Chiller Part Load Performance — Real Indian Project Case Studies

Chiller Part Load Performance — Real Life Case Studies

Chiller data sheets tell one story. The plant room tells another. After commissioning, measured performance rarely matches rated IPLV — and the gap is usually larger than engineers expect. Here are four Indian project case studies that reveal the real-world factors affecting chiller part load performance.

Case Study 1 — 5-Star Hotel, Mumbai (800 TR Water-Cooled Centrifugal)

Project Overview

Root Causes of Performance Gap

• Cooling tower approach temperature — design assumed 4°C, actual was 6.5°C due to scale buildup on fill media
• Chilled water delta-T collapse — AHU coils partially blocked by biofilm, reducing ΔT from 5°C to 3.8°C
• Condenser pump VFD set to constant speed — missed 12% energy saving opportunity
• Refrigerant charge slightly low — factory commissioning issue not caught at site

Corrective Actions and Result

• Cooling tower chemical dosing programme implemented — approach improved to 4.8°C
• AHU coil cleaning programme quarterly — ΔT recovered to 4.5°C
• Condenser pump VFD enabled — 11% reduction in pump energy

After corrections, measured average efficiency improved to 7.1 (vs rated 8.2). Remaining gap attributed to actual ambient conditions being higher than AHRI standard test conditions.

Case Study 2 — IT Park, Bangalore (3 x 300 TR Air-Cooled Screw)

Project Overview

Key Finding

One of the three air-cooled chillers was derated because the condenser air inlet was receiving recirculated hot air from the adjacent chiller. The 3-metre gap between units (as designed) proved insufficient in the enclosed roof-level plant area. Effective ambient temperature for the middle unit was 42°C — 7°C above design.

Lesson for MEP Engineers

• Air-cooled chiller spacing should be minimum 4–5 metres side-to-side in enclosed areas
• Computational fluid dynamics (CFD) analysis recommended for roof-level chiller plants with multiple units
• Condenser air discharge direction should be verified against prevailing wind direction
• Derate air-cooled chillers by 3–5% COP for every 5°C above rated ambient

Case Study 3 — Government Hospital, Delhi (500 TR Water-Cooled Screw, 24×7)

Project Overview

Key Finding

The hospital was designed for 500 TR but actual load reached 550 TR by Year 2 due to additional medical equipment installations not accounted for in the original brief. Both chillers ran at near full load daily, eliminating the part load advantage that drove the IPLV selection.

Lesson for MEP Engineers

• For hospital projects, add 15–20% future load allowance to the calculated peak load
• Medical equipment load is frequently underestimated — liaise with medical planner during design
• IPLV benefits only materialise if the chiller actually operates at part load — check the load profile
• Consider N+1 redundancy with capacity to absorb 30% future growth

Case Study 4 — Shopping Mall, Hyderabad (2 x 600 TR + VFD, Variable Primary)

Project Overview

Key Finding

This was one of the best-performing projects in the case study set. Variable primary pumping with VFD centrifugal chillers delivered near-predicted performance. Key success factors:

• Commissioning was conducted over 3 months including full load and part load testing
• Condenser variable flow implemented — reduced condenser pump energy by 18%
• BMS trending enabled monthly performance reporting and early fault detection
• Chilled water ΔT maintained at 8°C (high ΔT system) — reducing pumping energy significantly

Summary — Key Lessons Across All Cases