Thermodynamic Analysis of Air Source Heat Pumps and Micro Combined Heat and Power Units Participating in a Distributed Energy Future

Achieving the reductions in carbon dioxide emissions which are necessary will require improvements in the way in which domestic space heating is supplied. Air Source Heat Pumps and micro-Combined Heat and Power units both have the potential to reduce emissions while using primary energy resources more efficiently. The performance which these technologies can achieve is fundamental to fulfilling this potential and yet it is still subject to some uncertainty. This thesis analyses the performance of Air Source Heat Pumps and micro-Combined Heat and Power units in terms of their energy and exergy requirements and in terms of the carbon dioxide emissions associated with their operation. A review of the literature identified that it was appropriate to develop a novel modelling approach. Models of many components currently exist and these are adopted and extended wherever possible within this modelling approach. However, it is the unique way in which this research combines these models and adds additional components which delivers performance data relating to a wider range of conditions at a greater level of detail than that which was previously available. The model which was developed can dynamically simulate the heating and power demands in many dwellings simultaneously, facilitating meaningful study of effects which are dependent upon the sum of their power flows. Consideration of the effect of operating conditions includes permutations of climate, control systems (including those which engage with demand side management), grid generation mixes and building properties. Efficient Air Source Heat Pumps units have the potential to make energy and carbon emissions savings at present but their performance is sensitive to the conditions studied. In particular, appropriate control of the units can yield energy savings of around 25%. Additionally, the carbon emissions intensity of the grid is an important consideration which is explored in depth. Currently, energy requirements and carbon emissions can be reduced by the use of micro-Combined Heat and Power units. Their potential to further reduce carbon emissions diminishes if the grid is predominantly decarbonised but units with high electrical efficiencies can still save energy. The effect of the control approach which is adopted is also significant and has different effects on fuel-cell based units compared to combustion-based units. The key contribution of this work is the analysis of performance data for a selection of units operating under a range of conditions, calculated with a consistent, accurate methodology. Comparison is made between the technologies and between the effects of different operating conditions. A second significant contribution of this work is the development of the model which was used to generate the performance results. These advances allow more detailed comparative analysis of performance data in a wider range of conditions than previously possible.