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Acuario 07-24-15 01:17 PM

Split indoor unit as fancoil heater/cooler
I was just thinking about improving the heating/cooling in one of our rooms without under floor heating.

As the cold water feed for the under floor (cooling in summer :)) is common to all the rest of the radiators in the house (which are aluminium) it occurred that a fan coil unit would be ideal to replace the radiator - simply add power and a way to drain the condense.

Then I got to thinking - I have a pile of ex indoor units from splits sitting around - they have all the required elements - fan, heat exchanger, condense tray and even a remote control.

The indoor units on conventional splits are usually the 'brains' of the system, the outdoor unit being controlled by the indoor unit. I powered up an old unit and it sprung into life, a head with no body, but is happy to be there pretending to control the non existent outdoor unit.

So where is the catch - I guess it is in the tubes - small bore aircon tubes won't have much volume of water passing through them but would it be enough???

Has anyone out there dipped their finger in this pie and tried it out?


Acuario 07-26-15 02:40 AM

8 Attachment(s)
So maybe no one has tried - anyway I think I may have answered my own question - I really think the volume of water passing would be too small so a 'minor' modification is in order....

I removed the heat exchanger from the internal unit to see how it is configured.

12 loops interconnected to form two circuits, one feed split in the middle (the 3/8" tube) and re-combined by a T connected to the 1/4" tube.

Perfect - disconnect the links at the end where the tubes connect and make 6 individual circuits using 1/4" tube then re-combine them into one.

Next fit the heat exchanger back into the case..

Then cut the tubes to length and combine them into one 15mm tube - the connecting coupler is an 18mm to 15mm reduction.

...unfortunately the case got a bit hot but not to worry as this won't be seen...

Next to test it out....


Acuario 07-26-15 04:40 AM

Well I connected it up to a temporary cold water feed, powered it up and away it went - lovely cool air, dropping the air temperature some 5C with water at 19C entering. The air temperature drops from around 26C entering to 21C leaving the unit.

Next step, remove the radiator, plumb in the unit and a pipe for the condense.


jeff5may 07-26-15 09:47 AM

Super awesome mod! I don't think you can make a warranty claim on this one any more.:D To the manufacturers, there is no such thing as a minor mod.

Please enlighten us on the model and capacity ratings of the original indoor units. The mod looks very straightforward and promising. These mini-split units are beginning to hit the second-hand market en force in America, mainly due to the tug of war between the old school installers and the new wave of products. Most "seasoned" installers see the ductless units as toys compared to a full split system. When service is required, the owners get sold out of their mini-split, no matter what is actually wrong...

There is next to zero data on stuff like this, so any measurements you could produce as to operating conditions and effectiveness would be more gold from your effort. As always, many of us will be inspired by your work. Other, similar endeavors will follow.

Acuario 07-26-15 10:49 AM

Glad you like the mod...

The original unit was a fairly generic, probably badge engineered Chinese unit. The actual name/model was a Rainbow Electronics JS3210AH, 12000btu, R22 refrigerant and the indoor unit has an air capacity of 530M3 per hour.

I would imagine that almost any of these mini splits could be modified to work as a fan-coil. Most have little or any connection with the operating conditions of the external unit, at most they may have a wire that goes to a sensor on the evaporator, in the case of this machine it didn't even have that. Most just have power feeds to the compressor, fan and 4-way valve so they should work happily when disconnected from the outdoor unit.

The challenge is more a mechanical one than anything else, you need to make sure the bundle of pipes doesn't foul the existing electronics or motors as normally there are only 2 pipes leaving the unit. In this case I was fortunate as there was quite a bit of space.

You also need to know how to braze. Grouping the 6 x 1/4" tubes together wasn't too bad - I did slightly flange the 18mm reducer and slightly crushed the 1/4" tubes and that made it easier to insert them. To flange it out I used a narrow socket from a socket set and hammered it into the fitting, the shoulder on the fitting created the flange.

Brazing the tubes and sealing the pipe took a couple of attempts (hence the overheated case!). I checked it was all sealed by pressurising it with nitrogen.

At the moment the unit is hanging on my boiler room wall ad the cold feed isn't that cold but it was sufficient to do some basic proof of concept tests.


Daox 09-09-15 09:21 AM

Great project Acuario! I missed this one first time around.

Are there any updates on it?

Acuario 09-09-15 12:37 PM

Not yet - it's still hung on the wall in my workshop. I'll probably fit it somewhere during the autumn when I get a couple of free days.

Currently I'm working on several controllers for the solar heating, hot water and heat pump using Arduinos, a Raspberry PI and MQTT (maybe throw in an ESP8266 at some point too) along with refurbishing an 85 sq metre flat and the day to day job.....

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