IN CITY AREAS WITH LOW-TEMPERATURE DISTRICT HEATING: RETURN TEMPERATURE OPTIMIZATION OF RADIATORS INMULTI-FAMILY HOUSES For the district heating (DH) network to become more energy efficient in the future, it is relevant to improve the DH technology further. By lowering the temperatures, the production of heat and surplus heat is available from an even greater amount of variable energy sources, and the renew- able sources and network become even more efficient. When the DH temperatures are lowered, it is, however, essential to ensure that the thermal comfort in the buildings is maintained.
implementing new innovative thermostats from Danfoss. The thermostats have been developed to ensure better radiator performance and obtain a lower return temperature into the DH grid, thereby a more energy-efficient system. Compared to the existing electronic thermostat design availa- ble in the market, this new one is equipped with an additional temperature sensor connected to the return side of each radi- ator and an algorithm to secure more accurate control of the opening or closing of the valve based on a maximum return temperature setting. The purpose of this functionality is two- fold. First, it should help ensure low return temperature from the space heating systems by keeping a high delta-T across the radiator (Delta-T). This will help obtain a low DH return temper- ature and provide convenience for the occupant since it will ensure proper heating system operation even when windows are opened, or holiday setbacks are applied. Second, due to the automatic flow limiting effect of the return temperature control, the thermostat should help provide au- tomatic hydronic balancing of the heating system. This new thermostat could provide one combined solution for some of the essential issues in space heating systems in buildings con- nected to future low-temperature DH systems. The return temperature control functionality is becoming in- creasingly relevant for both the primary and secondary sides of larger heating systems, as there are implications related to sys- tems’ optimal performance (e.g., boilers operating in conden- sation mode are using less energy), environmental factors (less energy usedmeans less CO 2 impact), as well as comfort-related factors (e.g., experienced by tenants in residential multi-family buildings, as well as in light commercial or public buildings).
By Ida Bach Sørensen, Project manager, Damgaard Consulting Engineers
The main barrier to lowering the temperature is a lack of knowledge on how to implement this in existing areas with- out compromising thermal comfort in the buildings. It is also a lack of knowledge on the use of low-temperature DH in build- ings other than single-family houses. Former projects have aimed at single-family houses, mainly with floor heating. Until now, no one has solved the challenge in most existing homes, i.e., multi-family houses with radiators. Low-temperature DH is challenging in the existing building stock with radiators which requires a higher supply temperature than floor heating. Another massive problem in multi-family houses is a lack of hydronic balancing in the building, which leads to poor distri- bution of heat between all radiators on all floors in multisto- rey buildings. Today mechanical balancing valves are on the market that can be adjusted to control the proper flow, but they have the disadvantage that their (manual preset) settings are adjusted to cope with the coldest day of the year – which seldom occurs. This leads to non-optimal balancing in partial load situations most of the year. This is due to the lack of technology to cope with this segment, and not due to the relevance: By far the biggest part of living space, and most of the energy spent for space heating is con- sumed in cities with older multi-family buildings equipped with radiators. Field testing This project has investigated how the control of a given heat- ing system within an apartment building can be improved by
Lowering the return temperature will lead to higher efficiency in DH applications and save the building owner the ‘incentive
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