HERS Water Heating Systems 2 — Questions and Answers
Question 1: A heat pump water heater (HPWH) will operate most efficiently when installed in which location?
- A small sealed closet with minimal air volume
- An unconditioned space such as a garage with sufficient air volume (Correct answer)
- A fully conditioned living space with stable warm temperatures year-round
- Directly adjacent to the main electrical panel only
Correct answer: An unconditioned space such as a garage with sufficient air volume
HPWHs need access to a large volume of ambient air to extract heat efficiently; unconditioned spaces like garages provide a heat source without penalizing conditioned space HVAC loads.
Question 2: For HERS purposes, what does the 'hot water distribution system efficiency' credit account for?
- The efficiency of the water heater's tank insulation only
- Energy losses from pipe heat dissipation and water wasted waiting for hot water to arrive (Correct answer)
- The efficiency of the recirculation pump motor alone
- Water pressure losses throughout the distribution system
Correct answer: Energy losses from pipe heat dissipation and water wasted waiting for hot water to arrive
Hot water distribution efficiency credits in HERS account for both thermal losses from pipes and water wasted waiting for hot water to arrive at fixtures.
Question 3: What credit does a solar water heating system receive in a HERS rating?
- No credit; solar thermal is not recognized in HERS ratings
- A flat 10-point reduction in the HERS Index regardless of system size
- Credit based on the calculated solar fraction and system efficiency per RESNET standards (Correct answer)
- Automatic HERS Index of zero for the entire water heating end use
Correct answer: Credit based on the calculated solar fraction and system efficiency per RESNET standards
Solar water heating systems receive HERS credit based on the calculated solar fraction and system efficiency as specified in RESNET/ANSI 301 standards.
Question 4: Which of the following best describes a 'compact' hot water distribution system as recognized in HERS ratings?
- A system where all pipe runs are insulated with R-3 or greater insulation
- A system where total pipe volume from water heater to all fixtures is minimized using small-diameter pipes and short runs (Correct answer)
- Any system that uses a recirculation pump and timer
- A system limited to homes under 1,500 square feet
Correct answer: A system where total pipe volume from water heater to all fixtures is minimized using small-diameter pipes and short runs
Compact distribution systems minimize the pipe volume between the water heater and fixtures, reducing the amount of cooled water that must be purged before hot water arrives.
Question 5: Compared to a continuous recirculation system, how does a demand-controlled recirculation system affect energy use in HERS?
- Demand-controlled systems always consume more pump energy due to frequent start/stop cycling
- Demand-controlled systems reduce standby heat losses by running only when activated by occupant demand (Correct answer)
- Both systems have identical energy use in HERS calculations
- Demand-controlled systems are not recognized as a credit in current HERS ratings
Correct answer: Demand-controlled systems reduce standby heat losses by running only when activated by occupant demand
Demand-controlled recirculation systems activate only when hot water is requested, significantly reducing standby circulation losses compared to continuous or timer-based systems.
Question 6: In HERS energy modeling, how is incoming cold water (mains) temperature typically determined?
- A fixed 55°F is used regardless of location
- A fixed 65°F is applied for all US climate zones
- Location-dependent values based on ground temperature data (Correct answer)
- Always equal to the outdoor design dry-bulb temperature
Correct answer: Location-dependent values based on ground temperature data
RESNET/ANSI 301 uses location-specific mains water temperatures based on geographic ground temperature data, as cold water temperatures vary significantly across US climate zones.
Question 7: What is the primary advantage of a structured plumbing (central manifold) system over a traditional trunk-and-branch distribution system in HERS?
- Higher water pressure throughout the home
- Lower material cost for installation
- Reduced pipe volume per fixture, minimizing water waste and improving distribution efficiency (Correct answer)
- Compatibility with recirculation systems only
Correct answer: Reduced pipe volume per fixture, minimizing water waste and improving distribution efficiency
Structured plumbing systems use individual small-diameter home runs from a central manifold to each fixture, minimizing total pipe volume and reducing water wasted waiting for hot water.
HERS Water Heating Systems 2
A heat pump water heater (HPWH) will operate most efficiently when installed in which location?