Overview of Heat Activated Heat Pump Development Using the E/C Cycle Richard B. Peterson, Tom Herron, Hailei Wang, and Kevin Drost Department of Mechanical Engineering Oregon State University

Motivation and Opportunities  Motivation  Waste heat, or low-grade heat, is often a “free” resource.  Many applications for cooling involve engines with a hot exhaust stream.  Burning fuel releases 10x to 100x the energy contained in batteries.  Current technology (microchannel heat exchangers and inexpensive expander/compressor machinery) is poised for commercial viability.  Opportunities (not an exhaustive list!)  Tactical cooling systems for the military use (current funder)  Automotive air-conditioning in current and new technology vehicles (hybrids). Also RVs, Trucks, Planes, etc.  Chem and bio protection suit cooling for first responders  Combined heat, cooling, and power systems for residential service  Auxiliary power unit (diesel, micro turbine, etc.) add-ons where cooling is needed

Basic Expander/Compressor Cycle Power Cycle Vapor Compression Cycle Condenser Cooling Components QLQL Q out Power Generating Components QHQH Work Motive Fluid Cooling Fluid

Key Technologies – MECS MECS – Microtechnology-based Energy and Chemical Systems  MECS relies on …  High rates of heat and mass transfer afforded by microchannels  Extremely high degree of control of processes  To miniaturize a wide range of systems …  Chemical (reactors, mixers, separators, etc.)  Energy (heat transfer devices, combustors, etc.)  Biological (biosensors, bioreactors, etc.)  Enabling portable and distributed systems

How it Works - Heat Exchangers Why? Large surface area Laminar flow Change in relative importance of phenomena and enables systems integration  e.g. boiling (surface tension)  better thermal management Results in smaller, cheaper, better

Considerations  Use Commercially Available Components Where Possible  Military Systems  Cost is not much of a consideration  Reliability, size, and weight are critical  Non-portable Commercial Systems  Cost is a driver  Reliability is important  Size and weight not critical  Portable (automotive?) Commercial Systems  Size, reliability, and cost are critical  Weight important, how much is driven by specifics

Completed Work – Breadboard Setup Evaporator Flow Meters Vaporizer Pump Dyno Expander/ Compressor

Summary of Breadboard Work  We have demonstrated a prototype expander/compressor operating at 150 W of cooling  Mean device efficiency was shown to be 65-70% at 1500 rpm—adequate to reach a COP of 0.7 at design conditions.  No regenerator was used in the breadboard system.  Follow-on work will include:  Investigate the thermodynamic effects of a regenerator in the power cycle.  Build and test a 2 kW split cycle heat activated cooler.  Build and test a 5 kW combined cycle cooler.

Completed Work – 2 kW System  Split Cycle E/C System  Separate power and vapor cooling cycles  Oil loop used for the power cycle for lubricating the expander  Built from both commercial and semi- custom components  Status  System has been assembled  Testing of the individual components and overall system complete  Performance data shows expander component requires higher efficiency.

Summary  We have demonstrated working systems with promising performance.  Key technology remains in the development phase – an expander with the requisite efficiency.  No regenerator has been used so far in our efforts.  Microchannel component demonstration will be shown on the next generation system.

Next Step – 5 kW System  5 - kW system development is underway with modeling studies and expander development.  System will have a single fluid and a common condenser.  Microchannel heat transfer components will be included in the overall system.  Size, weight, and performance will be key issues to concentrate on.