📊 DCV Ventilation Savings
❄ Cooling Load
Sizing Breakdown
Full Calculation Table
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How to Use the School HVAC Calculator
Choose classroom, gymnasium, or cafeteria/auditorium for default occupant density and ventilation rate assumptions.
Enter floor area and peak occupant count, or leave occupant count blank to use the default density for the space type.
Indicate whether CO2-based demand control ventilation is used, and enter typical average occupancy during the school day.
Click Calculate School HVAC to see design ventilation airflow, average-condition airflow with demand control, and cooling load.
Understanding School HVAC Design
School buildings combine unusually dense occupancy in classrooms with wildly variable occupancy patterns across the building throughout the school day, plus specialized spaces like gymnasiums that behave nothing like a typical classroom. This mix means school HVAC design leans heavily on ventilation rate calculations and demand-responsive controls more than many other commercial building types.
Classroom Density Drives Ventilation, Not Cooling Load
A typical classroom packs one student per 2 to 3 square metres, far denser than an open-plan office at one occupant per 8 to 10 square metres, a per-person basis the CFM per person calculator also uses. Since outdoor air requirements scale with occupant count through the per-person component of the ventilation rate procedure set out in ASHRAE Standard 62.1, this density frequently makes ventilation airflow the governing factor over cooling load for classroom HVAC sizing, similar to the pattern seen in other densely occupied spaces like conference rooms.
Unit Ventilators: The Classic Classroom Solution
A unit ventilator combines a fan, heating and cooling coil, and outdoor air intake into a single package typically mounted along an exterior classroom wall, giving each room independent temperature and ventilation control. This suits schools well given how dramatically occupancy and outdoor air needs shift as different groups of students move between rooms throughout the day, something a single large central AHU serving many classrooms cannot respond to as precisely at the individual room level.
CO2-Based Demand Control Ventilation
Classroom occupancy swings from empty during breaks and passing periods to fully occupied during class time. Demand control ventilation measures actual indoor carbon dioxide levels, which the CO2 level calculator can evaluate against typical indoor thresholds, and modulates outdoor airflow accordingly, rather than delivering a fixed rate sized for full design occupancy at all times. This reduces conditioning energy for outdoor air during periods when a classroom sits partially occupied or empty, while automatically increasing ventilation when carbon dioxide readings indicate the room has filled with students. This calculator estimates average-condition airflow reduction from demand control against the fixed design rate.
Gymnasiums Need a Completely Different Approach
Gymnasium occupancy is highly variable, nearly empty between classes but packed during assemblies, games, or events, and physical activity raises occupant heat and moisture output well above the seated classroom assumption used elsewhere in the building, a school-specific load pattern the ASHRAE Handbook, HVAC Applications volume addresses in its educational facilities chapter. High ceiling volume also changes air distribution needs, sometimes favoring approaches similar to the displacement ventilation calculator for large-volume spaces rather than conventional overhead mixing distribution.
From Classroom Load to Equipment Selection
This calculator sizes one space at a time. For unit ventilator selection, feed the resulting airflow and cooling load into your manufacturer's unit ventilator sizing tables. For a central AHU approach serving multiple classrooms, use the AHU sizing calculator with the combined ventilation and cooling requirements across served zones, and consider the energy recovery wheel calculator to reduce the substantial heating penalty from classroom ventilation air in Canadian winters.
Frequently Asked Questions
Classrooms pack far more occupants into a given floor area than a typical office, often one student per 2 to 3 square metres compared to one occupant per 8 to 10 square metres in an open-plan office. Since outdoor air requirements include a per-person component, this higher density directly increases required ventilation airflow per unit floor area, frequently making classroom ventilation the governing factor over cooling load in HVAC sizing.
A unit ventilator is a self-contained HVAC terminal typically installed along an exterior wall in each classroom, combining a fan, heating and cooling coil, and outdoor air intake in one package. Unit ventilators let each classroom control its own temperature and ventilation independently, which suits schools well given how classroom occupancy and outdoor air needs vary throughout the day as different groups of students move between rooms.
Classroom occupancy varies significantly throughout the school day, from empty during breaks to fully occupied during class periods. CO2-based demand control ventilation modulates outdoor airflow based on actual measured indoor carbon dioxide levels rather than a fixed rate sized for full design occupancy, reducing heating and cooling energy spent conditioning outdoor air during periods when the classroom is partially occupied or empty, while still meeting ventilation requirements when the room is full.
Gymnasiums combine very high, variable occupant density during events with high ceilings and large open volume, creating a load profile quite different from a steadily occupied classroom. Physical activity also raises occupant heat and moisture output well above the seated classroom assumption, and gym HVAC needs to handle both nearly empty periods between classes and packed assembly or game-day occupancy without oversizing equipment for the rare peak event.
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