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Old 04-09-17, 09:56 AM   #41
jeff5may
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OK, so where did that bad boy come from, and how easy or difficult will it be to program? If you can get it tweaked in to your evaporator behavior, it should work really well.

I just had a profound thought: what if you ran an air-source heat exchanger in parallel with your stream bed? On those warmish (not so frigid) days, it could dramatically increase your performance. The EEV wouldn't care.

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Old 04-09-17, 11:24 AM   #42
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Jeff - elaborate on this parallel arraingement.

I am learning a LOT. Keep up the excellent discussion. For example, I had not completely thought out the trade off with larger heat exchangers (more efficient) with losses with turn off and turn on.

If the system is on almost all the time, then the transient inefficiency at turn on and off is minimized, but that means a tough sizing.

If the COP for this NZ system is 4+ then the EER will be spectacular. Knowing the specific area, they have little to no AC load. If you EVER have the chance, you MUST visit NZ. A simply incredible, friendly and beautiful country. Damn if it is a 17 hour flight from the USA to there . . . .

Great discussions between you two!


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Old 04-09-17, 10:47 PM   #43
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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.

Last edited by jeff5may; 04-10-17 at 06:41 AM..
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Old 04-10-17, 12:51 AM   #44
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Hi Jeff , some good ideas there .
I think i will K.I.S.S . May be if i had included a reciever in the design it may of been worth thinking about . With a system that has 2 plates the refrigerant charge is as small as you can get it , there would be a large variation in refrigerant needed for air coil compared to plate. Also oil could get trapped in any shut down part of the suction system . The prices of refrigerant in NZ have gone from $250 for 13kg to $1200 in the last 5 years so the smaller the charge the better.
All correct with your research on the Daikin Jeff , did you find out how much oil was in the compressor ? This took me ages to find , i changed from mineral to poe so i could run the r407f.
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Old 04-10-17, 01:09 AM   #45
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The climate in NZ is mild compared to the extremes that the USA can get. I ran the A/C on the Daikin unit for about 15 days this summer mostly to remove humidity. In winter we only have brief periods of freezing temperatures usually just over night.
If the days are clear and sun shining the house gets passive heating and no heating is needed during the day. Also there is no one home during the week.
The electric plan i am on has a night rate which is less than half of day rate , so i heat my hot water cylinder (300 Litre) , dish washer , clothes dryer and run the heat pump . I dont think that having the daikin out door as alternative hx would provide any benefits as this is when its coldest and in the past the daikin was not providing enough heat.
hope that makes sense.
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Old 04-10-17, 07:20 AM   #46
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OK, so the question of oil control always comes up, along with the "Hey, that's a lot more refrigerant" comment. Let me put this argument in its proper context.

When you are running a supermassive reciprocating piston unit (think Harley-Davidson V-twin or Vortec V6 in size) that has a crankshaft and bearings and unloaders and "stuff", any loss of oil leads to certain violent death in short order. Many of these types of "refrigeration powerplant compressors" split off to dozens of distant evaporators in display cases and/or walk-in coolers, water chillers, office spaces, etc. There are many places for oil to pool in low spots everywhere. Refrigeration load varies drastically over a short time as people come and go, store or office opens and closes, etc. After a certain level of complexity, it makes sense to employ an oil separator and a liquid receiver to keep the extra stuff close to the powerplant.

Residential scroll compressors of your size are teensy in comparison. Unless the compressor ingests enough liquid refrigerant to wet the scroll face, the oil sticks to the scroll (by surface tension in little bitty grooves) by design. Most non-hydrocarbon refrigerants don't dissolve oil very well. I believe the Sky Air units are only designed to split off to a maximum of 4 indoor units. The piping is relatively short between units, and is much smaller in diameter than an industrial sized unit. This leads to higher velocities and less oil stagnation in the nonexistent faraway places. The outdoor unit you took the compressor out of came with 1.5 liters of oil charge, which is a lot more than you will need in your compact unit. Much of that oil stays in the compressor sump.

I found lots of data on the unit here:
https://issuu.com/vietmastec.educati...ta__split-skya

Compressor and oil data is on page 8 of the document.
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Old 05-26-18, 04:55 PM   #47
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Ok guys , ive got this system running as best as it can.
I had a desuperheater before the condenser , i was heating a 300 litre cylinder over night to 65c but the underfloor was not getting up to temp as much as i wanted on cold mornings.
After using coolpack and running the info i had i found i had a massive pressure drop through dsh ( i didnt have a high side service port to attach to before dsh) .
I was using 3kw at 40hz and could not run it any faster as it was near max amps.
I bought a sporlan ORI 6 and cut it in to bypass the dsh , now i can run it on full bypass of dsh and condense at mid 30c .
It will now run 55hz and uses 2.2kw .
COP is between 6.4 at minimum and 4.9 at maximum not including pumping .
So pretty happy with the changes.

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