First Heatpump project

[jeff5may]

Originally Posted by stef110

Thanks for the help, the name on the unit is
Tkfr-26w but on google you probably only find the tkfr-26gw there is almost no information about this unit. Yes it has its default charche inside.

stef

The snobs at the "pro" forum have a long thread that thoroughly bashes and ridicules these units.

Solar Assisted A/C

The unit under scrutiny was a sedna aire. OEM is Westinghouse, sedna added the collector. A test tech that worked for Westinghouse stated the modified unit did not pass their testing procedures, so the OEM warranty was invalidated prior to release of the product. Sedna eventually released the line of products anyway. So in a way, the units were doomed to fail even before any were sold.

The mini split unit is not the problem. The solar collector is not the problem. But when you combine the two, that's where the problems begin. During warm, sunny weather, the solar collector pours its heat into an already hot compressor. The compressor quickly trips out on thermal overload. Meanwhile, the solar collector is allowed to stagnate, and is temperature skyrockets. When the compressor cools enough to reset the thermal overload, it is immediately fed overheated gas. This vicious cycle continues to roast the compressor until one of two things happens: either the sun goes down or the thermostat is satisfied. After a sufficient amount of abuse, the plumbing leaks or the compressor burns up.

[jeff5may]

The above being said, I believe the mini split outdoor unit is decent. As long as you don't try to run it like the knock-off manufacturers did, it will do a good job and last a long time. The units like the one you have tend to top out at about 16 SEER or 3.5 HSPF, and are very reliable. I believe the best thing to do is just leave your copper pipe where it is and connect the heat exchanger to the other ports on the heat pump.

Since the unit still has its factory refrigerant charge, there is really no need to add another fitting to check pressure. If you are concerned, you can check both pressures with the one fitting only. Since the service port is in the "gas" line, it switches between suction and discharge sides of the compressor with a change of heating or cooling operation. In heating mode, it is the high pressure side. In cooling mode, it is in the low pressure side. With a bone stock outdoor unit and factory charge, you probably won't have to worry about the workings inside the box. The one port will give you the pressure reading for your heat exchanger. Combining this reading with temperature measurements will tell you all you need to know about what your heat exchanger is doing.

There are many ways to rig this thing, and you obviously have the skill to integrate the heat pump into your existing system. However, I haven't seen pictures of an indoor unit, so you will probably need to trick the control board into working like it should. AC_HACKER had a unit similar to yours, and was considering integrating it into his geothermal heating system. It was gotten without an indoor unit, so he dissected it to figure out how to make it work.

http://ecorenovator.org/forum/geothe...heat-pump.html

I don't know if he ever got this project finished, but there is enough information in the thread to set you in the right direction.

[stef110]

thanks for the explanation, The hole idea was to override the solar collector with that copper tube.
Yesterday i received my bottle of nitrogen. And today I made my first braze on two spices of pipe. My first reaction was it looks good!
I used 5% silver solder.


Bottle of nitrogen and my small solder kit


Two pipes i want to braze together.


Right after brazing.


Picture of the inside, I think it looks quite nice.

I also bend the pipes between the unit and the heatexchanger.
Is this the way it should be connected?



The outdoor unit has no electroics inside at all. The inside unit was designed to control the outside unit simply by supplying the compressor fan and valve.
On my dally bases i am an electrician, i love to build electronics and program stuff so i want to build my one controls, the same as i did with my wood stove.
What i understood that it is possible once the gas in released in the heat exhanger. That i can suck the refrigerant back in the outside unit if I want to change some thing on the heat exchanger. Eventually I want the heat exchanger inside the house and i have to remake the connections between them.

stef

[NiHaoMike]

That will work in heating mode but some mini splits require an expansion valve to operate in cooling mode.

[AC_Hacker]

Originally Posted by stef110

thanks for the explanation...stef

This is an interesting project you have here. I have a nearly identical project that hasn't received the attention that I need to give it. My project isn't to combine solar with an Air Source Heat Pump, but rather to combine an Air Source Heat Pump with a small Ground Source Heat Pump. Really very similar indeed!

Your brazing job looks great to me! Good photo of the inside of the brazed tube... evidence that you got it just right!

One concern I have is that it looks to me like you are attaching your gas tubes to your Brazed Plate HX, with some kind of threaded fitting. I did this also, on an older project, and it ended up leaking gas & oil at that threaded connection. It was a slow leak, but over time, it leaked. I can't tell from your photo, what kind of threaded connection you are using... you may have a threaded fitting that is properly designed for the rigors of refrigeration service, but from my experience, this could be a problem point.

Here is a photo of my solution, which is to buy HXs that have fittings that will accept brazing on the gas-side connections, and use threaded-connectors for the water side connection. Your setup may work just fine as you are doing it. But should you discover that they leak, you can still braze to the threaded connector, if you braze to the INSIDE of the threaded connector, if the are not threaded. In that case you will need to be very vigilant to clean all the refrigerant oil residue out of the HX before you braze.

We also have another EcoRenovator, named Randen, who has had difficulties with the threaded water-side connection... in that he tried to use US/Canadian pipe thread connectors, but it turned out that his HX used British pipe thread which was slightly different... and just enough to leak water. This forced him to make custom adapters, but since he is an experienced machinist, he was well-equipped to do this. Hopefully, you are in the Metric world and these threading systems are standardized, and you'll have no problem.

I'm curious about the capacity (size) of your HX? It looks good to me, but I'm curious how you went about determining the capacity (size), and also what capacity (size) you ended up choosing.

I'm also highly interested in the controller aspects of your project, and what you come up with for that. I'm glad that you already have experience with this kind of thing, and your experience with designing and implementing a custom controller has long been a weak point for other projects on this forum (especially mine). When you get to that part of the project, please give us all the details of how you are going about designing your microprocessor for your system. This particular design process really needs to be “opened up” and made to be public knowledge. It would be widely beneficial to us all.

Good luck on your project,

-AC_Hacker

[jeff5may]

"What i understood that it is possible once the gas in released in the heat exhanger. That i can suck the refrigerant back in the outside unit if I want to change some thing on the heat exchanger."

Yes you can. But every time you open the refrigerant loop, you run the risk of letting moisture and atmosphere into the system. And you always lose a little refrigerant.

[stef110]

this HX has flare connections on the ac side, i bought two braze -> flare adapters. Because the connections sizes on the HX are bigger then the lines from the as unit now i can easily solder a smaller pipe inside this adapter and i know i will have a proper connection on the HX.



this is an 1/2 inch flare connection with a 3/8 pipe I made the end of the pipe a little wider with the flare tool so now i can easily solder it together.

For the sizing of the HX i looked how much power the compressor had an by that data i bought the HX. Probably not really the right way.

@ NiHaoMike
In the outside unit there is an fixed expansion valve it is a pice of think copper packed in isolation foam.

everybody thank you for the help i really appreciate it !

stef

[stef110]

So finished brazing:

[jeff5may]

IIRC, pretty much all of the mini-splits have their metering devices in the outdoor unit. The models without electronic expansion valves have a 2-section cap tube assembly. The main, longer section works in both directions. A shorter section has a check valve that shunts it for cooling mode. In heating mode, the extra length of cap tube allows lower-temperature operation (how low depends on the design: longer cap tube = lower minimum outdoor temperature, at the expense of raw BTU output in warmer conditions).

Very few mini-split units have TXV's in them. I suppose the economy of scale favors electronic valves and temp sensors running off the main microcontroller, rather than a self-regulating mechanical valve.

[AC_Hacker]

Originally Posted by jeff5may

Very few mini-split units have TXV's in them. I suppose the economy of scale favors electronic valves and temp sensors running off the main microcontroller, rather than a self-regulating mechanical valve.

Hmmm....

I think the economy of scale idea falls apart when you compare the price of TXVs compared to the price of EEVs.

Also, it looks to me like Electronic Expansion Valves and Variable Frequency compressors occurred at about the same time.

I think that the improvement in efficiency is much smaller when moving from cap tubes > TXVs when compaired to the improvement in efficiency when moving from cap tube (or TXV) > variable frequency + EEVs.

Once you gain the ability to optimize compressor efficiency, it is a small step to apply the same thinking to optimizing orifice behavior.

Asia now has a very large and growing population of engineers, whose expertise increases daily. The US pool of talent is rather small by comparison, and half of that talent is absorbed by by military interests.

So development time and costs which could seem untenable in the US are less prohibitive to Asian developers.

-AC