International. A paper recently published by Danish researchers in the International Journal of Refrigeration makes a critical analysis of known approaches to working fluid selection for the design of high-performance heat pump cycles based on numerical models.
The authors have compared different approaches to heat exchanger design and have shown that correcting for compression point temperature differences yielded results closer to the values for an economically optimized solution. This means that further investment must be accepted to allow mixtures to exploit their thermodynamic and economic potential.
The detection method was demonstrated for two case studies that focus on integrating a heat pump to use excess heat from data centers to supply district heating. Both cases assumed a temperature of 25°C at the data center entrance. Case I assumed an output temperature of 50°C, while a lower permissible temperature increase was assumed in server rooms for case II, resulting in an output temperature of 40°C. It was assumed that the required cooling load was 500 kW in both cases.
The two cases analyzed differed according to the temperature of the heat source. Several studies have already described the benefits that can be obtained by selecting working fluids among zeotropic mixtures with the aim of matching temperature profiles with the heat source and heat sink.
In the first case analyzed, the authors found that a zeotropic mixture of 30% propylene and 70% R-1234ze(Z) is expected to improve thermodynamic performance by> 35% and reduce the cost of leveled specific heat by 10% compared to ammonia. In the second case, a mixture of 60% propylene and 40% butane was found to show the best economic performance with an 8% cost reduction and a 30% improvement in COP, compared to the best performing pure fluid.
Based on these findings, it was concluded that zeotropic mixtures have the potential to significantly improve the thermodynamic and economic performance of heat pumps in suitable applications, but require proper cycle design. Suitable applications are applications where a potential increase in performance is expected when using zeotropic mixtures and where the conditions of economic limits remunerate solutions with high thermodynamic performance.
An appropriate design requires designing components based on specific refrigerants to take full advantage of the potential benefits, as evidenced by the suggested selection procedure.
Source: International Refrigeration Institute. - Image: https://es.wikipedia.org
