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 indoor pool is held at 28–32 °C year-round and drained via overflow gutters. The water runs in a constant loop: pool → surge tank → circulation pump → sand filter → heat exchanger → back to the pool.
That large water mass is the silent constant heat load — but the very same mass is a thermal battery: the AI can pre-charge it during PV and cheap-power hours, shifting grid draw and cost without any swimmer noticing.
Pool water, circulation, filtration, backwash (DIN 19643):
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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 DIN 19643, VDI 2089, DGfdB and the German Buildings Energy Act. Same knowledge base as the European reference site; presented anonymously.
DIN 19643-1 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: DIN 19643-1
Evaporation from the water surface is the dominant heat loss in an indoor pool (60-80 %). Smith/Löf variant of the Carrier formula: m_evap [kg/h] = β × A [m²] × (p_w_pool − p_w_hall) [kPa]. β-coefficient per VDI 2089 Sheet 2 Tab. 4: 0.013 unused pool (covered), 0.040 normal use, 0.080 wave/diving pool. Evaporation enthalpy at 30 °C: 0.694 kWh/kg. Pool saturation vapour pressure via the Magnus formula: 611.2 × exp(17.62 × t / (243.12 + t)) Pa.
Basis: VDI 2089 Sheet 2
DIN 19643-1 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: DIN 19643-1
VDI 2089 Sheet 1 defines the target hall climate: air temperature 30 °C ± 2 K, relative humidity 55 % ± 5 %. Outdoor-air rate at least 30 m³/h per person at full occupancy, at least 4 L/(s·m² of water surface) in base mode. For a hall with 355 m² water surface: 4 × 355 × 3.6 = 5,112 m³/h minimum; in practice VDI recommends ~16,000 m³/h for comfort and pollutant removal (trihalomethanes). Heat recovery via plate exchanger at 65-75 % efficiency is standard.
Basis: VDI 2089 Sheet 1
The German Buildings Energy Act GEG 2024 treats pools as non-residential buildings. Mandatory air-conditioning inspection every 4 years (ventilation > 12 kW). On change of ownership or major refurbishment, tighter envelope U-values apply (external wall U ≤ 0.24 W/(m²·K)). A demand-based energy certificate is required above 250 m² of heated floor area. A hall pool with 1,800 m² of envelope at U=0.8 does not meet new-build standards — so grant funding for envelope refurbishment (up to 35 % rate) is available.
Basis: GEG 2024 (German Buildings Energy Act)
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