[jeff5may]

Well, I looked up the model number of the Daikin unit and found the compressor inside the unit. It says JT160bc-ye in the parts list. That compressor is rated at 15KW at a COP of 3.2 in air conditioning mode (5C evap / 55C cond / 35C ambient). Rated line power is 4.7KW under these conditions. In high efficiency heat pump mode, the unit should be able to move more energy than 12.5KW.

As to what I was thinking about the parallel setup: the OP stated that his stream bed stays around 10 degC year-round. In the previous rig, he mentioned having to run a -11 degC refrigerant saturation temperature in the evaporator hx to pull enough heat out of the stream bed. That's a pretty large drop, and hopefully the new plate heat exchanger won't need to pull down so far, but it may still need to go below freezing on the saturation temp, depending on both the new plate exchanger and the new stream bed exchanger.

He extracted the compressor out of an air-source outdoor unit, which could be plumbed either DX, being fed refrigerant, or as another hydronic loop, being fed water. When outdoor air temperature is warmer than the stream, this air-source exchanger could be brought online, extracting additional heat from the outdoor air. The EEV would automatically adjust to the increased heat-gathering ability, regardless of the actual plumbing method employed. I would think that the air coil could dig deeper if it were plumbed DX, with a solenoid valve to control refrigerant flow.

I can't remember whether it was Randen or Mejunkhound that ran a system this way between an air-source unit and a closed loop ground source, but it was one of those two. A balance point was calculated, and two parallel circuits were plumbed, with each having a txv to control flow. An outdoor ambient thermostat allowed the air-source unit fan to run above the balance point when heat was requested. It was said to have worked better than expected.