Indoor-pool water loop — 24/7 load, usable as thermal battery. Part of the glass family — like our glass BESS, biogas plant and CHP.
During backwash the sand bed is flushed against the operating direction; the resulting water is warm (~25 °C) and normally goes to drain.
That warm backwash water is an ideal source for the pool heat pump: instead of COP 4 on outdoor air it reaches COP 12–17 on backwash water (chain K04). The AI switches the source accordingly.
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.
Filter backwash water is the most valuable heat source for pool heat pumps. Temperature: pool set-point minus 3-5 K (26 °C for a hall pool, 19 °C outdoor). Volume: typically 1× the filter-bed volume per day, approx. 5-10 m³ per filter. Energy content: with a 60 m² backwash tank surface at 25 °C water this yields 290 kWh/d of usable heat on the HP evaporator side. Connection: a heat exchanger between backwash water and the HP brine loop keeps the evaporator clean. Investment: ~10 k€ for the exchanger + controls.
Basis: DGfdB R 65.10 + manufacturer data
Filter backwash water and pool overflow are discharged as waste water — an additional heat-recovery opportunity. A plate exchanger between the fresh-water make-up (10 °C) and the waste water (warm, 20-28 °C) recovers 50-70 % of the fresh-water heating. Investment 8-15 k€, saving 15-30 MWh/a. Usually recommended as a second measure after the main heat-pump step. Example: at 2,340 m³/a fresh water × 1.16 kWh/(m³·K) × 18 K = 49 MWh/a of heating energy, of which 30 MWh/a is recoverable.
Basis: DGfdB R 65.10
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: DIN 19643-2
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
Modern inverter pool air-to-water heat pumps reach rated-point COPs (source 26 °C, sink 27 °C) between 14 and 18 (e.g. AquaForte InverterPro 16.5, Microwell HP1500 Split 17, Pontaqua Inverter+ 14). These are data-sheet values at the thermodynamically most favourable operating point. The seasonal COP (SCOP) — accounting for heat-up phases, cooler sources and standstill losses — sits at 8-12. Inverter pool HPs typically modulate between 30 % and 100 % of rated output; some industrial models (Carrier 30RB, Stiebel WPL) down to 25 %. The source must be > 5 °C for the evaporator to work without icing.
Basis: Manufacturer data sheets (AquaForte, Microwell, Pontaqua)
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