Page 2 of 9 HOT WATER RECIRCULATION Hot Water Recirculation (HWR) is a standard application that is necessary in many buildings. The energy consumption for HWR constitutes a large amount of the total consumption in buildings . The system works by a pump circulating the hot water from the water tank and to the final consumer. This ensures that the water temperature stays at an acceptable level, even at times with little or no tapping taking place. The challenge in these applications is to reduce the losses in the system to a minimum. The losses consist of heat loss from pipes in typically unoccupied areas of the building and from uncontrolled pumps. Energy loss when circulating the hot water typically varies between 30-75% in high-rise domestic buildings and 50-90% in commercial buildings and schools. There have been examples of the loss constituting from 2 to over 100 times the energy consumption used heating the water. It is therefore obvious that the potential for energy savings in this system is enormous. The following examples show 3 different approaches to solving the hot water recirculation task. Examples 2 and 3 show how it is possible to utilise the built-in temperature sensor in the MAGNA3. Temperature control to reduce losses Traditionally, HWR has been handled by a recirculation pump responsible for maintaining a constant duty point, or more economically, a variable circulating flow in combination with thermostatic valves to set a minimum return temperature. With the MAGNA3 it is now also possible to do without these valves as the temperature control is performed by the MAGNA3 and its built-in temperature sensor. However, balancing valves are still needed unless decentralised MAGNA3 pumps are utilised. Benefits of the MAGNA3 in HWR: • • • Reduced heat losses from pipes Easy commissioning via Grundfos GO Reduced initial cost (no termostatic valves) Minimum 55 °C Minimum 55 °C Cold water 10 °C Thermostatic circulation valves Minimum 60 °C From boiler or district heating Proportional pressure controlled MAGNA3 Hot water circulation Hot water Cold water Hot water tank Thermostatic circulation valves Example 1: Proportional pressure controlled pump with thermostatic balancing valves Minimum 55 °C Minimum 55 °C Minimum 55 °C Minimum 55 °C Cold water 10 °C Balancing valves Cold water 10 °C Temperature controlled MAGNA3 Minimum 60 °C Minimum 60 °C Temperature controlled MAGNA3 Hot water circulation Hot water Cold water Hot water tank Balancing valves Hot water circulation Hot water Cold water Hot water tank Temp. controlled MAGNA3 Example 2: Centrally placed temperature controlled MAGNA3 with static balancing valves Example 3: Decentralised temperature controlled MAGNA3s with balancing valves
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