Absorption-Compression Heat Pump for Space Heating and Cooling Using Organic Fluids
Abstract The combination of compression and absorption technologies can provide heat pumps with high efficiency and a wide operating range. The aim of this research project lies in the development and testing of a gas-fired double effect absorption-compression heat pump working with organic pairs for space heating and cooling. For these applications, the use of suitable organic working pairs makes possible heat pump operation at higher temperature lifts than that of conventional water-lithium bromide systems. In our research, the combination Methanol and Tetraethylenglycoldimethylether (TEGDME) has been selected as working pair. The heat pump is targeted to operate in both cooling and heating modes. Therefore, the basic structure of the heat pump is an absorption-compression double effect cycle for cooling mode, that can be switched to a single effect cycle, in order to achieve the required higher temperature lift for the heating operation. The nominal working conditions for cooling are 5°C at the evaporator and 35 to 45°C at me absorber-condenser. These conditions can be achieved with a double effect absorption-compression cycle. Different solution circuit flow configurations as serial, parallel and reverse flow have been considered. The heating operation of the heat pump aims at a temperature of the useful delivered heat between 45 and 60°C for an evaporator temperature of 0°C. In order to achieve the required temperature lift with an attractive performance (COP in the heating mode higher than unity), the unit should operate as a single effect absorption-compression heat pump. The performance analysis was based on a thermodynamic model considering the equilibrium properties of the working pair and energy and mass balances in the different components. Results in both operating modes have been evaluated in terms of the solution flow rate, the coefficient of performance COP and the primary energy ratio PER. Very interesting performances are found even for high temperature lifts. The serial flow configuration has been selected due to its good performance and technological aspects. This work forms part of the project CLIMABGAS. A prototype of this heat pump is under construction for a cooling power of 20 kW and a heating power of 24.5 kW.