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Commercial HVAC Systems Flashcards

7 cards from real HVAC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Commercial HVAC Systems flashcards as text

  1. What is 'static pressure' in the context of a commercial duct system, and why does it matter?

    Answer: The pressure of air in the duct perpendicular to flow, used to overcome resistance and size fans and ducts

    Static pressure is the outward force of air on duct walls and is critical for sizing fans and duct systems to ensure adequate airflow against system resistance.

  2. In a commercial Variable Refrigerant Flow (VRF) system, what distinguishes a 'heat recovery' system from a 'heat pump' system?

    Answer: Heat recovery allows simultaneous heating and cooling in different zones; heat pump can only heat or cool the entire system at once

    VRF heat recovery systems use a branch circuit controller to simultaneously deliver heating refrigerant to some indoor units and cooling to others, maximizing efficiency.

  3. Under ASHRAE 62.1, what is 'ventilation effectiveness' and how does it affect outdoor air calculations?

    Answer: A factor accounting for how well supply air mixes with zone air; poor mixing requires more outdoor air

    ASHRAE 62.1 uses ventilation effectiveness (Ez) to adjust outdoor air quantities — ceiling diffusers typically achieve Ez=1.0, while floor diffusers may require more OA if Ez<1.

  4. What is the role of a 'building pressure differential' control strategy in a commercial HVAC system?

    Answer: Maintaining slight positive building pressure relative to outdoors to prevent infiltration of unconditioned or contaminated air

    Slightly positive building pressure prevents unconditioned outdoor air, pollutants, and moisture from infiltrating through cracks and openings in the building envelope.

  5. What does 'integrated part load value (IPLV)' measure for commercial chillers?

    Answer: Weighted average efficiency across multiple part-load operating points, reflecting real-world performance better than full-load ratings

    IPLV weights chiller efficiency at 100%, 75%, 50%, and 25% load to reflect actual seasonal performance, since chillers rarely operate at full design load.

  6. In commercial HVAC commissioning, what is a 'functional performance test (FPT)'?

    Answer: A dynamic test verifying that HVAC components and systems operate correctly through all modes and sequences of operation

    FPTs simulate all operating modes (occupied, unoccupied, economizer, heating, cooling, alarms) to verify the system performs as designed before occupancy.

  7. A commercial building's HVAC design specifies a supply air temperature of 55°F. If the return air is 75°F, what is the temperature difference (ΔT) used in airflow calculations?

    Answer: 20°F

    The supply-to-return temperature difference (ΔT) is 75°F − 55°F = 20°F, which is used in the sensible heat formula Q = 1.08 × CFM × ΔT to size airflow.