The emerging challenge of balancing weather dependent electricity production and variable demand is creating new demands on the energy system. Without adding extensive flexibility to the power system these issues will lead to a costly transition to a decarbonized energy system.

In the Flexi-Sync project, the need of balancing volatility in the energy system is met by increasing flexibility in district heating and cooling systems. The flexibility potential is identified by researchers and implemented by practitioners; energy service providers, district energy companies and housing companies. The project aims to identify how flexibility in district energy can be optimized and, thereby, contribute to the management of variable electricity production and demand.

Allowing greater temperature variations
Flexibility in district energy systems can be realised in many different ways and one of them is to allow for greater variations in indoor temperature. In the Flexi-Sync project one of the aims has been to understand what impact greater variation in indoor temperature of buildings can have on the comfort of occupants of such spaces. This understanding was gained through:

  1. a scholarly literature review,
  2. creating three plausible flexibility scenarios for residential buildings,
  3. collecting Swedish building residents’ opinions about these three scenarios through a survey, and
  4. through a stakeholder workshop in Austria

Understanding of the technology important, but difficult
The findings that were corroborated by previous findings show that there are more aspects than the range in which the temperature is allowed to vary that is important for the acceptance of varying indoor temperature. First, it is important that occupants understand the flexibility setup, but it is difficult to inform in an understandable and accessible way. When and where (e.g., in the bathroom or bedroom) the variation takes place is also important and, to complicate matters, people often have specific and individual preferences regarding heating. Pricing models that incentivize variation in indoor temperature could enhance the acceptance rate of minor comfort losses.

End-users want control, but don’t demand compensation
The survey also resulted in interesting indications to be confirmed or rejected in future studies. For example, the survey showed that the respondents prefer flexibility setups in which they have control over the flexibility range and are compensated economically for ranges larger than ±0.5°C (Scenario 3) over flexibility setups with the same variation and no control (Scenario 1) and larger variations without control (Scenario 2). But interestingly, some respondents showed a willingness to accept a deterioration of the heating service without any compensation. In the survey, younger residents (aged 18 to 34) showed the highest acceptance of a heating service deterioration without compensation. The survey respondents’ satisfaction with their current heating seemed to influence the extent to which they accepted higher variations in indoor temperature. Finally, the survey indicated that if you spend more time at home, you will have higher demands on thermal comfort.


This article has been written by Sara Renström (RISE), Burcu Ünlütürk (IVL Swedish Environmental Research Institute) and Anna Nilsson (IVL Swedish Environmental Research Institute). You can find more information about the project on and in the Celsius Toolbox article “How to optimise district energy flexibility”



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