Chiller Module Guide
Commercial Chiller Design & Lifecycle TEA
A practical framework for picking between air-cooled, water-cooled, and absorption chillers — with realistic part-load modeling and a financial comparison that respects the actual cooling load profile.
Technology Overview
Commercial chillers spend most of their lives at part load. A chiller sized for the design-day peak runs near full capacity for maybe 200 hours a year and at 30-60% the other 2,000+ cooling hours. The economic winner is rarely the chiller with the best full-load IPLV on the data sheet — it’s the chiller with the right part-load efficiency curve for the building’s actual cooling profile.
The three architectures have very different economics. Air-cooled chillers have low CAPEX and zero water consumption but pay an efficiency penalty in summer when ambient air is hottest — exactly when the load is highest. Water-cooled chillers pair with a cooling tower for higher efficiency at the cost of water consumption and a larger-footprint plant room. Absorption chillers consume heat instead of electricity, making them a fit for waste-heat-rich sites (CHP, industrial process) or sites with extreme summer electric demand charges.
The CogenS™ Chiller Module models reciprocating, screw, scroll, centrifugal, and absorption chillers across air-cooled and water-cooled configurations. It uses BiQuadratic part-load efficiency curves at 8,760-hour resolution against the local TMY weather and tariff structure, so the financial comparison reflects how the chiller actually behaves through the year.
Module Specs at a Glance
Chiller Types
Reciprocating, scroll, screw, centrifugal, and absorption. Air-cooled and water-cooled. Single and multi-stage.
Capacity Range
From 10 tons small commercial through 4,000+ tons industrial. Multi-unit plants for very large loads.
Performance Modeling
BiQuadratic part-load efficiency curves vs entering condenser water/ambient air temperature. Hourly resolution.
Cooling Tower Pairing
Water-cooled chillers pair with cooling tower selection — the Module ties the chiller TEA to a Cooling Tower Module run.
Refrigerant Options
R-134a, R-410A, R-32, R-1233zd, ammonia, and water (for absorption). Refrigerant choice impacts efficiency, GWP, and code compliance.
Output
TEA report with NPV, IRR, payback, energy cost, water consumption, lifecycle CO₂, and multi-vendor comparison.
How to Design a Project
A high-level workflow that mirrors how the CogenS™ platform structures the analysis end-to-end.
Build the cooling load profile
An 8,760-hour cooling load profile is the input that matters most. The platform's reference profiles by building type already capture realistic part-load behavior; metered data is better when available. The peak-to-average ratio drives chiller sizing decisions.
Pick air-cooled vs water-cooled vs absorption
Air-cooled wins on simplicity and zero water — fits projects where cooling-tower water is expensive, restricted, or impractical. Water-cooled wins on efficiency and chiller life in hot climates. Absorption wins when waste heat is free or cheap (CHP host, industrial process exhaust).
Choose a compressor type
Reciprocating: small-tonnage, on/off staging. Scroll: 30-300 tons, smooth modulation. Screw: 100-1500 tons, robust, decent part-load. Centrifugal: 200+ tons, best full-load efficiency but penalty at low part-load. Match the type to your tonnage and modulation needs.
Size with margin and modularity in mind
Multi-unit chiller plants deliver redundancy, better part-load efficiency, and runtime spreading. Two 50% units beat one 100% unit at most operating conditions. Three 33% units are even better when feasible.
Pair with cooling tower (if water-cooled)
Water-cooled efficiency depends on entering condenser water temperature, which depends on cooling tower selection. Run a Cooling Tower Module simulation against the same load profile and feed the resulting tower water temp into the chiller TEA.
Run the lifecycle TEA and compare vendors
Pull 2-3 manufacturer models per architecture and run the standardized comparison. NPV/IRR/payback over a 20-year study period. Refrigerant phase-down regulations may favor newer refrigerants on lifecycle risk, even at slightly higher CAPEX.
Related Guides
Cooling Tower Selection Guide
Water-cooled chillers need a tower — the tower selection drives chiller efficiency.
CHP Module Design Guide
Absorption chillers fed by CHP waste heat can transform project economics.
Thermal Systems TEA Guide
Suite-level overview of how cooling integrates with the rest of the thermal stack.
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