VRF Refnet & Pipe Length Checker
Build a VRF piping tree from the outdoor unit through the refnet joints to every indoor unit. The lab sizes each pipe from the capacity downstream, checks the length and height limits and the connection ratio, adds up the refrigerant charge and tests the smallest room against the EN 378 concentration limit.
How to use: edit the piping table: each row is a pipe ending at a refnet joint or an indoor unit. Limits default to typical manufacturer values, so set them to your brand's figures. Tap i for explanations.
1. Outdoor unit and limits
Limits differ by manufacturer and model. Check the installation manual.
2. Piping tree
Liquid and gas sizes on every pipe. Red items break a limit.
3. Checks
4. Piping table
Type R is a refnet joint, type U an indoor unit. Height is relative to the outdoor unit (negative is below). Room volume is the smallest room the indoor unit serves.
5. How the checks work
Pipe sizes
Each pipe is sized from the total indoor capacity downstream of it, using a typical R410A sizing table. Manufacturers publish their own tables and some upsize the main pipe for long runs, so always confirm with the brand's design software.
Lengths and heights
Equivalent length adds about 15% for bends and 0.5 m per refnet joint to the actual length. The longest run, the run from the first joint and the height between units all have limits because oil return and refrigerant pressure drop get worse with distance and lift.
Connection ratio
Total indoor capacity divided by outdoor capacity. Diversity lets you connect more indoor capacity than the outdoor unit can deliver at once, typically up to 130%, but the units then share capacity at peak.
Refrigerant in small rooms
If the whole charge leaked into the smallest room, the concentration must stay within the limit. For R410A EN 378 uses a practical limit of 0.44 kg/m³. For R32, which is mildly flammable, the limit depends on room floor area and unit height: mmax = 2.5 × LFL1.25 × h0 × √A. If a room fails, add a leak detector with shut-off valves, ventilation, or split the system.
Learning and checking tool. Final design must follow the manufacturer's installation manual and selection software.