A Novel Ground-Source Heat Pump with R744 and R1234ze as Refrigerants

Abstract

The energy-saving potential of heat pump technology is widely recognized in the building sector. In retrofit applications, especially in old and historic buildings, it may be difficult to replace the existing distribution and high-temperature emission systems. Often, historical buildings, especially the listed ones, cannot be thermally insulated; this leads to high temperatures of the heat carrier fluid for heating. In these cases, the main limits are related, on the one hand, to the reaching of the required temperatures, and on the other hand, to the obtaining of good performance even at high temperatures. To address these problems, a suitable solution can be a two-stage heat pump. In this work, a novel concept of a two-stage heat pump is proposed, based on a transcritical cycle that uses the natural fluid R744 (carbon dioxide) with an ejector system. The second refrigerant present in the heat pump and used for the high-temperature stage is the R1234ze, which is an HFO (hydrofluoro-olefin) fluid. This work aims to present the effective energy performance based on real data obtained in operating conditions in a monitoring campaign. The heat pump prototype used in this application is part of the H2020 Cheap-GSHP project, which was concluded in 2019.

State of the Art, Perspective and Obstacles of Ground-Source Heat Pump Technology in the European Building Sector: A Review

“…Several recent studies present low GWP refrigerants for ground-source heat applications. Emmi et al [98] proposed a high temperature GSHP working with CO 2 and R1234ze(E) as refrigerants in a cascade arrangement. Bobbo et al [96] shows the benefit in terms of COP of R454B as R410A alternatives, but, at the same time, the volumetric heating effect reduction applied to GSHPs.…”

Experimental and Simulation Study of the Latest HFC/HFO and Blend of Refrigerants in Vapour Compression Refrigeration System as an Alternative of R134a

“…Van Vu Nguyen et al [30] investigated the performance of six refrigerants, R-1234ze(E), R-32, R-152a, R-290, R-600a, and R-1234yf, in terms of COP, operating pressure, and sensitivity of ejector geometry under different working conditions and found HFC R-152a and HFO R-1234ze(E) performed the best, R-600a was the most favourable, and R-1234yf was compatible with R-290. Emmi et al [31] presented the configurations and monitoring data to study the behaviour of a two-stage heat pump operated with R-744 in the ejector system and secondary refrigerant R-1234ze is used in the high-temperature stage. The study aimed to find out the effective energy performance of the system.…”

New HFC/HFO Blends as Refrigerants for the Vapor-Compression Refrigeration System (VCRS)

“…According to EN 378-1 [7], both HFO refrigerants have a very low level of GWP, at only 4 and 7, respectively. In addition to compressor cycles, HFOs are also considered for operation in other types of refrigeration equipment, such as ejector devices [8,9] or combined systems [10,11].…”