scope:

This Miscellaneous Publication (MP) details application of the TRNSYS modelling software to support assessment of the annual energy performance and CO₂ equivalent emission of water heaters to AS/NZS 4234:2021 requirements.

The performance evaluations use a combination of test results for component performance and a mathematical model of the complete product to determine the standardized annual purchased energy use. The procedure is applicable to electric, gas and solar water heaters with integral boosting or preheating into a conventional storage or instantaneous water heater and to heat pump water heaters. For solar and heat pump water heaters, displaced purchased energy relative to reference water heaters is also calculated.

For products not covered in the application of AS/NZS 4234:2021 and this document, or if it is not possible to model the product using the TRNSYS software, such products may be tested under AS 2984 to obtain an annual performance assessment.

Performance is determined for a range of climatic conditions using models implemented for use in the TRNSYS version 15 simulation package.

The modelling given in this document may be applied to the following water heaters:

(a) Electric and gas storage water heaters.

(b) Electric and gas instantaneous heaters.

(c) Solar water heaters with -

(i) flat plate, concentrating or evacuated tubular solar thermal collectors;

(ii) solar photovoltaic collectors;

(iii) thermosiphon or pumped fluid circulation through the solar collectors;

(iv) collector loop heat exchangers in a thermosiphon loop;

(v) horizontal or vertical water storage tanks;

(vi) storage tanks with single or dual electric element(s);

(vii) storage tanks with internal gas boosting; and

(viii) storage tanks with delivery side heat exchangers.

(d) Solar preheaters in series with electric or gas storage or instantaneous boosters.

(e) Solar-boosted heat pump water heaters with -

(i) solar collectors acting as the refrigerant evaporator;

(ii) water-cooled condenser; and

(iii) in-tank electric booster.

(f) Air-source heat pump water heaters with -

(i) internal tank condensers;

(ii) external wraparound, or in-wall embedded tank condensers; and

(iii) external condensers, circulating water into one or more tanks.

Example TRNSYS deck files for the following systems are provided with this document:

(A) Horizontal tank thermosiphon solar water heater with in-tank electric booster.

(B) Horizontal tank thermosiphon solar water heater with series instantaneous gas booster.

(C) Pumped circulation solar water heater with in-tank electric booster.

(D) Pumped circulation solar water heater with series instantaneous gas booster.

(E) Pumped circulation solar water heater with series instantaneous electric booster.

(F) Conventional electrical storage water heater.

(G) Conventional gas storage water heater.

(H) Conventional gas instantaneous water heater.

(I) Standalone air source heat pump.

(J) Integral air source heat pump with wraparound tank condenser.

(K) Pumped circulation solar water heater with standalone air source heat pump as primary booster and in-tank electric element as secondary booster.

(L) Electric water heater with indirect coupled photovoltaic (PV) electricity supply.

(M) Standalone air source heat pump with indirect coupled PV electricity supply.

Other water heater configurations incorporating the above components may also be modelled.

NOTE 1 Sample decks are suitable for modelling both flat plate and evacuated tube thermal collectors.

NOTE 2 In some instances, test data produced through physical test procedures that measure the performance of a system when it delivers hot water (e.g. AS/NZS 5125.1:2014 Appendix G; AS 2984) may assist in TRNSYS model development and to assess the accuracy of some TRNSYS inputs and some simulation outputs.

NOTE 3 AS 4552-2005 has been replaced by AS/NZS 5263.1.2:2016; however, energy performance tests to AS 4552-2005 are acceptable for use with this document, i.e. SA/SNZ MP 104.