Water Heating Efficiency Flashcards
7 cards from real HERS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Water Heating Efficiency flashcards as text
Which HERS software input directly accounts for the number of bedrooms when calculating domestic hot water consumption?
Answer: The hot water draw profile, which is sized based on number of bedrooms
HERS Reference Home hot water consumption is calculated using a draw schedule that scales with the number of bedrooms, assuming more occupants in larger homes.
An electric resistance water heater has a UEF of 0.92. What does this value imply about its energy conversion?
Answer: It converts 92% of input electricity into heat in the water, losing 8% to standby and cycling losses
A UEF of 0.92 means 92% of the electrical energy consumed ends up as useful heat in the water, with the remaining 8% lost to standby heat loss and inefficiencies during heating cycles.
What is the main limitation of condensing gas water heaters compared to non-condensing models?
Answer: They require a drain for condensate and special venting materials resistant to acidic condensate
Condensing water heaters extract enough heat from flue gases to condense water vapor, producing acidic condensate that must be drained and requiring corrosion-resistant PVC or stainless flue materials.
In hot climates, why might a heat pump water heater provide a dual benefit beyond just water heating efficiency?
Answer: It cools and dehumidifies the space where it is installed, reducing air conditioning load
By extracting heat from the surrounding air, an HPWH cools and dehumidifies the installation space—useful in garages or mechanical rooms in hot climates, where it effectively acts as a supplemental dehumidifier/AC unit.
What is a 'hot water recirculation system' and what is its primary energy tradeoff?
Answer: A loop that keeps hot water near fixtures for instant delivery, saving water but adding pump energy and pipe heat losses
Recirculation systems continuously or periodically pump hot water through a loop to minimize wait time, but this adds pump electricity consumption and significantly increases standby heat losses through the distribution piping.
Which of the following water heater features qualifies for HERS credit as a 'compact hot water distribution system'?
Answer: Designing the plumbing so that no fixture is more than a specified distance from the water heater
A compact distribution system limits the pipe length between the water heater and the farthest fixture, reducing both wasted water and the energy needed to maintain temperature in long pipe runs.
Why does the location of a water heater within a home affect its overall system efficiency?
Answer: Unconditioned locations such as garages or attics expose the tank to greater temperature differentials, increasing standby losses
A water heater in an unconditioned garage or attic faces larger temperature differences between the stored water and the surroundings, which drives greater heat loss through the tank walls and connected piping.