As part of the new-build project involving the construction of a retirement home on Hamburg’s Berner Heerweg, the planners and builders opted for decentralized Danfoss EvoFlat™ flat stations. This is certainly a good decision bearing the elderly residents in mind, as decentralized DHW heating is a proven way of preventing Legionella cases. In addition to the high degree of hygienic safety, flat stations also offer energy efficiency and structural advantages.
Assisted-living complexes, retirement homes and nursing homes can be seen popping up in many places – naturally, this has to do with demographic developments in part: an aging society needs new residential solutions. But it is also happening because investors prefer to invest capital in buildings rather than keeping it in the bank.
Commissioned in 2013 by the housing cooperative “Wohnungsgenossenschaft von 1904 e.G.”, the retirement home located on Berner Heerweg in Hamburg has 70 residential units with one and a half to three rooms each, spread across two buildings. All of the apartments have a balcony or terrace which is accessible from the living room without having to cross a threshold. The level-entry showers are fitted with handrails. The retirement home also has a large common room for events as well as two guest apartments, both of which are features typical of these facilities.
In principle, there are two ways of supplying the individual apartments with heating and domestic hot water: the traditional arrangement is to supply the water via a central heating system and with central DHW heating (structural characteristic: pipes run vertically from the basement). The alternative is to use decentralized heat distribution and decentralized DHW heating via a flat station (structural characteristic: pipes run horizontally in the apartment; small footprint thanks to in-wall and shaft installation). Although the traditional arrangement used to supply an apartment requires five pipes (cold water, HE supply, HE return, DHW, hot water circulation), a flat station manages with only three (cold water, HE supply, HE return).
Hygienic protection against Legionella
In addition to the retirement home’s heating and hot water engineering, construction planning office Otto & Partner was put in charge of planning the electrical work, sanitation and ventilation installations, as well as the fire alarm system. The heat supply relies on a contracting arrangement with the firm Lichtblick: the utility company operates a block heating system (CHP), which feeds energy into a heating water buffer accumulator.
Hot water is supplied to the decentralized flat stations from this buffer accumulator at 75°C. The stations installed are series Termix VMTD-F-B stations by Danfoss: flat stations for direct heating and a thermostatically controlled instantaneous water heater. This technology is particularly suitable for two-pipe systems in apartments that are supplied by a heating network, e.g. by a CHP or a gas boiler. In addition, bills can be generated individually for each apartment – the system has an integrated water meter and a heat meter.
Why decentralized heating distribution?
When the operators of the retirement home came face-to-face with the requirements stipulated by the new Drinking Water Ordinance (main feature: regular testing of hot water for Legionella), the cooperative decided not to install a traditional domestic hot water system.
This is because the alternative – decentralized domestic hot water via a flat station (freshwater heating) – circumvents the 3-liter / 400-liter requirements of the new ordinance in a very elegant way.
According to engineer Niels Carlsen, a partner with the engineering firm Otto & Partners, the decision to go with Danfoss technology was taken primarily because of the positive experiences they had with the company in the past: “We know from experience that this is a supplier we can rely on to provide competent technical support, including all the design calculations.” Danfoss is so flexible, he said, that they would also be willing to design e.g. a flat station with temperature specifications deviating from the standard. “It’s not a problem for Danfoss even if we request an oversized flat station – our experience has shown that other suppliers are frequently unable to honor these types of special requests.” By choosing Danfoss, Otto & Partners can be sure to receive rapid, flexible support for all issues related to district heating. “This is a key criterion for us.”
Danfoss took charge of performing the calculations for the stations in the retirement home project as well. The following points need to be taken into account to ensure correct dimensioning of decentralized systems:
• Heating requirement per residential unit, i.e. the required heating capacity (HE)
• Required domestic hot water performance (DHW)
• Primary and secondary supply and return temperatures (summer/winter)
• Cold water temperature (drinking water supply)
• Required hot water temperature
• Number of residential units in the building (apartment building)
• Additional heat losses in the system.
The size of the buffer accumulator must correspond to the heating requirement associated with peak flow lasting 20 minutes. The pipework is to be designed accordingly.