Domestic Water Demand Calculation

Domestic water demand calculation determines the peak flow rate that a building's water supply system must deliver. This flow rate drives pipe sizing, pump selection, and tank sizing.

1. **Fixture inventory** - List all fixtures with types, supply controls, and counts. 2. **WSFU assignment** - Assign cold and hot WSFU from the selected code's table. 3. **Summation** - Sum WSFU per branch, riser, floor, and building. 4. **Diversity factor** - Convert total WSFU to peak flow rate using code conversion tables. The non-linear conversion inherently applies diversity. 5. **Separate cold and hot** - Calculated independently for different piping systems. 6. **System type** - Flush tank vs flushometer have different conversion curves.

The diversity factor accounts for the fact that not all fixtures operate simultaneously. As fixture count increases, the probability of simultaneous use decreases. Example (IPC flush tank): - 1 WSFU -> 3 GPM (ratio: 3.0) - 10 WSFU -> 14 GPM (ratio: 1.4) - 50 WSFU -> 30 GPM (ratio: 0.6) - 200 WSFU -> 60 GPM (ratio: 0.3) A building with 200 WSFU needs only 60 GPM, not 600 GPM. The diversity factor is built into the code conversion tables.

A 3-story office building with public restrooms: Per floor: 3 x Water closet (flushometer, public) = 15 cold WSFU, 3 x Lavatory = 3 cold + 3 hot WSFU, 1 x Urinal = 5 cold WSFU. Per floor: 23 cold, 3 hot WSFU. Building (3 floors): 69 cold, 9 hot WSFU. IPC flushometer conversion: 69 WSFU -> ~38 GPM cold, 9 WSFU -> ~13 GPM hot. These flow rates drive cold/hot pipe sizing, booster pump sizing, and water heater sizing.

The Domestic Water module handles the entire calculation: enter fixtures per wet area per floor, and the System Summary shows total cold/hot WSFU, converted flow rates, and per-riser breakdowns. Results can be imported into the Pumps and Water Heaters modules.