When you find the perfect pairing of two components, their overall performance often exceeds the sum of its parts – and all with 100% renewable energy! Hoval, a well known Liechtenstein heating appliances company, has combined heat pumps with wood pellet boilers to create an “all-terrain” system tailor-made for apartment blocks in Brissago, southern Switzerland. Here more than anywhere else, efficiency has to be coupled with environmental protection: Lake Maggiore sparkles in the sun and the view from the buildings’ projecting balconies almost takes your breath away. In is here where an air/water heat pump and a wood pellet boiler have been brought together for the first time. The three apartment buildings, each of which contains eight apartments, were built in 2013. In spring and autumn, the Belaria® heat pump copes perfectly well on its own. In the depths of winter, the BioLyt® wood pellet boiler supplies the heat. And in between, the two units share the work between them.

In this system, each unit neutralises any potential weak points of the other unit: the pellet boiler does not have to keep switching on and off during spring and autumn; this would only reduce its efficiency, and there is no need for it to struggle in low-load operation. For its part, the heat pump – which would otherwise reach its limits at low outside temperatures and consume excessive amounts of power – can relax and let the pellet boiler take over. Claudio Galliciotti, service manager at Hoval Switzerland in the canton of Ticino, has been monitoring the system in Brissago over the past few years: “The pellet boiler covers 60-65% of the annual demand of 150,000 kWh, while the heat pump covers 35-40%.” Although the pellet boiler is designed for 100% of the heating load, the pellet store can be smaller than usual as the biomass only has to provide 60-65% of the annual heat. There is also a separate energy buffer storage vessel for each heat generator. This means that the efficiency of the heat pump can be kept high with its lower flow and return temperatures, and the energy can be stored and layered in accordance with the heat generator in question.

Daniel Hegele, who is responsible for developing the wood pellet boilers at Hoval, highlights some other key points: “The bivalent hybrid system, which combines a heat pump and a wood pellet boiler, excels in four key areas, for larger systems above 50 kW output, in particular: the investment is relatively low compared to other cascade heating systems, as are the space requirements. The system works with 100% renewable energy – and is still more efficient than a pellet heating system or a heat pump on its own.” The solution is particularly worthwhile for new builds, but is also an option when refurbishing apartment blocks because the pellet boiler can provide the high flow temperatures required on cold days. And in southern regions, a heat pump offers additional benefits in summer: it can be put into reverse operation and used for cooling instead.

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