2-Pipe vs 4-Pipe Decision Grid

Six questions. The answer usually turns on one of them — whether two rooms need opposite modes at the same hour. The tool also shows the heating trade-off that gets discovered too late.

Do two zones need opposite modes at the same hour, on a normal day?

A hospital wing, an office core against a glazed perimeter, a laboratory.

YesNo

Do you need independent humidity control by reheat?

Subcool to dry the air, then reheat — clean rooms, constant-humidity spaces.

YesNo

Is winter heating output per terminal critical?

Cold climate, glazed perimeter, the terminal is the only heat source in the room.

YesNo

Is first cost a primary constraint?

4-pipe roughly doubles pipework and adds a coil, a second valve and sequencing control.

YesNo

Are shoulder seasons long, with mixed loads?

2-pipe locks the whole building to the plant’s current mode until changeover.

YesNo

Can the plant deliver hot and chilled water simultaneously?

4-pipe needs a plant that serves both loops at once. If it cannot, the question is closed.

YesNo / unknown

Answer the questions and a recommendation appears here, with the reasoning behind each driver.

The trade-off most schedules miss. In a 2-pipe unit, hot water runs through the whole 3-row coil. In a 4-pipe unit, heating comes from a dedicated additional coil (3+1 rows) sized to reheat air, not to carry a design heating load. On the KAFP-05WA pair where KOVEN AIR engineers measured both configurations at 60 °C entering water, the 2-pipe unit delivered 7,425 W of heating against 3,127 W from the 4-pipe unit’s heating coil — 42% of the 2-pipe output.

2-Pipe vs 4-Pipe Decision Grid

2-Pipe vs 4-Pipe Decision Grid

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