Is VRF right for your school?
Whether it’s a new school or a systemic renovation, variable refrigerant flow (VRF) systems are being considered more and more by school systems across the industry. Five years ago, VRF was still a new and relatively unknown player in the HVAC market. School systems were sticking with the proven conventional systems such as unit ventilators and variable air volume (VAV) systems. Now with advancements in the system technology, product familiarity, and reduced costs, VRF systems are rapidly growing in popularity.
When considering an HVAC system for a new school with many available options, VRF systems should be strongly considered. Cost, energy efficiency, maintenance personnel, desired floor to floor elevations, and site conditions all play major roles when determining the best system for your building. For example, if cost and system familiarity are the two driving forces behind determining a system, often times a VAV system will be the best option. If the site lends itself to a geothermal borefield and energy efficiency is a top priority, a geothermal heat pump system may be right for that building. However, VRF systems still represent a strong option with a guaranteed performance similar to those more conventional systems. More than likely, it will provide higher energy savings when compared to VAV systems and will be less costly than geothermal systems.
While VRF should definitely be considered for new school buildings, it is systemic renovations where this product has really found its niche. Systemic renovation projects often have the following characteristics: a building at least 40 years old with limited floor to deck space, an existing two-pipe unit ventilator based HVAC system, humidity issues, and a phased occupied construction period. Trying to maneuver large ducts associated with VAV systems through limited ceiling space, which is already filled with existing utilities, is nearly impossible in most existing schools. Replacing a two-pipe unit ventilator can present several issues. Often times these systems are heating only systems which means the entire piping loop must be replaced and/or re-insulated. Depending on the layout of the classroom, alterations to 40-year-old casework could come into play. Also, inherent with unit ventilator systems are humidity concerns, noise issues, poor air distribution and the lack of temperature control flexibility during swing seasons. Any system which includes a chiller (or any other central source of cooling), fundamentally is not set up to accommodate a phased occupied renovation.
Able to address all of these concerns, VRF is a refrigerant-based system which utilizes small piping routed from localized condensing units on the roof to terminal units in the classrooms. Yes – whenever VRF is used, it must be coupled with a dedicated outside air system (DOAS) which will have ductwork. However, this ductwork is much smaller than VAV ductwork because it is only sized to handle ventilation air and does not contribute to the heating/cooling loads. The DOAS units also dehumidify the outside air which improves indoor air quality. Air distribution and noise concerns are addressed by the fact that the air is distributed from above at multiple centralized locations (typically with two cassettes or a ducted terminal unit) instead of having one large unit ventilator fan blasting air at two-three feet above the floor. Also, VRF systems can allow spaces on the same system to be in different modes. This comes into play during fall and spring seasons when the sun may be heating one side of the building and the other side be cooler and shaded. A VRF system will allow cooling in one space and heating in another. This is not possible in conventional HVAC systems that have a set heating/cooling switch over date.
The ease of phasing is another tremendous advantage of a VRF system. The building can be zoned such that each group of classrooms is completely independent of each other. One wing of eight classrooms can be its own system; once construction is completed in that area, the system can be energized and students be moved back in while work in another area begins. There is no dependence on a centralized chiller or complete building piping loop. In addition to its numerous practical advantages, VRF is typically more energy efficient that other typical systems which usually offsets the incremental first cost difference over the life of the building.
Finally, LEED certification is commonly desired (or even required) for new school buildings and major renovations. VRF systems can achieve these goals. While the Enhanced Refrigerant Management credit cannot be met with VRF due to the large amounts of refrigerant in the system, all other mechanical related credits are easily attainable. VRF is often times more energy efficient than conventional mechanical systems maximizing the Optimize Energy Performance LEED credit and moving a submission closer to the Silver, Gold or Platinum ratings. Next time you are considering which system will work best for your K-12 project, weigh your options and consider the benefits of VRF.