Indoor-pool water loop — 24/7 load, usable as thermal battery. Part of the glass family — like our glass BESS, biogas plant and CHP.
The surge/balance tank collects the water that spills over the gutters while people swim and buffers it for circulation. It is part of the pool-water treatment standard hygiene chain.
If uninsulated it loses heat continuously to the ground (U ≈ 2.0 W/m²K, ground 12 °C) — about 200 kWh/day around the clock at the reference site (chain K03). 80 mm of insulation cuts that by ~84 %.
Pool water, circulation, filtration, backwash (the pool-water treatment standard):
Overview: The Glass Pool → · Markets: pool markets →
Monitored: continuously · level in the surge tank
The scenario: The level swing widens as the bathing load shifts. The tank still fills and empties, but its buffer no longer catches the peak, and the shortfall appears downstream instead of here.
Method proven on a live European reference aquatic center; presented anonymously.
Estimate from metered / design values. Zero-grid-import windows are real (metered).
Grounded in the applicable national standards for pool water treatment, plant energy performance and building energy performance. Same knowledge base as the European reference site; presented anonymously.
Uninsulated surge tanks (steel or concrete, in the ground) lose heat continuously. Uninsulated U-value: 2.0 W/(m²·K) against ground (12 °C). Insulating with 80 mm PUR rigid foam reduces U to 0.32 W/(m²·K) — a factor of 6. Investment: 250-350 €/m² of tank wall including water-tightness and mould protection. For a 55 m² surge tank: 124 kWh/d uninsulated → 20 kWh/d insulated = 38 MWh/a saved, ~3,400 €/a in gas. Plus avoidance of condensation corrosion on the outside.
Basis: Practice (KSB, FLL)
the pool operating guideline fixes the order for refurbishments: 1) reduce losses (envelope, pool cover, insulate the surge tank, ventilation heat recovery), 2) recover heat (heat recovery, waste-water heat, filter backwash as a heat-pump source), 3) generate efficiently (heat pump > CHP > gas). This hierarchy is decisive for public grant applications: funders check whether losses were reduced before the generation investment. Concretely: insulate the surge tank, add an outdoor-pool night cover and service the ventilation heat recovery before or together with the heat-pump installation.
Basis: the applicable national standard.10
The applicable standard requires a minimum fresh-water make-up of 30 litres per visitor per day, independent of filter performance. This make-up dilutes metabolic products, urea and other substances introduced by bathers. At 1,500 visitors/week × 52 weeks that is 2,340 m³/a, which has to be heated from drinking-water temperature (~10 °C) to pool set-point (22-32 °C). At a 28 °C pool set-point this is roughly 50 MWh/a of heating energy for fresh water alone.
Basis: the applicable national standard
The applicable standard prescribes a maximum residence time of the pool water, depending on pool type: swimmer pools 4 h turnover, non-swimmer/paddling 1-2 h. This sets the minimum filter flow rate. For a 242 m³ lap pool at 4 h turnover that is 60.5 m³/h of filter capacity. Filter backwash once per day or above 0.5 bar differential pressure. Backwash water is warm (pool temperature − 3-5 K) and therefore a valuable heat-pump source.
Basis: the applicable national standard
Standard process combination for public pools: multi-layer sand filter + flocculation + chlorine-dioxide or chlorine-gas disinfection. Alternatives use activated carbon (treatment) or UV (disinfection). Sand-filter layering: fine sand 0.4-0.6 mm on top, gravel support layer below. Filter velocity max 30 m/h. Backwash at 50-60 m/h up-flow for 5-10 min, backwash volume approx. 5× the filter-bed volume.
Basis: the applicable national standard
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