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Old 03-15-11, 03:31 PM   #1
AC_Hacker
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Default Air Source Heat Pump (ASHP) Hacks & Mods

For those who are trying (or want to try) to DIY their own ASHP, or to mod an existing ASHP.

Refrigerant mods, Air-to-Water mods, etc. have a home here.

-AC_Hacker

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Old 03-16-11, 01:00 AM   #2
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I have some questions:

While poking around at a scrap metal yard a few months ago and I saw a mini-split A/C unit waiting to be hauled off. It was the outdoor part (compressor, radiator, electronics, and all that) of a Sanyo SAP-CR224EHA and looked intact.
I didn't take it since I wanted to ask what you guys thought about it first, then winter came, and a bunch of other stuff got me distracted, so it's long gone by now.

So why would a mini-split be at a junkyard? I mean, what could be broken and how hard would it be to fix it? What is usually the first thing to cause problems in mini-split units? And when is it feasible to grab one? (Remember that I'll have to justify any expenses to the Wife.)

The electronics? If so, is it possible to ditch the controller and force the unit to work, maybe swap a controller from another unit or make my own?

Or maybe there was a coolant leak? Are those hard to find and repair?

Compressor fault? Are compressors hard to fix, or maybe replace? Would it be possible to swap it for a compressor from a smaller model, and would that make it more efficient?

Also, can the indoor part of a mini-split be from a different model? Would taking it from a larger model increase efficiency?

There is also the slim chance that the unit is OK and was thrown out only because it had been replaced with a different model.

I'm asking all these questions so that I recognise a deal next time I see one.

BTW That scrap metal yard had some random A/C parts, too. Like Big radiators which would work great as heat exchangers in other projects.
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Old 03-16-11, 02:17 PM   #3
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Quote:
Originally Posted by Piwoslaw View Post
I have some questions:

While poking around at a scrap metal yard a few months ago and I saw a mini-split A/C unit waiting to be hauled off. It was the outdoor part (compressor, radiator, electronics, and all that) of a Sanyo SAP-CR224EHA and looked intact.
Here are some specs on the unit...


What you had there was a medium power unit, that could probably be made to work.

That unit was about the size of Xringers Sanyo.

Most likely, the controller was at fault.,

That unit was 3-phase, aprox. 400 volt.

Had a single speed compressor, so the controller would be pretty straight forward.

Quote:
So why would a mini-split be at a junkyard? I mean, what could be broken and how hard would it be to fix it? What is usually the first thing to cause problems in mini-split units? When is it (Remember that I'll have to justify any expenses to the Wife.)
Most likely, the controller failed. It is possible to build another one. I find it much simpler to work with single phase.

Quote:
And when is it feasible to grab one?
When you undertake something like this, you have to be calm, you have to be sober, and you have to meditate upon the idea that your wife might be much smarter than you are.

After you have done all that, then it is feasible.

Quote:
The electronics? If so, is it possible to ditch the controller and force the unit to work, maybe swap a controller from another unit or make my own?
Yes to all of the above.

Understand what you are doing before you try to force a compressor to work. I do it all the time, but I am extremely attentive to detail and danger when I do it. I check the wiring several times before I turn on power, and I am ready to cut power in a split second if required.

In the USA the compressors have a "LRA rating" (Locked Rotor Amps). This means that if the compressor locks up, it will draw an amount of power equal to LRA (for instance 36 amps). So you will want to make sure that the breaker for the AC circuit is less than 36 amps, like 30 amps.

You really want some kind of time delay, as I mentioned elsewhere, to protect your compressor, when it is in normal use.

Currently, I am temperature regulating my GSHP with an AC line level thermostat. When the temp goes too high, a micro-switch cuts power, when the temp goes too low, power goes on. Very reliable, simple and cheap ($1, used).


I want to replace the line-level thermostat with a microprocessor that also has the delay, and other functions, but line AC thermostat is fine for now.

Quote:
Or maybe there was a coolant leak? Are those hard to find and repair?
You need a complete circuit that you can pressurize with nitrogen or CO2 or some other inert gas, then get some soapy water and start looking for bubbles.

Once you find the leak, you'll need to braze it. so, you'll need a brazing setup.

You want inert gas inside the unit, but not under too much pressure, otherwise the inert gas escaping, will create an tiny pin-hole leak that is pretty hard to see, except with bubbles.

Quote:
Compressor fault? Are compressors hard to fix, or maybe replace? Would it be possible to swap it for a compressor from a smaller model, and would that make it more efficient?
Compressors are very reliable. The cap usually goes first.

But if you tried to force the compressor to start, and you KNOW that you did it correctly and it didn't work, buy a new cap. If that hasn't fixed the problem, don't try to repair it. You might want to cut it open to see how it works but, other than that it only has scrap value.

Yes, you could go with a smaller one, I would try to stay close to the same size, not go under 50% of the original.

Quote:
Also, can the indoor part of a mini-split be from a different model? Would taking it from a larger model increase efficiency?
Probably increase COP some. Try to stay close, as above

Quote:
There is also the slim chance that the unit is OK and was thrown out only because it had been replaced with a different model.
Quite possibly so. The newer variable-speed units are more efficient (and tougher to hack).

Quote:
BTW That scrap metal yard had some random A/C parts, too. Like Big radiators which would work great as heat exchangers in other projects.
... I think you are standing at the door to insanity, but we are here to pull you through!

If you buy something like that mini-split, you need to be of the mind that you may get nothing out of it but an education... That way, if you fail to get it working, it is not a total loss, and you may still be able to use some of the parts. You may want to keep this all in mind as you decide what you are willing to pay, too.

I don't know if you have any experience with HVAC or not. I would suggest starting with something much smaller and working up.

I would suggest a smaller single phase R-22 AC unit (R-290 compatible), you'll have plenty to learn about, believe me.

Remember to keep the metering device (cap tube or TXV) with the compressor, that will make the rest much easier.

You will also need to borrow or make or buy a really good vacuum pump and a refrigerant recovery unit.

You might be able to make these out of smaller AC compressors. Look around on the web, it's been done before.

Best Regards,

-AC_Hacker
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Old 03-17-11, 01:42 AM   #4
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Thanks AC
You're right about starting with something simple, so I'll look for small, single phase units, maybe a freezer compressor.

I'll add that European law forbids taking appliances apart. Not only A/C's or refrigerators, but even washing machines and toaster ovens I'll just have to keep quiet about any heat pump projects I dive into...
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Old 03-17-11, 12:48 PM   #5
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Quote:
Originally Posted by Piwoslaw View Post
Thanks AC
You're right about starting with something simple, so I'll look for small, single phase units, maybe a freezer compressor.
For this kind of experimenting, a compressor from an air conditioner or de-humidifier would probably work better because they are designed with the assumption that they will be running a high percentage of the time. If you have a freezer compressor or can get one free or cheap, use that of course. This is experimenting, after all.

Keeping the cap tube with the compressor will really save you a lot of heart ache and hassle. The cap tube will be balanced to the compressor's output and also the type of refrigerant.

The older refrigerants, R-12 and R-22 used mineral oil as a lubricant, which would be compatible with Iso-Butane and Propane, respectively. Mineral oil would not be compatible with R-134a, and the cap tube would probably be mis-sized for R-134a, also. However, the cap tube would be just about perfect for Propane (due to the similarity in the PT curves for both gasses). I'm not sure if the PT curves are similar for Iso-Butane and R-12.

So, the short story is that compressors meant for R-22 can be very easily switched to Propane, which is cheap and available. But great caution must be used when working with the stuff.

Quote:
I'll add that European law forbids taking appliances apart. Not only A/C's or refrigerators, but even washing machines and toaster ovens I'll just have to keep quiet about any heat pump projects I dive into...
Quietness is next to Godliness...

-AC_Hacker
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Old 05-14-11, 01:38 PM   #6
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Default Pool heater using recycled air conditioner

Ok, so here is my experience in this thread as suggested by AC Hacker.

At the beginning of the year I decided to heat my swimming pool. I had it covered last year to allow me to use it longer but I then decided it might be an idea to try to use it all year so I looked around to see what was available and came across heat pumps. As I've spent the last few years installing split air conditioners I had all the tools I needed but had never even tought about using an air conditioner to heat water, so I started investigating.

The commercial units are quite expensive and I love a challenge. Someone I knew was selling an old air conditioner for 30 euros so I bought it without knowing anything about how it might be made to heat the pool.

A bit more investigation and lateral thinking and finding out how air conditioner/heat pumps worked and I came up with a plan.

The condenser is in the unit; cut the pipes and 're plumb' the pipework to take direct from the compressor out through a 3 port valve and to an external heat exchanger (the new condenser) , back via another valve and through the capillary and into the condenser (which now has becomes the evaporator) and from the 'new' evaporator back to the compressor. The condenser has two circuits through it that are linked at either end. The liquid end I left but the gas end I cut and braised to feed the two tubes into a 1/2" tube to connect back to the gas side of the compressor.

MK 1 heat exchanger was interesting. I built it from a piece of 90mm soil pipe, 50mm connections on either end for the pool water and with a wound coil inside to take the refrigerant. I had no idea how long it would need to be so as I have limited space I just made it to fit the space which is about 90cm.

To elaborate on the heat exchanger construction, there needs to be 2 connections either end, one for water and one for refrigerant. Water is easy enough as pools are usually piped with 50mm pipe and it can all be glued together to provide a water tight seal. The refrigerant pipes, however, have to pass through the end caps and have a watertight seal. My solution to this was to buy a tank connector - is that what they are called? Basically it is a threaded tube that has a flange on one end and a set of washers and nut. You drill a hole in the tank (in my case the end cap) and the flange plus washers provide a watertight seal. If you look at the 1st and 4th photos on the second row of photos on my website (see address below) you'll see the end caps and tank connector. The refrigerant pipe passes through the middle of the tank connector and the gap is filled with solder. The whole assembly is then inserted into the main body of the heat exchanger, glued up and the nut tightened down to create a seal.

Commercial units seem to have titanium heat exchangers but I have no source of titanium pipe so it's copper. I was aware of the potential problem of corrosion but I've been pumping chlorinated water through copper solar panels for several years without problem. It all depends on pH values! To be on the safe side I have a piece of pipe in the filter basket of my pool pump - so far it shows no sign of anything adverse.

The original unit had R22 as the refrigerant but this is now
  • Banned for use in any new project or machine
  • Almost impossible to buy from anywhere to charge or refill a unit

Following a mini disaster I had with MK2 heat exchanger I was forced to use a drop in replacement and I opted for RS-44 as you don't then need to change anything and the PT is pretty similar to R22.

I've written some (not all yet) of it up with photos of the project on my website http://www.tortosaforum.com/poolheater.html that describes how I modified the air conditioner and built MK1 and MK2 heat exchangers to heat the pool.

I have no idea what the efficiency of the units is but they do heat the water really quickly! Maybe I'll try and work it out sometime as I'd love to know.

As a suggestion to anyone looking to try something similar, go for a conventional single phase compressor as you then don't need any control circuitry. The newer generation of inverter machines use brushless dc motors (bldc) which have complex control systems to vary the speed of the compressor motor. I'm might try one of these out at some point but for the moment I'm sticking with a basic unit as my projects don't need that level of control.

Nigel

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Old 05-14-11, 04:12 PM   #7
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Nigel,

Thanks again...

I spent a few minutes on ebay and I found more than a few single speed units similar to yours for sale pretty cheap. They were more than 30 euros, but still pretty cheap.

Quote:
Originally Posted by Acuario View Post
The condenser is in the unit; cut the pipes and 're plumb' the pipework to take direct from the compressor out through a 3 port valve and to an external heat exchanger (the new condenser) , back via another valve and through the capillary and into the condenser (which now has becomes the evaporator) and from the 'new' evaporator back to the compressor. The condenser has two circuits through it that are linked at either end. The liquid end I left but the gas end I cut and braised to feed the two tubes into a 1/2" tube to connect back to the gas side of the compressor.
This part is pretty interesting. A drawing or photo would help perhaps...

So on your first try, did you use the existing cap tubes? I'm assuming there were cap tubes, anyway... if you did use cap tubes, did you use them 'as is' or did you change the length any?

Thanks,

-AC_Hacker
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Old 05-14-11, 09:50 PM   #8
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Default Wow!

Nice work! I've got a broken (leaks) 24,000 BTU unit and have been thinking of using it with an Ebay heat exchanger.
24KHS72 - Sanyo 24,200 BTU Wall Mount Heat Pump Air Conditioner Kit
Want to make some domestic hot water.. (Hate burning oil for showers etc).

It's somewhat modern, but I may be able to use the Test mode jumper, and force it to run.
http://i46.photobucket.com/albums/f1...L/Fall2010.jpg

Your pool heating project has give me some fresh ideas..

Thanks,
Rich
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Old 05-14-11, 10:14 PM   #9
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Default Driving brush-less compressor and fan motors??

If you find a mini-split with a burned out controller board, could you
get the motors to run with hacked model airplane speed controllers?

In recent years, RC model airplanes have been using brush-less motors.
I know hardly anything about this type of motor, but I'm wondering
if there is any possible way to use an RC model ESC (Electronic Speed Controller)
to control larger brush-less motors? Maybe adding some power FETs to the
3 motor drive wires? Inserting more amps and volts.?.



TowerHobbies.com | Shop by Category: Radio Speed Controls - Brushless Motors - Aircraft


ESCs are controlled the same as airplane servos, with a simple TTL pulse.
The length of the pulse is what sets the speed.
Maybe a simple micro controller could be used to simulate the OEM mini-split controller.?.


Ideas??
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Old 05-15-11, 01:43 AM   #10
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Quote:
Originally Posted by AC_Hacker View Post
This part is pretty interesting. A drawing or photo would help perhaps...

So on your first try, did you use the existing cap tubes? I'm assuming there were cap tubes, anyway... if you did use cap tubes, did you use them 'as is' or did you change the length any?
There are photos of before mods and after mods on my website, the top row of photos show the unit before and after. It was a 'plumbing' exercise really to move the evaporator to the return side of the compressor rather than the flow. A/C heat pumps have a changeover valve that does the job for you (as has my second unit) so you only need to energise the solenoid to achieve the same result. As my first unit was cooling only I had to manually swap it around.

In the second unit I haven't changed anything as it was designed for heating so the capillary tube is correctly balanced to the system and it seems to be performing well with no overheating or excessive temperatures or pressures.

In the first unit I originally used the capillary tube but had all sorts of problems with pressures and tempeatures and couldn't seem to get the unit to function well. When I replaced the gas I took the oportunity to remove the capillary and replace it with a TXV (Danfoss TX2, 068Z3206 plus orifice #3 for anyone interested), and at the same time I added a drier into the system. Photos of this mod are the last 2 on the bottom line of photos.

Nigel

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