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Differences Between Unit Ventilator and Fan Coil Systems

One main difference is in the unit cabinetry. Unit ventilators typically have heavier sheet metal cabinets which hold up better in the school environment. Classroom unit ventilators also have architectural advantages. School room units can have shelving or cabinetry built alongside the unit to help hide the comfort source.

Another difference is that unit ventilators are usually designed to deliver large amounts of outside air through exterior wall openings. Indoor air quality has become a major issue, especially in schools. ASHRAE Standards recommend ever larger percentages of outside air per student (i.e. 15 cfm per student). This results in larger ventilation loads. A classroom unit ventilator is specifically designed to handle these loads. In addition, utilizing chilled water and hot water coils allows for more stable control of coil discharge air temperature than with a direct expansion coil.

Heat gains can be as large as 7F when a classroom suddenly fills with students. By taking in the outside air, unit ventilators can provide "free cooling" during cooler weather. A discharge air thermostat maintains a minimum leaving air temperature from the unit to prevent "dumping" of cold air onto students seated near the unit.

Unit ventilators are generally available in larger sizes than fan coils, and both unit types often have their controls hidden inside the cabinet or remotely mounted to prevent students or other occupants from tampering with them.


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