hvac_study Flashcards
(28 cards)
What is a ceiling plenum used for in HVAC systems?
To house ductwork, lights, and return/supply air systems above occupied space.
Why are air-based systems typically located in ceilings?
Because it’s cheaper, safer, and easier to maintain than under-floor systems.
What are the disadvantages of floor plenums?
More expensive structure, fire spread risk, potential tripping hazard, and maintenance complexity.
What is the primary fire concern with plenum spaces?
Fire can spread through the plenum, especially if it’s connected across multiple rooms.
What is a pressurized floor plenum used for?
To deliver air directly to individual workstations, offering personal comfort control.
What design impact does the location of AHUs have?
It affects duct length, shaft planning, maintenance access, and thermal efficiency.
What are the benefits of a centralized AHU?
Easier maintenance, consolidated noise, compact equipment layout, fewer units.
What is the drawback of centralized air handling?
Increased duct length leads to heat loss and more complex shaft planning.
What is a DX unit?
A Direct Expansion unit with its own refrigerant loop, typically roof-mounted for compact installations.
Why do DX units have shorter life spans?
Exposure to rain, snow, UV rays, and temperature fluctuations reduces longevity.
When is a fire damper required?
When ductwork penetrates a fire-rated wall or shaft.
What does a fire damper do?
Automatically closes to prevent fire from spreading through ducts.
Why should duct routing avoid unnecessary fire-rated wall penetrations?
To reduce fire damper needs, cost, and compromised fire ratings.
What is a hydronic system?
A heating/cooling system using water (or glycol) to transfer thermal energy.
Why are pipes in hydronic systems smaller than ducts?
Water carries more heat per volume than air, requiring less space.
What is a common layout strategy for hydronic piping?
Use of multiple loops to distribute heat evenly and efficiently.
What is the main benefit of hydronic heating?
High thermal comfort due to radiant heat and efficient energy transfer.
Why is hydronic cooling less common?
Condensation issues and less effective radiant heat removal.
Where should radiators be located?
Near exterior walls or under windows to counteract heat loss.
What is the risk of exposed radiators?
Scalding hazard, especially for children.
What is a major concern with in-floor radiant systems?
Leaks require breaking concrete to access embedded tubing.
Why do in-floor systems take long to heat?
Concrete mass takes hours to reach set temperature.
What is a key comfort benefit of radiant floors?
Warm floors heat feet directly, improving comfort in cold climates.
Why combine hydronic and air-based systems?
To use hydronic for energy distribution and air for final delivery or ventilation.
