Source
https://www.branz.co.nz/pubs/research-reports/sr239/ — original source (opens in a new tab; the file is not redistributed)
BRANZ SR239 (2010) — Practical Means of Assessing Solar Water Heater Performance and Operation
Pollard A. 2010. Practical Means of Assessing Solar Water Heater Performance and Operation. BRANZ Study Report SR239, BRANZ Ltd, Judgeford, New Zealand. ISSN 1178-4938. Funded by the Building Research Levy. (Follows SR184 install inspections and SR188 field performance; companion to SR237 on heat-pump water heaters.)
Retrieved for RT_282 — but this is a METHODOLOGY report, NOT a modern field-yield dataset
RT_282 sought a post-G12/AS2 (≥2008) NZ SWH field-performance dataset to pair against SR188’s pre-improvement (2004–06) baseline. SR239 is dated 2010 but presents no new field cohort — its data are re-analyses of the same 33–35 systems monitored in Pollard & Zhao (2008, SR188 / OT_084), installed 2004–06. It is a how-to-assess-performance report (cheap COP measurement) plus a pointer to where modern expected performance actually lives: EECA’s per-model TRNSYS / AS/NZS4234:2008 simulation listings. RT_282’s core ask (a modern field dataset) is therefore NOT resolved —
@solar_thermal_yieldstill rests on SR188 + CR_016’s extrapolation. RT_282 stays open; the more promising modern source is raised as a new RT below.
Summary
BRANZ Study Report SR239 describes practical, low-cost ways to verify how well a solar
water heater (SWH) is performing — chiefly by measuring the coefficient of performance
(COP): the ratio of hot-water draw-off energy to the non-environmental (supplementary +
auxiliary) electricity the system consumes. It argues COP can be established cheaply
(a <40 DIN-rail electricity meter plus a ~100 water meter) without measuring the
hard-to-quantify standing losses. The report re-uses the field data from SR188
(OT_084) — the same 2004–06
systems — to demonstrate the method (e.g. the draw-off-energy-vs-water-use correlation and
the Appendix A circulation-pump operation plots), and it documents how the regulatory and
testing landscape changed after SR188 (G12/AS2 Acceptable Solution 2007, ENERGY STAR
labelling, EECA’s AS/NZS4234:2008 TRNSYS per-model listings). For NI it is valuable as
methodological provenance for the @solar_thermal_yield chain and an independent
restatement of the COP anchors — not as a new yield source.
Key claims
- claim: "Water heating accounts for around 29% of New Zealand's residential energy use, with electricity accounting for a large proportion of this (citing HEEP — Isaacs et al, 2010)."
source_location: "§1 Introduction (p1)"
- claim: "COP anchors (restated independently of SR188): an instantaneous electric water heater has a COP of 1 (100% of electrical input becomes heated water); an average electric storage hot-water cylinder has standing losses of ~33% of total water-heating energy (HEEP, Isaacs et al 2010), giving it a COP of 0.67; a SWH system with a COP of 1.34 requires half as much water-heating energy as a standard electric storage cylinder."
source_location: "§2 SWH system performance (p4)"
- claim: "SR239 presents NO new field cohort — its performance data are re-analyses of the same systems monitored in Pollard & Zhao (2008, SR188): '35 SWH systems installed between June 2004 and September 2006 [whose overall energy performance] was varied and included many poorly-performing systems'; the worked draw-off analysis uses the 33 valid systems of that study."
source_location: "§1 (p1); §2.1.2 (p7)"
- claim: "For the 33 SR188 systems, draw-off energy correlates with average daily hot-water use as y = 16.105x + 19 (R² = 0.8791); the average draw-off temperature difference across the 33 systems was 36°C — so metered water volume alone gives a reasonable approximation of draw-off energy."
source_location: "§2.1.2, Figure 9 & Figure 10 (p7–8)"
- claim: "Installing a timer on the supplementary-heating element improves SWH system performance by over 50% (Kerr 2008, from TRNSYS simulation) — a large, controllable install-quality lever."
source_location: "§3.4 (p10); §4.1 (p13)"
- claim: "SWH performance can be verified cheaply: a DIN-rail electricity meter costs less than $40 (in quantity) to separately meter supplementary heating, and a standard water meter (around $100) recording throughput improves the draw-off-energy estimate."
source_location: "§2.1.1 (p5); §6 Conclusions (p18)"
- claim: "Since SR188 the landscape changed: DBH published the G12/AS2 Acceptable Solution for SWH (2007), top systems can carry the ENERGY STAR label, and the EECA (Energywise) website lists TRNSYS simulation results following AS/NZS4234:2008 for many SWH models — i.e. modern expected performance is now available as MODELLED (not field-measured) per-model figures."
source_location: "§1 (p1); §4 (p11–12)"
- claim: "The DBH (2009) slope/orientation performance-reduction table (Figure 12) was modelled with a 3.3 m² flat-plate collector under AS/NZS4234:2008 Climate Zone 5, which covers most of the country except Otago, Southland and the West Coast (steeper tilts favoured in those southern zones); collector tilt guidance is site latitude — Auckland 37°, Wellington 41°, Christchurch 43.5°."
source_location: "§4.1, Figure 12 (p13); §3.1 (p9)"Neobiome Intelligence relevance
Provenance and cross-check for @solar_thermal_yield — NOT a new yield input.
SR239 sits behind, not beside, the SR188 → CR_016 yield chain:
- It does not move the yield figure. SR239’s own data are the SR188 2004–06 systems
(OT_084) re-analysed. So the model’s
@solar_thermal_yieldstill rests on SR188’s pre-improvement per-system contributions and CR_016’s per-m² / “modern well-installed” extrapolation. RT_282 (a genuinely modern field dataset) is not resolved by this file. - It documents the measurement method behind SR188’s numbers — the COP “blackbox” (draw-off ÷ non-environmental energy) that excludes standing losses, and the six-minute water-metering + fixed-ΔT (36°C) simplification. This makes the audit trail for the yield primary explicit: the SR188 contributions NI relies on are COP-derived delivered energy, net of standing losses — the right quantity for displaced electric heating.
- It independently restates the COP anchors (storage cylinder 0.67; ~33% standing losses; COP 1.34 ≈ half the energy) already carried on OT_084 — a second BRANZ report stating the same values, strengthening that benchmark.
- It reinforces “install quality dominates”. The >50% timer-improvement result and the emphasis that a system “installed today” must still be verified to “actually perform well” are consistent with SR188’s ANOVA finding (technology type second-order, p=0.98) that NI uses to cost flat-plate generically.
- It relocates the modern-yield target. The real modern (post-standard) performance numbers are the EECA / AS-NZS4234:2008 TRNSYS per-model expected-performance listings and ENERGY STAR labelling — modelled, not field. That is a better RT_282 successor than SR239 was, and is raised below. A modern field dataset (EECA Innovation-Fund / SR237 HPWH monitoring) remains the harder, higher-value gap.
Research targets
Documents to retrieve
- RT_356 (new) — EECA Energywise / Gen Less SWH eligible-systems list with AS/NZS4234:2008 TRNSYS per-model expected performance (annual energy saving / solar fraction per SWH model) + ENERGY STAR-labelled top performers. This is the modern (post-G12/AS2) per-model performance source SR239 points to — modelled, not field — and is the most retrievable replacement for CR_016’s extrapolation of a “modern well-installed” yield.
- RT_357 (RESOLVED → OT_162) — BRANZ SR237 (Pollard 2010) — The Energy Performance of Heat Pump Water Heaters — the EECA-linked 2010 HPWH field-monitoring study named as the companion to SR239. A modern NZ DHW field dataset for the heat-pump water-heating cells; pairs with OT_038 and SR188’s summer HPWH figures. ⚠ SR237 read = 2010 R-134a-era units, so a field floor / low-draw-off warning, not a modern CO₂ field value.
Research gaps
- RT_282 stays OPEN (re-scoped, not resolved). SR239 read in full = methodology only, same 2004–06 cohort. The original ask — a modern NZ SWH field-performance dataset — is still unmet; the realistic candidates are now RT_356 (EECA AS/NZS4234 modelled listings, cheaper) and any EECA Innovation-Fund / SR237-style field monitoring (harder).
Connections
Links to
Referenced by
EDT domains (1): D01: Renewable Energy & Storage Systems