Part 2 – Method for solar water heaters with a volumetric capacity more than 700 litres
Division A – Introduction
This Part sets out the method for determining the number of STCs that may be created for models of SWHs that are large SWHs.
Division B – Method
The method for determining the number of STCs that may be created for a large SWH is based on AS/NZS 4234:2008 and AS/NZS 4234:2008 Amendments 1 and 2, with additional requirements specified in this Determination.
Large SWHs shall be rated for climate zones 1 to 4 specified in AS/NZS 4234:2008.
The method is as follows:
Using the TRNSYS computer modelling package, format the TRNSYS deck files as set out in the TRNSYS Modelling Guidelines in Part 3 of this Schedule.
Calculate the total annual auxiliary energy use (MWh) for the large SWH using the TRNSYS computer modelling package, using the following TRNSYS input parameters:
a. Solar collector slope = 20°.
b. Solar collector azimuth = 45°.
c. For the climatic zones, use the weather data published by the Clean Energy Regulator.
d. The modelling of the product shall show compliance with the legionella control requirements specified in AS 3498-2009.
e. To rate thermosiphon SWHs and thermosiphon sidearm heat exchangers, use extension package TRNAUS.
f. Tank heat loss for a storage tank must be determined in accordance with the requirements met by the storage tank under regulation 3A(3)(c) of the Renewable Energy (Electricity) Regulations 2001, as in force from time to time.
g. The modelled lengths of piping shall be based on the following:
i. For a pumped circulation system, the length of pipe between the storage tank and the closest corner of the solar collector array for shall be the manufacturer’s specification or 25 m (each way), whichever is the larger.
ii. For all systems the lengths of the supply and return pipes shall account for additional piping length associated with reverse return plumbing.
iii. For a pumped circulation solar preheat tank, the length of piping between the pre-heat tank and the series auxiliary booster shall be the manufacturer’s specification or 10 m, whichever is the larger. If the auxiliary booster is integral with the pre-heat tank, then the actual pipe lengths shall be used.
Subdivision Part 2 - Renewable Energy (Method for Solar Water Heaters) Determination 2016 - Method for solar water heaters with a volumetric capacity more than 700 litres | Zoe
iv. For a thermosiphon solar preheater, the length of piping between the preheater and the series auxiliary booster shall be the manufacturer’s specification or 25 m, whichever is the larger. If the auxiliary booster is integral with the pre-heat tank, then the actual pipe lengths shall be used.
v. For systems with solar preheat and finishing tank, where the finishing tank is heated by a recirculating instantaneous auxiliary booster, the length of piping between finishing tank and booster shall be the manufacturer’s specification or 2 m (each way), whichever is the larger.
vi. The diameter of all connecting piping shall be equal to the manufacturer’s specifications.
vii. If manufacturer’s specifications for the thermal conductivity of the pipe insulation are provided for the large SWH, then those specified values are to be used. If no such specifications are provided, then the default values of 0.06 W/ (m K) shall be used for closed cell foam insulation and 0.1 W/(m K) for rubberized insulation or polytube or fibre insulation.
h. All other input parameters and control strategies must be those used in the actual large SWH.
i. Input parameters and control strategies are subject to modification by Division C of this Part.
Select the peak daily winter load in accordance with the scale of the installation. The load shall be the same for all zones and set such that the large SWH achieves at least 60% annual energy savings in zone 3. A minimum delivery temperature of 45°C must be achieved for each zone in relation to which STCs are to be created. The individual hot water load draw-offs shall be applied over a period of 1 h.
The percent energy savings,
a. for the purpose of defining the peak daily winter load of electrically boosted systems, shall be calculated as per clause 3.14.1 of AS/NZS 4234:2008 (as in force at the commencement of the Renewable Energy (Electricity) (Method for Solar Water Heaters) Amendment (Correction of Minor Errors) Determination 2017), except the annual reference energy use shall be as calculated in Step 5.c., and
b. for the purpose of defining the peak daily winter load of gas boosted systems, shall be calculated as per clause 3.14.1 of AS/NZS 4234:2008 (as in force at the commencement of the Renewable Energy (Electricity) (Method for Solar Water Heaters) Amendment (Correction of Minor Errors) Determination 2017), except the annual energy use shall be as calculated in Step 5.d.
Determine the annual energy use of an electric reference water heater (‘the reference system’) supplying the same hot water load, as follows:
a. The heat loss from the reference system shall be 15% of the hot water load, therefore use a factor of 1.15.
b. The time weighted average seasonal load multiplier to be used is 0.905 (see AS/NZS 4234:2008).
c. For electrically boosted systems multiply number of days in a year (365) by time weighted average seasonal load multiplier (0.905), by heat loss factor percentage (1.15) by the peak daily winter load.
d. For gas boosted systems multiply number of days in a year (365) by time weighted average seasonal load multiplier (0.905), by heat loss factor percentage (1.15) by the peak daily winter load and divide by the reference gas water heater thermal efficiency (0.788) as stated in Table A9 of AS/NZS 4234:2008.
Determine the displaced energy as follows:
a. For electrically boosted systems subtract the total annual auxiliary energy use for the large SWH, calculated in Step 2, from the annual energy use, calculated in Step 5.c., to determine the displaced energy.
b. For gas boosted systems, the displaced energy is the equivalent displaced electric energy. The equivalent displaced electric energy shall be determined using Appendix G of AS/NZS 4234:2008 and the annual electrical energy use of the reference electric heater shall be as calculated in Step 5.c.
Convert the displaced energy to MWh/y.
Multiply the displaced energy (MWh/y) by 10 to determine the 10 year MWh savings.
Round down the 10 year MWh savings to the nearest lower whole number.
9A. If the large SWH was installed on or after 1 January 2022:
(a) multiply the number worked out under step 9 by the factor specified in the following table for the year in which the large SWH was installed; and
(b) if the result is not a whole number—round down the result to the nearest lower whole number.
Note: Step 9A (if applicable) is carried out by the Regulator in keeping the Register of solar water heaters under regulation 19C of the Renewable Energy (Electricity) Regulations 2001.
The number worked out under step 9 or 9A (as applicable) is the number of STCs that may be created for the large SWH in the relevant zone.
Division C - Special Circumstances
The input parameters and control strategies used to calculate the total annual auxiliary energy for step 2 in the method in Division B of this Part are subject to modification in the following circumstances.
Tanks with bottom element fitted
For systems where a bottom element is fitted in the tank (e.g. a dual element tank) the bottom element is to be used for rating purposes. The minimum boost time for a bottom element shall be nominal off-peak times of 11 pm to 6 am.
One-shot boosting
One-shot boosting is a manual control that allows a default boost mode (such as off-peak boosting) to be overridden so that the user can satisfy a short term high demand for hot water.
Where the system automatically resets to the default boosting mode within 24 hours of the user changing the boost mode, the one-shot boosting can be ignored.
Where the system does not automatically reset to the default boosting mode within 24 hours of the user changing the boost mode, the boosting mode activated by the manual control must be considered to be active at all times
SWHs with hybrid photovoltaic/thermal solar collectors
For a large SWH that utilises photovoltaic/thermal (PV/T) hybrid solar collectors, which generate both electricity and useable thermal energy from the same collector, the following testing regime must be documented.
(a) PV output
The PV output shall be assessed using a collector with the water heating part of the collector empty.
(b) Water heating output
The thermal efficiency of the collector shall be assessed in accordance with AS/NZS 2535:2007 with the PV output set to maximum power conditions. The electrical output of the collector shall not be included in the thermal efficiency assessment.
Note: A large SWH with PV/T collectors will only be eligible for STCs as a SWH in relation to the water heating component of the system.
Family of products
A ‘family of products’ means a combination of tanks, collectors, boosters and pumps that are used in a modular fashion to create a product range of different sizes. An interpolation or a sub-unit approach may be used for the performance rating of a family of products as detailed in the below two paragraphs.
a) Interpolation approach: interpolation of performance for a scaled family of products
An interpolation approach may be used if all members of a family of products must have the:
same solar collector;
same ratio of collector area to tank volume; and
same collector flow rate per unit area.
The performance of the family of products may be determined from detailed simulation of the performance of the largest, smallest and midpoint system sizes with the pipes, boosters and pumps they include. The performance of other members of the family may be determined by interpolation using a non-linear fit to the ratings of the largest, smallest and midpoint products. Auxiliary boosters and pumps for each interpolated model must have equal or greater efficiency than the smallest member of the interpolated range.
b) Sub-unit approach: parallel sub-unit family of products
A sub-unit approach may be used if a family of products consists of parallel sub-units that each have an identical solar collector array, storage tank, booster and pump configuration.
The system performance rating of the family of products may be determined by multiplying the STC of one sub-unit by the number of sub-units and rounding down the resulting STC. The volume of each sub-unit tank may be less than 700 litres, but the combined physical inner tank volume of each member of the family of products must be greater than 700 litres.
The following system configuration variations in the installed systems may be used:
the collector arrays of the multiple sub-units may be combined into one inter-connected collector array;
the multiple sub-unit pumps may be replaced with one or more larger pumps of lower overall power consumption;
the multiple sub-unit piping may be replaced with larger diameter piping provided the pipe insulation thermal resistance is equal to or larger than the pipe insulation resistance in the rated sub-unit; and
the collector flow rate per unit area in a composite system shall be the same as for the rated sub-unit. This also applies to composite systems in which the pump and/or piping has been modified from the rated sub-unit.