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AS/NZS 4234:2021


Heated water systems — Calculation of energy consumption

Sets out a method for evaluating the annual energy performance of water heaters using a combination of test results for component performance and mathematical models to determine the standardized annual supplementary energy use.
Published: 25/06/2021
Pages: 88
Table of contents
Cited references
Content history
Table of contents
About this publication
1 Scope and general
1.1 Scope
1.2 Application
1.3 Normative references
1.4 Terms and definitions
1.5 Notation
2 Component testing
2.1 Scope of section
2.2 Water heater technology types
2.2.1 Solar thermal collector systems
2.2.2 Pump flow and power consumption General Constant speed pumps Variable speed pumps
2.2.3 Air-source heat pump systems
2.2.4 Photovoltaic water heaters
2.3 Storage tank types
2.3.1 Electric resistive heated, unboosted and heat pump storage tanks
2.3.2 Gas-boosted storage vessels
2.4 In line water heater types
2.4.1 Instantaneous gas water heaters
2.4.2 In line instantaneous electric water heater
2.5 Solar-boosted heat pump storage water heaters
2.6 Solar collector
2.6.1 Collector efficiency
2.6.2 Incidence angle modifier General Flat plate collectors Evacuated tubular collectors
2.6.3 Collector efficiency correction for shadowing due to impact guard
2.7 Air source heat pump
2.7.1 Heat pump COP and electric power use General Fixed speed compressor heat-pumps Variable speed compressor heat-pumps
2.7.2 Additional tests for variable capacity compressors
2.7.3 Testing requirements for commercial heat pump water heaters
2.8 Domestic water heater configuration
3 Performance evaluation of domestic water heaters
3.1 Performance evaluation simulation program
3.2 Weather data
3.3 Domestic thermal energy loads
3.4 Domestic electrical energy consumption
3.5 Domestic hot water load selection
3.5.1 Water heaters with grid electric or gas supplementary heating
3.5.2 Water heaters with heat pump supplementary heating
3.6 Water temperature
3.6.1 Control of temperature
3.6.2 Legionella control
3.6.3 Minimum delivery temperature
3.7 Cold water inlet temperature
4 Modelling domestic water heaters
4.1 General
4.2 Thermal stratification and mixing in hot water storage tanks
4.2.1 General
4.2.2 Low-flow criteria
4.2.3 Controlled-flow pumped circulation
4.2.4 Uncontrolled-flow pumped circulation
4.2.5 External collector loop heat exchanger systems
4.2.6 Pump controllers
4.3 Modelling thermal stratification in storage tanks
4.3.1 General
4.3.2 Controlled flow-rate pumped circulation
4.3.3 Thermosiphon circulation
4.3.4 Uncontrolled flow-rate pumped circulation
4.3.5 Heat exchanger tanks
4.3.6 In-tank electric resistive heating from grid or PV power
4.4 Piping configuration for solar thermal water heaters
4.4.1 Collector loop piping
4.4.2 Collector loop piping insulation
4.4.3 Piping between primary storage tank and a series booster
4.5 Piping configuration for standalone heat pump
4.6 Energy consumed for freeze protection of solar and heat pump water heaters
4.6.1 Active pumped freeze protection
4.6.2 Electric heater freeze protection
4.7 Over-temperature control
4.7.1 General
4.7.2 Hot water discharge due to over-temperature
4.7.3 Vented system energy dumping
4.8 Modelling heat pump water heaters
4.8.1 Standard operating conditions
4.8.2 Standby electrical power
4.8.3 Water flow rate for standalone heat pumps Systems with constant speed water pumps Systems with water flow rate control Heat pump operation penalty at low temperatures
4.8.4 Low ambient temperature operation Systems not suitable for low temperature operation Systems suitable for operation at low ambient temperatures
4.8.5 Output for air temperature above lowest temperature test condition Integral heat pumps Standalone heat pumps
4.8.6 Output for air temperature below lowest temperature test condition Low temperature Class B products Low temperature Class A products Low temperature operation penalty calculation Calculation of low temperature performance during performance simulation
4.9 Modelling gas storage water heaters
4.10 Modelling instantaneous gas water heaters
4.11 Modelling instantaneous electric water heaters
4.12 Modelling of PV water heaters
4.13 Modelling of indirect coupled PV water heaters
4.14 Modelling solar-boosted heat pump water heaters
4.14.1 General
4.14.2 Compressor performance
4.14.3 Solar-boosted evaporator
4.14.4 Heat gain from condensation
4.14.5 Heat pump condenser
4.14.6 Solution procedure
5 Performance evaluation of commercial liquid heating systems
5.1 General
5.2 Standardized annual task performance
5.3 Weather data
5.4 Commercial thermal energy load
5.5 Liquid temperature
5.5.1 Legionella control for drinking water
5.5.2 Minimum delivery temperature for drinking water
5.5.3 Process heat systems
5.6 Cold water inlet temperature
5.6.1 Drinking water system
5.6.2 Open loop load system with partial recirculation
5.6.3 Closed loop load system
5.7 Reference water heaters for commercial systems
5.7.1 General
5.7.2 Electric-boosted products
5.7.3 Gas-boosted products
6 Modelling commercial liquid heating systems (all types)
6.1 General
6.2 Solar collector array configuration
6.3 Storage tank heat loss
6.3.1 General
6.3.2 Tank standing heat loss calculation
6.4 Storage tank stratification for booster recirculation loop
6.5 Collector loop fluid flow rate
6.5.1 General
6.5.2 Hydraulic circuit analysis
6.5.3 Flow rate calculation procedure
7 Test report
7.1 Product description
7.2 Simulation software features and validation
7.3 Calculation of annual energy savings relative to reference water heaters
7.4 Calculation of carbon dioxide equivalent emission from heated water systems (if required)
7.5 Presentation of results
7.6 Simulation files
Appendix A
A.1 Scope
A.2 Time-limited electric supply
A.3 Solar collector/PV panel inclination and orientation
A.4 Weather data for water heaters other than air-sourced heat pumps
A.5 Weather data for air-sourced heat pump water heaters
A.6 Hot water thermal energy loads
A.6.1 Peak daily thermal energy load
A.6.2 Daily load profile
A.6.3 Seasonal energy load multiplier profile
A.6.4 Hourly Load
A.7 Domestic electrical energy loads
A.7.1 Daily load profile
A.7.2 Seasonal electrical energy load multiplier
A.7.3 Equivalent thermal load scaling factor
A.7.4 Electrical load
A.8 Cold water inlet temperature
A.9 Characteristics of reference water heaters in zones 1 to 4 and HP1-Au to HP5-Au
A.10 Purchased energy of reference water heaters
A.11 Displaced energy
A.11.1 Electric-boosted products when referenced to electric storage products
A.11.2 Gas-boosted products when referenced to gas storage products
A.11.3 Gas-boosted products when referenced to electric storage products
Appendix B
B.1 Scope
B.2 Time-limited electric supply
B.3 Solar collector/PV panel inclination and orientation
B.4 Weather data
B.5 Weather data for air-sourced heat pump water heaters
B.6 Hot water thermal energy loads
B.6.1 Peak daily thermal energy load
B.6.2 Daily load profile
B.6.3 Seasonal energy load multiplier profile
B.6.4 Hourly load
B.7 Domestic electrical energy loads
B.7.1 General
B.7.2 Daily load profile
B.7.3 Seasonal electrical energy load multiplier
B.7.4 Equivalent thermal load scaling factor
B.7.5 Electrical load
B.8 Cold water inlet temperature
B.9 Characteristics of reference water heaters in zones 5 to 6 and HP1-NZ to HP2-NZ
B.10 Purchased energy for reference water heaters in zones 5 to 6
B.11 Displaced energy
B.11.1 Electric-boosted products when referenced to electric storage products
B.11.2 Gas-boosted products when referenced to gas storage products
Appendix C
Appendix D
D.1 General
D.2 Normal incidence shadowing
D.2.1 Cylindrical mesh guard
D.2.2 Flat cover guard
D.3 Incidence angle modifier correction
D.3.1 General
D.3.2 Cylindrical mesh guard — Incidence angle modifier
D.3.3 Flat sheet cover guard incidence angle modifier
Appendix E
E.1 Scope
E.2 Pressurized tanks
E.3 Low pressure tanks
E.4 Idealized tank
E.5 Insulation thickness on domed end
E.6 Heat loss from idealized tank
E.7 Top and bottom heat loss
E.8 Side wall heat loss
E.9 Fittings heat loss
E.10 Corrected total heat loss
E.11 Example
Appendix F
F.1 Introduction
F.2 Method of calculation
F.3 Limits of interpolation and extrapolation
Cited references in this standard
EN 13771-1
Compressors and condensing units for refrigeration — Performance testing and test methods — Part 1: Refrigerant compressors
Solar and heat pump water heaters — Design and construction
EN 12975-2
Thermal solar systems and components — Solar collectors — Part 2: Test methods
ASHRAE 23.1-93
Methods of Testing for Rating Positive Displacement Refrigerant Compressors and Condensing Units that Operate at Subcritical Pressures of the Refrigerant
Heat pump water heaters — Performance assessment, Part 1: Air source heat pump water heaters
Content history
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