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IS 16569:2016 is the Indian Standard (BIS) for solar water heating systems with evacuated tube collectors - general requirements and methods of test. This standard outlines the general requirements and test methods for solar water heating systems that use evacuated tube collectors (ETC). It covers specifications for materials, construction, safety, thermal performance, and durability to ensure system quality and efficiency. The standard is applicable to both thermosyphon and forced circulation type systems.
Specifies general requirements and methods of test for solar water heating systems utilizing evacuated tube collectors.
Quick Reference — Top IS 16569:2016 Values
Key material specs, performance metrics, durability tests, and water quality limits for evacuated tube collector solar water heaters.
✓ Verified 2026-04-27
Reference
Value
Clause
Inner Tank Material— SS 316L recommended for water with high chloride content.
SS 304 / SS 316L
Cl. 4.2.1
Inner Tank Min. Thickness (SS)— For systems up to 500 L capacity.
0.48 mm
Cl. 4.2.1
Insulation Material— Or other material with equivalent thermal resistance.
PUF (Polyurethane Foam)
Cl. 4.3
Insulation Min. Thickness
50 mm
Cl. 4.3
Insulation Max. Thermal Conductivity— At a mean temperature of 25°C.
0.025 W/m.K
Cl. 4.3
Evacuated Tube Glass Type
Borosilicate Glass 3.3
Cl. 4.5.1
Absorber Coating Min. Absorptivity (α)
≥ 0.92
Cl. 4.5.2
Absorber Coating Max. Emissivity (ε)— At 80°C.
≤ 0.08
Cl. 4.5.2
Grommets / Bushes Material— Must be UV resistant and withstand 150°C.
EPDM / Silicone Rubber
Cl. 4.4
Support Structure Wind Resistance— Structure must withstand this wind speed without damage.
150 km/h
Cl. 4.6
Water Suitability Limit (Hardness)— Special design required for harder water.
< 300 ppm (as CaCO₃)
Cl. 4.1, Note 2
Water Suitability Limit (Chlorides)— Use of SS 316L tank is recommended above this limit.
< 250 ppm
Cl. 4.1, Note 2
Recommended Collector Tilt Angle— Angle depends on winter/summer usage bias.
Latitude (φ) ± 15°
Annex A, Cl. A-2
Collector Min. Optical Efficiency (F'η₀)— Based on gross collector area.
≥ 0.50
Cl. 8.9.3
Collector Max. Heat Loss Coeff. (F'UL)— Based on gross collector area.
≤ 1.8 W/(m².°C)
Cl. 8.9.3
System Heat Loss Coeff. (U_L)— V is the rated volume of the tank in litres.
≤ 8.5 / V^0.33 W/(m².°C)
Cl. 8.10
Tank Hydrostatic Test Pressure— For non-pressurized systems; hold for 30 min with no leakage.
0.2 kg/cm² (2m water head)
Cl. 8.4.1
Collector Hydrostatic Test Pressure— Hold for 30 min with no leakage.
1.5 kg/cm²
Cl. 8.5
Internal Thermal Shock Test— Performed when collector is at stagnation temperature.
Fill with water ≤ 25°C
Cl. 8.6
Hail Impact Test— Impact at terminal velocity; must cause no damage.
25 mm dia. ice ball
Annex C
⚠ Verify against the latest BIS/IRC publication and project specifications. Amendment Slips may modify values.
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
Practical Notes
! The performance of ETC systems is highly dependent on the vacuum integrity of the glass tubes. Check for a 'silvered' or milky appearance at the bottom of the tube, which indicates a loss of vacuum and a faulty tube.
! In hard water areas, scaling inside the tubes can severely degrade performance. Regular cleaning or the use of a water softener is crucial for long-term efficiency.
! Ensure the mounting structure is robust and complies with local wind load requirements (e.g., as per IS 875 Part 3), as this standard focuses on the thermal system, not its structural mounting.
EN 12976-1:2017 & EN 12976-2:2017CEN (European Committee for Standardization), Europe
HighCurrent
Thermal solar systems and components - Factory made systems - Part 1: General requirements & Part 2: Test methods
Covers requirements and test methods for complete factory-made solar water heating systems, strongly aligning with the system-level scope of IS 16569.
ISO 9806:2017ISO (International Organization for Standardization), International
HighCurrent
Solar energy -- Solar thermal collectors -- Test methods
Provides the detailed test methods for solar collectors, which is a major component and testing section within IS 16569.
AS/NZS 2712:2007Standards Australia / Standards New Zealand, Australia/New Zealand
MediumCurrent
Solar and heat pump water heaters — Design and construction
Details design, construction, and safety for solar water heaters, but is broader as it also includes heat pumps and different collector types.
ISO 9459-5:2007ISO (International Organization for Standardization), International
MediumCurrent
Solar heating -- Domestic water heating systems -- Part 5: System performance characterization by means of whole-system tests and computer simulation
Focuses specifically on the methodology for whole-system performance testing, which is a key aspect covered in IS 16569.
Key Differences
≠IS 16569 is a single, comprehensive standard for ETC systems, while international standards are typically modular (e.g., ISO 9806 for collectors, EN 12976 for systems).
≠IS 16569 specifies minimum thermal performance criteria required for compliance, whereas international standards like ISO 9806 primarily define the test method, leaving performance thresholds to regional certification bodies (e.g., Solar Keymark).
≠The Indian standard is specifically tailored to local conditions, referencing Indian standards for materials (e.g., SS 304/316 for tanks) and water quality (IS 10500), which may differ from the broader material options or performance-based requirements in ISO/EN standards.
≠Test parameters can be adapted for the Indian climate. For example, freeze resistance testing, which is critical in European standards, is not a mandatory requirement in IS 16569.
Key Similarities
≈All standards are based on the same fundamental principles for characterizing thermal performance, using metrics like optical efficiency (η₀) and heat loss coefficients (Uʟ).
≈Core safety and reliability tests are common across all standards, including hydrostatic pressure testing of the tank, thermal shock resistance of the collector, and high-temperature stagnation tests.
≈The general methodology for determining collector performance through outdoor testing (steady-state or quasi-dynamic) is largely harmonized, with IS 16569 adopting principles found in ISO 9806.
≈All standards mandate clear marking and documentation, requiring manufacturers to provide technical specifications, installation manuals, and performance data to the end-user.
Parameter Comparison
Parameter
IS Value
International
Source
Storage Tank Hydrostatic Pressure Test
1.5 times max operating pressure (min. 0.2 MPa / 2 bar) for 30 minutes.
1.5 times max operating pressure (min. 150 kPa / 1.5 bar) for 15 minutes.
EN 12976-2:2017
Collector Internal Thermal Shock
After 1h stagnation, circulate fluid at 25±5 °C for 5 minutes.
After 1h stagnation (>800 W/m²), circulate fluid at ≤ 25 °C for 5 minutes.
ISO 9806:2017
Collector Impact Resistance Test
Impact with a 227 g steel ball dropped from a height of 2 m.
Impact with ice balls (e.g., 25 mm diameter) projected at a specified velocity to simulate hail.
ISO 9806:2017
High Temperature / Stagnation Test Condition
Exposure to solar radiation of at least 850 W/m² for a minimum of 3 hours.
Exposure to ≥ 1000 W/m² until stagnation temperature stabilizes (3 readings within 1K over 10 min).
ISO 9806:2017
Test Water Quality Reference
Potable water conforming to Indian Standard IS 10500.
Reference test water with defined hardness and chloride content (e.g., for corrosion tests).
EN 12976-2:2017
Rain Penetration Test
Spray water for 4 hours at a rate of 1.7 L/m² per minute; no water ingress allowed.
Spray for 30 minutes at 0.05 L/s per m² of collector aperture; no water ingress allowed.
ISO 9806:2017
⚠ Verify details from original standards before use
Key Values6
Quick Reference Values
Minimum borosilicate glass thickness for tubes1.6 mm
Maximum heat loss for storage tank (up to 200L)1.8 kWh/24h
Hydrostatic pressure test for unpressurized tankTested to a head of 3 m of water
Hydrostatic pressure test for pressurized tank1.5 times the maximum operating pressure (min. 3 bar)
Hail resistance test requirement withstand impact of 25 mm dia ice ball at 20 m/s
Minimum thermal insulation thickness (PUF)50 mm
Key Formulas
η = F'(τα)e - F'UL * (Ti - Ta) / G — Collector thermal efficiency formula used in performance testing.
Tables & Referenced Sections
Key Tables
Table 1 - Material Specifications for Components
Table 2 - Performance Requirements
Table 3 - Test Conditions for Thermal Performance
Key Clauses
Clause 4 - Requirements
Clause 5 - Methods of Test
Clause 6 - Marking and Information to be Provided
Annex A - Test Method for Thermal Performance of Solar Water Heating System
What is the main performance parameter for an ETC system under this standard?+
The key parameter is the thermal performance, determined by testing as per Annex A, which establishes the system's characteristic heat output curve.
Does this standard cover both pressurized and non-pressurized (thermosyphon) systems?+
Yes, it covers both types. The requirements for safety valves and pressure testing differ significantly between them (Clause 4.4 and Annex B).
What is the material requirement for the inner storage tank?+
The inner tank should be made of a corrosion-resistant material like stainless steel (e.g., SS 304/316L) or mild steel with an appropriate protective lining (Clause 4.2.2).
Is an impact resistance test mandatory for the collector tubes?+
Yes, the collector assembly must pass an impact resistance test, often simulating hail, to ensure its durability against environmental hazards (Clause 5.5).