Effective protection of the drinking water installation in 249 residential units
The treatment of our food and drinking water is no trivial matter. But why are the recommendations in DIN 1988-200 hardly ever applied in practice, while the technical specifications and standards for the quality of the water circuit on the heating side are strictly applied?
In the heating sector, both VDI 2035 and concrete specifications from manufacturers for filling and make-up water show the way. Lime protection is of great importance here. However, when it comes to hot and cold drinking water, safe limescale protection is not one of the basic requirements of system technology - it can hurt the hygiene of drinking water installations and reduce the energy efficiency of hot water treatment. A demanding residential project in the north of Munich shows that there is another way: the client, the planning engineering office, and the installation company had a clearly defined goal right from the start: the technical realization of the water with simultaneous effective protection of the drinking water installation against limescale formation for 249 residential units in the Carl-Wery-Hof building complex.
A direct district heating connection was to be replaced by an indirect one
Engineering company Linsmeier was invited to bid for the renovation of the heating and water heating systems in the Carl-Wery-Hof building complex in 2021. The specifications required the direct district heating connection from Stadtwerke München to be replaced by an indirect connection. Therefore, the renovation included the installation of two compact district heating stations consisting of a heat transfer station and a transfer station as a charging system for the hot water treatment. As the water hardness in the northern part of Munich is 17.5 degrees hardness (°dH), the installation of a limescale protection system was included in the tender to protect the entire hot water installation from damage caused by limescale.
Another technical requirement in the specifications was the installation of a magnetic-dynamic separator (MdA) for the permanent separation of ferrous solid particles of > 1 µm from the circulation systems to keep the heating water clean and protect metallic system components from corrosion.
Protection of the primary and secondary circuits
The tender included the protection of the heat exchanger surfaces on both the heating side and the drinking water side. The removal of impurities in the heating medium and effective limescale protection of the drinking water installation in the required volume dimensioning were two rather demanding technical challenges.
Alexander Löwentraut, Managing Director of CHRISTEVA Sonnenenergie-Technik GmbH, a wholesaler specializing in thermal solar systems and water treatment plants, was on hand to advise the planning office:
"The sale of solar thermal systems has been part of our core business for many years. That's why we encountered limescale damage to water heaters and storage tanks at an early stage. That's why we've been selling limescale protection systems for more than 20 years now," says Löwentraut.
The business proximity to regeneratively generated energy also led to the strategic decision to primarily offer chemical-free limescale protection technology where this could be technically integrated. "Of course, there are limits to chemical-free lime protection technology, for example in steam generation, where soft water is needed. However, in all other technical system integrations in water heating, we have only had positive experiences with chemical-free lime protection. The process principle of biomineralization works perfectly and provides the best drinking water quality. Since our first large-scale project with 16 m3/d 22 years ago, we have been selling BIOCAT limescale protection technology because it is the ideal complementary product to our portfolio. With solar thermal systems, we are talking about permanently high hot water temperatures of between 80 and 90 °C. To guarantee our customer's long-term efficiency in system technology and drinking water installations, we see it as our duty to recommend a sensible limescale protection system," Alexander Löwentraut summarizes the motives for modern limescale protection technology. In the Carl-Wery-Hof building complex, where two BIOCAT KS 5D systems were installed, each of which effectively protects up to 50,000 l/h of water from limescale formation.
Drinking water hygiene and energy efficiency: Has the target temperature been reached?
Another aspect that should not be overlooked in domestic and building technology on the drinking water side: Namely, that some heat exchangers remain below their original capacity due to limescale deposits. As a result, the target drinking water temperature of at least 60 °C, which is necessary to prevent legionella, is not reached.
In addition, the efficiency of the system decreases if there is a lack of limescale protection. More energy must be spent to counteract the disadvantages caused by limescale deposits on the surfaces in contact with the water. This correlation in turn has a direct impact on building-related CO2 emissions. It is interesting to note that the treatment of hot water through targeted efficient maintenance of the heat exchanger offers a savings potential that is still somewhat overlooked. In the discussion about cost-saving measures in the building sector, this aspect, in contrast to a supposedly justifiable lowering of the hot water temperature, receives almost no attention.
Energy savings must not be at the expense of health
The recommendations of the Federal Environment Agency and the German Association of Qualified Experts in Drinking Water Hygiene (DVQST e.V.) for maintaining drinking water hygiene are clear: Energy savings must not be at the expense of health. At water temperatures between 25 and 50 °C, there is an increased risk of legionella and other pathogenic bacteria multiplying in the drinking water installation. If the temperature in the drinking water heating system is set lower than 60 °C in the flow and 55 °C in the return flow prescribed by the regulations, the temperature can drop below 50 °C due to the inevitable cooling on the way to the tapping point and in the circulation system.
Conclusion:
For a variety of reasons, the property industry should not neglect limescale protection on the drinking water side. Effective limescale protection is an important component for operating drinking water installations with water heaters and heat exchangers in the most energy-efficient way. Technical limescale protection measures have a direct positive effect on operating costs. If the drinking water installer is also interested in ecology and sustainability, DVGW-certified chemical-free limescale protection systems are a good choice if their effectiveness is guaranteed without the use of dosing agents or salt.
With these processes, the wastewater is not contaminated, and the natural drinking water composition of the water supply is not changed, so there is no obligation to notify tenants according to the Drinking Water Ordinance (TrinkwV).
