HVAC Chiller Cycle Analysis

HVAC Chiller Cycle Analysis

& COP Characterization

Characterize the thermodynamic performance of a Trane CGAM-26 air-cooled chiller. Map the vapor-compression cycle across all four states, quantify efficiency under two heat exchanger delta-T conditions (5F and 10F), and evaluate the relationship between heat exchanger design and COP.
Fluid MechanicsRoot Cause AnalysisSustainabilityThermal Analysis
Thermodynamics student
Nov 2025
Measured COP of 5.437 at delta-T 5F and 4.415 at delta-T 10F, an 18.8% efficiency penalty. Quantified chilled water flow requirements at 33,075 lb/hr and 26,871 lb/hr. Established Carnot COP upper bound at 9.78, attributing the gap to compressor irreversibilities (isentropic efficiency 68%), finite heat transfer, and pressure losses. Determined minimum sensor count for full cycle characterization: 4 instruments.
SystemTrane CGAM-26 commercial air-cooled chiller serving the BU College of Communication. Vapor-compression refrigeration cycle using R410A refrigerant.State 1→State 2→State 3→State 4→State 1Labeled chiller componentsTrane CGAM-26 with state labels — evaporator, throttle valve, compressors, and condenser identified on site
Sensor Minimum
  • ·2 thermocouples — States 2 and 3 (State 1 doubles for State 4)
  • ·2 pressure transducers — high-side and low-side
4 sensors total fully characterize the system and allow calculation of β.
Key Components
  • ·Compressors (×2) — staged for redundancy and variable load
  • ·Condenser — rejects heat to outdoor air via axial fans
  • ·Expansion valve — isenthalpic throttling, reduces T and p
  • ·Evaporator — absorbs heat from water-glycol building loop
Vapor cycle schematicVapor-compression cycle schematic — condenser, compressor, expansion valve, and evaporator with energy flows Q̇_H, Q̇_C, and Ẇ_in
Thermodynamic States
  • ·State 1 — saturated vapor, evaporator exit, low p
  • ·State 2 — superheated vapor, compressor exit, high p
  • ·State 3 — saturated liquid, condenser exit, high p
  • ·State 4 — two-phase mixture, expansion valve exit, low p
T-s diagramT-s diagram — states 1–4 plotted on the R410A vapor dome with high- and low-pressure isobars