Why VSPs work — the physics
Pump power scales with the cube of flow rate (affinity law). Halving the flow rate cuts power draw to one-eighth, while turnover time only doubles. Running a VSP at 50% flow for 12 hours uses ~25% of the energy of running a single-speed at 100% flow for 8 hours, and delivers more turnover.
The ZAR model
A 35,000-litre Joburg pool:
- Single-speed 1.1 kW × 8 h/day = 268 kWh/month × R3.20 = R858/month
- VSP 1.5 kW @ 40% × 12 h/day = ~110 kWh/month × R3.20 = R352/month
- Saving: ~R506/month = R6,070/year
- Pump premium: ~R12,000 → payback ~24 months
Hidden benefits
Lower flow rate means longer skim time per pass (better debris capture), quieter operation (~50 dB vs ~75 dB), and less back-pressure on the salt cell and filter — extending both. Cartridge filters in particular get 2–3× the service life on VSP flow rates.
Brands available in SA
Speck Badu Eco Touch, Pentair IntelliFlo, Hayward VS Omni, and Davey PowerMaster Eco — all stocked through SA distributors. Avoid grey-market imports: warranty + parts availability is the difference between a 10-year asset and a 3-year disposable.
Sources
- Eskom Homepower tariff schedule — Eskom
- Pump affinity laws reference — Hydraulic Institute