⚙️ Procedure for Bypass Lines in Chilled Water Systems

engineer@mep.education

October 15, 2025

1. Identify the Purpose of the Bypass

Chiller protection (minimum flow through evaporator).
Differential pressure control (relieve excess pressure when valves close).
Temperature stabilization (mixing chilled and return water).
Coil control (allow partial or no cooling at AHU/FCU).
Pump bypass (maintain circulation during low load).

2. Determine Bypass Location

Chiller Bypass: Across evaporator (supply to return).
System Differential Pressure Bypass: Between main supply and return headers.
Coil Bypass: Across individual AHU/FCU coils.
Pump Bypass: Around pump discharge to suction line.

3. Sizing the Bypass Line

Calculate minimum flow requirement of the chiller (given by manufacturer).
For DP bypass, size to handle expected low-load excess flow.
Use thumb rule: typically 10–30% of total design flow (varies with system type).
Ensure velocity in bypass pipe does not exceed recommended limits (1.8–2.5 m/s for chilled water).

4. Select Control Device

Manual Balancing Valve: Simple bypass, fixed flow.
Automatic Differential Pressure Bypass Valve (DPBV): Modulates flow based on pressure difference.
3-Way Control Valve: At coil bypasses to mix supply and return water.
Motorized Valve with Controls: Integrated with BMS for smart operation.

5. Installation Guidelines

Install bypass pipe with minimum bends to reduce resistance.
Place valves where they are accessible for maintenance.
Provide isolation valves on both sides for service flexibility.
Ensure proper direction of flow (check arrows on valve body).
Insulate bypass lines to avoid energy losses or condensation.

6. Commissioning Procedure

Open bypass valve during flushing and filling of system.
Balance flow by adjusting bypass valves as per design.
Check chiller differential temperature (ΔT) and confirm stable operation.
Verify that differential pressure setpoint is correct (commonly 15–20 psi across system).
Integrate with BMS/controls for monitoring and automatic modulation.

7. Operation & Maintenance

Monitor bypass flow to ensure chiller minimum flow is maintained.
Inspect valves periodically for leakage or malfunction.
Adjust setpoints (if automatic) during seasonal changes.
Document flow test results and keep as baseline for O&M.

✅ Summary:
The procedure for bypass lines involves design (purpose, location, sizing) → selection (valve type) → installation (proper routing and accessibility) → commissioning (balancing and testing) → operation & maintenance (ensuring reliability and efficiency).

🎯 Purpose of Bypass Lines in Chilled Water Systems

Bypass lines are introduced into chilled water networks to ensure safe, stable, and efficient operation. Their purpose can be categorized into several key functions:

1. Maintain Minimum Flow Through Chillers

Chillers require a minimum flow rate through the evaporator to prevent tube freezing, vibration, and unstable operation.
The bypass ensures that when terminal unit valves close at low load, water still circulates through the chiller.
This protects the chiller and avoids short cycling.

2. Control Differential Pressure in the System

As AHU/FCU control valves modulate or close, pump head pressure rises.
A differential pressure bypass line (with DPBV) opens automatically to relieve pressure.
Prevents pump overload, pipe stress, and noisy valve operation.

3. Stabilize Water Temperature

Bypass lines allow mixing of chilled supply and return water.
Helps maintain stable supply temperature to coils, especially in variable load conditions.
Reduces risk of overcooling, coil frosting, or unstable room conditions.

4. Provide Flexibility at Coils (AHUs/FCUs)

With 3-way valves, a bypass line allows water to flow around the coil when no cooling is required.
Ensures continuous circulation in the loop while modulating coil cooling capacity.
Helps achieve precise temperature and humidity control.

5. Support Commissioning and Flushing

During initial system flushing and startup, bypass lines keep circulation paths open.
Allows air purging, filling, and balancing before final adjustments.
Makes system commissioning smoother and faster.

6. Enhance Energy Efficiency & Reliability

Prevents excessive pump energy use at low loads by providing alternate flow paths.
Reduces wear and tear on chillers, pumps, and valves.
Ensures stable, long-term operation with less maintenance downtime.

✅ In summary:
The primary purpose of bypass lines in chilled water systems is to protect equipment, maintain system stability, improve energy efficiency, and provide operational flexibility.

📍 Determining Bypass Location in Chilled Water Systems

The location of a bypass line depends on which component or function it is designed to protect or control. Below are the typical locations:

1. Chiller Bypass (Across the Evaporator)

Location: A pipe connecting supply header to return header around the chiller.
Purpose:
- Ensures minimum flow through the chiller when load is low.
- Prevents freezing in evaporator tubes.
- Common in primary-only systems or when chillers cycle on/off.

2. System Differential Pressure (DP) Bypass

Location: Installed between the main chilled water supply header and return header, usually near the farthest or most critical section of the distribution system.
Purpose:
- Maintains stable differential pressure when control valves close.
- Protects pumps and piping.
- Typically uses an automatic DP bypass valve.

3. Coil (AHU/FCU) Bypass

Location: Across individual coils in AHUs or FCUs, integrated with a 3-way control valve.
Purpose:
- Allows chilled water to bypass the coil when cooling is not required.
- Provides modulating control (part load operation).
- Maintains circulation in loop even if coil is not active.

4. Pump Bypass

Location: Installed around pump discharge to suction line.
Purpose:
- Maintains circulation when pump operates at low speed (VFD) or during partial shutdown.
- Protects against pump deadhead condition.
- Ensures water movement during standby mode.

5. Temporary Bypass (for Commissioning/Flushing)

Location: Often at ends of distribution loops or across risers.
Purpose:
- Keeps water circulating during flushing, filling, or balancing.
- Facilitates system commissioning before all coils/branches are connected.

✅ Quick Reference Table – Bypass Location & Purpose

Bypass Type	Location	Main Purpose
Chiller Bypass	Across chiller evaporator (supply ↔ return)	Maintain chiller minimum flow
Differential Pressure Bypass	Between supply & return headers	Control system DP, protect pumps
Coil (AHU/FCU) Bypass	Across coil (with 3-way valve)	Temperature & load modulation
Pump Bypass	Pump discharge ↔ suction	Prevent pump deadhead, maintain circulation
Temporary/Commissioning	End of loop/riser	Flushing, filling, balancing

👉 In short: Bypass locations are determined by system needs — protection of chillers, pressure balance, coil control, pump safety, or commissioning requirements.

Sizing the Bypass Line (Design Playbook)

1) Decide which bypass you’re sizing

Chiller (evaporator) bypass → protects the chiller’s minimum flow.
System DP bypass (header-to-header) → protects pumps/valves by bleeding excess pressure at low load.
Coil bypass (3-way valve) → provides load modulation around the coil.
Pump recirculation bypass → protects pumps from deadhead/minimum thermal flow issues.

2) Quantify the design flow that must pass through the bypass

A) Chiller bypass (primary-only or variable-primary)

Get the chiller minimum evaporator flow from the datasheet (often 30–50% of chiller design flow).
Estimate lowest concurrent load flow expected to be available through open coils at turndown.
Size bypass capacity for the difference: Qbypass = max⁡(0, Qchiller, min − Qload, min)Q_{bypass} \;=\; \max\Big(0,\; Q_{chiller,\;min} \;-\; Q_{load,\;min}\Big)Qbypass=max(0,Qchiller,min−Qload,min)

If you have multiple chillers on a common header: repeat per chiller operating scenario.

B) System DP bypass (supply→return headers)

Aim to pass the excess flow when many/most 2-way valves are closed.
Practical rule when data is scarce: 20–40% of system design flow (closer to 20% for well-tuned VAV/VFD systems; up to 40% for very peaky or small systems).
Better method: use the pump curve at minimum VFD speed and the network at low-load valve positions to compute the surplus flow that needs a path.

C) Coil bypass (3-way control)

The bypass branch is typically same size as the coil branch and the control valve sized for coil design flow (since at 0% load the full branch flow goes through bypass).
Prioritize valve authority ≥ 0.25–0.5 across the coil/control assembly.

D) Pump recirculation bypass

Use pump manufacturer’s minimum continuous stable flow (often 20–30% of BEP flow).
Size the bypass line/valve to guarantee that minimum at the expected differential when throttled/at low speed.

3) Convert required bypass flow to pipe size (velocity check)

Use chilled-water velocity targets: 1.5–2.5 m/s (≈ 5–8 ft/s). D = 4QπvD \;=\; \sqrt{\frac{4Q}{\pi v}}D=πv4Q where QQQ is volumetric flow and vvv is chosen design velocity.
Select the next standard nominal pipe size ≥ computed diameter.
Check friction loss (keep reasonable, e.g., 0.3–0.6 m/100 m or 1–2 ft/100 ft) and fittings K-values.

4) Size the control device (valve) for the bypass

For water at ~20 °C, Cv/Kv sizing:
- IP: Q [gpm]=CvΔP [psi]/SG⇒Cv=Q/ΔP\; Q\,[\text{gpm}] = C_v \sqrt{\Delta P\,[\text{psi}]/SG} \Rightarrow C_v = Q/\sqrt{\Delta P}Q[gpm]=CvΔP[psi]/SG⇒Cv=Q/ΔP
- SI: Q [m3/h]=KvΔP [bar]⇒Kv=Q/ΔP\; Q\,[\text{m}^3/\text{h}] = K_v \sqrt{\Delta P\,[\text{bar}]} \Rightarrow K_v = Q/\sqrt{\Delta P}Q[m3/h]=KvΔP[bar]⇒Kv=Q/ΔP
DP bypass valve (DPBV): choose a setpoint that maintains design DP at the index circuit. Common ranges 15–35 kPa (2–5 psi) at the critical branch. Pick a valve with Cv/Kv ≥ 1.2–1.5× required to ensure controllability.
3-way valves at coils: valve sized for coil design flow; select equal-percentage trim; verify authority.

5) Control & setpoint notes (to preserve ΔT and stability)

Don’t let the bypass over-bleed—excess bypass flow crushes ΔT and invites low-ΔT syndrome.
For DPBV, sensor near the remote/index coil; set just high enough that the worst-case coil can meet load at minimum pump speed.
Integrate with VFD logic so the bypass opens only when VFD turndown can’t meet the DP setpoint without hunting.

6) Quick worked example (Chiller Bypass)

Given

System design flow: 600 gpm
Chiller minimum evaporator flow (datasheet): 300 gpm
Lowest credible building load flow (open coils at night): 120 gpm
Target velocity in bypass: ≤ 6 ft/s
Candidate DPBV setpoint near plant: 12 psi (for Cv check)

Bypass capacity Qbypass=300−120=180 gpmQ_{bypass} = 300 – 120 = \mathbf{180\;gpm}Qbypass=300−120=180gpm

Pipe diameter (velocity check)
Convert 180 gpm → 0.401 ft³/s.
Area A=Q/v=0.401/6=0.0669 ft2A = Q/v = 0.401/6 = 0.0669 \text{ ft}^2A=Q/v=0.401/6=0.0669 ft2.
Diameter D=4A/π=0.292 ft=3.50 inD = \sqrt{4A/\pi} = 0.292 \text{ ft} = \mathbf{3.50\;in}D=4A/π=0.292 ft=3.50in.
→ Select 4-in nominal (next standard size). Verify pressure drop is modest.

Valve Cv (at 12 psi drop) Cv=18012=1803.464≈52C_v = \frac{180}{\sqrt{12}} = \frac{180}{3.464} \approx \mathbf{52}Cv=12180=3.464180≈52

→ Choose a DPBV/control valve with Cv ≈ 60–70 for margin and good authority.

7) Sanity checks before you lock it in

With bypass active at low load, chiller ΔT should remain within design (e.g., 5–7 °C / 9–12 °F). If ΔT collapses → reduce bypass setpoint/flow.
Verify pump NPSH and min thermal flow are satisfied in all modes.
Confirm air separator & sensor placement aren’t short-circuited by the bypass.
Commission by trending: DP at index coil, pump speed, bypass position, ΔT, chiller loading.

Handy thumb rules (when data is thin)

Chiller bypass capacity ≈ chiller min flow – minimum credible coil flow.
System DP bypass capacity ≈ 20–40% of design flow.
Bypass velocities: ≤ 2.5 m/s (8 ft/s); quieter systems target ~2.0 m/s (6–7 ft/s).
DPBV setpoint: just enough to keep remote coil happy, typically 15–35 kPa (2–5 psi) at that branch.

Select Control Device (Bypass Lines)

1) Start with the purpose → device “shortlist”

Maintain minimum chiller flow (evaporator bypass)
- Preferred: Modulating control valve (globe/ball) with BMS logic, or a Pressure-Independent Control Valve (PICV) set to required bypass flow.
- If simple/fixed: Manual balancing valve (commissioned to a fixed minimum).
Stabilize system differential pressure (header DP bypass)
- Preferred: Differential Pressure Bypass Valve (DPBV) (self-acting, spring/diaphragm).
- High-integration plants: BMS-modulating valve (with remote DP sensor) or PICV.
Coil bypass (3-way control at AHU/FCU)
- Preferred: 3-way modulating valve (equal-percentage), diverting or mixing as per piping.
- Low ΔT programs / variable-primary plants: Consider 2-way at coil + system DPBV instead of 3-way to reduce bypassing.
Pump recirculation (anti-deadhead/min thermal flow)
- Preferred: Modulating globe/ball tied to pump logic (speed/ΔP), or check + orifice for minimum fixed flow on small pumps.

2) Select the valve type (hydraulics + authority)

Globe valves: best control authority and rangeability; higher pressure drop; great for DPBV/BMS-mod bypass.
Characterized ball valves: compact, good rangeability, lower cost; ensure equal-percentage characterization for stability.
PICVs: hold set flow regardless of upstream DP swings—excellent for minimum flow guarantees and simplified commissioning.
Self-acting DPBV: no controls required; set opening DP (e.g., 2–5 psi / 15–35 kPa). Fast, stable, low-maintenance.
3-way valves: choose mixing (two inlets, one outlet) or diverting (one inlet, two outlets) to match your coil piping.

Valve authority target: ≥0.25–0.5 across the controlled path at design; ensure sufficient pressure drop across valve vs. branch to avoid hunting.

3) Size for controllability (not just “will it pass the flow?”)

Cv/Kv method (water ~20 °C):

IP: Cv=QgpmΔPpsiC_v = \dfrac{Q_{gpm}}{\sqrt{\Delta P_{psi}}}Cv=ΔPpsiQgpm
SI: Kv=Qm3/hΔPbarK_v = \dfrac{Q_{m^3/h}}{\sqrt{\Delta P_{bar}}}Kv=ΔPbarQm3/h

Good practice

Choose Cv (or Kv) 1.2–1.5× the calculated minimum to keep the valve mid-stroke at typical operation.
Verify rangeability (e.g., ≥50:1 globe; ≥100:1 characterized ball) for smooth low-load control.
For DPBV, select spring range that brackets your target opening DP and verify stable turn-down with pump VFD minimum speed.

4) Actuator & control strategy

Signal: modulating (0–10 V / 2–10 V / 4–20 mA). Avoid 2-position unless it’s a fixed bypass.
Fail-safe: spring-return to fail-open (to protect chiller minimum flow) or fail-closed (to protect ΔT), per design intent.
Speed: 30–120 s stroke typical; very fast actuators can cause oscillation with large water volumes.
Feedback: end-switch or position feedback for BMS trending and alarm logic.
Sensor placement (if BMS-modulated):
- DP control: sensor at/near index coil or far header, not at the pump.
- Minimum-flow control: measure flow (ultrasonic or DP across a flow element) rather than infer from valve position.

5) Materials, ratings, and endurance

Body/trim: bronze/brass or ductile iron; stainless trim for treated water or higher DP.
Pressure rating: match system MAWP; common 16/25 bar (232/363 psi) ratings—verify against pump shut-off.
Leakage class:
- DPBV / minimum-flow valves often Class IV–VI (low leakage) for precise DP.
- 3-way valves: ensure proper port leakage spec for your mixing/diverting function.
Cavitation/noise: check N1N_1N1 / FL factors (manufacturer data) if ΔP is high; consider staged ΔP, larger size, or low-noise trim.

6) Special cases & tips

Variable-primary flow plants: prefer 2-way coils + remote-sensed DP control; use a small, guaranteed min-flow bypass per online chiller (PICV works well).
Low-ΔT syndrome risk: avoid “easy” bypass paths; add minimum valve ΔP or use PICV to protect ΔT.
Commissioning-only bypass: manual balancing valve with tagged position; isolate after commissioning.
Redundancy: for critical plants, select actuators with manual override, and consider parallel valves for serviceability.

7) Quick example (DP header bypass)

Required relief flow at low load: 180 gpm
Desired control ΔP across bypass path: 10 psi
Cv=180/10=57C_v = 180/\sqrt{10} = 57Cv=180/10=57 → pick globe valve Cv ≈ 70 (authority margin).
Actuator: modulating, spring-return fail-closed, 60–90 s.
Control: BMS holds remote DP at setpoint; valve opens only when pump at min speed can’t maintain DP.

8) Final checklist (fast)

Device matches purpose (min-flow / DP / coil / pump).
Cv/Kv sized with margin; authority verified.
Actuator: modulating, correct fail-safe, suitable stroke time.
Sensor located at the right place (remote/index).
Materials/pressure/leakage ratings meet spec.
Anti-hunting: adequate valve ΔP, proper control loop tuning, VFD coordination.
Document setpoints and stroke for O&M.

🔧 Installation Guidelines for Bypass Lines in Chilled Water Systems

Bypass lines, whether across chillers, pumps, coils, or system headers, must be installed carefully to ensure they function correctly without compromising efficiency.

1. General Piping Practices

Correct Location: Place the bypass line exactly as per design intent — across chiller evaporator, between supply/return headers, around coils, or across pumps.
Pipe Sizing: Confirm the pipe matches the calculated bypass flow capacity (not oversized, to avoid short-circuiting; not undersized, to avoid choking).
Routing: Keep the bypass line short and direct with minimal bends to reduce friction loss.
Insulation: Insulate bypass piping to prevent energy loss and condensation issues.

2. Valve & Device Installation

Accessibility: Install bypass valves (manual, DPBV, or 3-way) in locations where maintenance staff can easily reach them.
Orientation: Follow manufacturer recommendations for valve orientation (e.g., actuator upright).
Isolation Valves: Provide isolation valves on both ends of bypass lines for serviceability.
Strainers: Install strainers upstream of control valves to prevent fouling/damage.
Flow Direction: Ensure bypass valves are installed with correct flow direction arrow.

3. Differential Pressure Bypass Valve (DPBV)

Location: Ideally placed between supply and return mains, near pumps or at far end of loop.
Setpoint Access: Install with test ports for differential pressure measurement and setpoint adjustment.
Stability: Avoid placing DPBV too close to the pump (to prevent oscillation).

4. Chiller Bypass Line

Position: Across the chiller evaporator inlet and outlet.
Balancing Valve: Install a manual or automatic flow control valve to regulate bypass flow to meet minimum chiller requirements.
Check Valves: If multiple chillers are connected, install check valves to avoid reverse flow between chillers.

5. Coil (AHU/FCU) Bypass Line

Valve Selection: Use 3-way modulating valves for bypass around coils if specified.
Bypass Connection: Ensure bypass piping is the same size as coil branch.
Actuator Clearance: Provide space for actuator servicing and wiring.

6. Pump Bypass

Location: Connect between pump discharge and suction.
Control: Install a valve to ensure minimum pump flow when load is low.
Check Valves: Prevent reverse circulation when pump is off.

7. Commissioning & Balancing

Temporary Bypass: Provide flushing bypass loops at risers or ends of branches for cleaning and air removal.
Balancing: Use calibrated balancing valves to adjust bypass flows as per design.
Pressure & Flow Testing: Confirm differential pressure and flow at all bypass valves during commissioning.

8. Safety & Maintenance

Tagging: Clearly label bypass lines and valves for identification.
Drains & Vents: Provide drain valves at low points and air vents at high points near bypasses.
Service Access: Leave adequate clearance for tools, actuators, and instrumentation.
Monitoring: Connect automatic bypass valves (DPBV, motorized) to BMS for trend logging.

🛠️ Commissioning Procedure for Bypass Lines

1. Pre-Commissioning Checks

✅ Verify that bypass lines are installed in the correct locations (across chillers, pumps, headers, coils).
✅ Ensure valves are correctly installed with flow direction matching manufacturer arrows.
✅ Check for isolation valves, strainers, and test ports provided as per design.
✅ Confirm that bypass lines are insulated to prevent condensation.
✅ Inspect actuators (if automatic): wiring, control signal (0–10V, 2–10V, etc.), and power supply.
✅ Confirm DP sensors (for DPBV or BMS control) are installed at the correct remote/index location, not just near the pump.

2. Flushing & Cleaning Stage

Open bypass valves fully during system flushing and filling to provide alternate flow paths.
This ensures removal of air, dirt, and debris from the system.
Monitor flushing velocity (≥1.5 m/s recommended) to properly clean bypass lines.
After flushing, close/adjust bypass valves to design positions.

3. Hydronic Balancing

Establish design flow conditions with pumps running at rated capacity.
Adjust manual balancing valves (if installed) on bypass lines to allow the correct bypass flow.
For chiller bypass: set bypass flow to maintain minimum chiller flow (per manufacturer’s data).
For coil bypass: check valve authority and ensure proper modulation between coil and bypass.
For DP bypass valve: set the differential pressure setpoint (commonly 15–35 kPa / 2–5 psi) using test ports.

4. Functional Testing

Chiller Bypass Test:
- Close some terminal unit valves to simulate low load.
- Confirm bypass opens to maintain minimum flow.
- Monitor ΔT across the chiller (should remain within design, e.g., 5–7 °C / 9–12 °F).
System DP Bypass Test:
- Run pumps at minimum VFD speed.
- Gradually close 2-way valves at AHUs/FCUs.
- Confirm DP bypass valve opens automatically to relieve pressure.
- Verify pump operation is stable (no hunting).
Coil Bypass Test:
- Command 3-way valve from 0–100% load.
- Confirm coil and bypass flows modulate smoothly.
- Check supply air temperature is stable.
Pump Bypass Test:
- Reduce system load to minimum.
- Verify pump bypass keeps minimum continuous stable flow (MCSF).
- Check for noise, cavitation, or vibration.

5. Integration with Controls (BMS)

Ensure valve positions, flow sensors, and DP sensors are visible in BMS.
Trend data for DP, valve position, chiller flow, and ΔT under varying load conditions.
Fine-tune DPBV or BMS setpoints for stable control (avoid oscillations).

6. Documentation & Handover

Record:
- Valve positions and setpoints.
- Chiller minimum flow confirmation.
- DP setpoint values.
- Pump operating curves with bypass engaged.
Provide O&M team with as-built drawings, valve schedules, and recommended seasonal adjustment guidelines.

✅ In summary:
The commissioning procedure involves pre-checks → flushing → balancing → functional tests → BMS integration → documentation. Each bypass (chiller, system DP, coil, pump) must be tested under real operating scenarios to guarantee stable, efficient, and safe operation.

⚙️ Operation & Maintenance of Bypass Lines in Chilled Water Systems

Bypass lines are critical for chiller protection, system stability, differential pressure control, and energy efficiency. Proper O&M ensures they remain reliable and effective.

1. Operation Guidelines

Normal Operation
- Bypass valves (manual, DPBV, or 3-way) should operate automatically in response to load and pressure conditions.
- Ensure minimum flow through chillers is always maintained (per manufacturer’s requirement).
- Avoid continuous over-bypass (excessive short-circuiting), as it reduces ΔT (temperature difference) and lowers chiller efficiency.
Seasonal/Load Changes
- During low-load conditions (nights, winter, partial occupancy), bypass valves may remain more active.
- During peak load (summer), bypass activity should be minimal if system balancing is correct.
BMS Monitoring
- Monitor bypass valve positions, differential pressure, and chiller ΔT via the Building Management System (BMS).
- Set alarms for abnormal conditions (e.g., valve fully open for long periods, unstable DP, low ΔT).

2. Maintenance Guidelines

Routine Inspection (Monthly/Quarterly)
- Inspect bypass lines for leakage, insulation damage, and corrosion.
- Verify valve actuators and linkages are secure and functioning.
- Check DP sensors and wiring for accuracy and stability.
- Confirm isolation valves on bypass lines are operable.
Functional Testing (Semi-Annual/Annual)
- Simulate low-load conditions by closing selected terminal valves.
- Verify bypass valves open smoothly and system DP stabilizes.
- Test chiller bypass to confirm minimum flow is achieved without short cycling.
- Check coil bypass valves (3-way) for smooth modulation between coil and bypass.
Calibration & Adjustment
- Calibrate differential pressure setpoints (e.g., 15–35 kPa / 2–5 psi) to match actual system requirements.
- Adjust chiller bypass flow balancing valves to maintain manufacturer-specified minimum flows.
- Review BMS trend data and fine-tune control loop settings to avoid valve/pump hunting.
Cleaning & Flushing
- Flush bypass lines during annual shutdown to remove sludge, rust, or debris.
- Clean strainers upstream of control valves to prevent fouling.
Spare Parts & Reliability
- Keep spare actuators, DP sensors, and valve kits available.
- Maintain a service log with details of adjustments, replacements, and failures.

3. Common O&M Issues & Remedies

Issue	Cause	Remedy
Bypass valve always open	Incorrect setpoint, failed actuator, or oversizing	Recalibrate setpoint, repair actuator, review sizing
Chiller trips (low flow alarm)	Bypass not opening or undersized	Inspect bypass valve, confirm flow balance, resize if necessary
Low ΔT syndrome	Excessive bypass flow	Adjust DPBV, reset control loop, verify coil valves
Pump hunting or cavitation	Improper DP control	Relocate sensor, retune PID loop, check pump VFD logic
Noise/vibration at bypass	High velocity or cavitation	Check valve Cv, reduce ΔP, consider staged bypass

4. Documentation & Training

Maintain O&M manuals with valve schedules, setpoints, and flow diagrams.
Train facility staff on when and how bypass valves should operate.
Keep trend logs from BMS for at least one year to establish performance benchmarks.

✅ In summary:
Bypass lines should be monitored regularly, tested under different load conditions, calibrated annually, and kept clean and accessible. Good O&M prevents chiller damage, avoids low-ΔT problems, and ensures long-term system efficiency.