Multi-Zone Charge Distribution Visualizer

What it does. Animated diagram showing how a multi-zone outdoor unit’s refrigerant charge distributes at idle vs disperses into a single small bedroom during a leak event under ASHRAE 15 § 7.3.4.2.

Detailed Overview

The Multi-Zone Charge Distribution Visualizer is the geometric companion to the A2L Room-Volume Compliance Calculator. The Calculator gives the tech the per-room pass/fail math; the Visualizer shows the leak event spatially so the “the whole charge legally disperses into one room” concept becomes gut-clear in two seconds.

Purpose

ASHRAE 15 § 7.3.4.2 defines releasable refrigerant charge as the largest charge in an independent circuit. On a multi-zone mini-split, that means the entire system charge is legally treated as releasing into a single indoor head’s room during a leak event, even though the refrigerant is physically distributed across the outdoor unit, the linesets, and four or more indoor coils.

That code interpretation is counterintuitive. The Visualizer makes it intuitive. Two modes:

• At Idle. Shows the room floor plan with each indoor head positioned, color-coded by whether that room would pass or fail RCL if it experienced a leak. Refrigerant circuit lines connect each head back to the outdoor unit.
• Leak Event. Animates the dispersal of the full system charge into the selected target room, with particle effects radiating from the indoor head. The compliance math (charge vs RCL limit vs ratio over limit) is called out in real time.

Manufacturer Presets

• Mitsubishi MXZ-SM (4 zones, R-454B, 6.6 lb factory)
• Daikin 4MXM36 (4 zones, R-32, 4.9 lb factory)
• Fujitsu AOUH24 (3 zones, R-32, 3.97 lb factory)
• LG KUMXA361A Multi F MAX (5 zones, R-32, 9.26 lb factory)

When and Where to Use It

• Homeowner conversation. “Why can’t you just put a wall-mount in this bedroom?” gets a 5-second answer with the visualizer.
• Inspector / AHJ pre-meeting. Shows the compliance reasoning that drives the equipment selection.
• Apprentice training. The releasable-charge concept is the single hardest part of A2L compliance to teach verbally. The visualizer is the visual aid.
• Equipment selection. Toggle between the four manufacturer presets to see how different multi-zone outdoor units behave under the same room geometry.

Limitations

• The visualizer is illustrative, not bespoke. For a specific home, use the Room-Volume Compliance Calculator to enter the actual room dimensions.
• The leak-event animation is conceptual. Actual A2L leak behavior depends on indoor unit placement, ductwork, ambient air movement, and the specific refrigerant’s vapor density.
• Particle effects are a visual aid and do not represent specific concentration measurements.

Sources

• ASHRAE Standard 15-2022, § 7.3.4.2 (releasable refrigerant charge).
• ASHRAE Standard 34-2022 Addendum a (RCL values).
• UL 60335-2-40 4th Edition, Annexes GG and LL.
• Manufacturer submittal documents for Mitsubishi MXZ-SM, Daikin 4MXM36, Fujitsu AOUH24, LG KUMXA361A (2024-2025).