Absorption heat pump cycles with NH3 – ionic liquid working pairs

Carlos A Infante Ferreira,Meng Wang

doi:10.1016/j.apenergy.2017.07.074

Carlos A Infante Ferreira, Meng Wang

Open Access

https://doi.org/10.1016/j.apenergy.2017.07.074

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Journal: Applied Energy	Publication Date: Aug 7, 2017
Citations: 68	License type: cc-by

Affiliation: Delft University of Technology

Abstract

Ionic liquids (ILs), as novel absorbents, draw considerable attention for their potential roles in replacing water or LiBr aqueous solutions in conventional NH3/H2O or H2O/LiBr absorption refrigeration or heat pump cycles. In this paper, performances of 9 currently investigated NH3/ILs pairs are calculated and compared in terms of their applications in the single-effect absorption heat pumps (AHPs) for the floor heating of buildings. Among them, 4 pairs were reported for the first time in absorption cycles (including one which cannot operate for this specific heat pump application). The highest coefficient of performance (COP) was found for the working pair using [mmim][DMP] (1.79), and pairs with [emim][Tf2N] (1.74), [emim][SCN] (1.73) and [bmim][BF4] (1.70) also had better performances than that of the NH3/H2O pair (1.61). Furthermore, an optimization was conducted to investigate the performance of an ideal NH3/IL pair. The COP of the optimized mixture could reach 1.84. Discussions on the contributions of the generator heat and optimization results revealed some factors that could affect the performance. It could be concluded that the ideal IL candidates should show high absorption capabilities, large solubility difference between inlet and outlet of the generator, low molecular weights and low heat capacities. In addition, an economic analysis of the AHP using NH3/[emim][SCN] working pair with plate heat exchangers was carried out based on heat transfer calculations. The results indicated that the NH3/IL AHP is economically feasible. The efforts of heat transfer optimization in the solution heat exchanger and a low expense of ILs can help the IL-based AHP systems to become more promising.

Highlights

The Paris Agreement adopted by 195 countries in the 2015 Paris climate conference (COP 21) reset the global ambition: limiting the temperature rise from pre-industrial levels well below 2 K
4 pairs were reported for the first time in absorption cycles
An optimization was conducted to investigate the performance of an ideal NH3/Ionic liquids (ILs) pair

Summary

Introduction

The Paris Agreement adopted by 195 countries in the 2015 Paris climate conference (COP 21) reset the global ambition: limiting the temperature rise from pre-industrial levels well below 2 K. Efforts responding to climate change are accelerating the way the energy sector is developing [1]. Especially for buildings take up the majority of the energy consumption and the greenhouse gases emission. According to the European Commission, heating and cooling consumed 50% (22.85 EJ) of the final energy consumption in the EU in 2012. 45% of energy for heating and cooling in the EU was used in the residential sector, 37% in industry and 18% in services [2]. In the US, 41% (42.2 EJ) of the primary energy in 2010 was consumed by the buildings sector, compared to 30% by the industrial sector and 29% by the transportation sector. Heating and cooling took 59% of the buildings energy consumption [3]. As an increasingly significant energy consumer in the buildings sector, China is the largest energy-consuming economy in the world, and buildings energy used in China was the second-largest in the world after the US, representing nearly 16% of total global energy consumption in buildings in 2012 (more than 18 EJ) [4]

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