Process Chillers by the Numbers

About this book

A process chiller is the refrigeration plant most factories own: a packaged machine that cools water for moulds, machine tools, hydraulic systems, lasers, welders, plating baths and food processes, and sends it round the plant in a closed loop. It is usually bought on a single number, its rated capacity, and then run for fifteen years by people who are rarely told what its gauges mean. Yet its performance, its running cost and most of its faults can be read from a handful of measurements, if they are interpreted with the right refrigerant data.

This book works through one process chiller with numbers. It sets out what the chiller is asked to do and the second law’s limit on it, calculates the cooling load, works the vapour-compression cycle point by point from NIST’s refrigerant data, and then looks in turn at saturation pressure and temperature, throttling and flash gas, compressor work and discharge temperature, the effect of temperature lift, running cost, and commissioning and fault-finding. Each chapter follows one running case, includes a plausible mistake and how it was found, and ends with an exercise and its worked answer.

It is written as a companion to the Library’s Heat Pumps and Refrigeration by the Numbers, which sets out the second law, the cycle, heat pump water heating, cold rooms and refrigerant rules for a food factory. This book does not repeat that ground. It goes deeper into one kind of machine, calculating its state points from published property data and showing how to read and diagnose it in service. It assumes school algebra and physics; the Library’s Heat Transfer by the Numbers covers the heat flows that evaporators and condensers rely on.

The running case

Every chapter follows one fictional machine. This is an illustration. A plastics moulder cools its injection-mould circuits with a process-water chiller, called CH-30 here, rated at 30 kW of cooling. Water leaves the chiller at 12 °C and returns from the moulds at 17 °C, a flow of about 1.43 kg/s. The chiller uses R-134a in a single vapour-compression circuit with an air-cooled condenser, sized to work in ambient air up to 35 °C. At its design point it evaporates at 2 °C with 5 K of superheat at the compressor’s inlet, condenses at 45 °C with 5 K of subcooling, and its compressor has an isentropic efficiency of 0.70.

All refrigerant properties are NIST’s, in the ASHRAE reference state. The moulder, the chiller’s ratings, its prices and its problems are invented. None describes KEVOS® work or a real business.

How to use the book

Read Chapters 1 to 3 first: they set out the job, the load and the cycle that every later chapter uses. Chapters 4 to 6 look inside the cycle, Chapter 7 at what changes its performance, Chapter 8 at what it costs to run, and Chapter 9 at commissioning a chiller and finding its faults. Every calculation was checked by running it, and values are given to more figures than a shop needs so that the arithmetic can be followed.

Source limits and professional responsibility

The thermodynamics in this book is standard, and the refrigerant data are NIST’s. The chiller’s efficiencies, operating hours, tariffs and prices are illustrations. Refrigerating systems contain gases under pressure, and in Australia the people who handle refrigerants must be licensed. Chillers are designed, installed and serviced by qualified, licensed people to the applicable standards and regulations, and qualified review governs real work. This book teaches how process chillers behave and how to check them. It is not a design for any system.