Lowering district heating temperatures – Impact to system performance in current and future Danish energy scenarios

Abstract

Combined heat and power (CHP) production in connection with district heating (DH) systems has previously demonstrated a significant reduction in primary energy consumption. With extended installation of intermittent sustainable sources, such as eg. wind turbines rather than thermal units, the changed distribution of generation technologies may suggest a reconsideration of optimum for DH network temperatures, in order to achieve low cost and minimize carbon emissions. A mixed integer linear optimisation model was used to investigate the changed operation based on changed network characteristics. Utility plants and demand curves corresponded to the current and future scenarios for the DH system of Greater Copenhagen. Performance curves from typical CHP-plant technologies were used to represent the changed operation of power and heat production for changed DH temperatures. The results show that primary fuel consumption is reduced approximately 5-7 % at DH design temperatures of 60 -70 C. Further reduction in DH temperatures resulted in opposing tendencies, as hot tap water requires electricity to reach the required temperatures. The results are network-specific, as they represent the given network and production units, but similar trends can be expected for other large networks.

Integration of large-scale heat pumps in the district heating systems of Greater Copenhagen

“…Münster et al (2012) [9], Ommen et al (2016) [22], Ommen et al (2013) [21], and Hedegaard & Münster (2013) [23]. Heat pumps utilising natural heat sources will in most cases experience variations in temperature of the source stream which influences both COP and capacity of the heat pump.…”

Performance of ultra low temperature district heating systems with utility plant and booster heat pumps

“…This may be done without interfering with consumers requiring DH at traditional temperature levels. 2 The design of new or updated systems with better performance of utility units according to the production temperatures and lower losses in DH network [7,13].…”

“…To add to this, DH may further improve cost effectiveness of other sectors, as it is a key component in the Smart Energy Systems approach [5] stating that the "Smart Energy Systems concept is essential for 100 % renewable energy systems to harvest storage synergies and exploit low value heat sources". A reduction in DH supply temperatures is proposed in order to increase district heating efficiency, as M A N U S C R I P T temperatures to e.g., 60°C [7] may in many cases be an acceptable solution for both existing and new buildings [8].…”

Analysis of possibilities to utilize excess heat of supermarkets as heat source for district heating

“…Several studies have therefore compared various DH technologies under consideration of different conditions, such as consideration of existing network components, availability of heat sources, network layouts and other aspects [2][3][4][5].…”

“…The 4 th generation of DH is described by supply temperatures between 40 °C to 70 °C, [1,2]. The 4 th generation of DH comprises low-temperature district heating (LTDH) and ultra-low-temperature district heating (ULTDH) networks.…”