The future load curve of the Swedish building stock – Interactions between the heating load and district heating

Licentiate thesis, 2018

In line with global efforts directed against climate change, the building sector is required to undergo significant changes in terms of its energy management. This is the case for both the use of energy (reduced energy consumption) and the supply of energy (heat and electricity), and how these two interact. Thus, the overall aim of this work was to investigate potential flexibility of the energy demand in buildings, i.e., demand response (DR), and how it can affect the energy supply side. More specifically, we studied the potential of space heating DR in buildings to improve the operation and efficiency of district heating (DH) systems.

This work applies several techno-economic optimisation models, which include estimation of the space heating demand in buildings, as well as the optimal dispatch and utilisation of heat generation and thermal energy storage technologies in a DH system. By applying the developed models, we examine the potential for flexible space heating demand. In principle this is done through allowing for indoor temperature deviations from the set-point temperature. The present work applies the building stock of Gothenburg, Sweden, as a case study, and thus, studies the operation of the city’s DH system. The interplay with the power sector is included in this work by using hourly electricity prices as input.

The results of this work indicate that a realised DR in buildings, allowing for indoor temperature deviations from a set-point temperature, significantly affects the cost optimal heating load of the city by smoothing the variations. We show that upward indoor temperature deviations of as little as +1 ͦC can smoothen the short-term (daily) fluctuations of the system heating load by up to 20% over a year. The modelling results also indicate that the potential of DR in buildings to moderate short-term daily heat-load variations in a DH system is comparable to the use of a centralised thermal energy storage system, e.g., a hot-water tank. However, on longer time-scales (from few days to weeks), the performance of a centralised storage in smoothening variations is superior. The smoothening of the heating load results in more efficient heat generation: the heat supply and number of full-load hours of base-load units increase, while the peaking units decrease their output. The results indicate that the DR via 1 ͦC overheating of buildings can lead to an 85% decrease in the number of starts and stops of peaking, fossil-fired heat generation units, leading to improved carbon footprint of the system. Finally, the availability of CHP plants and HPs in DH systems is proven to be mutually beneficial both to DH systems and the power sector.