by HFM PHE 0 comment
Water’s environmental profile makes R718 refrigerant an excellent choice for sustainable, water-based refrigeration systems.
Water (R718) refrigeration under deep vacuum is gaining attention in the refrigeration sector as the shift toward environmentally friendly refrigerants increasingly influences engineering practice.
For several decades, conventional vapor-compression systems have relied primarily on chemical refrigerants such as HFCs and, more recently, HFOs. These working fluids provided stable efficiency and well-established implementation pathways. However, under intensifying global decarbonization pressures and stricter refrigerant regulations, the industry is now seeking forward-looking, low-impact refrigeration alternatives.
In this context, vacuum-based water refrigeration has re-emerged as a promising and sustainable cooling solution.
HFM has maintained a long-standing focus on high-efficiency, water-based thermal management technologies. In our assessment, R718 refrigerant systems offer particular engineering significance.
Water’s environmental profile is the most direct advantage of R718 as a refrigerant: it has zero ozone depletion potential (ODP) and zero global warming potential (GWP). In addition, water is non-toxic, non-flammable, and widely available, offering inherent benefits in terms of safety and supply robustness. Beyond these attributes, water also exhibits strong thermodynamic merit. Within temperature ranges typical of many cooling applications, its latent heat of vaporization is high, enabling substantial heat transport per unit mass compared with many conventional refrigerants.
At the same time, an R718 vacuum refrigeration system operates in a regime that differs fundamentally from conventional refrigeration. On the evaporator side, deep vacuum conditions must be established so that water can boil at near-ambient temperatures and absorb heat through evaporation. The generated low-pressure vapor is then compressed—typically by a high-speed centrifugal (turbo) compressor—to a higher absolute pressure, which correspondingly raises the saturation temperature. The resulting high-pressure vapor enters the condenser, rejects heat to a cooling-water loop or an external heat sink, and condenses to liquid. The condensate then returns to the evaporator, completing a closed water-based refrigeration cycle.
In practical operation, R718 systems commonly run at absolute pressures on the order of several tens to slightly over one hundred millibar, far below atmospheric pressure (~1013 mbar). This vacuum environment enables stable evaporation and condensation in the 20–40 °C temperature band, supporting near-ambient-temperature cooling. However, vacuum operation also defines core engineering challenges, including compressor operability in low-density vapor, long-term leak tightness and sealing integrity, reliability of piping and joint interfaces, pressure-drop management, and non-condensable-gas control.
HFM Plate Heat Exchanger in Refrigeration
Under these operating conditions, the plate heat exchanger used as a condenser faces particularly stringent requirements.
First, the thermofluid conditions on the two sides are highly asymmetric: one side involves low-pressure, two-phase condensation of water vapor, while the other side typically comprises a cooling-liquid loop operating at several bar. The sustained differential pressure imposes continuous mechanical loading on the plate pack. If structural stiffness is insufficient or mechanical support is inadequate, even small plate deflections can constrict condensation passages, increase pressure drop, and disturb two-phase flow regimes—ultimately degrading phase-change heat transfer and reducing system stability.
Second, deep-vacuum operation makes long-term ingress and accumulation of non-condensable gases difficult to fully avoid. Within the condenser, non-condensables can introduce an additional mass-transfer resistance layer, suppress condensation heat transfer, and drive system pressure upward, thereby reducing efficiency; this sensitivity is particularly pronounced in low-pressure water vapor systems. Finally, long-term stability depends critically on phase and gas management within the condenser volume: condensate must be collected at the lowest point and reliably drained by gravity, whereas non-condensables tend to accumulate in low-velocity regions and therefore require dedicated venting ports located above the liquid level, together with vacuum purging and/or active evacuation strategies, to prevent performance degradation over time.
For HFM, the practical deployment of water (R718) refrigeration systems ultimately constitutes a test of system-level integration—specifically, the coupling between the plate heat exchanger and the vacuum-based cycle architecture. A heat exchanger that maintains pressure integrity, provides high mechanical robustness, and sustains high phase-change effectiveness is not only a demanding engineering deliverable, but also a concrete expression of HFM’s commitment to advancing sustainable, environmentally responsible thermal systems.