HVAC and Building Envelope Flashcards
7 cards from real CEM practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 HVAC and Building Envelope flashcards as text
What energy efficiency measure does 'supply air temperature reset' provide in a VAV system?
Answer: Raises supply air temperature at part load to reduce chiller and reheat energy
Resetting supply air temperature upward during part-load conditions reduces chiller lift energy and minimizes terminal reheat, saving significant energy.
What is the primary function of a cooling tower in a water-cooled chiller plant?
Answer: Reject condenser heat from the chiller to the atmosphere via evaporation
A cooling tower rejects heat from the chiller's condenser water loop to the atmosphere primarily through evaporative cooling, completing the refrigeration cycle.
Which building envelope parameter describes the fraction of incident solar radiation that passes through a window as heat?
Answer: Solar heat gain coefficient (SHGC)
SHGC is a dimensionless value from 0 to 1 representing the fraction of solar radiation admitted through a window, both directly transmitted and absorbed then re-radiated inward.
A facility engineer wants to reduce pump energy in a chilled water system. Which measure has the greatest single impact?
Answer: Installing variable frequency drives (VFDs) on pumps
VFDs reduce pump speed at part load, and because pump power varies with the cube of speed, even small speed reductions yield large energy savings.
What is 'sensible heat ratio' (SHR) in HVAC system design?
Answer: Ratio of sensible cooling load to total (sensible + latent) cooling load
SHR is the fraction of a zone's total cooling load attributable to sensible heat; it guides coil selection and determines how much dehumidification the system must provide.
Which standard provides minimum energy efficiency requirements for commercial HVAC systems in the U.S.?
Answer: ASHRAE 90.1
ASHRAE 90.1 (Energy Standard for Sites and Buildings Except Low-Rise Residential Buildings) sets minimum efficiency requirements for HVAC, lighting, and envelope in commercial buildings.
What is the benefit of using a heat wheel (rotary energy recovery ventilator) in an AHU?
Answer: It transfers both sensible and latent energy between exhaust and supply airstreams
A heat wheel rotates between exhaust and supply airstreams, recovering both sensible (temperature) and latent (moisture) energy and significantly reducing conditioning loads on outdoor air.