Technoeconomic and whole-energy system analysis of low-carbon heating technologies
Creators: name: Olympios, Andreas V.
Publisher: name: Imperial College London
Year: 2022

description: Despite developments in renewable electricity production, space heating and hot-water provision still account for a high proportion of the total greenhouse gas emissions in the world. Decarbonising heating requires an in-depth understanding of the candidate technology options. Should investments in energy systems focus on large-scale/centralised options, or small-scale/distributed ones? How should end-users operate their heating systems to maximise economic and environmental benefits? Should manufacturers design high-performance yet high-cost technologies and reduce the transition cost to the wider electricity system infrastructure, or should they promote more affordable, lower-performance end-use alternatives at a cost to the wider system? In this thesis, technoeconomic models that capture the cost and performance characteristics of heating technologies are developed and used to analyse the design and operation of competing solutions from the perspectives of different stakeholders. An extensive analysis of commercially available air-source and ground-source heat pumps, combined heat and power systems, district heating infrastructure and thermal energy storage systems on the UK market is first conducted. Fitting techniques are used to determine relationships arising from the collected data and quantify the related uncertainty in technology characteristics between the data and fitted relationships. Then, thermodynamic and component-costing models are developed for technologies for which there is a substantial spread in the available data, or for which data are not available. These include electricity- and hydrogen-driven heat pumps and involve dedicated compressor efficiency maps, heat exchanger models, and equipment-costing methods. The resulting technoeconomic models are first used to assess the economic and environmental performance of different centralised and distributed low-carbon heat provision pathways, with a London district as a case study. Centralised gas-fired combined heat and power systems are found to be favourable in terms of annual total cost. However, in recent years, the carbon footprint of grid electricity has reduced significantly, meaning that heat pumps installed at household or community level achieve a higher degree of decarbonisation. Furthermore, an uncertainty propagation analysis reveals the significance of properly accounting for technology performance and cost variations when modelling energy systems. In fact, the use of technoeconomic models is shown to reduce the uncertainty in the results by more than 75% compared to the use of black-box approaches. Two different optimisation studies are then conducted to investigate smart operation strategies of heating technologies in the domestic and commercial sectors. First, thermal network models of a domestic electric heat pump coupled to a hot-water cylinder or to two phase-change material thermal stores are developed and used to optimise heat pump operation for different objective functions. As demonstrated, smart heat pump operation can lead to a decrease in operational costs of more than 20% and an increase in self-sufficiency by up to four times. For the commercial sector, a multi-objective control framework is designed and installed on an existing combined heat and power system that provides heat and electricity to a supermarket. By using a stochastic optimisation approach and considering the uncertainty related to the price of exporting electricity, energy savings higher than 35% can be achieved compared to using a typical gas boiler. The integration of technoeconomic models of technologies within whole-energy system models can be used to extend the capabilities of the latter, so that they can, apart from optimising network infrastructures, provide explicit information about future technology design. Thermodynamic and component-costing models of a domestic electric heat pump, a hydrogen boiler and a hydrogen-driven absorption heat pump, as well an existing whole-energy system model of the UK, are used to compare electrification and hydrogen pathways for the domestic sector. The technologies are compared for different weather conditions and fuel-price scenarios, first from a homeowner’s and then from a whole-energy system perspective. It is shown that, in the UK, hydrogen technologies can be economically favourable only if hydrogen is supplied to domestic end-users at a price below half of the electricity price. From a whole-energy system perspective, electric heat pumps are the least-cost decarbonisation pathway under the investigated scenarios. Lastly, this thesis includes an effort to demonstrate how different component choices when designing domestic electric heat pumps can influence the national energy generation mix and heat-decarbonisation transition cost. Using the developed electric heat pump model, a set of optimal heat pump configurations representing competing components is obtained. The size of heat exchangers and the choice of compressor type and working fluid are shown to have a remarkable influence on the technology’s performance and cost. These configurations are integrated into an existing whole-energy system capacity-expansion and unit-dispatch model, to show that, from a UK energy system perspective, although high-performance heat pumps enable a reduction in the required installed electricity generation capacity by up to 50 GW, low-to-medium performance heat pumps can lead to a reduction of more than 10% in the total system transition cost and end-user investment requirements.