Mechanical Engineering Flashcards
7 cards from real Building Engineering practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Mechanical Engineering flashcards as text
What is 'thermal bridging' in a building envelope, and why is it a concern for mechanical engineers?
Answer: Heat transfer through continuous conductive elements that bypass insulation, increasing heating/cooling loads
Thermal bridges like structural studs or fasteners conduct heat around insulation layers, increasing envelope heat loss or gain and raising the design heating/cooling load.
Which NFPA standard governs the installation of refrigerating systems in buildings and specifies machinery room requirements?
Answer: ASHRAE 15 (also adopted as ANSI/ASHRAE 15)
ASHRAE Standard 15 (Safety Standard for Refrigeration Systems) is the primary reference for machinery room ventilation, refrigerant quantity limits, and detector requirements.
In a variable air volume (VAV) system, what happens to the supply air temperature when outdoor conditions require maximum cooling on a hot day?
Answer: Supply air temperature stays at the cooling design set point while VAV boxes open to maximum
On peak cooling days, the AHU maintains its cooling set point (typically 55°F) and VAV terminal boxes open to their maximum airflow position to deliver maximum cooling capacity.
What is the significance of the 'wet-bulb temperature' in evaluating cooling tower performance?
Answer: It represents the minimum achievable condenser water supply temperature from the tower
Cooling tower outlet water temperature approaches but cannot fall below the ambient wet-bulb temperature, since evaporative cooling is driven by the wet-bulb depression.
A domestic hot water recirculation system is designed to keep hot water at every fixture within how many seconds of draw, per common plumbing guidelines?
Answer: 15 seconds
Most plumbing design guidelines and water efficiency programs (such as EPA WaterSense) target hot water delivery within 15 seconds at any fixture to minimize water waste.
What is the purpose of a 'relief opening' or pressure relief damper in a supply air duct system serving a large open-plan office?
Answer: To relieve excess supply air pressure when VAV boxes close to minimum, avoiding duct over-pressurization
When VAV boxes throttle simultaneously, duct static pressure rises; relief dampers or bypass dampers open to dump excess air back to the return, protecting the duct system.
During commissioning of a new chiller plant, a functional performance test (FPT) is conducted. What does this test verify?
Answer: That controls, safeties, and sequences operate correctly under simulated operating conditions
An FPT exercises the control sequence, interlocks, and safety shutoffs under real or simulated conditions to confirm the system operates as designed before occupancy.