Sustainable heating: TDT AG relies on heat pump cascade from Hoval for renovation

Prior to the renovation, the modern four-story building was heated by a gas-fired combined heat and power (CHP) unit, which also provided emergency power. "The CHP unit was aging and would have needed replacement. Given our focus on sustainability, switching to a renewable heating system was a logical step for us," emphasizes Hubert Mirlach. A groundwater heat pump was initially planned, but the groundwater supply on the property proved insufficient. Following a quick redesign, the choice fell on two Hoval Belaria pro (24) air-to-water heat pumps.

Extensive renovation work on the interior and exterior of the company building took place even before the new heating system went into operation in October 2024. To improve efficiency, the large glass facades were upgraded from double to triple glazing, and additional insulation was installed behind the radiators. Furthermore, the approximately 100 radiators distributed throughout the building were replaced.

Not only the renovation was a large overall package, but also the heating solution itself. The two heat pumps are connected in cascade and run alternately weekly. Only when necessary do both work at the same time. This reduces wear and tear and increases operational reliability. In the event of unexpected malfunctions or very high heat demand, the existing gas boiler – also from Hoval – can also step in. However, this has never been necessary. The electricity for the heat pumps comes from the 34kW photovoltaic system, which was installed together with a storage tank about a year before the heating system was renovated. "With the PV system and the storage system, we are always able to have sufficient energy available, even on rainy days. In the summer months, it works so well that we don't have to buy any electricity at all and even use it for the servers instead of for heating," Hubert Mirlach emphasizes.

A well thought-out building technology networked with KNX Bus, which controls temperature, shading and ventilation throughout the building, completes the overall system. This means that optimal temperatures prevail at all times according to individual needs. This happens completely automatically and manual intervention is almost never necessary. The improved insulation also compensates for the increased inertia of the new low-temperature heating system.

Hubert Mirlach is satisfied and Franz Ramsauer adds: “The support and coordination provided by Hoval throughout the entire project were simply excellent. Everything was so well planned and prepared that all the tradespeople could work together perfectly, and the entire job was completed in just one visit.” Another key factor in the project's success was the collaboration with an energy consultant, who was responsible for energy-related advice, heat demand calculations, and radiator sizing.

Published in July 2025.