Managing school energy use requires understanding on how spaces are being used, which rooms are occupied at what times, and how effectively the various systems in the facility are performing.
Facility managers everywhere are tasked with improving energy efficiency to control costs. Those strides cannot be achieved at the expense of system performance and reliability, or the comfort of the people within those properties.
There are few places where this is truer than in schools and universities. K-12 schools and university lecture spaces must be kept comfortable to maximize student performance.
The question for most schools comes down to budget: What upgrades are needed, and what can be achieved in a retrofit vs. a new system? Similarly, how can new site builds maximize energy efficiency while containing upfront system costs?
Finding the capital for major upgrades or high-end alternative energy systems may be difficult for many schools, but modern control techniques can help improve the efficiency of existing legacy systems and new installations by executing HVAC processes more efficiently.
The U.S. government mandates that schools meet standards for fresh air in each classroom. Standard airflow measurements signify the cubic feet of fresh air supplied to a room or space each minute. These measurements translate to cfm, or cubic feet per minute.
The ASHRAE 62.1 Standard on Ventilation for Acceptable Indoor Air Quality, in its 2010 edition, ranges from 0.06 of cfm of fresh air per square foot for lecture halls, to as much as 0.18 cfm per square feet for scientific laboratories. Most K-12 classrooms land in the middle at 0.12 cfm per square foot.
Per person, these figures should allow for between 7.5 and 15 cfm depending on the age group and room size. In layman's terms, this means bringing enough outside air into the space to maintain appropriate fresh-air levels. This sounds simple in theory, but how efficiently the school heats and cools that air to create a comfortable environment will affect energy bills noticeably.
Many new schools are being designed with variable air volume (VAV) systems, which direct more or less air to each classroom or zone based on occupancy or load. This is achieved by providing airflow from a central air-handling unit, and opening or closing dampers in VAV boxes to control the amount of air being supplied to each individual zone.
The main air-handling unit, typically installed in a mechanical room, brings in and conditions the fresh air from the outside. It pushes the appropriate amount of flow out to the building depending on how many zones are occupied. These AHUs utilize variable frequency drives (VFDs) to control fan speed based on how much air is needed throughout the building. Classrooms and lecture halls are equipped with VAV boxes capable of releasing more or less air into the room.
The goal is to limit the amount of fresh air to the absolute minimum needed to satisfy guidelines and provide a safe environment. In most cases, the amount of outside air brought into a building correlates directly to energy consumption.
Modulating dampers and air-flow sensors often are utilized to measure and control fresh air intake and usage. The ability to monitor and control the amount of air being exchanged will ensure that a school is following guidelines and operating efficiently.