Hot water storage sizing

Assumptions used

Method

energy-balance method per EN 12831-3 (via EU 814/2013 tapping profiles). An implementation of the EN 12831-3 approach, not the standard itself.

Tapping profile

L: 24 draw-offs from 07:00, 11.655 kWh a day (Qref), from Commission Regulation (EU) No 814/2013, Annex III, Table 1 "Load profiles of water heaters".

Profile energy base

The profiles' energies are counted from a 10 °C cold feed (Annex I (7); Tm = 10 °C for bath and dishwashing draw-offs).

Mixed to stored water

Each draw-off is delivered at its peak temperature Tp where the table gives one, else its useful temperature Tm. Its litres at that temperature are worked out from the profile energy, then re-based to your 10 °C cold feed and converted to stored water at 55 °C.

Water

Specific heat 4.186 kJ/(kg·K), 1 kg per litre.

Heat source

5 kW available to the store, whenever needed (24 hours), putting back what has been drawn up to that duty.

Standing loss

1.14 kWh/24h, the declared standing loss of 90CLIMACYLSS2 (90 L), the smallest matching World Heat cylinder; the declared figure is used as it is, not adjusted to the storage temperature. Spread evenly over the day.

Usable volume

90% of the stored volume can be drawn off hot enough (mixing and stratification allowance). Adjust for the cylinder.

Time step

One minute. Each draw-off is spread evenly over its duration at the profile's flow rate. Days are repeated until the pattern settles, so the store starts the day as the previous day left it.

Outlets

Recorded for World Heat's check. The method sizes from the 24-hour profile, not from counting outlets (no loading units).

Not included

Limits on the duty the cylinder's coil can take, secondary circulation and pipework losses, energy for thermal disinfection, draw-offs beyond the profile (e.g. several showers at once), and diversity across several dwellings.