Increasing Airflow through Condenser.
The new DC only compressor fridge I will soon have in my possession has a 92 mm computer muffin fan pulling air through only a portion(~85%) of the ~120mm tall condenser. It then blows this warmed a...
Forum Discussion
Well, Call me a pessimist or a cynic or both, or something else entirely, but I don't believe these manufacturers went to such extremes to perfectly tailor fan CFM to compressor speed and condenser size.
Judging by your reply, I don't believe you read the subsequent 6 pages since my first post(don't blame you), but basically I left the airflow in the same direction as designed, but used a better, quieter fan and have it pushing air through the whole condenser, then across the compressor and controller. This is now a single pass airflow system, Cool air is sucked from the floor, pushed through the condenser once, funneled around the compressor and controller and then is forced out a vent, all with a single fan that draws half the current of the original fan and makes less noise doing so.
I removed the resistor to slow the compressor speeds to minimum as apparently from everything I have read about Danfoss compressors, the slowest the compressor speed to maintain a sub 50% duty cycle and sub40f internals is most efficient, and with the resistor(2500 rpm) I was running ~25% duty cycles at ~ 80f ambient IIRC for sub 36f internals and slightly over 30% at 2000 rpm for the same internal and ambient temps.
My cooling unit is now shielded from installation/removal stresses with the added benefit of forcing air to flow around the compressor and controller. The Fan I used has a slower CFM rating, but a higher static pressure rating. It is pushing air through resistance instead of both pulling and pushing it. It also has a 6 year warranty which is pretty confidence inspiring compared to some noname fan manufacturer that used a steel sleeved bearing.
I asked on some other forums what size and rating fans were used on units with very similar condensers and evaporator sizes and compressor speeds, and pretty much the fan's CFM ratings varied from 92mm and ~40 cfm to 120mm and 73 cfm, with the 120mm 73 CFM fans on the 1.8 cubic foot Vitrifrigos and the 92 mm ~40 CFM fans on the 2.2 Cubic foot Tundra and TruckFridges. The Tundra has increased compressor speeds, the TF's do not.
If you were to squint your eyes and look at these fridges, you would be hard pressed to detect any differences between their design or construction.
I for one don't believe that all manufacturers everywhere always have their product dialed in perfectly. The bean counters have the final say, not the engineers. Good enough is far from ideal. Maximum profit always wins out and if they can get a case of fans for 10 dollars cheaper that have different cfm ratings, then that is 10 more dollars in the pocket of the guy up top who gets to praise the bean counters for allowing him to by another useless bauble for his trophy wife/mistress for whom nothing will ever be good enough.
I really tried to do my research before actually changing things. I've certainly seen many cases of people who try to out think designers and engineers, and understand the reasoning behind why it is better not to screw with things. I try not to doubt the engineers, only the bean counters and those who sign their paychecks. Everything is a compromise.
Perhaps the words 'Cynic' or 'pessimist' is not inclusive enough to describe me, perhaps Misanthrope is more accurate. :)
If I found that all these fridges had the same fans or fans with the same airflow ratings I would have insisted on a Quieter fan of the same CFM rating too. As it turns out, while the fan I installed has a lower CFM rating, it has a higher static pressure rating, so it probably moves just as much air, and does so for less current consumed and noise made. Ultimately the fridge performance, from calculating Duty cycle vs internal temperature readings and taking into account ambient temps has, increased significantly with my modifications.
Not much more can be done for sound insulation inside my cabinet. The new Fan's noise is not bothersome, but on really quiet nights the low rumble of the compressor and its initial start up are louder than desired from bed while the fan itself is now inaudible. I am researching how to better dampen these low frequencies, but this fridge is already magnitudes of order quieter than my previous Norcold's Sawafuji swing compressor which I was able to feel vibrate the whole van.
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In an update to my internal fridge fan performance, I never found a good way to mount it behind the thermostat dial as described in my last post.
I found the internal freezer door was always getting in my way requiring the main door be opened beyond 120 degrees. I removed the freezer door as nothing I place in there needs a door to be held in place. the Gel packs I keep in there remain frozen solid. I then found that without the restriction of the freezer door, the 40 mm fan blowing air inside the freezer portion against the back wall, the box temperatures fell by an average 2 degrees more all over the box for the same ambient temp and T stat dial setting. For grins I then turned the fan around so it blows air into the main door instead. The internal temperatures dropped another average .5 degrees F, and the very back of the fridge, which according to my IR temp gun was always the warmest spot in the fridge, by up to 14 degrees with no internal fan, was now within 1.5 degrees of the rest of the fridge box.
I now need to drop the t stat setting to 1.75 out of 7 to prevent fridge contents from freezing overnight, but I suspect above 75f ambients I will need to raise it back to 2 or above depending on the frequency of door openings.
I don't believe the internal fan reduces overall duty cycle, but it does, without doubt, even out the internal temperatures, cool down contents placed within faster, and allow lower T stat settings to be used.
The Lower T stat settings might just be warm and fuzzy and inconsequential, but it is nice to know I need to only use 2 out of 7 instead of 4 out of 7 to keep food within sub 40f.
The internal fan also allows me to better take advantage of a solar or alternator amperage surplus. I can turn it up when surplus is available cooling contents quicker tothe low 30's, and turn it back to normal when not. The fridge then has a better duty cycle overnight as the internal temps are allowed to slowly rise to the high 30's from the low 30's.
Judging by your reply, I don't believe you read the subsequent 6 pages since my first post(don't blame you), but basically I left the airflow in the same direction as designed, but used a better, quieter fan and have it pushing air through the whole condenser, then across the compressor and controller. This is now a single pass airflow system, Cool air is sucked from the floor, pushed through the condenser once, funneled around the compressor and controller and then is forced out a vent, all with a single fan that draws half the current of the original fan and makes less noise doing so.
I removed the resistor to slow the compressor speeds to minimum as apparently from everything I have read about Danfoss compressors, the slowest the compressor speed to maintain a sub 50% duty cycle and sub40f internals is most efficient, and with the resistor(2500 rpm) I was running ~25% duty cycles at ~ 80f ambient IIRC for sub 36f internals and slightly over 30% at 2000 rpm for the same internal and ambient temps.
My cooling unit is now shielded from installation/removal stresses with the added benefit of forcing air to flow around the compressor and controller. The Fan I used has a slower CFM rating, but a higher static pressure rating. It is pushing air through resistance instead of both pulling and pushing it. It also has a 6 year warranty which is pretty confidence inspiring compared to some noname fan manufacturer that used a steel sleeved bearing.
I asked on some other forums what size and rating fans were used on units with very similar condensers and evaporator sizes and compressor speeds, and pretty much the fan's CFM ratings varied from 92mm and ~40 cfm to 120mm and 73 cfm, with the 120mm 73 CFM fans on the 1.8 cubic foot Vitrifrigos and the 92 mm ~40 CFM fans on the 2.2 Cubic foot Tundra and TruckFridges. The Tundra has increased compressor speeds, the TF's do not.
If you were to squint your eyes and look at these fridges, you would be hard pressed to detect any differences between their design or construction.
I for one don't believe that all manufacturers everywhere always have their product dialed in perfectly. The bean counters have the final say, not the engineers. Good enough is far from ideal. Maximum profit always wins out and if they can get a case of fans for 10 dollars cheaper that have different cfm ratings, then that is 10 more dollars in the pocket of the guy up top who gets to praise the bean counters for allowing him to by another useless bauble for his trophy wife/mistress for whom nothing will ever be good enough.
I really tried to do my research before actually changing things. I've certainly seen many cases of people who try to out think designers and engineers, and understand the reasoning behind why it is better not to screw with things. I try not to doubt the engineers, only the bean counters and those who sign their paychecks. Everything is a compromise.
Perhaps the words 'Cynic' or 'pessimist' is not inclusive enough to describe me, perhaps Misanthrope is more accurate. :)
If I found that all these fridges had the same fans or fans with the same airflow ratings I would have insisted on a Quieter fan of the same CFM rating too. As it turns out, while the fan I installed has a lower CFM rating, it has a higher static pressure rating, so it probably moves just as much air, and does so for less current consumed and noise made. Ultimately the fridge performance, from calculating Duty cycle vs internal temperature readings and taking into account ambient temps has, increased significantly with my modifications.
Not much more can be done for sound insulation inside my cabinet. The new Fan's noise is not bothersome, but on really quiet nights the low rumble of the compressor and its initial start up are louder than desired from bed while the fan itself is now inaudible. I am researching how to better dampen these low frequencies, but this fridge is already magnitudes of order quieter than my previous Norcold's Sawafuji swing compressor which I was able to feel vibrate the whole van.
-------
In an update to my internal fridge fan performance, I never found a good way to mount it behind the thermostat dial as described in my last post.
I found the internal freezer door was always getting in my way requiring the main door be opened beyond 120 degrees. I removed the freezer door as nothing I place in there needs a door to be held in place. the Gel packs I keep in there remain frozen solid. I then found that without the restriction of the freezer door, the 40 mm fan blowing air inside the freezer portion against the back wall, the box temperatures fell by an average 2 degrees more all over the box for the same ambient temp and T stat dial setting. For grins I then turned the fan around so it blows air into the main door instead. The internal temperatures dropped another average .5 degrees F, and the very back of the fridge, which according to my IR temp gun was always the warmest spot in the fridge, by up to 14 degrees with no internal fan, was now within 1.5 degrees of the rest of the fridge box.
I now need to drop the t stat setting to 1.75 out of 7 to prevent fridge contents from freezing overnight, but I suspect above 75f ambients I will need to raise it back to 2 or above depending on the frequency of door openings.
I don't believe the internal fan reduces overall duty cycle, but it does, without doubt, even out the internal temperatures, cool down contents placed within faster, and allow lower T stat settings to be used.
The Lower T stat settings might just be warm and fuzzy and inconsequential, but it is nice to know I need to only use 2 out of 7 instead of 4 out of 7 to keep food within sub 40f.
The internal fan also allows me to better take advantage of a solar or alternator amperage surplus. I can turn it up when surplus is available cooling contents quicker tothe low 30's, and turn it back to normal when not. The fridge then has a better duty cycle overnight as the internal temps are allowed to slowly rise to the high 30's from the low 30's.
