CO₂ HEAT PUMPS: Design, Installation, and High-Efficiency Applications

Carbon dioxide (CO₂), designated as refrigerant R744, is not a new idea. Carl von Linde and Franz Windhausen demonstrated CO₂ refrigeration cycles in the 1880s, and the compound dominated commercial refrigeration well into the mid-twentieth century before being supplanted by synthetic halocarbons. Yet in the opening decades of the twenty-first century, CO₂ has returned with extraordinary force — this time carrying the weight of climate policy, energy efficiency mandates, and a global drive to eliminate high-global-warming-potential (GWP) refrigerants.

By 2026 the trajectory is unmistakable. The European F-Gas Regulation, the Kigali Amendment to the Montreal Protocol, and parallel legislation across North America and East Asia have collectively pushed industry to reconsider every fluorinated refrigerant in current use. R744, with a GWP of exactly 1 and zero ozone depletion potential (ODP), is the benchmark against which all alternatives are measured. More than a regulatory refuge, however, it is now a genuine performance technology: transcritical CO₂ heat pumps can deliver water temperatures exceeding 90 °C from ambient air sources, achieve seasonal performance factors above 4.0 in moderate climates, and integrate naturally with district heating networks, domestic hot-water systems, and high-temperature industrial processes.

This book is written for the engineer, the advanced technician, and the informed specifier who wants more than a surface treatment of the subject. We begin with thermodynamics — because CO₂ is physically different from every conventional refrigerant and its behavior near and above the critical point demands a different mental model. We then move through system architecture, component selection, controls and regulation, and the full arc of practical installation, commissioning, and service. Separate chapters address the major application domains: residential and commercial hydronic heating, hot-water systems, supermarket and food-retail refrigeration, cold-chain logistics, industrial heat recovery, and the emerging field of CO₂-based district energy.

Throughout, numerical examples, performance tables, and engineering rules of thumb anchor the theory in practice. Case studies drawn from operating installations in Europe, Japan, North America, and Australia illustrate how design decisions translate into measured outcomes. Safety — always paramount with a high-pressure, asphyxiant refrigerant — is treated comprehensively in its own chapter and revisited wherever specific hazards arise.

We live in a moment of genuine transition. The skills, habits, and business models built around R-22, R-410A, and R-404A are being superseded. The engineers who master CO₂ technology today will be indispensable for the next generation of building services, food infrastructure, and industrial heat supply. It is our hope that this book equips them to do that work with confidence, precision, and safety.