[jeff5may]

Ok, so I've been studying these "mixed flow ejector" configured systems since you posted in the previous thread that you were considering building one from scratch. It seems the mfr's have two types of these systems in production: one for med/low temp refrigeration (reefer trucks) and one for A/C (passenger vehicles).

The first design looks eerily like a flooded evaporator system, with the ejector feeding the flash tank (sometimes through an evaporator, sometimes not) instead of a level control valve. The evaporator runs at near zero superheat, and discharges into the venturi side of the ejector. Major energy savings is said to be accomplished by supercooling the condenser. Sounds great for low condenser discharge temps (near ambient), but not for heating water.

The second design reminds me of an Acadia cold climate heat pump, only the ejector provides the pressure drop required instead of a second compressor. With the Acadia design, on cold heating days, a compressor of large capacity and designed for R- 134a systems was used to provide added pressure and mass flow to raise condensor output. A cap-tube fed intercooler ran from the discharge line to the intermediate line between the two compressors. The "prius design" has only one compressor, but the similar "intercooler" evaporator runs between the discharge line and the venturi side of the ejector. It serves the same purpose, only in reverse: the superheated gas from the "intercooler" evaporator would increase the effective area of the "main" evaporator.

This looks like it would have great potential for energy savings, especially in your application. At higher water temperatures, the "intercooler" evap would help diffuse the warm stream of high pressure liquid and atomize it immediately. With a near-constant air temp going through the evap assembly, it would not be difficult for an HVAC engineer to optimize the flows through each branch of the suction side. Mechanical metering would be best done with a "subcooling" expansion valve like some of our members are integrating into their present geothermal designs. However, with a digital control circuit, you could use an electronic expansion valve to meter your mass flows, both at the condensor discharge and at the intercooler input. This could result in highly improved COP and capacity if done right.

However, there is great potential in this system to push the main evaporator too hard and flood it. With the intercooler gurgling and/or burping a foggy or foamy mixture into the ejector, it could cavitate or stall if overfed. This effect would domino in the main evaporator, causing compressor slugging without ample accumulator volume. At less violent conditions, the refrigerant would rush through the first portion of the evaporator, ruining heat transfer.

It looks like you might have your homework cut out for you if you pursue this configuration.