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Old 07-11-17, 12:40 PM   #1
Fordguy64
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Default 12kbtu heat pump

Ok so I'm starting a thread to be more specific to my first refrigeration system hack.

I have 2 12kbtu compressors. 1 is an r22 unit and the other is r134a. I plan to use the r22 unit and swap it over to r290. I would like some help sizing the brazed plate heat exchangers(or coax) so I can start keeping an eye out for good deals.

Also I work with a guy who is an electronics engineer and loves playing with arduinos and raspberry pi's so I lm going to ask for his help with the controls. I have some very fancy flow control valves that are good for 2000psi and really high and low temps. I want to make an electronic expansion valve with one of these flow meters and a stepper motor.

My next question is what parts of the system do I want to monitor to control the exv? Pressures on high and low? Temps in and out of hi and low sides? Amp draw of compressor?

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Old 07-11-17, 01:56 PM   #2
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Or do I simplify the heat exchangers and just go with direct exchangers. Just throw some copper coils in some 55 gallon drums?
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Old 07-11-17, 07:52 PM   #3
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For your first rig, I would begin with something simple. Bullet and stupid proof is the goal. Keep to the KISS and YAGNI methods to build a framework that is strong and healthy. Leave room for bells and whistles with room to spare. Run the unit and collect data and find out if the thing is the right size for the application. See if it survives for a while.
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Old 07-11-17, 08:30 PM   #4
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I was actually thinking about that a little while ago.. Simple and cheap to see if I even like tinkering with it lol
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Old 07-11-17, 11:01 PM   #5
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If you ever might try the rig out as an ice making chiller, don't use a brazed plate heat exchanger unless you are planning on using a secondary refrigerant (aka antifreeze loop) that isn't water. BPHE'S should be prevented from freezing at all cost! They tend to crack like an egg after a couple of seconds. Coaxial HX are a little more tolerant: one of those might last a minute or three. Your idea of a coil in a drum would be much more tolerant of ice conditions.

For monitoring, I tend to load my units up like they are on life support when they are young. As inexpensive as the kill-a-watt meters, digital thermometer sensors, and current clamp monitors are, you can monitor a dozen different things constantly and log them for less than $50 spent. For pressure readings, I just leave my gauge set connected for the first little while. After some torture testing and confidence building, only a few temperatures really need to be monitored to take care of automating the operation. Compressor head / discharge pipe temperature, ambient temperature, evaporator discharge or compressor suction temperature or defrost temperature need to be monitored. If deemed necessary, high and low pressure limit sensors can also remain. With liquid circuits, a flow sensor in each loop can help immensely.

Last edited by jeff5may; 07-12-17 at 05:53 AM..
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Old 07-12-17, 06:53 AM   #6
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Jeff that's a good point about the brazed plate heat exchangers. I can see them splitting under that condition. I think for this first test I'm just going to buy some copper tube and put it in a bucket of water and go from there. After I get over the learning curve or refrigeration I'll spend some money on better parts
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Old 07-12-17, 07:35 AM   #7
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Lots of the super-duper duty ice storage systems have a thermal store that resembles a plastic rain barrel with a wort chiller coil inside. Made of the same thing as milk jugs and igloo coolers. A few companies have designed residential size units in the 2 to 5 ton range that provide for around 4 hours of compressor-free operation. This allows homeowners to shift the electrical consumption away from peak rate hours and save lots of money. Most of these units are guaranteed for decades, as water is going to freeze the same in 20 years as it does today. Battery and brine-based solutions degrade in capacity over time.

Look around the web at the wort chiller coils. Many of them are rated the same as conventional heat exchangers, and the prices for some of them are not much more than rolling your own. Obviously they are not going to be rated for high pressure refrigerant duty, but if you are going to be running an antifreeze loop, that won't matter. The specs will give you a good idea of how to size the heat exchange pipes.
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Old 06-20-18, 07:02 PM   #8
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Well like all my projects they take a lot longer then I would like.. anyway I’m finally in a place to be able to play a little.

I hacked into the system today.. it was a cap tube system so I removed that and added a needle valve of sorts. Vacuumed the system down checked for leaks and so on.. so I start filling it up with bbq gas and I can’t get the high side to go high and the low side to go low. As I turn the needle valve from one extreme to the other the pressures never do what the are supposed to do. I can hear the gas in the system. But I felt I reached a point where I couldn’t put more gas in (around 130psi) because it was no longer sucking it from the propane tank..

Thoughts?t

LOL I’m an idiot.. I figured it out. In my hast to work on it I wasn’t really paying attention to the way I hooked up the gauges.. and well I put the high side on the low side and obviously low side to high side..grrrr o well I’ll mess with it more tomorrow
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Old 06-20-18, 09:58 PM   #9
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Quote:
Originally Posted by jeff5may View Post
Lots of the super-duper duty ice storage systems have a thermal store that resembles a plastic rain barrel with a wort chiller coil inside. Made of the same thing as milk jugs and igloo coolers. A few companies have designed residential size units in the 2 to 5 ton range that provide for around 4 hours of compressor-free operation. This allows homeowners to shift the electrical consumption away from peak rate hours and save lots of money. Most of these units are guaranteed for decades, as water is going to freeze the same in 20 years as it does today. Battery and brine-based solutions degrade in capacity over time.

Look around the web at the wort chiller coils. Many of them are rated the same as conventional heat exchangers, and the prices for some of them are not much more than rolling your own. Obviously they are not going to be rated for high pressure refrigerant duty, but if you are going to be running an antifreeze loop, that won't matter. The specs will give you a good idea of how to size the heat exchange pipes.
might be best for another thread, but I'd love to build a DIY two tank thermal storage setup - make ice from water in one, perhaps water or PCM (wax) in the other. a mixing valve in the refrigeration line to take/steal heat from a ground loop/air source/sink HX for when you're looking to max out COP or have met the latent capacity of your tank and want to keep going.
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Old 06-21-18, 04:27 PM   #10
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Well I switched the hoses around and sure enough that fixed my problem.. anywho got the pressures about where they should be and the seals on the valve started to let go. So back to the drawing board on that one..

I need some help sourcing some refrigerant to water heat exchangers something in the 24kbtu range

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