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Old 01-01-16, 06:13 PM   #141
MEMPHIS91
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Jeff, I do not follow what do you mean psi gauge and absolute?

I have 3 data loggers getting water temps in the pond as we speak, I will pull them out on sunday. The extremely questionable thermometer I have in there right now is saying 50F, but that isn't on the bottom because my loop wasn't long enough to go all the way to the 17' deep area.

The TXV is not allowing me to get anymore than about 82psi suction, everything I add to the charge goes straight to the discharge psi.
I will have a larger capacity compressor soon I hope.

More data, one was last night, one was just now. These are both with the water to water heating mode on. Water temp says 65F and pond water temp is about 50F, no idea what temp the ground is.

Last night, 251psi discharge, 80psi suction

Tonight, 226psi discharge, 78psi suction

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Old 01-01-16, 09:38 PM   #142
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1 bar of pressure is atmospheric pressure. At atmospheric pressure, your gauges will read 0 psi. Absolute pressure is at 0.000000X psi at a deep vacuum. This is what a micron gauge reads: microns of pressure above absolute zero. At atmospheric pressure, there is close to 15 psi of absolute pressure. The offset is much like the difference between degrees Kelvin and degrees Celsius. Water freezes way above absolute zero, at zero degrees Celsius.

A larger compressor is not going to make your evaporator behave much differently than it does now. The txv is serving two purposes: maintaining consistent superheat and limiting maximum suction pressure. When your evaporator gets cold, it will choke the flow so the compressor sees only superheated vapor. When the evaporator is warm, it limits evaporation pressure to keep the compressor cool. With a larger compressor, the evaporating pressure may actually drop compared to a smaller compressor with the same load conditions. This is because a larger compressor "sucks" more gas. Even though the txv may be opened further, the pressure may be a tad lower if the hx is working harder. With faster moving juice (higher flow rate), the txv knows to choke the flow, to force a colder, more heat hungry evaporator. These valves are a lot smarter than a cap tube.

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Old 01-02-16, 06:34 AM   #143
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Ah OK that makes sense now. Thank you.

Sorry I should have clarified, I am happy with everything. The pressures and temps are starting to really look better, though more tuning can be done.
Why I want a larger compressor is because when it was 28F with the big 10,500 btu one I could heat everything with .5 kWh, now it takes 3-5 kWh. 400 gallons is a crazy amount of water to heat, this little compressor just can't keep up. It can heat the air to 75F in no time but its the water loop that is killing me. And I know the water loop is fine I was pushing 125F in and getting 78F out.
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Old 01-02-16, 11:14 AM   #144
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What are the numbers on the digital gauge in your last few pics monitoring? I assume one is your suction line but the other is a mystery. FWIW, the txv is watching your evaporator now. Unless something major changes in that part of the circuit (clog, rupture, ice age, etc) that temp will not change much. Your DX loop is on autopilot now. Whatever you do, don't adjust the txv until you get a solid grip on the consequences.

The other side of the circuit is where the changes will happen. When you add charge, you will have more current draw and more subcooling in the condenser. If your condenser can't keep up, the liquid line temp will rise. This temperature rise represents wasted heating energy. If you remove charge, your current draw and subcooling will drop. If the compressor can't keep up, your discharge temperature will drop and flash gas will form in the liquid line. The txv will compensate by lowering the suction pressure until there is again a solid column of liquid in the line. If the charge is severely low, the txv will hunt as the liquid fills up and drains from the liquid line.

The happy place for this rig is the minimum charge that keeps flash gas out of the liquid line. You will have to experiment to find out how much subcooling your system actually needs to stay stable. Since hydrocarbon refrigerants do not superheat as much as fluorocarbons in the compressor, your discharge temperature will be lower, which is ok if your condenser is effective enough.
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Old 01-02-16, 11:44 AM   #145
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Sorry I did not explain the digital readings. They are for superheat and subcooling. So suction temp is the lower reading, and the temp 6" from the txv is the higher temp.

Yes this txv is non adjustable.

Yes that is why I charged up more in the first picture with a subcooling of around 5-7F because low subcooling tells me I have a staved condenser. But the R1270 bar to psi through me off.
So far the condenser has taken everything I have thrown at it. Every 15 minutes an air pump comes on for 2 minutes and stirs the water around the coil nicely.
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Old 01-02-16, 12:00 PM   #146
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From your last post, I can see your concept of the heat exchange mechanism in the condenser is flawed. The heat transfer function is not simply gas temperature in vs liquid temperature out. The majority of the heat transfer happens at phase change, at saturation pressure and temperature. Once you charge the system past a certain point, your discharge pt will rise as your superheat and subcooling outrun the phase change in the condenser.

I just forced this condition in my latest window shaker thread as part of preliminary tests. Even though my rig was severely overcharged, it still worked. Nevermind the detail that the compressor was running at 2000 watts or better of power draw (due to the 100 degrees of combined superheat and subcooling), the thing blew hot air.
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Old 01-02-16, 12:17 PM   #147
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Jeff, I am simply shooting for 12-15 subcooling temps. More than that I have no clue.
My best research says low subcooling (less than 12-15F) is a staved condenser and I am not keeping the condenser as full of liquid as I could be, therefore loosing efficiency. High subcooling (more than 12-15F) is a flooded condenser and I am just wasting power like you said.
As long as I am in the 12-15 range I should be as close to a correct charge as possible right?
I am not taking the gas temputure in, and am taking the pressure reading and convert to the saturation temp.
Or am I still WAY off on this whole idea?
I check out your thread.
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Old 01-02-16, 02:38 PM   #148
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Quote:
Originally Posted by MEMPHIS91 View Post
Jeff, I am simply shooting for 12-15 subcooling temps. More than that I have no clue.
My best research says low subcooling (less than 12-15F) is a staved condenser and I am not keeping the condenser as full of liquid as I could be, therefore loosing efficiency. High subcooling (more than 12-15F) is a flooded condenser and I am just wasting power like you said.
As long as I am in the 12-15 range I should be as close to a correct charge as possible right?
I am not taking the gas temputure in, and am taking the pressure reading and convert to the saturation temp.
Or am I still WAY off on this whole idea?
I check out your thread.
Ok, this conversation is quickly moving in the right direction. Your level of knowledge has progressed to the point where you can make accurate, measurable snapshots of what is happening inside the system, as it is happening. You have your system pretty closely charged to your assumed "normal" design conditions. If you were a fridgie tech setting up a factory unit to prescribed specs, you could simply tell the owner the unit is set up and working like it should. If the owner doubted your statement, you could point to gauges and verify values to something printed in a manual somewhere to prove it. You could be happily on your way to the next stop on your schedule.

This is not the situation at all. You have a system that is completely custom, with no factory specs to obey. This rig would be considered "abnormal" or "downright strange" by pro service techs in general. Without regard to the hydrocarbon refrigerant (you could lie and tell them it was filled with R22), none of them would want to lay a hand on it for any amount of money, at least not while they were on the clock. Knowing the unit was filled with propane, the daring techs would then not want to touch it, even on their own time. Its existence stands against their factory-taught premise for earning a decent living. To them, there is a righteous place in hell for people like us. The powers that be are not far behind in their positions on this subject.

Now that you know where you and your system stand, the time has come for you to leave the realm of the factory service manual and its limitations. For example, a 10 SEER air handler condenser, properly sized to the compressor and evap exchanger, would have 15 degrees of subcooling at a certain point on a chart in a manual, flowing a certain cfm, at a certain return air temperature, and you should see a certain pressure in the condenser. Changing any of these design conditions would put you at a different place in the chart, and interpreting this shift would give you a clue where to look in the system to find out how to eliminate the shift, for better or worse.

Looking at what you did this week, your system changes reflected this defined approach:

@210 psig, 97.7 degF condenser; 75 psig, 62.2 degF evaporator conditions:
5 degF subcool, 19 degF superheat, ? amps, ?btu/hr

Adding charge, the balance has now shifted to:

@250 psig, 103 degF condenser; 80 psig, 63 degF evaporator:
15 degF subcool, 23 degF superheat, ? amps, ?btu/hr

Since the dP across the compressor increased from 135 psi to 170 psi, we can assume the amp draw also increased. Since the superheat has risen, we can assume the txv is limiting maximum suction pressure. The added superheat is leading to additional de-superheating in the condenser, and its exit (liquid line) temperature is following this upward trend, indicating reduced effectiveness of the condenser. The extra superheat is being wasted as a rise in the liquid line temperature.

Whether or not any charge was added/recovered, the system found another balance point later:

@226 psig, 93 degF condenser; 78 psig, 64.3 degF evaporator:
17 degF subcool, 18 degF superheat, ? amps, ?btu/hr


The dP across the compressor has dropped from 170 to 150 psi, so we can assume the amp draw has decreased. The subcooling did not drop, so the liquid is exiting the condenser at a lower temperature, indicating a more effective condenser and less heating capacity being wasted.

Do you follow this analysis? Over the course of these readings, your evaporating pressure and temperature didn't change enough to count, which means the txv is doing a good job, and that your evaporator isn't working very hard. If your water tank was around 60 or 65 degF, your condenser is doing the best it can at trying to digest the hot gas you are feeding it. The condensing saturation temperature has risen and fallen from 105 to 118 to 111 degF, while the liquid line temperature changed from 97.7 to 103 to 93 degF. Assuming your tank temperature did not change significantly between readings, it seems to have been moving the most heat during the last reading.

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Old 01-02-16, 03:43 PM   #149
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Jeff, yes I have long past stopped trying to ask local people questions, they really have no idea other than what the factory tells them or what can make the most money. I only know one honestish company around.
So a 12-15F subcooling may not be the target because this is a custum system. That makes sense.
I did adjust my charge back to 230psi discharge simply because when it switched to air heating mode my pressures were higher than I would like.

So I am wasting power by increasing charge. I think you are right the middle reading does seem the best so far.

The power draw of each reading was 680 watts, 710 watts, 760 watts. I did not calculate the btu/hr yet. Been having some really cold nights.

The temp never drops less than 64.5F before the compressor kicks on.

Does it make sense that I larger compressor would help, or are you saying that my condenser is already maxed out? I can easily add an extra loop if needed. I just want those .5kWh nights back. lol
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Old 01-02-16, 07:34 PM   #150
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I edited my last post to reflect the order your pics were posted. It further illustrates the skill level you are using in dialing in your parameters. So the middle is now the last, so to speak.

I so get what you are saying about the two condensing coils. Since the one is air and the other is water, they will find different balance points when you switch between them. According to your last post, it seems the water tank is already running at closer approach temperatures than the air coil. This is indicated by the high head pressure of the air coil at the middle reading. If the water condenser ran at a lower head pressure, it is already more effective than the air condenser.

This doesn't mean you can't improve it. Adding more surface area to the water tank loop will increase your heat transfer. The system will find a balance point with less head pressure. Your amp draw and liquid line temperature will drop accordingly. This is a case of diminishing returns, so at a certain size it becomes uneconomical to add more surface area. It is up to you to decide how big is too big.

The other factor that makes a big difference is the compressor displacement. If you optimize your water loop with this compressor, it won't be big enough to move enough heat at the same level of performance with a larger compressor. The added displacement (and resulting increase in mass flow) would raise the balance point to a higher compression ratio.

The txv in the system will amplify this effect until your evaporator reaches its limit. As you can see, the txv is already trying to feed your air coil more head pressure than you are comfortable with when there is enough refrigerant in the loop. With any compressor, the upper limit on system charge will be found during summer conditions while running the air coil. When the ambient air is close to 100 degF, it is easy to find the critical charge by measuring head pressure and compressor head temperature. Keeping the total charge below this critical charge will prevent overheated oil and overpressure of plumbing.

Once you set this critical charge using the less effective air coil, you can rest assured that the water loop will always be running at a more efficient, less extreme balance point. Depending on how much more effective the water loop actually is, the system will always be saving you compressor amps and run time.

For now, you can simulate these conditions by blocking the airflow of the air coil or enclosing it so the heat it produces is recycled until it gets hot air running through it. At this point, you can adjust the charge and watch what happens to the compressor discharge pt.

Once you get the condenser operating within your level of comfort, I would highly recommend running it like you stole it with all obstructive measures removed. Take lots of readings during this run to establish baseline operating conditions (subcooling and liquid line temps, refrigerant and air dT, condensing pressure, amp draw, etc.) over a range of indoor temperatures. Then switch to the water loop and jot down readings once the system finds its balance.

This sounds like a long and drawn out process, but it isn't as difficult as it seems. It is a short and sweet version of what design teams do during early prototyping of concept systems. Having baseline measurements and establishing upper limit conditions is super valuable. If some plumbing leaks or pops, you can look at this data to set your charge after a repair. If you change part of the system, you can use the parts that did not change for comparison. When seasons change, something good or bad may happen. If you don't have log data to look at, you may never realize a change until the electric bill comes.

Sorry for the long posts, but the answers that lie ahead of you are not so simple. From your involvement level , both in this and past projects, and speed at which you are perfecting your knowledge and rigs, I feel it would be cheating you out of doing your best. I can tell all these ramblings are not falling on deaf ears and blind eyes.

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