Thermal analysis of combined Organic Rankine-Vapour compression system forheating and cooling applications

[摘要] Climate change due to global warming is a matter of major global concern. Greenhouse gases emissions are a key culprit in this process. It is therefore important to reduce energy consumption in order to protect the environment. The decarbonisation of the heating sector would have a significant positive impact on the environment. A wide range of heating technologies have been investigated and developed, such as gas boilers, electric restrictive heaters, heat pumps (HP), and others. In order to reduce fossil fuel consumption and greenhouse gas emissions, researchers have focused on improving the performance of the existing technologies as well as on developing new fuel-efficient systems such as cogeneration and trigeneration cycles. These integrated technologies allow the production of multi-mode energies including heating, cooling, and/or mechanical power from the same primary energy source. The energy source can be a fossil fuel, or renewable energy such as solar, geothermal, biomass or wasted heat. Waste heat utilization (from a data centre, internal combustion engine, chamber exhaust stream, etc.) also has the potential of enhancing the system performance by reducing fuel consumption.In this thesis, an innovative gas fuelled heating system based on a combined heat engine and its reverse heat pump cycle is proposed and investigated. This system consists of a gas burner, an organic Rankine cycle power generator, and an air source heat pump vapour compression cycle. For the theoretical analysis, in-house MATLAB code is developed, and the steady state results are compared with the results acquired from ASPEN PLUS as a benchmark. Both software programs use REFPROP as the database for working fluid thermophysical properties. In order to identify a suitable working fluid for each cycle, a comparative study on various working fluids was initially carried out. The selection of refrigerant was based on performance and environmental safety profile. The proposed cycle is designed for domestic hot water supply and utilizes gas burner flue gases and ambient air to enhance the system overall fuel to heat efficiency while maintaining the heat pump cycle in a frost free state at low ambient temperature. The combined cycle shows promising performance, with a fuel to heat efficiency of 136%. However, the results also show that ambient air temperature fluctuations can have a significant impact on the combined system’s performance. To tackle this, various control strategies are proposed and investigated. Also, a dynamic model has been built using ASPEN PLUS software to simulate and validate the control strategy.

[发布机构] University:University of Glasgow;Department:School of Engineering

[关键词] Combined heat pump and ORC cycles, heat recovery, dynamic modeling, heat pump water heater, domestic hot water, data center cooling with central heating, diesel engine waste heat recovery for refrigeration.