Plumbing

DHW circulation

V

38,5l/h

Pipe

12 × 1,0

Circulation calculates the flow of a domestic hot-water pipe to DVGW W 551. Heat loss and the allowed temperature drop give the flow, and the pipe range gives the size at 0.5 m/s at most.

Flow rate

38,5

l/h

Heat

220

W

m³/h
0,038
Return
55,0°C
Pipe
12 × 1,0
Velocity
0,14m/s

Typical insulated values, check against DIN 1988-300.

Circulation pipe

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How it's calculated

Circulation follows DVGW W 551 from the heat loss of the hot pipe. Q = L1 · q1 + L2 · q2. The flow is V = Q / (ρ · cp · ΔT) at the mean temperature, supply minus half the drop. Density and specific heat are those of water. If the return is below 55 °C, W 551 is not met. Pipe size is the smallest domestic-water size whose velocity stays within 0.5 m/s.

Worked example

Distribution 20 m at 11 W/m, riser 8 m at 7 W/m, 60 °C, ΔT 5 K: 276 W, 48.2 l/h. Copper 12 × 1,0 at 0.17 m/s.

FAQ

Why 55 °C on the return?
DVGW W 551 keeps the hot water at 55 °C or above, so the circulation does not fall below the hygiene limit.
What do 11 and 7 W/m mean?
Guide values for an insulated distribution pipe and riser. The actual insulation to DIN 1988-300 can differ.
Is the pipe size included?
Yes, with the domestic-water pipes at 0.5 m/s at most. That is the circulation pipe, not the draw-off pipe.
Does this cover a bare pipe?
Only if the heat loss per metre is set higher. The defaults of 11 and 7 W/m are insulated guide values.