Zoned Map for Solar Water Heaters
November 2015
Zoned Map for Solar Water Heaters 1
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© Commonwealth of Australia (Department of Industry. Innovation and Science) 2015.
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Zoned Map for Solar Water Heaters 1
Contents
Executive summary
Next Steps
Guiding Questions for stakeholder submission
1. Introduction
2. Factors influencing solar water heater energy efficiency
2.1 Design factors influencing solar water heater energy efficiency
2.2 Climate factors influencing solar water heater energy efficiency
2.3 Demand factors influencing solar water heater energy efficiency
3. Software modelling of solar water heater energy efficiency
3.1 Selection of a software modelling environment
3.2 Composition of the models
3.3 Calculation of an energy efficiency metric
3.3.a Running Costs and Greenhouse Gas Information
4. Production of zoned maps for an energy efficiency label
4.1 Implementation
4.2 Zoned boundaries
4.3 Zoned maps
4.3.a Pumped Electric
4.3.b Thermosiphon Electric
4.3.c Instantaneous Gas
4.3.d Selection and conclusions
4.4 Reference cities
4.5 Utilisation of modelling of 87 zones
Conclusion
References
Appendix A – Modification of AS/NZS 4234 TRNSYS input files for energy efficiency label modelling
1.Modified climate zone include files
2.Modified reference electric water heater performance
3.Modifications to TRNSYS 17 Input Files (Decks)
4.Weather Converter
5.Climate data in TRNSYS 15
6.Modifications to TRNSYS15 Input files (decks)
Appendix B – TRNSYS Modelling Results (Energy Savings)
Appendix C – TRNSYS Modelling Results (Energy savings bands)
Appendix D – Mapping of HERS zone numbers to location
Zoned Map for Solar Water Heaters 1
Executive summary
Installed location can have a significant impact on the performance, energy efficiency and/or usage patterns of certain appliances including air conditioners, space heaters and water heaters. Factors that can impact on performance and energy efficiency include air temperature, humidity, cloud cover, water temperature and frost. For this reason, the Equipment Energy Efficiency Committee (E3) is currently investigating the introduction of a Zoned Energy Rating Label (ZERL). A ZERL will provide enhanced information to consumers and advisors about product energy efficiency and other key performance attributes relevant to their location.
This report outlines the development of a zoned map for Solar Water Heaters (SWH) and documents the methodology used in its development. The map characterises the performance of SWHs in differing regions of Australia and New Zealand. With the intention to display the map on a ZERL it will enable comparisons across and within all residential water heater categories. This work is particularly important as water heating in Australia and New Zealand is a major contributor to energy use and energy costs in the residential and commercial sectors. Water heating is the second largest household energy user comprising approximately 25% of household energy use in Australia, and 30% in New Zealand. There is also significant opportunity for consumers and installers of hot water systems to decrease energy use and costs through better selection of technologies.
The E3 Committee is seeking feedback and views on the technical elements of the methodology for designing a map for SWHs set out in this report. A set of questions listed at the end of the Executive Summary will help readers provide feedback on the proposal. The list is not meant to be exhaustive or exclusive, simply a guide to assist in considering the approach set out here.
Currently, water heaters in Australia and New Zealand do not display an E3government energy rating label. This report contributes to the broader work program for developing a ZERL for all water heaters. The ZERL will provide performance information at a greater level of detail and accuracy than what is available on the existing energy rating label. As a result it will enable consumers, suppliers and installers of water heaters to make better informed decisions. It will enable products that are suited to particular climate conditions to be highlighted and clearly identify areas where others may not be suited. By providing this information, energy efficiency gains and greater product satisfaction can occur from selling and promoting existing products in regions where they will work more efficiently and effectively. The display of location or zoned based information will also provide incentives for manufacturers to innovate new products targeted to particular conditions as these differences will be clearly displayed to consumers.
Focus group testing on the draft ZERL was consistent with international studies in concluding that more than three zones displayed on a map is likely to lead to consumers disconnecting from the information (Sweeney, 2013). Meeting this objective has important implications for the methodology used to define the three zones to ensure they reflect accurate and useful performance information for SWHs. Due to this, the map presented in this paper has different zones to those defined in the joint Australia and New Zealand standard AS/NZS 4234:2008: Heated water systems – Calculation of energy consumption (AS/NZS 4234). The ZERL will use the 69 Nationwide House Energy Rating Scheme (NatHERS) climate regionsfrom Australia and the 18 New Zealand Climate Files . Using these zones and their climate files will allow for improved spatial resolution on the zoned map for SWHs and the ability to drill down for location specific information on the web or viamobile application.
The decision to adopt the higher resolution spatial zoning enables future alignment of appliance and building energy performance. These zones have also been used to produce the energy performance map for the air conditioner and Heat Pump Water Heater zoned label (Peterson, 2014).
The map presented in this paper consists of three consolidated areas classified as:
▪An area where a reference solar water heater has energy savings greater than 80% compared to a reference electric water heater system. This area is referred to as the ‘hot zone’.
▪An area where the expected savings are between 60% and 80%. This area is referred to as the ‘mixed’ zone’.
▪An area where the expected savings are below 60%. This area is referred to as the ‘cold zone’.
When modelled to deliver a medium load (as specified in AS/NZS 4234), reference solar water heaters in the hot zone have been shown to require up to a maximum of 20% auxiliary energy from either electricity or gas. Similarly, a modelled SWH would require up to a maximum of 40% auxiliary energy in the ‘mixed zone’ and up to a maximum of 100% auxiliary energy in the ‘cold’ zone.
For development and production of the ZERL, the three zones will be represented by one location for the purpose of rating and labelling. Future development of online and smartphone applications will utilise climate data from all 87 NatHERS zones and NZ Climate Files, allowing consumers and installers to access more targeted information for their location.
Next Steps
Comments and feedback on this paper will be considered as part of the broader project developing a ZERL for hot water technologies. Consultations on the application of a ZERL to hot water technologies with hot water industry and stakeholders are planned to commence in late 2015.
E3 intends to release a formal Consultation Regulation Impact Statement (CRIS) in 2016. This will include details on specific proposals for a ZERL for hot water systems and provide opportunity for review and comment on this proposal.
Guiding Questions for stakeholder submission
Responses to the questions below will assist the E3 Committee to obtain stakeholder views and fill information gaps. Stakeholder submissions are not limited to the following questions. The material in this document, as well as written submissions and any additional information or views will be considered in helping define a map for solar water heaters.
General questions
- Do you agree with the concept of a zoned map for SWHs with boundaries defined by energy savings relative to a reference electric water heater similar to the approach set out in AS/NZS 4234?
- The proposed map for the label is the split system SWH with circulation pump and electric boost, denoted “Pumped Elec”. Do you agree that this SWH is an adequate representation of the market and displays generally typical performance in the three zones? If not please provide suggestions and reasons for this.
- Three systems were selected for a sensitivity analysis (split system with electric boost, thermosiphon with electric boost and a split system with instantaneous gas boost). Do they adequately represent the solar water heater market? If not, please provide an explanation and alternatives.
- In section 2, a number of factors which influence the performance of SWHs were identified. Are there any additional design factors which have not been assessed, are important and are relevant to this paper? If so, please outline and explain.
- Do you have any related concerns or issues you would like to raise with respect to the methodology behind the parameters used to define the boundaries?
Methodology and modelling
- Do you agree with the methodology and modelling process outlined in the report? If not, please explain why and provide an alternative method.
- Are any important factors missing from the model? Please explain and provide evidence.
- Do you see any problems in using the 69 NatHERS climate regions and 18 NZ climate files to provide enhanced spatial resolution of zones for solar hot water systems? If so provide your concerns along with alternatives and publicly available data to support your suggestion.
- Do you agree with the selected reference cities outlinedin section 4.4? If not, provide evidence and suggestions for alternative reference cities.
- Section 3.3 discusses the use of a linear versus a logarithmic basis for the calculation of energy efficiency stars. Do you have a preference and if so why? Do you have views on the method for this calculation?
Zoned Map for Solar Water Heaters 1
1. Introduction
The Australian, state, territory and New Zealand governments, through the Equipment Energy Efficiency (E3) Committee, are examining the development of a Zoned Energy Rating Label (ZERL) for all water heaters to show the impact of installed location on energy efficiency, performance and energy use. Particularly, Solar Water Heaters (SWH) are expected to perform differently when subjected to differing environments and local conditions. Other factors such as the characteristics of the hot water load (i.e. household use of hot water) and the design of the appliance also influence the energy consumption.
The approach presented in this paper for SWHs draws on work already completed including:
▪Qualitative and quantitative market testing of climate label design features with consumers, retailers and installers;
▪Development of climate mapping methodologies for air conditioners and heat pump water heaters.[1]
Focus group testing on the draft ZERL was consistent with international studies in concluding that more than three zones displayed on a map is likely to lead to consumers disconnecting from the information (Sweeney, 2013). As such there are three zones of energy performance presented, which correspond to modelled annual energy savings the appliance would be expected to achieve.
This report details a methodology for the development of a zoned map for SWHs. Following the principles outlined in the joint Australia and New Zealand standard AS/NZS 4234:2008: Heated water systems – Calculation of energy consumption (AS/NZS 4234) software modelling is used to establish the likely energy efficiency performance of a solar water heater within each of three regions, using a nominated location (or reference location) to represent the entire zone.
The modelling utilises the 69 Nationwide House Energy Rating Scheme (NatHERS) climate regionsfrom Australia and the 18 New Zealand climate files to create much higher geographic spatial resolution to the climate boundaries. While the three zones are primarily used for depiction on the physical label, the energy efficiency modelled in each of the 87 NatHERS climate regions and NZ climate files can be accessed through online or mobile applications. It is important to note that the underlying resolution for the TRansient SYstem Simulator (TRNSYS) model is the same for the modelling of each of the NatHERS climate regions and NZ climate files as it is for modelling the three energy efficiency zones.
This report sets out the technical elements of the proposal for consultation with the solar water heater industry and interested stakeholders.
Zoned Map for Solar Water Heaters 1
2. Factors influencing solar water heater energy efficiency
2.1 Design factors influencing solar water heater energy efficiency
The energy efficiency response of each class of water heater to a given set of environmental conditions will naturally differ in accordance with the system design. Some of the design factors that influence a SWH’s energy efficiency include:
▪The underlying efficiency of the system components;
▪How the system is sized relative to its climate and hot water demand;
▪How and when gas or electric auxiliary heating is provided;
▪The parasitic electrical load of the system; and
▪How the system deals with freezing, overheating and water expansion heat losses.
The existing modelling principles outlined in AS/NZS 4234 capture these influences and are retained in this work.
In recognition that the setting of zoned boundaries might be sensitive to the SWH design, three classes of SWH were used in this work. The details of the sensitivity analysis are set out as follows:
•Split system with circulation pump and electric or gas in-tank boost. An electric boost system with water circulation, denoted“Pumped Elec”, was used for this analysis.
The solar water heating collectors are roof mounted while a vertically oriented tank for water storage is installed at ground level. A small, electrical water circulation pump is used to transfer heat from the collectors to the tank.
Auxiliary boosting would be provided by an electric resistive heating element or gas burner.
The solar collector loop may contain water or a freeze tolerant solution for cold climate application.
•Thermosiphon with electric or gas boost. An electric boost system with afreeze tolerant solution, denoted “TS Elec”, was used for this analysis.
The solar water heating collector (s) and the hot water storage tank are both mounted on the roof in close proximity.
Heat transfer to the storage tank is accomplished by natural convection of water as it heats then rises in the collector.
Auxiliary boosting would be provided by an electric resistive heating element or gas booster.
The solar collector may contain water or a freeze tolerant solution for cold climate application
•Split system pre-heat with water circulation pump and instantaneous gas boost denoted “Inst Gas”.
This design operates similarly to the “Pumped Elec” design, except that auxiliary heat is provided on demand as water leaves the hot water storage tank to satisfy a load.
Auxiliary energy consumption required to overcome storage tank teat loss may be reduced in these systems.
2.2 Climate factors influencing solar water heater energy efficiency
It is important that energy efficiency modelling captures as many performance influencing factors as possible at the highest spatial resolution available.
As previously mentioned, climate sensitive parameters captured by the modelling used in this study are based on the methodology used in TRNSYS software modelling set out in AS/NZS 4234. In this work, however, increased spatial resolution has been achieved by using hourly weather data from the NatHERS[2]climate regions and NZ climate files. This climate data includes solar radiation, ambient dry bulb and wet bulb air temperature, cloud cover and cold water supply temperature.
The composition of these weather files described by Peterson (2014)[3] and the weather files can be accessed from the Department of Industry, Innovation and Science for Australian data or Energy Efficiency and Conservation Authority (EECA) for New Zealand data.