Ericsson Cycle Heat Engine

About

Summary A revolutionary Ericsson cycle heat engine was developed through an Innovate UK Energy Catalyst R3 Feasibility Study. This proof of concept showed what is possible for the system as a heat pump and external heat engine. The system is now being developed as a micro-Combined Heat and Power system in as part of a three-year development program. The unique geometry and dynamics of the system will allow a new level of performance in heat pump applications such as both mobile and fixed refrigeration, coolers, and air -conditioning. As an external heat engine, applications include low grade waste heat, mCHP, mCSP, and generators. The unique geometry with an unsurpassed heat exchange are to volume ratio allow compression and expansion to approach isothermal heat exchange. The simple system has only four moving parts with motor-generators directly driving the rotors. This arrangement eliminates mechanical drive elements and allow full control over the cycle, allowing a greatly increased operating range. Project Status The one-year Innovate UK project came to an end in November 2016 with the most basic of systems confirming the feasibility of the concept. The concept is to first be developed as an external heat engine version as a mCHP system being developed. This 3-year EPSRC project will continue development to include extensive thermodynamic modeling of the system and rotor dynamics. While this system is aimed at mCHP parameters, the same system will be used to demonstrate capabilities as a low-grade waste heat to power system. Concurrent development as a heat pump system is being coordinated at this time, allowing the system to be demonstrated as a small fixed refrigeration system with applications for small commercial units and mobile refrigeration systems. This development will also include motor-generator system optimized for this application, increasing efficiency and greatly reducing the end product cost of the system. Description The Ericsson cycle, in its ideal form, achieves Carnot efficiency, the higher physically possible of a machine/system. While the Ericsson system was developed in the 1800’s, few examples have been made since the cycle requires the complication of valves. The systems that were made proved superior, yet steam turbine and then internal combustion engines became prominent – although much less efficient. The Stirling cycle system was developed about the same time as the Ericsson, and has seen examples throughout the years. It is similar to the Ericsson in that, in the ideal form, can achieve Carnot efficiency and is a closed cycle system, using benign fluids such as nitrogen, or H2, He. Most important, the cycles are reversible, meaning they can operate as heat pumps and as external heat engines. Unfortunately, the Stirling systems include many technical issues and require high cost materials, making their efficiency and commercial success very much less than the ideal potential and unviable for most markets. The developed Ericsson system uses two pair of rotors, creating a valve-less system of compressor and expander, connected by a simple counter flow heat exchanger. This system overcomes all of the pitfalls of the Stirling concept and development shows will be about 30% more efficient than current system. Being a reversible cycle, the system will be applicable to <10kW heat engine and heat <5kW heat pump applications. The commonality between the heat pump and heat engine systems allow low cost, concurrent, low cost development since the two directions of the cycle share greater than 90% in in development and engineering. Most important is the fact that this system does not require HFC’s, the fastest growing and most damaging of greenhouse gases. With wide deployment of this HFC system in the incredibly fast-growing air conditioner and refrigeration markets will have a major global warming reduction impact. Innovative Aspect The concept is truly revolutionary, using proven elements in a completely new geometry and dynamic system. The two primary aspects, both coved by granted and newly field IP, are the unique geometry and the method of driving the rotors. The geometry allows significantly greater heat exchange than other systems, as well as a valve-less design, greatly simplifying the system. The driving of the rotors directly with motor-generators allows the complete elimination of mechanical linkages for a system with truly only four moving parts.  These new aspects are combined with very efficient heat exchange additive manufactured compressor/expander chambers and recuperator (a simple counter flow heat exchanger) to create a system that is highly efficient, simple, and reduces to a low cost commercial unit. Benefits The system is applicable to heat pumps <5kW and external heat engines <10kW. In all of their incarnations, these are incredibly large market, almost of of which are dominated by systems that require HFC’s as their working fluid. This combined with a simple, low cost system that is 30% more efficient than current systems can have a monumental positive green impact. HFCs, in accordance with the Montreal Treaty, must be eliminated. This creates a unique market opportunity. This is shown by the UC Berkeley report: estimate that shifting the 2030 world stock of room air conditioners (<3kW) from the low efficiency technology using high-GWP refrigerants to higher efficiency technology and low-GWP refrigerants in parallel would save between 340-790 gigawatts (GW) of peak load globally, which is roughly equivalent to avoiding 680-1550 peak power plants of 500MW each. This would save 0.85 GT/year annually in China equivalent to over 8 Three Gorges dams and over 0.32 GT/year annually in India equivalent to roughly twice India’s 100GW solar mission target. Similar numbers can be derived for small refrigeration systems, as well as smaller scale impacts of other applications. While it is realized that the system as it is developed from feasibility system to market demonstration, to actual commercial product may not be commercially viable for all possible markets, the wide possibilities insure a large impact of some size. Markets include: Small air conditioners, small fixed refrigeration systems, mobile refrigeration systems, mCHP, mCSP, Ground Source Heat Pump, Air Source Heat Pumps, low grade waste heat system, etc. All of the listed systems require HFC, which must be eliminated. The impact of the system is twofold: helping to eliminate HFCs and delivering a system that is approximately 30% more efficient than current systems, all in a simple, so cost package.