Primary-Secondary Pumping System Design

Engineered hydraulic decoupling for efficient, stable chiller plant operation.
A Primary-Secondary pumping system is a standard, reliable design that hydraulically separates the chiller (primary) loop from the building distribution (secondary) loop using a common pipe (decoupler). This allows constant, stable flow through chillers while enabling variable, energy-efficient flow to the building. EKG Malaysia provides complete design, installation, and optimization services for these systems, ensuring optimal performance for medium to large commercial and institutional buildings.

System Overview & Key Components:

• Primary Loop (Constant Flow):

  • Pumps: Constant speed (or dedicated VFD for each chiller).

  • Function: Maintains design flow through each operating chiller evaporator as required for safe, efficient chiller operation.

• Secondary Loop (Variable Flow):

  • Pumps: Variable speed drives (VFDs) controlled by differential pressure (ΔP) sensors.

  • Function: Distributes chilled water to building zones (AHUs, FCUs) and varies flow in response to cooling demand.

• Common Pipe (Decoupler): The critical hydraulic bridge. A short section of pipe that connects the two loops, allowing them to interact thermally without forcing equal flow.

How It Works & The "Zero Flow" Principle:
The design ensures flow in the common pipe can be zero when the secondary flow exactly matches the primary flow. When secondary demand is less than primary supply, excess primary flow "short circuits" back through the common pipe. When secondary demand exceeds primary supply, flow reverses in the common pipe to make up the difference.

Design Advantages:

• Chiller Protection: Ensures each chiller always receives its required minimum flow.

• Pump Energy Savings: Secondary pumps slow down at part load, saving 30–50%+ in pumping energy.

• System Stability & Control: Simplifies chiller staging and provides stable conditions for building control valves.

• Flexibility & Expandability: Easier to add chillers or building zones independently.

Critical Design Rules We Follow:

1. Common Pipe Length & Sizing: Must be kept short (typically 10 pipe diameters) and sized for very low pressure drop to ensure proper hydraulic decoupling.

2. ΔP Sensor Location: Placed to represent the "worst-case" pressure drop in the secondary system (often at the farthest or most critical branch).

3. Pump Head Calculations: Primary pump head is calculated for the chiller and primary piping only. Secondary pump head is for the building distribution system only.

4. Control Sequences: Clear logic for primary/secondary pump interlocking, VFD control, and chiller staging.

Our Design & Implementation Service:

• Load Analysis & Hydraulic Modeling: Calculating flows and heads for both loops.

• Component Sizing & Specification: Selecting chillers, pumps, pipe sizes, and valves.

• Control Strategy Development: Writing sequences of operation for the BMS.

• Commissioning & Balancing: Verifying zero flow in the common pipe at design conditions and balancing all flows.

• Performance Optimization: Fine-tuning setpoints and sequences post-occupancy.

The proven standard for efficient large-scale cooling.
A correctly designed primary-secondary system balances efficiency, reliability, and cost for decades of service.

Contact EKG Malaysia for expert primary-secondary pumping system design and implementation. We engineer systems that perform efficiently from day one.