The long explanation is much more than we can get into here as it involves a thorough understanding of how an absorption refrigerator works and some fairly heavy physics and thermodynamics, but if it were that simple don't you think NorCold would have done it that way?
Fridge: How Level is "enough"?
- Thread starter Gary RV_Wizard
- Start date
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Gary RV_Wizard
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I don't think you are missing much of anything, Ernie. The basics are as you say - turn off the heat if it ever begins to exceed what is necessary to boil the ammonia solution, and turn it back on again when it is safe to do so. The algorithm to figure out when to shut off and when it is safe to turn it back on is more complicated than a simple thermostat, and each make and model of fridge has different temperature parameters, but the net effect is still just off and then on again.
The operational concept, however, is totally different. The Norcold recall device is a simple fail-safe, intended to catch catastrophic failures after the 12xx's standard management controls have failed. Norcold's standard control is to run the boiler flat-out as long as the fridge interior has not reached the desired temperature. The ARP acts like a governor, limiting the boiler operation to the heat range necessary to drive the absorption process. Once the boiler reaches the temperature to make ammonia gas from liquid, there is no possible benefit from making it any hotter, and a couple major drawbacks from allowing it to get hotter. ARP adds the management needed to keep the boiler in that optimum range, whereas Norcold (and Dometic too) simply allow the boiler to run amok.
The operational concept, however, is totally different. The Norcold recall device is a simple fail-safe, intended to catch catastrophic failures after the 12xx's standard management controls have failed. Norcold's standard control is to run the boiler flat-out as long as the fridge interior has not reached the desired temperature. The ARP acts like a governor, limiting the boiler operation to the heat range necessary to drive the absorption process. Once the boiler reaches the temperature to make ammonia gas from liquid, there is no possible benefit from making it any hotter, and a couple major drawbacks from allowing it to get hotter. ARP adds the management needed to keep the boiler in that optimum range, whereas Norcold (and Dometic too) simply allow the boiler to run amok.
Ernie n Tara
Well-known member
Thank you Gary. I wasn't trying to cast aspersions, just make an observation.
I do understand how these refrigerators work. I've written software to permit use of a bang bang controller on large steam heated platens; a considerably more difficult task, but one that is quite analegeous. It occurs to me that he could have implemented a similar PID control to some advantage here in that different refrigerators will have different thermal inertia (although probably not much) and therefore require different delays in removing and reapplying heat. That would permit running closer to the optimum temperature. He could also have incorporated tilt sensors. Either or both of these, particularly PID control, could prove beneficial. But I didn't see any suggestion that he has done either one.
I'm sorry, but he simply doesn't have the data to do any more than I've described! All of the slides and diagrams have absolutely nothing to do with with the "HOW" except to perhaps explain how he picked the temperature something I could determine from any physics book in a few minutes.
As to the appropriateness of this venue for the discussion, you guys get to determine that, but I do think it's the right place for it and that many here will benefit from the discussion.
My Last 2c Worth on the Subject,
Ernie
I do understand how these refrigerators work. I've written software to permit use of a bang bang controller on large steam heated platens; a considerably more difficult task, but one that is quite analegeous. It occurs to me that he could have implemented a similar PID control to some advantage here in that different refrigerators will have different thermal inertia (although probably not much) and therefore require different delays in removing and reapplying heat. That would permit running closer to the optimum temperature. He could also have incorporated tilt sensors. Either or both of these, particularly PID control, could prove beneficial. But I didn't see any suggestion that he has done either one.
I'm sorry, but he simply doesn't have the data to do any more than I've described! All of the slides and diagrams have absolutely nothing to do with with the "HOW" except to perhaps explain how he picked the temperature something I could determine from any physics book in a few minutes.
As to the appropriateness of this venue for the discussion, you guys get to determine that, but I do think it's the right place for it and that many here will benefit from the discussion.
My Last 2c Worth on the Subject,
Ernie
The ARP is tailored to each refrigerator at installation time using a procedure called auto-tune. That let the ARP determine the normal steady state operation of the refrigerator and program the ARP for that particular unit. It's much more complicated than just a simple temperature sensed off switch, as we've stated before.
I'll have a review of the Amish cooling unit, along with the ARP, in a few days when we get done with the installation and testing. Paul is doing considerable data collection on the cooling unit as this is the first one he's had an opportunity to work with. So far, the performance of the cooling unit is exceptional.
To those that have installed the ARP on a norcold 1210 or similiar unit:
I received my ARP and am getting ready for the install. Looking through the small access that Winnebago provides, it appears the fiberglass wrap around the burner/heat assembly is solid, no obvious way to unwrap. Do I slit this with a razor knife then use the metal ac tape to tape the slit back together? Trying to determine the best way to gain acccess to the boiler tube. The insulation seems to be solid fibergalss with an aluminized exterior layer on the wrap. It seems pretty rigid not spun like the illustrations shown for the 1200.
My concern is sealing it back after slicing through it. I suppose I could add an additional layer across the slit to seal it.
Any thoughts or suggestions?
David
I received my ARP and am getting ready for the install. Looking through the small access that Winnebago provides, it appears the fiberglass wrap around the burner/heat assembly is solid, no obvious way to unwrap. Do I slit this with a razor knife then use the metal ac tape to tape the slit back together? Trying to determine the best way to gain acccess to the boiler tube. The insulation seems to be solid fibergalss with an aluminized exterior layer on the wrap. It seems pretty rigid not spun like the illustrations shown for the 1200.
My concern is sealing it back after slicing through it. I suppose I could add an additional layer across the slit to seal it.
Any thoughts or suggestions?
David
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Gary RV_Wizard
Site Team
Yes, easiest method is to slit it with a razor knife. Then tape it back together with the foil-back duct tape (not the cloth type). If you damage or lose some of the insulation, it can be replaced with high temperature insulation, available at places such as Grainger Supply.
Thanks for the replys. I had looked at the directions, I just don't see a picture that looks exactly like mine and was concerned about cutting into the insulation, but I figured that was what was going to be required.
Probably will not tackle until I travel to Beaumont as the weather here is turning wet and cold, so not too conducive to working outside.
Safe Travels,
David
Probably will not tackle until I travel to Beaumont as the weather here is turning wet and cold, so not too conducive to working outside.
Safe Travels,
David
Ernie n Tara
Well-known member
Ned asked "why don't the companies use this method?" or words to that effect. It caused me to rethink a statement that I made to the effect that "they both do the same thing, just at different temperatures". After some reflection, I suspect that I was wrong and I decided to reenter the discussion because there may well be a SAFETY reason. My reasonig:
A. The manufacturer is atempting to identify an overtemp condition due to the boiler running away due to the loss of fluid. This would identify a leaking system and FIRE HAZARD.
B. The new device simply regulates the operating temperature. This may well extend the life of the refrigerator, but it may also defeat the SAFETY feature of the manufacturers device.
A system that may last longer, but will then fail catastrophically is not progress. I honestly hope I'm wrong here, but nothing I've seen addresses this question. Thoughts Gary?
Ernie
PS Ned, the only tuning possible is the PID function I described above, so perhaps he did incorporate it. This is standard throughout industry for control of characteristics that have inertia.
PPS I considered posting this as a seperate subject, but decided that would be inappropriate if he has actually addressed the above case and found a solution (I don't see one myself).
A. The manufacturer is atempting to identify an overtemp condition due to the boiler running away due to the loss of fluid. This would identify a leaking system and FIRE HAZARD.
B. The new device simply regulates the operating temperature. This may well extend the life of the refrigerator, but it may also defeat the SAFETY feature of the manufacturers device.
A system that may last longer, but will then fail catastrophically is not progress. I honestly hope I'm wrong here, but nothing I've seen addresses this question. Thoughts Gary?
Ernie
PS Ned, the only tuning possible is the PID function I described above, so perhaps he did incorporate it. This is standard throughout industry for control of characteristics that have inertia.
PPS I considered posting this as a seperate subject, but decided that would be inappropriate if he has actually addressed the above case and found a solution (I don't see one myself).
The failures usually occur because the boiler has been allowed to get extremely hot, and over time it fails. The ARP prevents those overheating conditions and prolongs the life of the system. The overheating typically is caused by out of level operating conditions, and from Gary's experience, it doesn't take much to allow the temperature to climb quite high. Not high enough to trip the manufacturer's catastrophic shutoff, but enough to cause cumulative damage to the system.
The ARP doesn't use a snap switch sensor but an RTD (thermistor) that reads the actual temperature of the boiler. I don't know what PID you're referring to but the ARP does not use any of the cooling unit circuitry for its operation. I doubt that the cooling unit controller even puts out any PID codes.
The ARP doesn't use a snap switch sensor but an RTD (thermistor) that reads the actual temperature of the boiler. I don't know what PID you're referring to but the ARP does not use any of the cooling unit circuitry for its operation. I doubt that the cooling unit controller even puts out any PID codes.
Ernie n Tara
Well-known member
Actually, I have figured out how he could possibly have avoided catastrophic failure, but your response does not give me confidence that he has.
PID does not require anything other than data on how fast the system responds to an input. In this case, how fast the boiler raises the temperature of the unit. It then uses that data to shut off the heat early so that temperature does not overshoot.
It would be theoretically simple for an intelligent system to avoid catastrophe as follows:
A. On activation, determine the slope and record. This value would never update after that time. Itis also a "sloppy" value since the slope will be different for electric than gas.
B. Watch for an extremely high slope indicating a dry boiler and shut off completely if it should happen. This will be much more difficult in practice than theory, but might be possible.
I have acknowledged that the new device may extend the life of the system and may alleviate ONE potential cause of failure. It does not address the other potential causes of failure and it is ASSURED that the unit will eventually fail. I am not at all certain that it will outlast the motor home.
We all make choices like this one often, but I strongly believe we are entitled to know we are! Incidentally, there are 10's of thousands of refrigerators in service and a few hundreds of the older ones fail each year. Six years experience on a few units is not sufficient to even demonstrate actual improvement in reliability!
Ernie
PS My comments are not a personal attack on anyone, including the originator of the device, although they may reasonably be construed as being critical questioning.
PID does not require anything other than data on how fast the system responds to an input. In this case, how fast the boiler raises the temperature of the unit. It then uses that data to shut off the heat early so that temperature does not overshoot.
It would be theoretically simple for an intelligent system to avoid catastrophe as follows:
A. On activation, determine the slope and record. This value would never update after that time. Itis also a "sloppy" value since the slope will be different for electric than gas.
B. Watch for an extremely high slope indicating a dry boiler and shut off completely if it should happen. This will be much more difficult in practice than theory, but might be possible.
I have acknowledged that the new device may extend the life of the system and may alleviate ONE potential cause of failure. It does not address the other potential causes of failure and it is ASSURED that the unit will eventually fail. I am not at all certain that it will outlast the motor home.
We all make choices like this one often, but I strongly believe we are entitled to know we are! Incidentally, there are 10's of thousands of refrigerators in service and a few hundreds of the older ones fail each year. Six years experience on a few units is not sufficient to even demonstrate actual improvement in reliability!
Ernie
PS My comments are not a personal attack on anyone, including the originator of the device, although they may reasonably be construed as being critical questioning.
A PID (Parameter ID) is a string of data output from a device, usually a computer controller, that contains the value of a particular measurement. I don't understand your use in this context, as no PIDs are involved in the operation of a cooling unit.
I suggest that if you want to pursue this further you contact Paul directly and discuss it with him. He is more than willing to go into whatever level of detail you desire to explain exactly what the ARP controller does. His email address is on the web site that we referred you to earlier.
I suggest that if you want to pursue this further you contact Paul directly and discuss it with him. He is more than willing to go into whatever level of detail you desire to explain exactly what the ARP controller does. His email address is on the web site that we referred you to earlier.
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Gary RV_Wizard
Site Team
I can't imagine what you are alluding to, Ernie. Nothing in the ARP in any way interferes with the fridge's own safety mechanisms. Whatever the fridge's own controller does, it still does it. And if it has a catastrophic temperature sensor, ala the Norcold recall box, that should be left in place and it still functions if the boiler ever got hot enough to trip it. The boiler shouldn't ever get that hot because the ARP will shut off the heat source long before the catastrophic temperature is reached, but the fail-safe is still there if needed. If, for example, the ARP failed to measure the heat properly, the safety sensor still works.
Ernie n Tara
Well-known member
I understand that Gary, but I fear the efect is that the temperature will never be permitted to exceed the regulated temperature and therefore the gas gets turned off and then back on when the temp drops. Remember this device is in series with the manufacturers device, the cycle might repeat until ignition. It is an avoidable problem as I described or by inhibiting operation if it heats too soon and probably other means, but nothing I've seen says it is.
That is to say the EMERGENCY cut off never gets to function.
Ned, PID is exactly what I described. If he incorporated it, the output of the device is effectively the output of a PID controller.
This discussion is here and people are buying the device based on recommendations made here. I have no interest in disputes with the manufacturer, just in making sure all sides of the issue are discussed.
Ernie
Ernie
That is to say the EMERGENCY cut off never gets to function.
Ned, PID is exactly what I described. If he incorporated it, the output of the device is effectively the output of a PID controller.
This discussion is here and people are buying the device based on recommendations made here. I have no interest in disputes with the manufacturer, just in making sure all sides of the issue are discussed.
Ernie
Ernie
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Gary RV_Wizard
Site Team
;D I'm chuckling, because Paul and I had a vigorous debate on this very issue just a couple weeks ago, with me as the devil's advocate. There simply isn't enough reliable evidence to know ALL the possible causes of fridge failures, but we do know that boiler temperatures can get excessive even though the RV is operated within normal parameters. We also know that elevated temperatures cause a loss of sodium chromate, and that reduction of the sodium chromate definitely leads to internal corrosion of the cooling unit and ultimate failure. What nobody seems to know is whether other potential causes may also exist, e.g. defective welds, impurities in the coolant cocktail, insufficient sodium chromate from the factory, too thin a metal in the tubing, poor installation practices at RV builders, etc. Many of these things could easily result from poor quality control at the fridge manufacturer (or after market cooling unit manufacturer), and some could result from poor design decisions. What seems probable, though, is that many of these unknowns would still either result in a boiler overheat condition or be exacerbated by higher boiler temperatures. My conclusion is that an ARP would still be available addition to a fridge for most of those possible "other causes". Whether it catches most of them or just some of them is a matter of conjecture, but I see no downside to installing a device just because it may not solve 100% of the possible problems.
My bet is that an ARP will catch a substantial portion of the conditions, regardless of the root cause. At the very least it should extend operational life, even if flaws exists, and at the worst case it will prevent a catastrophic failure well before the built-in safety measures. That seems like a valuable tool to me.
By the way, Paul's wife (Mao Unmak) is also an engineer and her specialty is the design and control of pressure vessels, of which an absorption cooling unit is a prime example. She is an expert in high temperature and high pressure containment systems, so Paul has her expertise to draw on as well.
Whatever your motives are, to dispute or just understand, I still say you should contact Paul directly rather than rely on our second hand knowledge of the ARP unit specifics if you truly want to know more.
As this discussion seems to be going nowhere, I'm done here.
As this discussion seems to be going nowhere, I'm done here.
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Gary RV_Wizard
Site Team
By "ignition" do you mean it catches fire? How is that going to happen if the heat source if always cut off (whether gas or electric) before temperatures get excessive?
In any case, the ARP has a progressive restart algorithm that extends the cool-down and restart period in each repeat cycle and will lock-out any further restarts after 5 repeats. It won't just keep restarting over and over again. The ARP is more than just a simple boiler thermostat that switches off and on again.
weewun
Well-known member
For what it is worth I installed the ARP and elected not to control the Frig operation via NorCold's overheat circuitry. I do not wish to argue with NorCold that my addition of the ARP Control affected their normal operation thus negating their culpability in case of a "fire".
I wired the ARP to control the input 12vdc to the NorCold and it is doing all I understood it would do. If it fixes one deficiency of the NorCold that is a deficiency I don't have to worry about.
I wired the ARP to control the input 12vdc to the NorCold and it is doing all I understood it would do. If it fixes one deficiency of the NorCold that is a deficiency I don't have to worry about.
Ernie n Tara
Well-known member
Gary,
I meant the motor home catching fire from the repeated gas ignition. As long as the new device is operative, the manufacturers device is prevented fron working! The progressive restart is the answer to my comments/concerns. We can argue whether five restarts is the right number, but now everyone is on the same page.
As to pressure vessel experts, I've designed three unique steam autoclaves, all of which are still in use after at least 20 years in service. The largest is 12 feet in diameter. My concerns were primarily vibration effects and I suspect that is one of the primary reasons for refrigerator failure.
PID =proportional-integrative-derivative, usually applied in a controller.
Ernie
PS I'd like to believe he has introduced a leak and found that the five restarts is not sufficient time for a dangerous condition to develop (at least three times).
I'll leave it alone now.
I meant the motor home catching fire from the repeated gas ignition. As long as the new device is operative, the manufacturers device is prevented fron working! The progressive restart is the answer to my comments/concerns. We can argue whether five restarts is the right number, but now everyone is on the same page.
As to pressure vessel experts, I've designed three unique steam autoclaves, all of which are still in use after at least 20 years in service. The largest is 12 feet in diameter. My concerns were primarily vibration effects and I suspect that is one of the primary reasons for refrigerator failure.
PID =proportional-integrative-derivative, usually applied in a controller.
Ernie
PS I'd like to believe he has introduced a leak and found that the five restarts is not sufficient time for a dangerous condition to develop (at least three times).
I'll leave it alone now.
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Gary RV_Wizard
Site Team
Maybe you should start engineering your own control, Ernie. Seems as though you have a handle on what needs to be done and the skills to do it. Opportunity is knocking at your door!
