This thesis is concerned with advancing the modelling of indoor air flow and internal surface convection within dynamic whole-building simulation. The path taken is the conflation of computational fluid dynamics (CFD) techniques with dynamic whole-building simulation, with an accurate treatment of the co-dependencies between these modelling domains. Two flow responsive modelling techniques were devised and implemented within the ESP-r simulation program to achieve the research objectives. The adaptive convection algorithm enhances ESP-r's thermal simulation domain by dynamically controlling the simulation of internal surface convection. Empirical methods were extracted from the literature and a new method for characterizing mixed flow convective regimes was created to provide the algorithm with a basis of 28 convection coefficient correlations. Collectively these methods can calculate convection coefficients for most flows of practical interest. Working with this suite of correlations, the algorithm assigns appropriate equations to each internal surface and adapts the selection in response to the room's evolving flow regime. The adaptive conflation controller manages all interactions between the thermal and CFD modelling domains. The controller incorporates the latest turbulence modelling advancements applicable for room air flow simulation and possesses a suite of handshaking and thermal boundary condition treatments. The job of this adaptive conflation controller is to monitor the evolving thermal and air flow conditions in the room and dynamically select an appropriate combination of modelling approaches for the prevailing conditions. The two control schemes implemented to demonstrate the controller make use of a double-pass modelling approach. Each time-step that the thermal domain handshakes with CFD, the adaptive conflation controller performs an investigative simulation to approximate the room's flow and temperature field. Using these estimates, the controller calculates dimensionless groupings to determine the nature of the flow (forced, buoyant, mixed, fully turbulent, weakly turbulent) adjacent to each internal surface. This information is used to select suitable boundary condition treatments for each surface. A second CFD simulation is then performed using the refined modelling approach to more accurately resolve the room's air flow and temperature distribution, and to predict surface convection. In order to protect the thermal domain, a two-stage screening process is used to assess (and where necessary reject) the CFD-predicted surface convection estimates. These adaptive modelling techniques advance the modelling of indoor air flow and internal surface convection within whole-building simulation.

The purpose of the work described here has been to seek methods of narrowing the present gap between currently realised heat pump performance and the theoretical limit. The single most important pre-requisite to this objective is the identification and quantitative assessment of the various non-idealities and degradative phenomena responsible for the present shortfall. The use of availability analysis has been introduced as a diagnostic tool, and applied to a few very simple, highly idealised Rankine cycle optimisation problems. From this work, it has been demonstrated that the scope for improvement through optimisation is small in comparison with the extensive potential for improvement by reducing the compressor's losses. A fully instrumented heat pump was assembled and extensively tested. This furnished performance data, and led to an improved understanding of the systems behaviour. From a very simple analysis of the resulting compressor performance data, confirmation of the compressor's low efficiency was obtained. In addition, in order to obtain experimental data concerning specific details of the heat pump's operation, several novel experiments were performed. The experimental work was concluded with a set of tests which attempted to obtain definitive performance data for a small set of discrete operating conditions. These tests included an investigation of the effect of two compressor modifications. The resulting performance data was analysed by a sophisticated calculation which used that measurements to quantify each dagradative phenomenon occurring in that compressor, and so indicate where the greatest potential for improvement lies. Finally, in the light of everything that was learnt, specific technical suggestions have been made, to reduce the losses associated with both the refrigerant circuit and the compressor.

No description available.

Heat pumps are becoming increasingly popular, but poor electricity generating efficiency limits the potential energy savings of electrically powered units. Thus the work reported in this thesis concerns the development of a range of gas engine driven heat pumps for industrial and commercial heating applications, which recover heat from the prime mover, normally rejected to waste. Despite the convenience of using proprietary engine heat recovery packages, investigations have highlighted the necessity to ensure the engine and the heat recovery equipment are compatible. A problem common •to all air source heat pumps is the formation of frost on the evaporator, which must be removed periodically, with the expenditure of energy, to ensure the continued operation of the plant. An original fluidised bed defrosting mechanism is proposed, which prevents the build-up of this frost, and also improves system performance. Criticisms have been levelled against the rotary sliding vane compressor, in particular the effects of lubrication, which is essential. This thesis compares the rotary sliding vane compressor with other machines, and concludes that many of these criticisms are unfounded. A confidential market survey indicates an increasing demand for heat pumps up to and including 1990, and the technical support needed to penetrate this market is presented. Such support includes the development of a range of modular gas engine driven heat pumps, and a computer aided design for the selection of the optimum units. A case study of a gas engine driven heat pump for a swimming pool application which provided valuable experience is included.

No description available.

This thesis records the design and development of an electrically driven, air to water, vapour compression heat pump of nominally 6kW heat output, for residential space heating. The study was carried out on behalf of GEC Research Ltd through the Interdisciplinary Higher Degrees Scheme at Aston University. A computer based mathematical model of the vapour compression cycle was produced as a design aid, to enable the effects of component design changes or variations in operating conditions to be predicted. This model is supported by performance testing of the major components, which revealed that improvements in the compressor isentropic efficiency offer the greatest potential for further increases in cycle COPh. The evaporator was designed from first principles, and is based on wire-wound heat transfer tubing. Two evaporators, of air side area 10.27 and 16.24m2, were tested in a temperature and humidity controlled environment, demonstrating that the benefits of the large coil are greater heat pump heat output and lower noise levels. A systematic study of frost growth rates suggested that this problem is most severe at the conditions of saturated air at 0oC combined with low condenser water temperature. A dynamic simulation model was developed to predict the in-service performance of the heat pump. This study confirmed the importance of an adequate radiator area for heat pump installations. A prototype heat pump was designed and manufactured, consisting of a hermetic reciprocating compressor, a coaxial tube condenser and a helically coiled evaporator, using Refrigerant 22. The prototype was field tested in a domestic environment for one and a half years. The installation included a comprehensive monitoring system. Initial problems were encountered with defrosting and compressor noise, both of which were solved. The unit then operated throughout the 1985/86 heating season without further attention, producing a COPh of 2.34.

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No description available.

No description available.

Uptake of geothermal heat pump (GSHP) systems has been slow in some parts of the world due to the unpredictable operational performance, large installation space requirement and high installation costs. Therefore, design modification was searched in order to improve the feasibility. With regard to relatively small impact of the construction costs, efficient thermal energy collection was targeted in horizontal ground-loop systems with shallow underground construction. The research started with a sensitivity analysis of the underground heat collection system using computational fluid dynamics (CFD). The results indicated essential design parameters to enhance the performance. Strategies to improve one of the parameters, thermal conductivity of soil surrounding the heat exchanger, were investigated through lab experiments. Subsequently, further design optimisation with the CFD intended to select the most competitive modified design against the existing design. It was discovered that an indication to achieve economic and practical modifications for efficient heat collection was to increase the moisture content of sub-soil up to the optimum moisture content (OMC). Annual operation analysis with the CFD disclosed that additional costs for even simple design modifications could easily worsen the payback period. Consequently, solutions to improve the performance of the GSHP within reasonable payback period were proposed.