Bac Cooling Tower Pumping And Piping

Below is a clear, engineering-level overview of BAC (Baltimore Aircoil Company) cooling tower pumping and piping, aligned with how BAC actually designs and recommends systems.

1. BAC Cooling Tower Pumping Concept

BAC cooling towers do not include circulation pumps.

The condenser water pump is external and sized by the system designer.

Basic Flow Path

Chiller / Heat Exchanger → Condenser Water Pump → Cooling Tower → Basin → Back to Chiller

2. Pump Types Used with BAC Cooling Towers

  Condenser Water Pumps (Most Common)

* Horizontal end-suction or split-case centrifugal pumps

* Installed at or below tower basin water level

* Designed for continuous duty

Sump / Vertical Turbine Pumps

* Used when tower is remote or basin is below grade

* Less common in BAC factory layouts

3. Typical Pump Design Parameters (BAC Systems)

Item	Typical Range
Flow rate	3 gpm / ton (2.7–3.2 gpm/ton common
Design head	15–30 m (50–100 ft)
Water temperature	27–35°C (80–95°F)
Temperature range	4–6°C (7–10°F)
Pump efficiency	≥ 80% (large systems)

4. BAC Cooling Tower Piping Arrangement

 4.1 Supply (Hot Water) Piping to Tower

* Routed to top hot-water distribution header

* Usually carbon steel, stainless steel, or HDPE

* Includes:

 * Isolation valve

 * Flexible connector

 * Strainer (recommended)

 * Flow balancing valve

4.2 Cold Water Return from Basin

* From basin outlet / sump

* Large-diameter, low-velocity piping

* Includes:

 * Suction diffuser or strainer

 * Isolation valve

 * Drain connection

5. BAC Recommended Piping Velocities

Location	Max Velocity
Pump suction	≤ 1.5 m/s (5 ft/s)
Pump discharge	≤ 3.0 m/s (10 ft/s)
Tower risers	≤ 2.5 m/s (8 ft/s)

Low velocity = less cavitation, lower energy loss, better pump life.

6. Equal Flow Piping for Multiple BAC Towers

When multiple BAC cells or towers are installed:

Preferred Method – Reverse Return

* Self-balancing

* Minimal balancing valves

* BAC strongly recommends this layout

Alternative – Direct Return

* Requires manual balancing valves

* Higher commissioning effort

7. Make-Up Water, Blowdown & Overflow Piping

7.1 Make-Up Water

* Connected to float valve or electronic level control

* Includes:

 * Isolation valve

 * Backflow preventer

 * Strainer

* Typical pressure: 2–5 bar

7.2 Blowdown (Bleed-Off)

* Controls TDS and scaling

* Manual or conductivity-controlled

* Routed to drain with air gap

7.3 Overflow

* Gravity line sized for full make-up failure

* Never valved ❗

8. Bypass & Minimum Flow Protection

Why a Bypass Is Needed

* Prevent pump dead-heading

* Protect tower in cold weather

* Allow chiller operation during tower maintenance

 Common Bypass Options

* 3-way bypass valve

* Motorized isolation + bypass line

* VFD-controlled pump + minimum flow line

9. NPSH & Basin Considerations (Critical ⚠️)

* Pump suction must always be flooded

* Basin water level must satisfy:

 NPSHa > NPSHr + safety margin

* Avoid elbows within 5D of pump suction

10. BAC Piping Best Practices

✔ Use flexible connectors at tower nozzles

✔ Provide access for basin cleaning

✔ Install thermometers & pressure taps

✔ Provide freeze protection drain points

✔ Use corrosion-resistant materials near tower

11. Common Pumping & Piping Problems in BAC Systems

Problem	Root Cause
Low flow	Air entrainment, poor piping layout
Pump cavitation	High suction velocity, low basin level
Uneven cell loading	Direct return piping
Excess energy use	Oversized pump / high head losses