🔄 Chilled Water Decoupler Loop

Size primary-secondary hydraulic decoupler bridge pipes, identify flow direction, mixed supply header degradation, and Low Delta-T syndrome penalties.

⚡ Fortran 90 Engine Double Precision (IEEE 754) ✓ ISO / ASME Validated

Hvac

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👁️ Views 36

⚡ Solves 29

💾 Downloads 279 📦 Fortran Code 4.4 KB

📅 Released Jun 2026

⏱️ Latency < 1 ms

🔄 Primary-Secondary Chilled Water Hydronic Decoupler Bridge

Real-time visual simulation of production vs distribution flow balance, bridge direction & mixed temperatures

📝 Configuration & Presets

✅ Forward Flow (200 / 175 m³/h) ⚠️ Reverse Deficit (150 / 220 m³/h) 📉 Low ΔT Syndrome (8.5°C Ret) 🏥 Hospital Plant (320 m³/h)

💧 Primary & Secondary Hydronic Flows

Primary Production Flow Q_prim [m³/h]: Operating constant speed chillers

Secondary Distribution Flow Q_sec [m³/h]: Variable speed pump loop

🌡️ Water Temperatures & Sizing Velocity

Chiller Supply Temp T_sup [°C]:

Design Return Temp T_ret,des [°C]:

Actual Return Temp T_ret,act [°C]: Low value triggers Low ΔT syndrome

Max Bridge Velocity [m/s]: ASHRAE standard: ≤ 0.50 m/s

Decoupled Hydronic Formulations:
• Decoupler Flow: Q_bridge = Q_prim − Q_sec
• Minimum Bridge Diameter: D_min = √[ (4 · Q_max) / (π · v_max) ]
• Mixed Supply (Reverse): T_mix,sup = (Q_prim T_sup + |Q_b| T_ret) / Q_sec
• Low ΔT Penalty: Loss = [1 − (ΔT_act / ΔT_des)] × 100%

📊 Decoupler Sizing Results

📊 Output Summary
💾 Fortran Source

Recommended Decoupler Bridge Pipe Size

DN250 (Ø 250 mm)

🚨 REVERSE FLOW (Warning: Warm Return Degrades Coil Supply!)

-70.0 m³/h

Mixed Supply to Coils (T_mix,sup) 7.75 °C Chiller Setpoint = 6.0 °C

Mixed Return to Chillers (T_mix,ret) 11.50 °C Actual Secondary = 11.5 °C

Low ΔT Capacity Penalty 0.0 % ΔT_act = 5.5 °C (Des: 6.0 °C)

Decoupler Flow Velocity 0.40 m/s Limit: ≤ 0.50 m/s

📈 Required Decoupler Diameter vs Bypass Flow

📉 Mixed Supply Temperature Degradation vs Secondary Overpumping

=================================================================
 THERMOFLUIDCALC — CHILLED WATER DECOUPLER ANALYSIS REPORT
=================================================================
Case Title                 : Severe Secondary Overpumping (Reverse Flow & Supply Degradation)
Primary Production Flow    : 150.00 m3/h (660.4 GPM)
Secondary Distribution Flow: 220.00 m3/h (968.7 GPM)
Decoupler Bypass Flow      : -70.00 m3/h
Hydronic Bridge Status     : 🚨 REVERSE FLOW (Warning: Warm Return Degrades Coil Supply!)
-----------------------------------------------------------------
MINIMUM DECOUPLER PIPE DIA : DN250 (250.0 mm ID)
Mixed Header Supply Temp   : 7.75 °C (Chiller out: 6.00 °C)
Mixed Header Return Temp   : 11.50 °C (Secondary out: 11.50 °C)
Low Delta-T Penalty        : 0.0 % capacity derating
=================================================================

📘 Calculation Methodology & ASHRAE Standards

Hydraulic Decoupling Bridge

The bridge pipe provides a zero pressure drop junction ($v \le 0.5\,\text{m/s}$), hydraulically isolating the constant-flow chiller loop from variable-flow loads:

                    Qbridge = Qprimary − Qsecondary
                

Reverse Flow & Low Delta-T Risks

If $Q_{secondary} > Q_{primary}$, warm return water flows backward across the bridge into the coil supply header, causing loss of space dehumidification control.

Key Engineering Assumptions

Water velocity in decoupler bridge limited to $0.5\,\text{m/s}$ ($\Delta P < 1.5\,\text{kPa}$).
Perfect adiabatic mixing at header tee junctions.
Sized for max flow mismatch or 100% capacity of largest chiller module.

ThermoFluidCalc Engineering Report