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Sustainability at the highest level
Central domestic hot water technology (HIU) with cascading for Valsana Hotel & Apartments in Arosa, Switzerland
Arosa in the Swiss canton of Graubünden has long been one of Switzerland's best-known tourist destinations. In summer and winter there is a lot to experience and discover, therefore hotel rooms are in demand all year round. The Valsana Hotel & Apartments, opened in December 2017, offers modern rooms and apartments across three buildings. The style and design includes wood, stone and glass, providing comfort with a unique view of the Arosa mountains. In the new buildings, emphasis was placed on sustainable materials, products from Switzerland and a visionary energy concept. Taconova's central domestic hot water technology is used in the hotel's three sustainability buildings.
The Valsana Hotel and the apartments are equipped with ice storage and waste water heat recovery. The ice reservoir in particular is innovative: in a reservoir - similar to a large water tank - there are over 400 m of pipe registers connected to the heat pump circuit through which a water-glycol mixture flows. If a lot of energy is drawn from the heat pump, the water freezes around the registers and forms an ice block. Then, if there is more waste heat than energy is being extracted, the ice melts again and the water can heat up to 15° C. This forward-looking energy concept fits in perfectly with the sustainable materials and regional products that are used.
The hotel also uses a modern and sustainable solution for heating drinking water: central domestic hot water technology.
This central drinking water heating in the flow principle is efficient and hygienic: the risk of legionella proliferation is considerably reduced. In order for the 40 rooms, 9 holiday apartments, the restaurant kitchen, the spa area and the indoor tennis hall to be supplied with clean hot water around the clock, precise planning of the required water quantities was necessary.
Precise planning for optimum operation
In order to meet the requirements of the various areas of the hotel for heated drinking water, several versions of the TacoTherm Fresh Peta X cascade heat interface units were installed used in the three buildings, according to their respective hot water requirements and taking redundancies into account. The main building was particularly exciting: 40 hotel rooms and the restaurant are located there.
Rolf Wende, Managing Director at novis Energy AG, who installed the heat interface units, knows what important in hotel operations: "Hot drinking water must always be available quickly and reliably when guests need it - even in the middle of the night. The kitchen has additional rush hours, which add on to the guest demand. So we had to install a solution that could easily cover the peak loads between 9 and 22 o'clock." The decision was quickly made in favour of Taconova's TacoTherm Fresh Peta X, also based on a recommendation from novis AG, who have had good experiences with the installation of the units in other buildings.
Under the condition 70/50 (70 °C primary flow temperature, 50 °C tap temperature), this heat interface unit can heat 80 litres of hot drinking water per minute.
"For the main building, a much larger quantity of heated drinking water must be available than an individual unit can supply. For this reason, we have designed a cascade of four TacoTherm Fresh Peta X units. This was also very interesting for us, as we don't build heat interface units for such a volume of water every day," explains Wende.
Cascading for efficient operation
The cascade consisting of 4 heat interface units combines the outputs of the units in such a way that the primary water exits at 70°C, enabling for potable water at 60°C to be instantly available, up to a flow rate of 304 l/min
Martin Stapfer, Customer Service Manager at Taconova Group AG, explains the technical structure of the cascade:
"To ensure that the cascade works efficiently, we decided not to install each circulation pump externally, but instead install one pump internally only . Hence, this unit is the master unit, controlling the other three slave units ." This means: The heat interface unit with the circulation pump is constantly in operation, the other three units are switched on as required. The activation is controlled individually by the percentage output of the primary pump that produces the hot water. If the output of the master station exceeds 60% for 15 seconds, the second unit is switched. If the power of the second unit also exceeds those limits, the third unit is switched on and so on. Special feature: The software can be used to adjust both, the values for the power percentage and the maximum duration respectively.
"This optimisation ensures that the hotel rooms and kitchen are always supplied with sufficient hot water. In addition, setting a lower speed for the primary pump ensures that the fourth unit is also used regularly," Martin Stapfer explains.
Hot water supply for all three buildings
In addition to the 4-heat-interface-units cascade, TacoTherm Fresh Peta X units were also used in the other buildings. In the middle premise, Haus Ciara, there are nine holiday apartments as well as a 800 m² spa area with a relaxation pool and sauna world. These areas are also supplied via a cascade, where two units are combined. The third part of the building, Haus Montagna, with holiday apartments, also receives its hot water via a 2units-cascade. The indoor tennis centre with its six showers has a more selective demand, so that a single TacoTherm Fresh Peta X unit was considered sufficient there. In addition to the highly efficient cascading, the TacoTherm Fresh Peta X also has other technical advantages.
The plate heat exchanger guarantees high transfer performance with low pressure loss and a low return temperature of the heating water to the buffer storage tank. In addition, the electronic control system determines and stores the amount of heat consumed by recording the temperature difference and volume flow data. Rolf Wende is particularly enthusiastic about the trouble-free installation of the units: "All fittings and components are completely pre-assembled and wired ready to plug in - this made installation much easier for us. The setting on the 4-piece cascade was also astounding. We only had to set the values once at the master station - the unit with integrated circulation pump - and all the parameters were transferred to the other units."
The installations of the piping with a cascade set connecting the units to one another were very intuitive, so that there were no queries on site. Rolf Wende draws a positive conclusion for the project: "The cooperation with Taconova was exemplary. The company was there to support us. Another great advantage is that the heat interface units are being developed in Switzerland, which gives Taconova a high level of specialist knowledge that benefits us. This is shown, among other things, by the fact that the units worked perfectly immediately under full load." Martin Stapfer is also convinced of the result: "The Valsana Hotel is a great project of which we are very proud, because many different combinations of the TacoTherm Fresh Peta X are used. The hotel has been open since December 2017 and there hasn't been a single problem with the domestic hot water treatment so far - it can hardly get any better.
Date: 12/2019
