General
HIIO determines the water supply requirements needed to deliver adequate flow and pressure to all plumbing fixtures served by a system. Constant flows such as irrigation and make‑up water are also included.
HIIO incorporates the fixture unit methodologies found in the appendices of the International Plumbing Code (IPC), Uniform Plumbing Code (UPC), and National Standard Plumbing Code (NSPC).
Segments
All pipe segments from the water source to the fixtures are entered. The input for each segment includes length, upstream elevation, valves, and other components.
Both pipe sizes and elbow quantities are automatically assigned to each segment based on the selected profiles, but those sizes and quantities but can be overridden for each segment.
For systems where hot water piping parallels cold water piping, hot water segments can be linked to their corresponding cold water segments such that changes to the cold water segments automatically update the hot water segments.
Pressure
Segment pressure losses are calculated calculated using the Darcy‑Weisbach equation, with equivalent lengths for elbows and tees added to the length. Flow coefficients (Cv) are used to calculate the pressure loss of valves and components.
Each fixture has an independent required pressure. The required pressure at the water supply equals the total pressure loss of the critical path segments, plus the critical path fixture’s required pressure, plus the elevation difference between the critical path fixture and the supply.
Sizes
Multiple sizing profiles can be created for cold/total water and hot water. Each profile includes all pipe sizes from 3/8" to 12", with a flow range assigned to each size.
Profile assigned sizes can be overridden per segment, however doing so reduces the effectiveness of automatic sizing.
A built‑in solver (Excel goal seek) can generate sizing profiles automatically by calculating the flow rates corresponding to an input pressure loss rate or velocity.
Fixture Units
Segment flow is calculated using a conventional fixture unit methodology based on Hunter’s curve, which provides a non‑linear relationship between fixture units and flow. As a result, the flow in a segment is less than the sum of the flows of its upstream segments.
Each segment is designated as cold water, hot water, or total water, with fixture units independently assignable for each fixture for each designation. A selectable option incorporates the additional fixture unit requirements of UPC Section 610.10 for the first several flush valves.
Fixture Groups
Fixtures can be assigned in groups to streamline data entry. For example, a fixture group could include 16 water closets, 4 urinals, and 8 lavatories.
Elbows
Profiles can be created to automatically assign elbows to segments, where each profile has a length‑to‑elbow‑quantity ratio for each size. Assigned elbow quantities can be overridden per segment.
Features
240 cold water segments.
240 hot water segments.
48 elevations.
8 cold water pipe sizing profiles.
8 hot water pipe sizing profiles.
3/8" to 12" pipe.
16 pipe types (roughnesses and inside diameters).
8 sets of equivalent lengths for elbows and tees.
8 automatic elbow profiles.
8 fixture unit‑to‑flow curves.
Up to 250,000 fixture units.
4 sets of additional fixture units for flushometer valves.
24 fixture groups.
8 fixtures per group (fixture quantity unlimited).
16 constant demands.
16 valves (components with Cv values).
12 valve assemblies.
4 valves per assembly (valve quantity unlimited).
All data is editable.
Limitations
Only Inch‑Pound (I‑P) units are supported; SI units are not.
Only “tree” type systems are supported; systems with more than one path from the supply to a fixture are not.
Other Considerations
HIIO is not inherently a critical path calculator. However, when the critical path is clear by experience, HIIO can be used for that purpose, though doing so reduces the effectiveness of automatic sizing.