306A Water Heating Systems 3 — Questions and Answers
Question 1: What is a 'heat pump' water heater?
- A water heater that uses a boiler coil
- A water heater that extracts heat from ambient air and transfers it to the water, operating like a refrigerator in reverse (Correct answer)
- A water heater powered by solar panels
- A water heater that uses steam from a furnace
Correct answer: A water heater that extracts heat from ambient air and transfers it to the water, operating like a refrigerator in reverse
A heat pump water heater uses a refrigeration cycle to extract heat energy from the surrounding air and transfer it to the water in the tank. It is 2 to 3 times more efficient than a conventional electric resistance heater.
Question 2: What is the energy factor (EF) or uniform energy factor (UEF) used to measure in water heaters?
- The maximum temperature the heater can achieve
- The overall efficiency of the heater, accounting for recovery efficiency, standby losses, and cycling losses (Correct answer)
- The speed of heating
- The tank insulation R-value
Correct answer: The overall efficiency of the heater, accounting for recovery efficiency, standby losses, and cycling losses
The energy factor (or the newer uniform energy factor) measures the overall efficiency of a water heater by accounting for how efficiently it heats water (recovery), how much heat it loses from the stored water (standby), and the energy consumed during cycling on and off.
Question 3: When installing a solar water heating system, what is the purpose of the backup heating element?
- To cool the water if it gets too hot
- To provide supplemental heating when solar energy is insufficient, such as during cloudy days or high demand (Correct answer)
- To power the circulation pump
- To preheat the solar collector
Correct answer: To provide supplemental heating when solar energy is insufficient, such as during cloudy days or high demand
The backup heating element (electric, gas, or a conventional water heater in series) ensures hot water availability when solar energy cannot meet the demand, such as during extended cloudy periods, winter months, or peak usage times.
Question 4: What is the purpose of a mixing valve at the water heater outlet?
- To increase the water pressure
- To blend the hot water stored at 60°C with cold water to deliver a safe temperature (typically 49°C) to fixtures (Correct answer)
- To filter sediment from the hot water
- To prevent backflow into the cold water line
Correct answer: To blend the hot water stored at 60°C with cold water to deliver a safe temperature (typically 49°C) to fixtures
A thermostatic mixing valve at the water heater outlet blends the 60°C stored water (maintained at this temperature to kill Legionella) with cold water to deliver tempered water at a safe 49°C to fixtures, preventing scald injuries.
Question 5: What is 'first-hour rating' (FHR) for a storage water heater?
- The amount of hot water produced in the first hour of a new installation
- The number of litres of hot water a fully heated tank can deliver in the first hour, combining stored volume and recovery capacity (Correct answer)
- The time required to heat the first batch of cold water
- The warranty period in hours
Correct answer: The number of litres of hot water a fully heated tank can deliver in the first hour, combining stored volume and recovery capacity
The first-hour rating represents the total litres of hot water the heater can deliver starting with a fully heated tank, combining the stored hot water with the water heated during that hour (recovery). This is the best indicator of the heater's ability to meet peak demand.
Question 6: What safety device prevents a gas water heater from operating if the flue is blocked?
- The T&P relief valve
- A spill switch or blocked vent safety shutoff that detects exhaust gas spillage (Correct answer)
- The thermocouple
- The gas regulator
Correct answer: A spill switch or blocked vent safety shutoff that detects exhaust gas spillage
A spill switch (or blocked vent safety device) detects when combustion gases are spilling from the draft hood instead of going up the flue. It shuts off the gas supply to prevent carbon monoxide from accumulating in the living space.
306A Water Heating Systems 3
What is a 'heat pump' water heater?