K–12 schools across the country are under increasing pressure to meet energy efficiency, sustainability, and occupancy comfort goals. With limited funding, aging infrastructure, and unique operational challenges, school districts must evaluate their mechanical systems and find a balance between performance, durability, and long-term value.
Mechanical systems in K–12 facilities face a distinct set of operational challenges. Schools often feature exposed mechanical equipment that can be subject to accidental damage or vandalism. Occupancy patterns in schools are highly variable. Abrupt classroom loading and unloading caused by students filling or vacating classrooms or gymnasiums creates high thermal and ventilation demands. Schools are also typically not fully occupied during the summer months, making it inefficient to run systems at full capacity year-round. The mechanical systems serving K-12 schools must be robust, operate efficiently at partial load, and be controlled based on real-time demand.
School funding plays a pivotal role in shaping the mechanical systems selected for K–12 facilities, especially given that these systems are expected to last for decades due to infrequent replacement cycles. With limited budgets and long-term performance in mind, districts often prioritize simplicity over complexity. For example, while Variable Refrigerant Flow (VRF) systems can be energy efficient and flexible solutions, they can be challenging to maintain and may be unfamiliar to building engineers, making them less suitable for school applications. Simpler, more robust systems, like central cooling provided by a chiller plant, are often favored. Additionally, renovation projects are far more common than new school construction, requiring engineers to work within existing architectural and mechanical constraints.
K-12 schools can implement proven technologies such as geothermal, heat pump chillers, airside energy recovery systems, and enterprise building automation systems. These systems all have unique benefits and limitations. When properly implemented, these technologies provide schools with a path towards sustainable, efficient, and lasting building operation.
Geothermal Systems
Geothermal systems are a compelling option for K–12 schools due to their exceptional energy efficiency and minimal environmental impact once installed. Geothermal systems replace the heat sink, such as a cooling tower, of a mechanical system. Cooling towers include large fans which consume energy, require constant make-up water, and need frequent cleaning to maintain efficient operation. Cooling towers transfer thermal energy from the water in the condenser water loop to the air. Geothermal systems work using the ground as the heat sink by harnessing stable temperatures found underground. Below 15 feet underground, the earth’s temperature is relatively stable at approximately 55°F. In a geothermal system, large piping networks are buried underground. These networks are known as ground loops. The piping is then routed to a heat pump at the school. Water is circulated through the piping network by pumps. During the cooling season, the heat pump discharges heat into the geothermal loop causing the water temperature to rise to around 65°F. As the water is circulated through the ground loop, the water is cooled by the ground. The water is returned to the heat pump and the cycle is repeated. During the heating season, the same process is followed in reverse. The heat pump will pull energy out of the water, dropping the temperature to around 45°F. The water is circulated through the ground loop where the temperature will increase to around 55°F to match the ground temperature. The water is then returned to the heat pump.
By leveraging the stable temperatures underground, these systems provide reliable heating and cooling with very low operational costs. Outside of the circulation pumps and valves, which are systems most building engineers are familiar with, the design includes no moving parts, which means the system is low maintenance. Geothermal systems come with high upfront costs and require significant land area for ground loop installation. For schools that have limited land area, geothermal systems are not a feasible solution. Despite these challenges, their long-term performance and sustainability benefits make them a strong candidate for districts with the upfront capital and available land area.
Heat Pump Chillers
Heat pump chillers are emerging more in K-12 schools for their ability to provide both heating and cooling. In cooling mode, heat pump chillers operate like a standard chiller. Chilled water, that is warmed from cooling the building, is circulated through the chiller. Heat is transferred from the chilled water into a refrigerant. The chilled water temperature drops and the refrigerant temperature increases. The refrigerant discharges heat to an air or water source heat sink. With a heat pump chiller, the refrigerant cycle can also be reversed. This allows the chiller to provide heating to the building as well. In heating mode, heat is pulled from the atmosphere. Hot water that has given a portion of its energy to terminal equipment, returns to the chiller. The refrigerant transfers its energy into the hot water causing the temperature to increase. Heat pump chillers are often capable of simultaneous heating and cooling.
Although more complex, heat pump chillers are an attractive option for schools because many building engineers have experience with operating standard chiller plants. The compressors, pumps, and control systems are already understood. Heat pump chillers are 2-4 times more efficient than even a condensing boiler plant operating at 99% efficiency. Heat pump chillers can also be paired with geothermal loops to further increase their sustainability. Heat pump chillers derate as temperatures drop and often require either electric or gas supplemental heating below 20°F. Some schools located within colder environments, or those that must heat water above 140°F, may still require a small boiler plant to increase the supply temperature to an acceptable range. Additionally, to utilize simultaneous heating and cooling capabilities, the school must utilize a four-pipe system that has separate hot and chilled water piping loops. Dual temperature systems can use heat pump chillers, however, dual temperature systems can only provide heating or cooling at a single time and require a seasonal changeover.
Airside Energy Recovery
Airside energy recovery systems are rising in popularity as a means to meet energy efficiency codes throughout the country. These systems transfer energy from air that is being exhausted to the outdoors into the air that is being brought inside the building. Metal plate and frame heat exchangers and run-around coils are popular choices for heat recovery, however, these systems leave a significant amount of savings on the table. Plate and frame heat exchangers and run-around systems are only capable of changing the temperature between the outside air intake and exhaust. They cannot transfer moisture or humidity which represents the latent load of the building. To provide full energy recovery as opposed to just heat recovery, a system that is capable of transferring moisture between airstreams must be used. The most common type of energy recovery device is the enthalpy wheel.
Enthalpy wheels are made of polymer sheets that are embedded with a desiccant made to absorb moisture. The wheel constantly spins, allowing the desiccant to absorb and reject moisture into and out of the air streams. Although enthalpy wheels are extremely efficient, the construction assembly does allow a small amount of the exhaust air, around 3-5%, to leak back into the supply air. Considering that the exhaust may be coming from a bathroom, some building owners have chosen to avoid this technology. There is an alternate energy recovery system that is able to achieve almost no air leakage known as an energy core. Energy cores are made of corrugated polymer of fiber sheets that are stacked in an alternating pattern, similar to a plate and frame heat exchanger. The membrane allows for moisture transfer between the supply and exhaust airstreams but prevents direct cross contamination. Energy cores provide excellent efficiency, however, they can come with a high price tag depending on size. Additionally, energy cores need to be cleaned throughout the year and may need to be replaced when clogged or damaged.
Enterprise Building Automation Systems
Enterprise building automation and management systems are essential for K–12 districts managing increasingly complex mechanical systems across multiple campuses. These platforms can provide centralized data visualization, allowing facility managers to monitor Heating, Ventilation, and Air Conditioning (HVAC) performance, lighting, and energy use in real time. Building automation systems can be integrated with an Energy Management System (EMS) allowing schools to track energy usage trends and identify inefficiencies. School districts invest significant capital into collecting data. Districts need to easily access and view that data to make informed decisions on where to allocate funds and address problems. Building automation systems should not operate in a vacuum to turn equipment on and off. They are capable of providing significantly more value to the schools they serve.
By understanding these systems’ strengths and limitations and tailoring them to the specific needs of K–12 environments, districts can create healthier, more sustainable, and cost-effective learning spaces for generations to come.
