The transition from fossil fuels to renewable energy sources brings along the reduction of the supply temperature of the distribution heating networks, because renewable energy sources usually provide heat at lower temperatures. This master thesis specifically focuses on the buildings because it is uncertain which adaptations are necessary to ensure thermal comfort when the supply temperature decreases. Especially in existing buildings, since they were originally designed for high operating temperatures. A case study was conducted by studying the performance of a non-residential building under different simulated scenarios to enable lower operating temperatures in the heating network. The objectives of the research are two: 1) to develop of a protocol for data collection and selection of promising adaptations that facilitates a case study on this topic and 2) to compare the observed effects of the different possible adaptations on the required operating temperatures in this case study with the results of the few other studies available. The most interesting results derived from the case study are that it is possible to lower the peak power, and thus the operating temperatures, in the current situation of the selected building, without any adaptation, from 78/70oC to 63/55oC. Assuming that the mass flow is decreased in order to achieve a bigger temperature difference between supply and return, operating temperatures can be 70/50oC. Mass flow control through radiators should then be implemented in order to obtain the lowest possible return temperature for a given supply temperature. During the implementation phase of the geothermal project, the implications of this measure need to be studied. When heat losses are small, smart settings in the building management system prove successful to lower the supply temperature further. In the controls and operation scenarios, adjusting the room temperature setpoints and the heating schedules enables even lower supply and return temperatures, 50/35oC. In old, poorly insulated buildings, minimal renovations in the buildings’ envelope are crucial (and often sufficient) to enable low temperature heating. When the building without renovations was simulated, it was not possible to lower the operating temperatures; instead, the required temperature increased to 90/70oC.
Changes in the energy system, such as the installation of radiators designed for lower temperature heating, also enable supply and return temperatures of 50/35oC. The case study building has a ventilation system with heat recovery and pre-heating of air to 19oC. A scenario is simulated with a system with only heat recovery. The ventilation air is introduced in the room at lower temperatures, and the heating system takes over the heat demand. For the same operating temperatures, 70/50oC, the heat recovery scenario suffers a decrease in the thermal comfort. Seeing the effect of the heating through ventilation air in lowering the supply and return temperatures, a central ventilation system with heat recovery and pre-heating that can operate at low temperatures can represent a good alternative to other decentralised adaptations in the energy system, such as changing radiators. The protocol for data collection and selection of promising adaptations created during this research facilitates the first stages of a case study, by providing an inventory of the main elements for the data collection and their implication in lowering the operating temperatures in the heating network. It also presents a list of possible adaptations to enable low temperature heating. Future case studies could focus on fixing thresholds for the properties of the envelope that limit the lowering of the supply and return temperature. Further research could also continue exploring the optimisation of schedules and room temperature settings to lower the temperatures in the heating network even more, considering the possibility to use the thermal mass of the building as passive storage. Generalisations from case study findings are necessary to start developing one common standardised procedure, with recommended tools and guidelines for simulation as well as practical tests. The standard procedure at building level ought to be included as part of a holistic district level and building level approach in order to facilitate the transition to more efficient and sustainable heating networks.

The Dutch government set two environmental goals by 2050. One of them is being climate neutral and the other one is to have a circular economy. In order to meet both goals in the best environmental conditions, extensive environmental research is required. This thesis is one of these researches and its main focus is on the climate neutral goal by 2050. In this thesis I start by creating a generic model in ArcGIS that will calculate the required materials and their environmental impacts for the implementation of high and low district heat networks and for air-water heat pumps in residential buildings. The model uses national spatial data of buildings, heat networks, and energylabels and combines them with material data that is retrieved from life cycle inventories (LCI) out of life cycle assessment (LCA) papers, material databases, several manuals, technical specifications on websites and own examination. The model is applied to the Merenwijk in Leiden. The model’s results show that for the Merenwijk the indirect environmental impact of the materials will reduce the total reduction in the heat pump scenario by approximately 10% and will be covered in the first 2 years of operation. On the material demand side, the model shows that the Netherlands will face problems with the demand for glass and glass wool. The current market for both materials should be intensified by 4 to 5 times in order to meet the expected demand. Glass wool demands will even reach 2% of the current global mineral wool market. In conclusion this thesis provides an addition to current environmental calculations by looking at the material environmental impact in the Dutch heat transition. The environmental impact of materials does have a significant impact on the overall environmental calculations.

The demand of energy increases steadily due to the growing global population and the increasing living standard of emerging markets. The increasing energy demand and reduction of greenhouse gasses require a significant increase of renewable energy sources and energy efficiency of buildings. Also, the increasing degree of renewable energy sources increase the demand to store excess energy and to bridge the gap between energy production and consumption. This thesis focusses on the possible energy reduction for air-conditioning systems by the application of thermal energy storage and phase change materials (PCMs).

Tetra-n-butylammonium bromide (TBAB) is a promising PCM for air-conditioning applications. PCMs store thermal energy in the form of latent heat. PCMs are also promising cold storage media because of the capacity to store energy at constant or near constant temperature. TBAB has a high solubility in water and hydrate crystals are formed in a TBAB aqueous solution at temperatures from 0-12.5 °C depending on the concentration of TBAB in the solution. The solid mass fraction of the slurry is limited to maintain the slurry pumpable.

A pilot system to control the temperature of a 144 m² space is installed. The system is equipped with multiple sensors to monitor the system. The air-conditioning system consists out of a primary loop, which uses the conventional refrigerant R134a, and a secondary loop, which uses a TBAB solution as distribution fluid. An initial mass fraction of 36.5 wt% TBAB is used, resulting in a phase equilibrium temperature of approximately 12.5 °C. The hydrate crystals are produced in the generator and stored in a storage vessel of 300 l. The capacity of the air-conditioning system is around 3.5 kW.

The pilot system is modelled with both water and a TBAB solution as secondary distribution fluid by improving and extending an existing model. The crystals are produced in the generator by evaporation of the primary refrigerant. The crystals are removed from the heat transfer surface by the friction of the flow. The crystal layer thickness and flow velocity in the generator are calculated by comparing the friction losses to experimental determined scrapping forces required to remove the crystals. Experimental data of the pilot plant are used to validate the model.

The model simulations of the air-conditioning system show a COP increase from 3.27 to 4.30 when a 36.5 wt% TBAB solution is used as a secondary distribution fluid instead of water. Simulation results show also an increased performance when the initial mass fraction of TBAB is lowered to 35 wt%. The COP of the system increased to 4.50 mainly due to the reduction of the energy consumption of the compressor. The force required to remove the crystals from the heat transfer surface lowers by lowering the initial mass fraction of TBAB. Therefore, the steady state crystal layer thickness in the generator reduces, increasing the heat transfer rate by lowering the thermal resistance. However, reducing the initial TBAB mass fraction also lowers the evaporation temperature of the primary refrigerant and the total cooling capacity of the slurry.

Several operational optimization problems occur in the current situation related to the district heating system (DHS) of Utrecht. The present control strategy is not optimized for the current operation of the DHS. This leads to energy losses, exergy losses and higher operational cost.
The goal of this research is to find improved control strategies for the DHS of Utrecht. This is obtained by the construction of a model of a DHS that enables the minimization of exergy losses as a method to reduce operational cost. Heat production and distribution from the heat production unit towards the city centre of Utrecht are modelled in Excel. The model includes the following model sub systems: the heat recovery unit in the production plant, the primary grid, the heat transfer station and the secondary grid. Fourdifferent control strategy scenarios are modelled next to the current control strategy, taking different primary heating trend lines into account.
Model results of the current control strategy show that the exergy losses are highest in the heat transfer station compared to the other components. Exergy losses in the pipelines and heat recovery unit are generally lower, but in the same order of magnitude. The exergy losses due to pressure drop are lower than 6% of the total exergy losses. Exergy losses in the pumps are very small, lower than 1% of the total exergy losses.
Decreasing the primary supply temperature improves a control strategy; this leads to smaller overall exergy losses as compared to the current control strategy. Operation of the heat recovery unit improves, operation of the preheater and low-pressure condenser increases and operation of the higher-pressure condenser(s) decreases. Exergy losses in the heat transfer station and in the primary pipelines are smaller as well. The primary mass flow increases, so exergy losses due to pressure drop and pump exergy losses increase as well, however these are still relatively low. Due to a maximum velocity constraint and unexpected weather conditions, the improved control strategy should increase the primary supply temperature during peak moments. Overall exergy losses for an improved control strategy are 7.8% up to 18.5% lower as compared to the current control strategy.