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
What is the primary advantage of a demand (tankless) water heater over a storage water heater?
Answer: It eliminates standby heat losses because it heats water only when needed
Tankless water heaters eliminate standby losses entirely because they heat water on demand and do not maintain a stored volume at setpoint temperature between uses.
A solar water heating system's 'solar fraction' refers to:
Answer: The proportion of total annual water heating energy supplied by solar energy
Solar fraction is the percentage of a home's annual domestic hot water energy demand met by the solar thermal system, with the remainder supplied by a backup conventional heater.
For HERS credit purposes, what information is required to model a solar water heating system?
Answer: Collector area, collector orientation/tilt, and solar fraction or system details
HERS modeling of solar water heating systems requires collector area, orientation, tilt angle, and either a rated solar fraction or sufficient system details to calculate one using software like REM/Rate.
What does 'first-hour rating' (FHR) indicate about a storage water heater?
Answer: The gallons of hot water the unit can deliver in the first hour of use starting with a full tank
First-hour rating indicates how many gallons of hot water the heater can supply per hour starting with a full tank, reflecting both tank capacity and recovery rate.
Which pipe configuration minimizes hot water wait time and distribution energy losses?
Answer: Structured/compact plumbing layout that minimizes pipe length between heater and fixtures
A structured plumbing layout that minimizes total pipe length between the water heater and fixtures reduces both the wait time for hot water and the heat lost to the surrounding structure.
What temperature setting is generally recommended for residential water heater storage tanks to balance scalding prevention and Legionella control?
Answer: 120°F (49°C)
120°F is the standard recommended storage temperature—hot enough to inhibit Legionella growth while low enough to reduce scalding risk and standby losses compared to higher settings.
How does a desuperheater connected to a heat pump HVAC system contribute to water heating efficiency?
Answer: It pre-heats domestic hot water using waste heat recovered from the refrigerant during the cooling cycle
A desuperheater captures superheat from the heat pump compressor discharge—heat that would otherwise be rejected—and uses it to pre-heat domestic hot water, providing essentially free hot water during cooling operation.