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The Glass Pool · WARMWASSER

Circulation loop

Hot water — tank, charging and circulation. Part of the glass family — like our glass BESS, biogas plant and CHP.

Circulation loop
Tank → Circulation pump → Pipe loop → Draw-off points
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What is Circulation loop?

The circulation loop keeps the pipework warm so hot water arrives at the tap instantly. It is a continuous consumer: it runs around the clock, even when nobody draws water.

Legionella control sets the lower limit — the German DVGW W 551 code requires at least 55 °C in the circulation return; US properties apply their governing standard (e.g. ASHRAE 188). Anything above that is paid-for loss, anything below is a hygiene risk. The operating point sits just above the limit.

What is measured here

  • Circulation flow and return — the spread across the loop
  • Flow rate and power draw of the circulation pump
  • Time spent below the hygiene limit
  • Loop loss = spread × flow rate

How we connect it — read-only

  • Flow and return sensors on the loop over Modbus or from the BMS.
  • Circulation pump over Modbus — speed, power, running hours.
  • Heat meter in the loop where present — otherwise the loss is computed.

Schematic (native, live)

Hot water — tank, charging and circulation.

TankPipe loopDraw-off points

Overview: The Glass Pool → · Markets: pool markets →

Live —

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What the AI does

  • Holds the return just above the hygiene limit instead of blanket-hot.
  • Reduces the flow rate in low-draw periods without breaching the limit.
  • Detects a shrinking spread — a sign of a failed check valve.
  • Provides evidence for riser balancing when individual risers return persistently colder.

Method proven on a live European reference aquatic center; presented anonymously.

Loop loss

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Estimate from metered / design values. Zero-grid-import windows are real (metered).

Standards & norms

What the rules require — Circulation loop

Grounded in DIN 19643, VDI 2089, DGfdB and the German Buildings Energy Act. Same knowledge base as the European reference site; presented anonymously.

Why does circulation cost more than the hot water actually drawn?

The loop gives off heat to its surroundings 24 hours a day, regardless of draw-off. In buildings with long pipe runs and modest consumption this continuous loss exceeds the hot water actually used.

Basis: plant engineering

Can circulation be switched off at night?

In potable water systems that is hygienically risky: longer stagnation at lukewarm temperatures favours legionella growth. The safe route is to reduce the flow rather than stop it — the temperature limit stays respected.

Basis: plant engineering

What does the spread tell you about the loop?

A very small spread means a lot of water circulating without giving up heat — usually short-circuiting through a failed valve. A very large spread means the return comes back too cold and the hygiene limit is at risk.

Basis: plant engineering

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