Deterministic duct sizing and checks for HVAC drawn in Pascal Editor. Pascal holds the geometry, ports, and MCP edit tools; this package supplies the airflow, equal-friction sizing, and findings, and hands the result back as one apply_patch batch (one undo step).

# with a local Pascal editor running (`npx @pascal-app/cli start`):
npx openmep-pascal mcp size
# or offline, on an exported scene:
npx openmep-pascal size scene.json --pretty

What it does

Reads a Pascal scene: export_json / get_scene output, a saved scene file, or the raw JSON string. Only duct-segment, duct-fitting, duct-terminal, hvac-equipment, and level nodes matter; the rest are kept for parent lookup.
Rebuilds connectivity from port coincidence (5 cm, supply and return kept apart), re-implementing Pascal's port geometry for the four HVAC kinds so no editor runtime is needed.
Reads engineer-approved airflow per terminal (supply register, diffuser, or return grille) from metadata.requiredCfm (also metadata.openmep.requiredCfm or metadata.cfm; the key is configurable).
Sizes every supply and return run on a path from a terminal with CFM to a furnace or air handler with @openmep/hvac-domain (recommendDuctSegments, equal friction at 0.08 in. w.g./100 ft with role-based velocity caps per system).
Grades each run's actual size against the recommendation and emits findings plus an apply_patch batch that sets round duct-segment.diameter to the standard size and records CFM, velocity, friction rate, and status under metadata.openmep.

CLI

openmep-pascal size  <scene.json|-> [--out file] [--patch-out file] [--items-out file]
                     [--metadata-key key] [--tolerance-m metres] [--no-resize] [--pretty] [--fail-on-findings]
openmep-pascal items <scene.json|-> [--out file] [--pretty]
openmep-pascal mcp size   [connection] [--dry-run] [--no-verify] [sizing flags as for size]
openmep-pascal mcp export [connection] [--out file] [--pretty]

size prints { summary, findings, segments, patches, items }. --patch-out writes { "patches": [...] }, which is exactly the apply_patch argument. items prints the scene as NetworkItems so any other engine or grader can consume it. Exit codes: 0 ran, 1 error findings with --fail-on-findings or a failed post-apply verification, 2 malformed input, engine, or MCP error (typed name and code on stderr).

Live: `openmep-pascal mcp size`

Talks to a running Pascal editor through Pascal's own MCP server and does the whole round trip: export_json → size → apply_patch (validated as a batch, one undo step in the editor) → export_json again to verify every patched segment landed. Re-running is idempotent: segments whose diameter and recorded result already match get no patch, so nothing is added to the undo history.

Connection, in order of preference:

nothing: finds the local editor started by npx @pascal-app/cli start (or pascal editor) from $PASCAL_HOME/run/mcp.json (Pascal CLI 1.0.0; 0.1.x used mcp.url in run/editor.json) and $PASCAL_HOME/run/mcp-token, default ~/.pascal, exactly as pascal mcp connect does;
--url http://127.0.0.1:PORT/mcp --token-file ~/.pascal/run/mcp-token (or --token) for a Streamable HTTP server elsewhere;
--stdio "pascal mcp connect" or --stdio "pascal-mcp --stdio" to spawn a stdio server.

--dry-run exports and sizes without applying. The output adds target, applied (appliedOps, and Pascal's persistence warning when the editor kept the change in memory only because no scene is bound), and verification. The library equivalent is sizeThroughPascalMcp(session); connectPascalMcp / openPascalMcpSession give a narrow typed session (exportScene, applyPatch, undo, redo, callTool).

Verified against Pascal 0.1.5 from @pascal-app/cli on 2026-09-09 (examples/live-roundtrip.mjs, npm run live:roundtrip): the bundled scene created through apply_patch, sized 6 → 9/8/7 in in one batch, undo restored all three diameters in one step, redo reapplied them, and a second pass patched nothing.

Offline

export_json → save as scene.json.
openmep-pascal size scene.json --patch-out patches.json.
apply_patch with the contents of patches.json.

Try it on the bundled scene (a furnace, a round main, a tee, two runouts to a ceiling diffuser at 150 CFM and a floor register at 100 CFM, and a separate return drop):

npm run size:example --workspace @openmep/pascal-adapter

Library

import { sizePascalScene } from "@openmep/pascal-adapter";

const result = sizePascalScene(sceneJson);
result.findings;   // undersized runs, terminals with no path to equipment, missing CFM, ...
result.patches;    // [{ op: "update", id, data: { diameter, metadata } }]
result.segments;   // per-run CFM, role, recommended size, actual equivalent diameter, comparison
result.network;    // NetworkItems, ports, connections

readPascalScene, buildPascalNetwork, and sizePascalNetwork expose the stages separately. Errors are typed: PascalAdapterError (invalid-json, invalid-scene, invalid-node, invalid-argument) from this package, and DuctNetworkError / DuctSizingError / PortGraphError from @openmep/hvac-domain.

Findings

code	severity	meaning
`undersized`	error	actual (or equivalent) diameter is below the exact required diameter
`no-equipment-path`	error	a terminal with CFM has no same-system path to a furnace / air handler
`no-equipment`	error	the scene has no furnace or air handler
`invalid-required-cfm`	error	CFM metadata present but not a positive number
`diameter-out-of-host-range`	error	recommended size is outside Pascal's 2–48 in `duct-segment.diameter` range
`dangling-reference`	error	internal consistency failure from the engine
`mixed-system-segment`	error	internal consistency failure: one run loaded by supply and return
`unsized-segment`	warning	a supply run (or a return run, once any grille has CFM) on no terminal-to-equipment path
`missing-required-cfm`	warning / info	supply terminal (warning) or return grille (info) without CFM metadata; it does not contribute
`oversized`	info	at least one full standard size above the recommendation
`shape-not-resized`	info	rect / oval run graded but left as drawn
`unsupported-fitting-type`	info	fitting kind this adapter does not know; treated as unconnected

Scope and limitations

Supply runs always size; return runs size once their grilles have CFM (return air is not derived from supply). Equipment is shared by both sides.
Only round runs are resized. Rect and flat-oval runs are graded by their ASHRAE circular equivalent and get metadata only.
HVAC nodes must be reachable from the scene's rootNodeIds (normally a level under a building). Pascal's editor drops unreachable nodes when it opens a project and autosaves the pruned graph, while MCP export_json still shows them; the adapter reports such nodes as detached-node.
Pascal's apply_patch update is a shallow merge, so the patch carries the full metadata record with existing keys preserved. Apply patches to the same scene state you exported.
Level floor elevations are stacked per building as Pascal does; building position / rotation is not applied (it does not change coincidence within a building).
Airflow comes from metadata an engineer supplies; there is no load calculation here. Zone loads from Pascal zone polygons are a later step.
Pascal's node schemas move quickly. Port formulas here match pascalorg/editor at 2026-09-09; the tests pin the expected positions.
The published @pascal-app/core and @pascal-app/mcp packages are bundler-only ESM (extensionless imports), so this package never imports them: the live path speaks MCP over HTTP or stdio and needs only a running editor.