this environment and used a series of performance metrics to rank them. These metrics included:
- Energy Use Intensity (EUI) – Expresses a building’s energy consumption
- Annual Utility Cost – Estimated cost of a year’s worth of energy consumption
- First Year Capital Cost – Estimated cost to purchase the system
- Total Life Cycle Cost (LCC) – Estimated total cost of facility ownership, including acquiring, owning, and disposing of the system
- Unmet Hours – A measure of system performance for thermal comfort; unmet hours are hours of operation when the building is outside of the set heating and cooling range (For example, an unmet hour in “heating season” is an hour when the space gets cold before the system can adjust.)
Our evaluation showed the chilled beam system would provide the best energy performance. However, this type of system would be unable to respond to densely occupied spaces with high turnover—like a classroom. This made it a poor choice for a K-12 school.
Our top recommendations for LaPorte were the ERVUV system and the Fan Coil DOAS system. Both of these options would reduce energy consumption by more than 40 percent. However, the ERVUV had a lower capital cost.
The ERVUV system also provides greater control of ventilation in classroom spaces. Coupled with demand control CO2 sensors—which measure the CO2 in the air to estimate the number of people in a space—the system can adjust air intake based on actual occupancy and only use what it needs.
For the new addition, we implemented the ERVUV system for classrooms and Rooftop VAV for large spaces. We re-worked the existing HVAC system in the original building by adding new VAV boxes for classrooms and replacing the air handling units for the gymnasium. To help with phasing of construction, the new addition has a stand-alone chilled water/hot water system. We kept the existing mechanical equipment in the original building.
This energy efficient mechanical work at Kesling Campus qualified the school corporation for thousands of dollars in utility incentives. Utility companies may provide incentives, or rebates, to building owners for equipment and work they do that conserves energy. The incentives are based on the actual reduction in energy consumption in the building. LPCSC’s utility provider, NIPSCO, paid out a certain rate per kilowatt hours (kWH) and per therms saved. This refund money will be put back into the operations budget for ongoing building maintenance and projects.
Thanks to strategic mechanical design and capitalizing on available incentives, LPCSC will see significant energy and operation savings on the new campus, as well as a healthy, comfortable learning environment for students.