Low-temperature heating and efficient cooling with maximum use of the hydronic resources
As demand for energy-efficient building retrofits increases, integrating heat pump technologies into existing heating systems presents both opportunities and challenges. This paper explores a mixed technology approach combining different heat pump types - air-to-water, water-to-water, and water-to-air micro heat pump systems - aiming to maintain as much as possible existing infrastructure while transitioning to low-temperature systems. The paper focuses on the strategic use of water-to-air heat pumps, which can directly replace conventional radiators. This approach allows to overcome retrofit challenges, reusing existing piping, addressing heat losses and high temperature differentials (?T) in systems where traditional fan coils or low-temperature emitters are less effective. This enables a significant reduction in supply temperature to as low as 15 °C. Thus, the primary heat pump, typically a water-to-water or air-to-water unit can cover, 75–80% of the buildings total heating load, with the remaining demand is met locally by water-to-air units. This configuration reduces both the design capacity and installation complexity of the primary system, leading to significant cost savings, particularly for ground-source heat pumps, where borehole drilling or direct heat exchange with probes can be minimized. Additionally, integration with solar systems and/or dry coolers is feasible, enhancing energy savings during cooling mode. With waterloop solutions, LT heating and cooling are simultaneously possible, delivering same possibilities as 4-pipes systems with 2-pipes system only. Heat extracted from indoor air can be repurposed for domestic hot water production, achieving temperatures up to 55 °C. Heat recovery can be done without the need for a condensation drain system due to a specially designed injection kit designed for certain countries. This combined technology approach offers a practical and scalable pathway to decarbonize existing building stock, including hotels, hospitals, and multi- family buildings, facilitating energy efficiency improvements without extensive modifications and supporting the transition to low-energy, renewable-based building services.