The current Dutch building sector is heavily dependent on natural gas for its energy consumption, of which a very significant part is used to meet the space heating demand. To mitigate the climate crisis, a transition from fossil fuels to renewable energies has to be made. However, renewable energy sources are usually low-temperature heating sources, prompting the need for renovation. There are often multiple renovation solutions per project, with each their unique effect. Determining the optimal solution out of those renovation concepts that enable low-temperature heating (LTH) is challenging due to the varying performance of the renovation scenarios, multi-stakeholder involvement with each their own preferences and the lack of a clear decision-making process.
This research aims to provide holistic decision-support and aid in the identification of the most suitable renovation alternative. The research question central to this study is: ‘How can the decision-making process of selecting an energy renovation concept be supported that aims to make existing residential buildings compatible with low-temperature heating?’. This research focuses on multi-family buildings in the Netherlands and considers a temperature range of 30-55 °C to be LT.
To answer the research question, an extensive literature research is conducted on the topics of LTH and decision-support in energy renovations. Based on the results from the literature study, a LTH decision-support framework and tool is developed. The MCDM TOPSIS method is used to evaluate the performance of the renovation alternatives and is combined with the pairwise comparison method to capture the stakeholders preferences. The framework and tool is validated on its function and usability through a case study application on a 1979 apartment building and a workshop with 4 expert stakeholders. In addition to the evaluation of the 4 renovation scenarios from the case study, 9 additional renovation scenarios are developed and compared. A LTH-Rhino/grasshopper tool is used to simulate the heating demand and thermal comfort for all 13 scenarios to evaluate the LT-readiness of the alternatives.
One of the key findings of this research is that the developed framework and tool can support the decision-making process on LT-renovation scenarios. This support is provided by structuring the decision-making process through aiding in the identification of decision parameters, making the stakeholders’ preferences explicit through pairwise comparison and ranking the renovation alternatives based on quantified performance values and criteria weights representing the stakeholders’ preferences through TOPSIS. The framework evaluates LT-readiness to identify if there is a need for renovation, and filters non-suitable scenarios based on the LTH-grasshopper simulation results.
The framework ensures that all relevant decision-making aspects are considered systematically, and the tool facilitates a transparent and data-driven selection process. Together, they provide holistic decision-support, leading to better-informed decisions. This research motivates to enable LTH, thereby mitigating climate change and ensuring a sustainable future.

The Netherlands aims to reduce greenhouse gas emissions by 49% before 2030, with the built environment contributing 15% of these emissions largely due to the heavy reliance on natural gas to meet space heating demands. To phase out natural gas, alternatives such as heat pumps and district heat networks are being considered. However, adapting existing buildings to lower supply temperature district heating requires effective refurbishment to maintain thermal comfort for occupants. The challenges hindering this process include i) addressing multiple housing typologies at the neighbourhood scale, ii) complexity of evaluating refurbishment measures by decision-makers, iii) uncertainty due to lack of consideration of life cycle costs and occupancy behaviour pre and post-refurbishment leading to performance gaps in energy savings and iv) current computationally demanding and inaccessible tools to assess refurbishment measures. Therefore, this thesis proposes a method to develop a surrogate model-based decision-making tool that can help homeowners efficiently assess optimal, combined refurbishment measures to help homeowners transition to low-temperature district heating. In order to develop this tool, the study examines literature studies that help define the input parameters for the underlying parametric simulation including. This also helped define the key performance indicators including energy savings, hours too cold and global cost. Furthermore, the underlying simulation model with 13 input parameters provides the synthetic training data with 2000 design samples using the uniform Latin hypercube sampling method for each of the three housing archetypes including i) terraced, ii) detached and iii) Portiek apartments. The best-performing model in this instance included artificial neural networks with an R-squared above 0.95. The surrogate model is then integrated into the optimization workflow that forms the framework for an interface decision-making tool that users can use to generate optimal low-temperature ready refurbishment packages. The common low-temperature ready refurbishment packages include maximum airtightness, type C2 CO2 control ventilation system, cavity wall insulation, triple glazing, and internal roof insulation. Furthermore, it can be concluded that its more financially feasible to maintain existing radiators when transitioning to low-temperature heating instead of replacing the radiators with higher capacity. This is because the initial investment in other refurbishment measures not only improves comfort but also delivers significant energy savings that help reduce global costs in the long term.

To prepare the housing stock for the transition to collective, low-temperature heating, minimal renovation strategies for the integration of low-temperature heating and optimal comfort are studied within this research for various single-family housing typologies. Renovation measures on the building and installation scale were considered for the different typologies, which vary in terms of the construction period and building type. The simulations are performed in the software DesignBuilder, on a case study dwelling located in the Netherlands. The low-temperature readiness is assessed based on heat balance and air temperature simulations. Computational Fluid Design within the software is used to determine the effect of the renovation measures on the draught rate and radiant temperature, as these aspects are critically affected by the lowering of the radiator's supply temperature. Additionally, the effect on radiant asymmetry is measured in the software program Stralingsverloop. The outcomes of the study regarding low-temperature readiness indicate the differences in effectiveness of the measures for the different typologies. The study on thermal comfort shows the posibilities for optimizing the thermal comfort through the integration of renovation measures, in particular through the installation of balance ventilation and high performance glazing. Based on the outcomes of both the studies, a individual recommendation is given for each typology.

The Dutch building stock has to switch to alternative energy-efficient heat sources, such as district heating or heat pumps, which will provide a lower supply temperature for the heating system in dwellings. Yet, the consensus is that dwellings need to be intensively renovated, to provide thermal comfort with low-temperature heating. However, it can be argued that a more affordable renovation with less renovation measures can also provide the same level of thermal comfort as the original situation. To this day, it is unknown what the minimal combination of renovation measures could be. Thus, this research aimed to design combinations of renovation measures, which are both affordable, and are able to provide thermal comfort in Dutch terraced houses. These renovation concepts are referred to as LT-Ready concepts. Hence, the main research question answered in this thesis is: “What combination of renovation measures for residential buildings is affordable and provides thermal comfort when using a lower supply temperature for heating?” First, a literature study is conducted. It investigated the available renovation budget of house owners, as well as thermal comfort, including current guidelines and local comfort aspects. Also, possible renovation measures to enable low-temperature heating were researched. Second, to select the most cost-effective renovation measures, a cost analysis was performed. Using this, renovation concepts were developed and tested with dynamic simulation software. Here, the thermal and energy performance was simulated with an adaption of the ATG-method for dwellings. The renovation concepts included the placement of a ventilation system and additional renovation measures. Results provided a variety of renovation concepts that were LT-Ready within a budget of €10,000. Different scenarios were developed with building or budget limitations, after which the best LT-Ready option was selected. In general, it was concluded that demand-driven exhaust ventilation (C2) or balanced ventilation with heat recovery (D1) is preferable. Wall insulation and replacing windows also showed a large effect on improving thermal comfort and reducing the heating demand. Add-on ventilators can boost thermal comfort, while having only a minimal effect on energy performance. In case no insulation can be applied, LT-radiators are an option to provide thermal comfort. This however increases the heating demand. Additionally, local comfort was investigated for different measures on the room. It was shown that small interventions such as add-on fans and furniture placement could substantially influence the air currents and temperature distribution within the living room. Also a tool which compares the heating demand of a dwelling with the available heating capacity at a lower supply temperature to determine whether a dwelling is LT-Ready, or what combination of measures is needed to make it LT-Ready. The tool is based on ISSO-51 and has a general approach which can be used for every terraced dwelling It can be downloaded from http://ltreadytool.nl. Overall, it can be concluded that there is a variety of possible LT-Ready renovations that provides thermal comfort and is affordable, depending on the specific scenario. It is proven that deep renovations are not essential to provide thermal comfort with low-temperature heating.