Method
Recirculation mass and volume flow from loop heat loss and allowable return-temperature drop.
Equations
ṁ = Qlcp · ΔT
V̇ = ṁρ
Symbols and units
| Symbol | Quantity | Unit |
|---|---|---|
| Inputs | ||
| Ql | Heat loss of the circulation loop | kW |
| cp | Water specific heat | kJ/kg·K |
| ΔT | Allowable supply-return ΔT | K |
| ρ | Fluid density | kg/m³ |
| Results | ||
| ṁ | Recirculation mass flow | kg/s |
| V̇ | Recirculation flow | m³/s |
| V̇ | Recirculation flow | L/s |
Assumptions and limits
- Loop heat loss is supplied, not calculated.
- Piping and pump head are out of scope.
In practice
- Work out the loop heat loss from the pipe lengths and insulation first; the circulation pump head is a separate calculation.
Worked example
The input values are the calculator's own verification test, run through the calculator. They show the working; they are not design values.
Inputs
| Ql | Heat loss of the circulation loop | 10 kW |
| cp | Water specific heat | 4.186 kJ/kg·K |
| ΔT | Allowable supply-return ΔT | 5 K |
| ρ | Fluid density | 1,000 kg/m³ |
Results
| ṁ | Recirculation mass flow | 0.477783 kg/s |
| V̇ | Recirculation flow | 0.000477783 m³/s |
| V̇ | Recirculation flow | 0.477783 L/s |
A preliminary check for engineer review, not an engineering approval. The project calculation to the applicable codes, authority requirements and specification governs.