Heating, ventilation and air conditioning (HVAC) units are present in most office buildings and schools. They are designed to maintain optimal indoor conditions through ventilation, filtration, and temperature regulation. HVAC systems can be problematic in two key ways: they may fail to maintain an optimal environment or they may simply be too energy intensive. The following three methods can help to optimize the performance of an HVAC system while minimizing its energy requirements (1).

Energy Recovery Ventilation (ERV)
The typical central HVAC system pumps fresh air from outdoors to indoors, and pumps polluted air from indoors to outdoors.  While this system works to maintain good air quality, it often maximizes energy expenditure, as energy spent to thermally regulate incoming air is lost when this thermally optimal air is pumped outdoors as waste.  Energy Recovery Ventilation allows energy in the waste outflow air to be transferred to a median material before exiting the building.  The median material transfers the energy to fresh intake air, helping to heat it and thus reducing the amount of additional energy required (1).  

Filtration Systems
HVAC systems filter incoming air to reduce dust and other particulates, as well as mould spores, pollen, lead, and bacteria.  To maximize the amount of particles removed from intake air, it is essential that filters are changed regularly, and have a Minimum Efficiency Rating Value between 8 and 13, encompassing a wide range of particle sizes.  Other filters available on the market are also capable of removing volatile organic compounds and other contaminant gases (1). 

Ventilation Controls
Optimizing ventilation controls is also important to ensuring that the HVAC system is taking in the required amount of fresh air, which is 10 litres per second per person, according to ASHRAE 1989 standards (2).  Meeting this criteria is difficult in older HVAC systems, which have no accurate mechanism for regulating the amount of outdoor air being brought in.  In these instances a measuring station can be installed into the HVAC system to monitor and regulate the intake of fresh air.

Sources:
¹ U.S. Environmental Protection Agency, 2008.  IAQ Design Tools for School: Heating, Ventilation and Air-Conditioning (HVAC) Systems (webpage).
² American Society for Heating, Refrigerating, and Ventilating Engineers, 1989. ASHRAE Standard 62-1989: Ventilation for Acceptable Indoor Air Quality.