Flow Control – Separate Heat Pumps

Pump Type and Flow Rate

1. Check pump type: Is it constant speed or variable? This determines the TRNSYS template selection and pump modelling approach.
2. Check pump flow rate: Obtain from the AS/NZS 5125.1 test report.

Flow Control

3. Determine whether flow is controlled or uncontrolled. Reference: AS/NZS 4234 Clauses 3.7.3, 3.7.4, H3.2.

4. If controlled flow, verify evidence is provided for:

   • Flow meter installed at each installation
   • Flow meter used during commissioning
   • Flow rate set by controller
   • Orifice restrictor instructions

5. If variable flow: Check that the HP is tested over a range of flow rates.

Read fixed vs variable from the test behaviour, not the manual prose. A fixed outlet temperature with a modulated draw or flow indicates variable flow: record the outlet target Tset_out. A constant loop flow across the test indicates fixed flow: record the tested loop flow in L/min. Take this from the test data, not from a description in the manual.

Computed Flow Rate and Mode60

For a variable flow separate system the loop flow is computed, not read directly. Capacity Q = COP × Power, evaluated at the rating point Tin = 20°C, Tamb = 19°C, Twb = 15.4°C, Tdp = 12.9°C. The variable flow rate is then Q / (4.18 × (Tset_out − 20)) × 60, in L/min, where Tset_out is the HP outlet target. Override this computed value only with a measured tested loop flow.

Mode60 follows from the flow-to-capacity ratio at the same rating point. If pflow / Q < 1 (L/min)/kW, set Mode60 = 1, otherwise set Mode60 = 2.

Piping

6. Pipe length: Model the connecting pipe length as 5 m. This is fixed at 5 m for residential separate systems, with no exceptions.
7. Pipe diameter and insulation: Obtain evidence for specifications, otherwise use 16 mm inner diameter as default.