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Advanced PID Tuning – Condenser Water Pump Optimization

A commercial central plant experienced instability within its condenser water system. The secondary pumps, controlled via a BAS-driven PID loop, were unable to maintain stable differential pressure, directly impacting system efficiency.

Problem

The differential pressure fluctuated between 16–26 psi. This instability resulted in:
– Constant VFD speed oscillation
– Increased electrical demand
– Reduced chiller heat rejection performance
– Premature mechanical wear

Approach

A full control loop analysis was conducted, including trend logs, response curves, and system reaction under varying loads. Adjustments were made incrementally to avoid system shock.

Root Cause Analysis

Control loop tuning was overly aggressive. The proportional gain caused rapid response, while the integral action accumulated too quickly, resulting in overshoot and oscillation.

Solution

– Reduced proportional gain significantly
– Increased integral time to slow correction
– Allowed system to settle between adjustments
– Verified stable operation under multiple load conditions

Results

– Maintained DP within ±1–2 psi
– Reduced pump energy consumption by 15–25%
– Improved system stability and chiller efficiency
– Extended equipment lifespan due to reduced cycling