By Michele Tunzi, Associate Professor, Technical University of Denmark, DTU Construct
Tom Diget, Chief Operating Officer, Viborg District Heating Company
Kees van der Veer, Vice President, IT and Software, Brunata
Anders Nielsen, Application Manager, Grundfos
Introduction The current technological challenge of district heating is to develop new solutions to sustain the 4th Generation DH (4GDH) transitions. The core idea is to secure the expected comfort and hygiene for space heating and domestic hot water systems in buildings with low average supply and return temperatures in the range of 55 °C and 25 °C in the networks. Reducing network operating temperatures can secure the phase-out of fossil-fuel-based heat generation, integrate low-grade heat sources, minimize distribution heat losses, and reduce overall heating costs. This article aims to share the latest knowledge from surveys in typical Danish multi-apartment buildings with water radiators used as heating elements for space heating systems. In particular, to highlight the impact of common user behaviors on the overall operating temperatures and their effect on the heating bills.
Can existing buildings be operated with lower temperatures? Contrary to a common belief, existing buildings can operate effectively at temperatures lower than their original ‘design’ temperatures during most of the heating season without undergoing extensive retrofitting of their heating systems or building envelopes. [1] Heating systems are designed to maintain indoor comfort even during extreme outdoor temperatures with no heat gains. However, the heat demand during the heating season can fluctuate significantly, rarely close to the calculated design heat demand. Additionally, commercial components are available in discrete sizes, and the heating elements and heat exchangers are typically oversized. A survey conducted in ordinary apartment buildings connected to the Viborg district heating network in Denmark highlighted that existing buildings from the 1940s to 1990s can be comfortably heated with a supply temperature of 40- 55 °C for the majority of the heating seasons. Even during cold spells, the supply temperature in those buildings was below the “design” radiator supply temperature of 70 °C.
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