Logano plus SB315, SB615, SB745 - Buderus

8 System examples8.1.3 DHW heatingGiven an appropriate design, the DHW temperaturecontrol by means of a Logamatic control unit offersspecial functions, such as the switching of a DHWcirculation pump or thermal disinfection to protect againstthe growth of legionella bacteria, for example.When connecting a DHW cylinder with an internalindirect coil to the high temperature return, werecommend operating the heating circuit with the lowestreturn temperature at the same time as DHW heating.This increases the efficiency and additional energy andheating cost savings of up to 4 % are possible. Due to thesignificant cooling of the heating water, primary storesystems with external heat exchanger must be connectedto the low temperature return ( fig. 33, page 48).The floor standing condensing boiler achieves its highestefficiency at low system temperatures. To achievemaximum efficiency, we recommend implementing DHWheating, which requires high flow temperatures, with aseparate boiler that has a matching output.If DHW heating is connected to the boiler, the DHWcylinder should be sized to ensure that the lowest boilerheating output (subject to burner) does not exceed thetransfer rate of the DHW heat exchanger.An excessive boiler output in relation to the transfer rateof the indirect coil results in the burner starting toofrequently.For more detailed information, see the technical guides“Sizing and selecting DHW cylinders” and “Logamatic4000 modular control system”.8.2 Safety equipment to DIN EN 128288.2.1 RequirementsNo claim is made as to the completeness of the diagramsor the corresponding design information for systemexamples. Each system example is a non-bindingrecommendation for certain versions of the heatingsystem. The practical implementation is subject tocurrently applicable technical rules. Safety equipmentshould be installed in accordance with local regulations.DIN EN 12828 specifies the safety equipment for safetytemperatures up to 110 °C.The schematic diagrams in fig. 34 and fig. 35 can be usedas engineering aids.8.2.2 Low water indicatorAccording to DIN EN 12828, a minimum pressure limitercan be installed instead of the low water indicator. Afurther reasonably priced alternative to the low waterindicator is the minimum pressure switch sold byBuderus. This can be used for boiler outputs ≤ 300 kW ifverified by the manufacturer. At an equally competitiveprice, Buderus offers a water level limiter as a low waterindicator for boiler outputs from 310 kW ( page 81).The Logano plus SB315, SB615 and SB745 floorstanding condensing boilers have a special connectorfitted as standard to facilitate the installation of thisattractively priced safety equipment.See chapter 9.5 for detailed information.8.2.3 Pressure maintenanceThe system must be equipped with an expansion vessel.It is designed in accordance with the applicablestandards and regulations. It is essential to prevent waterhammer from pump-controlled pressure maintainingdevices without or with an undersized expansion vesselby fitting every heat source with an additional diaphragmexpansion vessel. For further information, see BDHinformation sheet no. 30 and Code of Practice K4Buderus catalogue for large heat sources/applications.50Technical guide Floor standing gas/oil condensing boilers Logano plus SB315, SB615, SB745 – 6 720 802 589 (2012/01)