Tank Model Parameters

Tank parameters tell the TRNSYS model how the physical tank is configured: its volume, insulation, fitting heights, and heat exchanger geometry. These feed directly into the stratification model and heat loss calculation, so accuracy here is important.

Where to Find the Parameters

All tank parameters come from the tank drawing provided by the client. The drawing must include a data table showing:

• Total internal volume (litres)
• Heights above the tank base for all inlets, outlets, elements, and temperature sensors
• If the tank has an internal coil HX: coil dimensions (height, inner/outer diameter, number of turns or length)
• Insulation thickness and material (used for the Appendix E heat loss calculation if tank >700L)
• Wall thickness and material

If the tank drawing does not include a data table, or if dimensions are missing, request an updated drawing from the client before proceeding.

Entering Parameters in the TRNSYS Tool

Step 1: Navigate to the Tanks sheet in the Commercial TRNSYS Tool.

Step 2: Add each tank model name to the first row of the table.

Step 3: For each tank model, enter all parameters from the tank drawing. Add screenshots of the drawing alongside your entries so the reviewer can verify values against the source document.

Key parameters to enter:

Parameter	Source	Notes
Tank volume (L)	Tank drawing	Internal volume, not nominal
Tank height (mm)	Tank drawing	Used to derive node heights
Height of HP inlet/outlet	Tank drawing	Measured from base
Height of cold water inlet	Tank drawing	Measured from base
Height of hot water outlet	Tank drawing	Measured from base
Height of element (if fitted)	Tank drawing	Measured from base
Height of temperature sensors	Tank drawing	All sensor locations
Coil HX height (if applicable)	Tank drawing	Bottom and top of coil
Tank heat loss (W/K or kWh/24h)	4692 report or App E	See Tank Heat Loss Calculation

Step 4: Select the tank model for each heat pump system in the FAM_COM sheet. Once selected, the tank parameters will populate automatically from the Tanks sheet.

Sanity Checks

Before moving on, verify:

• The sum of volumes at each node height looks consistent with the total tank volume.
• HP inlet and outlet heights make physical sense for the system (e.g. HP return is at the bottom, HP outlet is at the top).
• If the tank has multiple inlets for a gas booster or second heat source, confirm all are represented.
• For systems with multiple tanks of the same model, confirm the number of tanks is set correctly in FAM_COM — the total system volume affects the CPL calculation.