Tank Heat Loss Calculation
How to determine tank heat loss for large commercial systems.
Every commercial submission requires a tank heat loss value for each tank model.
How this value is obtained depends on the tank’s physical storage volume.
| Tank volume | Method | Deliverable |
|---|---|---|
| 700L or less | Physical test to AS/NZS 4692.1 | AS/NZS 4692.1 test report from accredited lab |
| Greater than 700L | Calculation to AS/NZS 4234:2021 Appendix E | All tank parameters compiled in Commercial TRNSYS TOOL ‘Tanks’ sheet |
Tanks 700L or Less
An AS/NZS 4692.1 test report from an accredited laboratory is required. This must be obtained by the client before modelling can begin. Check that:
- The tank model name on the test report matches the model being submitted exactly.
- The heat loss value (in kWh/d) is clearly stated in the report.
- The test report is signed by the testing laboratory.
Enter the heat loss value from the test report into the Commercial TRNSYS Tool.
Tanks Greater than 700L
For tanks larger than 700L, no physical test is required. Instead, a calculation is performed using AS/NZS 4234:2021 Appendix E, which estimates heat loss from the tank’s geometry and insulation properties.
The calculation is implemented directly in the TRNSYS .dcks, you just need to collect the input parameters in the Tanks sheet in the TRNSYS Tool.
Study AS/NZS 4234:2021 Appendix E before performing this calculation for the first time. The methodology calculates heat loss through the cylindrical wall, top, and bottom of the tank separately, accounting for insulation thickness, thermal conductivity, and surface area.
Inputs Required
To complete the Appendix E calculation, the following data must be available from the tank drawing:
- Internal tank diameter (mm)
- Internal tank height (mm)
- Insulation thickness on wall, top cap, and bottom cap (mm)
- Insulation material (to determine thermal conductivity)
Typical insulation thermal conductivity values used in Appendix E:
| Insulation material | Thermal conductivity k (W/m·K) |
|---|---|
| Polyurethane foam | 0.025 |
| Polystyrene | 0.035 |
| Fibreglass | 0.040 |
If the insulation material is not specified on the drawing, request clarification from the client. Do not assume a conductivity value without confirmation.
Including in Audit Files
For both cases, the heat loss evidence must be included in the audit package:
- For 4692 reports: include the PDF test report in the audit folder, named
Brand_Model_4692.pdf.