Improved HVAC Systems

All discussions of wellness in today’s buildings usually include a focus on HVAC systems. In fact, the AIA report identifies one of the commonly recognized risks as “aerosolized transmission of virus droplets.” Hence, the report goes on to recommend “recommissioning and enhancing ventilation systems.” Attention to these systems should include the ways in which the building is heated and cooled as well as how it is ventilated. Furthermore, the energy use impacts of these systems is always critical in school buildings, so this factor plays a critical part as well.

With the above in mind, we look at two types of HVAC systems that are relevant.

Photos courtesy of Mitsubishi Electric Trane HVAC US (METUS)

Variable refrigerant flow (VRF) heating and cooling systems are available in different sizes and configurations for schools, providing greater design flexibility, more precise comfort control, and quiet operation.

Variable Refrigerant Flow (VRF) Systems

While schools have incorporated many different types of heating and cooling systems, considerable success has been found in recent years by using variable refrigerant flow (VRF) systems. VRF systems move conditioned refrigerant directly to the zone requiring heating or cooling, allowing the temperature of that area to be more precisely controlled. They can simultaneously cool some zones while heating others or just provide conditioning to zones that are in use. VRF systems provide educational buildings with efficient, personalized comfort and can meet the needs of a wide variety of spaces within schools: classrooms, lecture halls, administrative offices, athletic facilities, and others. The quiet operation of VRF systems also makes them ideal for environments like libraries and classrooms where students need to focus on their studies.

There are a range of product types and sizes available that can be used to suit the needs of different school buildings or even different parts of a larger facility. Manufacturers offer a variety of indoor units that can be discreetly located without the need for ducting. On the exterior, compressor units can be air-source or water-source heat pumps that optimize energy usage through very high efficiency. They can be designed to operate in a zoned manner as an energy-efficient method of providing improved comfort control to indoor environments. Zones can be defined as single- or multiple-room spaces that are conditioned to a set temperature and operated independently from other rooms within the same structure. This allows facility managers to control multiple zones or defined areas within a building independently (instead of the full building all at once).

Ventilation Systems

Coupled with heating and cooling systems, ventilation of school buildings is required by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) minimum standard for ventilation rates per Standard 62.1-2010. Proper ventilation in schools is a priority but is escalated further during times of viral outbreaks. Other ASHRAE guidelines specific to schools address daily air flushing, temperature ranges (68–78 degrees Fahrenheit), and relative humidity in rooms (between 40–60 percent).

Ventilation systems are commonly installed separately from heating and cooling systems. However, manufacturers may provide both types of equipment, which is preferable for initial design, pricing, and installation. Using a single manufacturer for all equipment streamlines ongoing service and maintenance as well. Ventilation systems need to be ducted to move air and are designed to exhaust air from inside the building and replace it with fresh air from the outside. Removing the conditioned air and replacing it with unconditioned outside air requires energy to ensure that the proper temperature and/or humidity level is met. As such, with high volumes of air brought in for conditioning, it is critical that ventilation equipment operates in an energy-efficient manner.

With the above understanding, there are two major types of commercial ventilation systems that need to be kept in mind:

• Dedicated outdoor air systems (DOAS): As a premier solution for conditioning outside air for commercial buildings, DOAS is designed to handle up to 100 percent outdoor air. This type of product offers premium features that can be ideal for handling ventilation air, particularly when coupled with VRF systems.
• Energy-recovery ventilators (ERVs): The ability to exhaust indoor air and precondition incoming outside air is the primary role of an ERV. The technology to do this varies a bit between manufacturers, but some are based on using a low-maintenance, cross-flow core that prevents the inbound air and exhaust air from intermingling. Essentially, this means that the exhausting air passes through multiple chambers with a high surface area, while the incoming air passes by the other sides of those chambers to pick up or release heat. The result is that the incoming air is partly conditioned by the outgoing air, thus decreasing the heating and cooling load of the spaces.

Photos courtesy of Mitsubishi Electric Trane HVAC US (METUS)

Ventilation equipment used in schools can include dedicated outdoor air systems (DOAS) or energy-recovery ventilators (ERVs) with the capability to provide energy efficiency and highly filtered air.

Air Filtration

All ventilation systems are compatible with air filters to capture and remove particles in the air. Such filters are categorized based on their minimum efficiency reporting values (MERV). While the minimum MERV rating is 8, a filter with a MERV rating of 9–12 is expected to capture particles of one micrometer or larger, which includes most dust and common pollutants. A MERV rating of 13–16 is considered hospital-level air quality and capable of capturing very small particles, including those that are hazardous to human health. ASHRAE guidelines note that schools should install MERV 13 filters or higher for optimal student wellness. Where airborne viruses are a concern, it is advisable to specify up to MERV 16 filters.

Both VRF and its ventilation offerings (DOAS, ERVs) are available in compact units that allow flexibility in design. Certain models also do not require the addition of dampers and adapters. These high-performing systems can offer educational facilities both high indoor air quality and optimal energy use. This all makes it easier to coordinate the rest of the building with these systems and still achieve the desired aesthetic. For architects, VRF systems with ERVs mean flexibility in design, quiet operation, and the ability to modify the systems as needs change during the design or life cycle of the building.