Coil Circuitry Designer
Design and optimize coil tube circuitry: circuit count, feed/return positions, counter-flow vs parallel-flow, and visualization of tube connections.
1. Overview
The Circuitry Designer visualizes how tubes are connected within the heat exchanger. Proper circuitry design is critical for uniform fluid distribution, optimal heat transfer, and manageable pressure drop. The tool shows the path each circuit takes through the coil, from the supply header through the tube rows and U-bends to the return header.
2. Key Parameters
| Parameter | Description |
|---|---|
| Number of Circuits | How many parallel flow paths through the coil (must divide evenly into total tubes) |
| Number of Passes | How many times each circuit crosses the air stream (= number of rows per circuit) |
| Feed Position | Location of the supply header (top, bottom, left, right) |
| Return Position | Location of the return header |
3. Counter-Flow vs Parallel-Flow
The arrangement of the circuitry relative to the air flow direction significantly affects performance:
| Arrangement | Description | Advantage |
|---|---|---|
| Counter-Flow | Fluid enters at the air outlet side | Higher LMTD, 5–15% more capacity |
| Parallel-Flow | Fluid enters at the air inlet side | More uniform surface temperature |
Counter-flow is generally preferred for cooling coils (chilled water, DX evaporator) as it maximizes the temperature difference. Parallel-flow may be preferred for heating coils where uniform surface temperature prevents freezing.
4. Circuit Count Guidelines
The optimal number of circuits balances heat transfer performance against pressure drop:
- Too few circuits → high fluid velocity → excessive pressure drop
- Too many circuits → low fluid velocity → poor heat transfer (laminar flow)
- Water coils: target 0.5–3.0 m/s fluid velocity
- DX coils: target 3–8 m/s refrigerant velocity in two-phase region
5. Visualization
The circuitry diagram uses color-coded paths to show each circuit's route through the coil. Each circuit is displayed in a different color, making it easy to trace the fluid path from supply to return. U-bend connections between rows are shown as curved lines.
Note: The number of circuits must divide evenly into the total number of tubes per row. If you have 24 tubes per row, valid circuit counts include 1, 2, 3, 4, 6, 8, 12, and 24.