This study reviews gas engine-driven heat pump (GEHP) systems for residential and industrial applications in terms of energetic and exergetic aspects for the first time to the best of the authors’ knowledge. These systems are novel heat pump systems (one of today's promising new technologies). Although the first investigations had been performed at late 1970s, the first merchandized GEHP was produced and introduced in the market in 1985. Gradually, it has become widespread all over the world for various purposes. Main application of GEHPs are for space and water heating/cooling purposes. However, they can be integrated to industrial applications, especially to drying processes. In this study, historical development of GEHP systems was briefly given first. Next, the operation of these systems was described, while studies conducted on them were reviewed and presented in tabulated forms. GEHPs were then modeled for performance evaluation purposes by using energy and exergy analysis methods. Finally, an illustrative example was given, while the results obtained were discussed. In addition, a new project on integration of GEHP systems to food drying processes in Turkey initiated by the authors was introduced. It is expected that this comprehensive study will be very beneficial to everyone involved or interested in the energetic and exergetic design, simulation, analysis and performance of assessment of GEHP systems.

A review of gas engine driven heat pumps (GEHPs) for residential and industrial applications

Linear compressor has no crank mechanism compared with conventional reciprocating compressor. This allows higher efficiency, oil-free operation, lower cost and smaller size when linear compressors are used for vapour compression refrigeration (VCR) system. Typically, a linear compressor consists of a linear motor (connected to a piston) and suspension springs, operated at resonant frequency. This paper presents a review of linear compressors for refrigeration system. Different designs and modelling of linear compressors for both domestic refrigeration and electronics cooling (miniature VCR system) are discussed. Key characteristics of linear compressor are also described, including motor type, compressor loss, piston sensing and control, piston drift and resonance. The challenges associated with the linear compressors are also discussed to provide a comprehensive review of the technology for research and development in future.

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A review of linear compressors for refrigeration

A thermoacoustic generator includes a housing with a thermoacoustic core supported in the housing. The core is operable to introduce acoustical power into the housing to thereby oscillate the pressure of the gas in the housing at a frequency. A piezoelectric alternator is also supported in the housing and has a face that is movable when acted on by the acoustical power. The alternator includes a portion of piezoelectric material operable to produce electrical power when acted upon by a stress. The piezoelectric material is in mechanical communication with the movable face so that movement of the face stresses the piezoelectric material. The alternator has a moving mass that serves as a substantial portion of the resonating mass inside the housing, thereby providing a pressure oscillation frequency in the housing substantially lower than for a similar system with a rigid member replacing the alternator.

Thermoacoustic piezoelectric generator

Power-to-Gas integration in the Transition towards Future Urban Energy Systems

Reciprocating compressors, driven by induction motors through a crank mechanism, have been commercially used over many years for refrigeration. An oil-free linear compressor driven by a moving magnet motor was designed, for a refrigeration system with a compact heat exchanger. Measurements using nitrogen are reported here to compare the motor performance and overall efficiencies of the two types of compressor with comparable design parameters. The experimental results show that the moving magnet linear motor has a much higher motor efficiency than the conventional induction motor, particularly at low power inputs. However, with a much smaller clearance volume (approaching zero), the crank-drive compressor demonstrates a higher volumetric efficiency based on the swept volume, that is approximately 20% higher than the linear compressor when operated at its maximum stroke (13 mm). It is anticipated that with a revised design, the overall performance of the linear compressor could be enhanced further.

/pdf/comparison-between-a-crank-drive-reciprocating-compressor-4okdhb4y63.pdf

Comparison between a crank-drive reciprocating compressor and a novel oil-free linear compressor

A linear electrodynamic machine is disclosed having non-axisymmetric, interdigitating interfaces between moving and fixed magnetic circuit elements. The moving magnet elements may be of permanent magnet or electromagnetic construction, and in one embodiment constitute low reluctance elements moving relative to fixed energizing and output coils. Magnetic elements on a reciprocating plunger couple to fixed elements of a magnetic circuit in an interdigitating manner. Alternators and motors with non-axisymmetric, interdigitating interfaces are disclosed.

Linear electrodynamic machine

HOTS to WATTS - The FPSE linear alternator system re-invented

This paper describes recent results in a project at KUBOTA to develop an efficient CFC-free multifunctional heat supply system. A heat pump in the system is a gas engine driven Stirling heat pump. The heat pump is mainly driven by engine shaft power and is partially assisted by thermal power from the engine exhaust heat. By proportioning two energy sources to match the heat balance of the driving engine, this heat-assisted Stirling heat pump can be supplied with the maximum share of the original energy fueling the engine and can be operated at the most efficient point. The authors have developed a system heat pump composed of 6 cylinders, the doubled E-3 prototype. This prototype uses helium gas as a working gas and is constructed as two sets of three-cylinder machines, each a combination of two Stirling sub-systems (one a power producer and one a heat pump). Design and performance simulations of the prototype are presented in conjunction with the driving engine characteristics. This heat supply system is expected to produce cooling and heating water at high COP. Developing the system will provide a CFC-free thermal utilization system technology that satisfies both wide heat demands and various fuel systems.

Performance characteristics of a gas engine driven Stirling heat pump

This paper describes recent results in a project at KUBOTA to develop a gas engine-driven Stirling heat pump using both engine shaft power and engine exhaust heat source. The design, simulation and test results of the third prototype three-cylinder machine (C-3) are presented. The three-cylinder machine is modeled as a combination of two Stirling sub-systems, one a power producer and one a heat pump. These have been separately optimized then joined into the three-cylinder heat-assisted heat pump case. Shaft power is augmented by thermal power. Performance is effectively controlled by the phase shifting of the third piston to adjust the absorbing of thermal power. The test results of the C-3 prototype machine are given and are shown to compare well with predictions made in the Sage simulation code.

Design, simulation, and test results of a heat-assisted three-cylinder Stirling heat pump (C-3)

This paper describes a method for analysis and optimization of multi-cylinder regenerative machines. The authors have devised the method in a project at KUBOTA to develop an improved gas engine-driven heat pump using both shaft power and exhaust heat sources. Based on combinations of included Stirling cycles, this analytical approach allows use of well-established and validated Stirling simulation models to optimize partial systems. The technique further provides a method of integrating such optimal partial-system Stirling cycles into a complex combination system. It is shown that this remains an optimum solution for the three-cylinder fire assisted heat pump case. Results from hardware tests of the main Stirling heat pump cycle (2-cylinders) are given and compared with analytical expectations using the Sage simulation code. This is extended to validate Sage modelling of 3-cylinder machines.

J. Corey

Papers

Linear electrodynamic machine

HOTS to WATTS - The FPSE linear alternator system re-invented

Performance characteristics of a gas engine driven Stirling heat pump

Design, simulation, and test results of a heat-assisted three-cylinder Stirling heat pump (C-3)

An analytical approach to multi-cylinder regenerative machines with application to 3-cylinder heat-aided Stirling heat pump