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Old 04-09-17, 04:40 AM   #1
Stoker
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Default Inverter multi-split with a hydronic zone?

I recently completed my first install of a 2 zone Pioneer multi split in my suite. Painless install. No problems.

I was talking with a close friend this evening about it. He has a little different problem. He's got a 2000 sq/ft shop on a slab with hydronic heat. It is currently heated electrically. (Need I say ouch!).

We began to wonder if it would be plausible that one could take a zone from a similar split unit and plumb it into a brazed plate heat exchanger to heat water.

Without diving into the wiring schematics, I recall that the wiring to the indoor units used 4 wires, black and red are power, green is ground and blue is labeled as S presumably for signal. I suspect this signal is probably a variable voltage value based on how much heat the indoor unit would like to receive. The outdoor unit I expect takes the signal inputs from the indoor units and sets the inverter drive for the appropriate compressor output to cover all the zones.

So, my question is; if an appropriate signal is coming down the blue wire, and the refrigerant goes out hot and returns cold, would the unit know or care if the zone it was supplying was an OEM air handler or a brazed plate heat exchanger?

Second, has anybody tried this?

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Old 04-09-17, 06:05 AM   #2
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Perhaps I should read more and post less. It seems Acuario's thread on controlling a dc inverter machine has a great discussion which goes to the heart of my question.
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Old 04-14-17, 03:30 PM   #3
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So if you have 3 zones calling for heat (or cooling) the inverter just ramps up the compressor enough to supply all 3???
And i suppose each zone has its own eev?
I think its a great question on using 1 zone as hydrionic but the split systems are supposedly really finely balanced.
Did you figure out anything from Actuario?
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Old 04-15-17, 10:16 PM   #4
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What I learned from Acuario's thread is that my assumption about the "s" wire using a variable voltage signal is dead wrong. It is almost certainly a serial data stream. Several guys on that thread are working on decoding and reverse engineering it. If they are successful that will open the door for some beautiful hacks.

I'm currently contemplating a simpler approach involving getting a suitable indoor unit and chopping the evaporator core and fan out of it. Then brazing in a refrigerant to water heat exchanger. This would allow me to use the OEM control card and temperature probes etc. and not have to decipher the language to get the correct function.

Does anyone have thoughts on this approach?
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Old 04-17-17, 08:12 AM   #5
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Before you cut and paste, be sure to take some good readings of the old coil at various operating points - you will likely have to have a close match with the new one. Are you thinking about this in a split system?
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Old 04-19-17, 11:15 AM   #6
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At this point it's mostly theoretical. I'm thinking of trying to find a used 18 to 24K single zone unit to chop into. But ultimately if it would work on a single zone, why not a split unit?
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Old 04-19-17, 04:12 PM   #7
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I think you're right - when you think about it you're doing on a bigger scale what the guys here have done for a water heater - a small window unit with the outside air coupled condenser replaced by 1/4 tubing spiraled around in the heater tank.
Your friend won't need to go up to the water heater temps in his slab so that would make it easier. (and more efficient) Get a big window unit or split unit and have at it. The larger 240v window units are all over the place for free.
And if that works, an inverter driven multi zone coupled to water would be a real accomplishment - maybe even a separate zone & EEV for domestic hot water.
You'd only be worried about matching up the heat exchangers not figuring out how to manipulate the data stream. The inverter keeps the comp. at whatever is required to handle the load of all the zones and the separate eevs respond to their separate thermostats and loads?
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Old 04-20-17, 11:43 PM   #8
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Quote:
Originally Posted by Stoker View Post
At this point it's mostly theoretical. I'm thinking of trying to find a used 18 to 24K single zone unit to chop into. But ultimately if it would work on a single zone, why not a split unit?
The main difference between mini-splits and standard-size split systems lies in the outdoor unit. All standard-sized systems have a liquid and gas line leaving the box. These two lines may or may not have the same pressures in them when the unit is running. There are no metering devices inside the outdoor unit if it is an air conditioner. If it is a heat pump, there is one metering device in the unit, which is matched to run the outdoor heat exchanger as an evaporator. Each indoor unit that is connected has its own metering device (and maybe shutoff valve) if the unit provides cooling. The gas and liquid lines leaving the outdoor can branch out to many individual indoor zones.

In contrast, most mini-split outdoor units contain all of the metering devices. In multi-split units, there is a metering device for every zone that has a connection. The liquid and gas lines in these systems are nearly always at the same pressure. In cooling mode, both lines are at much lower pressure than when the system is in heating mode. The indoor units typically do not have any metering devices in them. In essence, the indoor units always appear as unrestricted runs of straight plumbing to the outdoor unit. Each zone doesn't typically branch out once it leaves the outdoor unit.

This makes a big difference as to what you can connect to a certain system and what you cannot. It also makes a big difference when trying to troubleshoot the system when it isn't working correctly.
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Old 04-21-17, 12:49 PM   #9
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Quote:
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We began to wonder if it would be plausible that one could take a zone from a similar split unit and plumb it into a brazed plate heat exchanger to heat water.
This approach needs to tried by SOMEBODY on a single-head system. Seems to me that a multi-head system greatly multiplies the potential problems.

I think that a key issue to success is whether or not the IDU senses the state of fans and frost, and vane position, etc. and sends that info to the ODU.

In other words if these devices are part of a closed-loop or open-loop system.

It might not be too difficult to determine, prior to hacking into the refrigeration lines...

If you disconnect the fan wire and/or vane actuator, you could test for normal functioning. If everything continues as before, look to see if there is any kind of frost detector... there probably is, maybe in the fins of the IDU HX. If you temporally physically remove that sensor from the fins (do not disconnect electrically) and test for proper operation, you may well be standing in the clear to proceed with your diabolical plan.

The final problem, that should be easy to solve, is the IDU heat sensor. Of course you will want to keep this sensor, or use an equivalent sensor. The next problem will be where to place this sensor to send the relevant info to the ODU. That would be a problem, but should not be too difficult to solve.

With all possible encouragement,

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Old 05-02-17, 03:35 AM   #10
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Pretty much exactly what I was thinking AC.

If the vane and fan use closed loop, that would certainly complicate things, although perhaps the vent just registers open or closed.
Possibly the frost detector probably could be fooled with an appropriate resistance. May be irrelevant as the unit would be for heating only. The IDU heat sensor would preferably be securely insulated on the HX water output line or in a thermo-well.

So next, shopping for an appropriate unit, and finding time.

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