AC Hacks a Heat Pump - Page 6

AC_Hacker · 04-27-13, 10:27 PM

New parts have arrived for the conversion...

The photo above is the TXV, that is sized for about 1-Ton, which is the nominal output of the Heat Pump.

The photo above is the nice-sized Brazed Plate HX (fork for scale). Not so visible is that the HX has sweat fittings (brazed) on the refrigerant side and water pipe fittings on the water side. I used a Brazed Plate sizing tool and this BPHX is pretty darn close to the one that is called out by the program. I also used this Brazed Plate sizing chart to cross check. I didn't want the HX to be the bottle neck of the machine. There were a fair number of BPHXs that were of a fair price, and in the aproximate size that I needed, but getting one that had appropriate connectors for refrigerant AND that had a substantial pressure rating really narrowed the choices.

I still have questions about how I should best handle the issue of 'frosting up', when the machine runs during the high humidity Western Oregon winters, and the evaporator is running much colder than the ambient air.

I was inclined to remove the reversing valve, just to make the whole job simpler... but it occurred to me that the reversing valve could be useful for melting off frost during the long, wet winter.

So I need to collect a bit more information before I start cutting & brazing.

Another issue that I'm mulling over is the location of the Brazed Plate HX itself. It would be really handy to mount it inside the Heat Pump case, but we do have cold snaps that could freeze it solid, and ruin it.

An alternative would be to put the BPHX inside the house, out of the weather. Which could admit the remote possibility of hydrocarbon refrigerant leak inside the house.

A third choice would be to build a Hydro Box (not an original term) that would be attached to the house, but outside the envelope. This would keep all refrigerant outside the envelope and would put the BPHX water loop nearly inside the house. I could insulate the Hydro Box and put a freeze-point thermostat inside the box to guard against freezing. The perfect-storm disaster would be a loss of power during extremely cold weather... it has happened here before.

Best,

-AC

Northern Diver · 05-21-13, 03:39 AM

AC,
Could you explain a little about the TXV, where you found it, how you sized / specified it etc?
Thanks.
Jim

AC_Hacker · 05-22-13, 11:47 AM

Quote:

Originally Posted by Northern Diver

AC,
Could you explain a little about the TXV, where you found it, how you sized / specified it etc?
Thanks.
Jim

Sure,

It's primarily dictated by your chosen refrigerant (R22 is almost identical in behavior to R290), then by compressor size, and then by the application (refrigeration, heat pump), and lastly by price.

I asked both Brad_C and also Vlad, who both have more experience than I do in these matters, and based on their advice, I found an appropriate device on ebay. Both Brad_C and Vlad agreed on the particulars, and in addition, Vlad included the "application type" specifier. There are on-line catalogs that have component selection tables, that can be very helpful in narrowing down your search.

Normally the TXVs sell for 2X to 3X or even 4X what they can be found for on ebay.

Although you didn't mention it in your question, the compressor you use will need a starting capacitor to kick it over with the initial surge of current. If you can locate a scrap compressor, it will surely have the appropriate starting cap already there. If you get a new compressor it will need to have an appropriately sized starting cap. They aren't too expensive, but they are another piece of hardware you'll need to acquire.

I know that you live in an area where heating is the norm, so air conditioners are not often found. But if you could locate an air conditioner, they have a metering device already built in, usually a cap tube. And if you're careful when you disassemble the machine, you can re-use the cap tube. Don't rule out the possibility of finding a used air conditioner in your area, because they may be used in industrial or data center cooling operations.

I imagine that there are metal scrap yards where you live, and this is where compressors ultimately go to die. Becoming friendly with the people who work in the scrap yards can be very rewarding... they know that they are at the bottom of the food chain, and a little respect can go a long way.

Best,

-AC

theoldwizard1 · 11-01-14, 10:44 AM

Bump !

Why the dead end on this thread ?

AC_Hacker · 11-01-14, 04:30 PM

Quote:

Originally Posted by theoldwizard1

Bump !

Why the dead end on this thread ?

I'm stuck on the controller part.

My mini-split unit is a nicely hackable minisplit, as it is prior to "inverter technology" complexities, and it is R-22 (R-290 compatible). As far as I'm concerned, it's the ideal candidate.

But I'm stuck on the controller part.

I thought that there are probably other folks, just like me who could be stuck at the very same place, so I started the thread called, "Designing a General Purpose Heat Pump Controller", in the hopes that enough Arduino-savvy people could collectively design a simple controller that could be modified to suit several configurations that other hackers might encounter.

I built a test bed to test out parts of code as I wrote it to assure that it functioned. Here's a photo of a test-bed that I built:

(the photo came from THIS post.)

... so far I'm stuck on code due to my limited programming experience.

As to the controller thread, it has brought to light various examples of cleverly designed controllers with fairly specific characteristics.

But none of the examples have been general enough to suit my needs.

To make a long story short, I am still stuck on the controller.

-AC

roflwaffle · 11-02-14, 10:14 AM

What functionality do you need to generalize?

AC_Hacker · 11-02-14, 10:51 AM

Quote:

Originally Posted by roflwaffle

What functionality do you need to generalize?

This deserves a detailed answer.

Right now, I'm swamped, but I should be able to give your question the attention it warrants later this evening...

Best,

-AC_Hacker

jeff5may · 11-02-14, 03:29 PM

I am working on some sketches for the controller that will hopefully go in this unit. I am having problems with the Dallas Temp Control library and the OneWire library working together.

Using onewire ds18b20 sensors, it is much easier to program using the dallas library. The thing is, every time the sketch changes, the Arduino compiler won't understand what happened and pre-processes everything just a little differently, and the sketch won't compile without serious debugging. I don't know why, but when I started encountering problems, I let everyone know and begged for some code that works.

The problem is, everyone who contributed their snips and sketches (thanks everyone, you know who you are) had written specialized code for their custom creations. I could do the same thing for this unit, and whip up something that would work for just this unit. But that wouldn't produce something that would be useful for everyone.

04-27-13, 10:27 PM	#51
AC_Hacker Supreme EcoRenovator Join Date: Mar 2009 Location: Portland, OR Posts: 4,004 Thanks: 303 Thanked 723 Times in 534 Posts	New Parts Have Arrived... New parts have arrived for the conversion... The photo above is the TXV, that is sized for about 1-Ton, which is the nominal output of the Heat Pump. The photo above is the nice-sized Brazed Plate HX (fork for scale). Not so visible is that the HX has sweat fittings (brazed) on the refrigerant side and water pipe fittings on the water side. I used a Brazed Plate sizing tool and this BPHX is pretty darn close to the one that is called out by the program. I also used this Brazed Plate sizing chart to cross check. I didn't want the HX to be the bottle neck of the machine. There were a fair number of BPHXs that were of a fair price, and in the aproximate size that I needed, but getting one that had appropriate connectors for refrigerant AND that had a substantial pressure rating really narrowed the choices. I still have questions about how I should best handle the issue of 'frosting up', when the machine runs during the high humidity Western Oregon winters, and the evaporator is running much colder than the ambient air. I was inclined to remove the reversing valve, just to make the whole job simpler... but it occurred to me that the reversing valve could be useful for melting off frost during the long, wet winter. So I need to collect a bit more information before I start cutting & brazing. Another issue that I'm mulling over is the location of the Brazed Plate HX itself. It would be really handy to mount it inside the Heat Pump case, but we do have cold snaps that could freeze it solid, and ruin it. An alternative would be to put the BPHX inside the house, out of the weather. Which could admit the remote possibility of hydrocarbon refrigerant leak inside the house. A third choice would be to build a Hydro Box (not an original term) that would be attached to the house, but outside the envelope. This would keep all refrigerant outside the envelope and would put the BPHX water loop nearly inside the house. I could insulate the Hydro Box and put a freeze-point thermostat inside the box to guard against freezing. The perfect-storm disaster would be a loss of power during extremely cold weather... it has happened here before. Best, -AC Attached Thumbnails __________________ I'm not an HVAC technician. In fact, I'm barely even a hacker... Last edited by AC_Hacker; 04-30-13 at 12:41 PM..

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05-21-13, 03:39 AM	#52
Northern Diver Lurking Renovator Join Date: May 2013 Location: Shetland Posts: 10 Thanks: 0 Thanked 0 Times in 0 Posts	AC, Could you explain a little about the TXV, where you found it, how you sized / specified it etc? Thanks. Jim

11-01-14, 10:44 AM	#54
theoldwizard1 Apprentice EcoRenovator Join Date: Oct 2014 Location: SE MI Posts: 105 Thanks: 3 Thanked 12 Times in 9 Posts	Bump ! Why the dead end on this thread ?

11-02-14, 10:14 AM	#56
roflwaffle Apprentice EcoRenovator Join Date: Sep 2008 Posts: 116 Thanks: 29 Thanked 12 Times in 11 Posts	What functionality do you need to generalize?

11-02-14, 03:29 PM	#58
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	I am working on some sketches for the controller that will hopefully go in this unit. I am having problems with the Dallas Temp Control library and the OneWire library working together. Using onewire ds18b20 sensors, it is much easier to program using the dallas library. The thing is, every time the sketch changes, the Arduino compiler won't understand what happened and pre-processes everything just a little differently, and the sketch won't compile without serious debugging. I don't know why, but when I started encountering problems, I let everyone know and begged for some code that works. The problem is, everyone who contributed their snips and sketches (thanks everyone, you know who you are) had written specialized code for their custom creations. I could do the same thing for this unit, and whip up something that would work for just this unit. But that wouldn't produce something that would be useful for everyone.