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Open Roads Forum  >  Tech Issues

 > Increasing Airflow through Condenser.

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landyacht318

Near a large body of salty water

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Posted: 10/07/12 10:48pm Link  |  Quote  |  Print  |  Notify Moderator

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 air directly onto the Danfoss compressor and the electronic controls on the other side of it.

I think it would be better/ more efficient if air flow from the fan flowed through 100% of the condenser rather than ~85%.

The generic fan is said to be louder(25db & 38 cfm) than the compressor itself. I could easily find a quieter fan which moves slightly more air, and also uses less electricity, fabricate a shroud which covers 100% of the condenser's face.

With a reversed airflow I could use this single fan on the shroud to also evacuate the cabinet in which the fridge resides.


[image]

I think that if I can use this single fan to pull air from future passive vent in the enclosed cabinet on the left side of the photo so that it flows around the electronic controls, then around the compressor and funnels through 100% of the condenser then through the shroud, then the fan itself, and out of the cabinet that I can ensure maximum efficiency, and minimum battery consumption.

The only valid reason I can think of for NOT doing this is that somehow warmed air from the condenser blowing directly on the compressor is beneficial to the compressor's performance or longevity.

When I saw photos of the fan's orientation, I joined the forum on which it was posted and asked if the person installed the fan backwards but her responded he was sure that was the orientation it was originally installed.

So does an artificially warmed compressor somehow increase it's performance/ longevity?

Golden_HVAC

Fulltime, CA, USA

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Posted: 10/08/12 12:44am Link  |  Quote  |  Print  |  Notify Moderator

Funny I was looking up 170 CFM axieal fans in the Grainger catalog yesterday, and found one for my needs, they do sell smaller ones.

The large 1" diameter tubing looks like a freon receiver, and might be one. The warmest compressor gas is flowing directly to the top right freon tube, then it goes to the back, down one level to the front and continues. If the air intake is from the right to left, it would not make much sense. However it will work almost equally well with air flow from either direction. The coldest tube would be the lower left one, so if the air goes in the left side, it would be better, but really the efficiency change would probaly only be 2% to 4% difference.

By increasing air flow, you probably will decrease compressor amp draw, and the net effect should be less overall power consumption. Depending on the temperature where it s installed, it might save anywhere from -2% to 15% in energy by increasing from whatever size fan they have to a Grainger fan.

Look for Grainger part # 2RTJ6, and on the same page you will find several 12 VDC fans, this being the largest 4-11/16" square and about 1.2 amps, or 14 watts. I am considering 2 of these fans to help provide 12,000 cubic feet of make up air per hour into a 4,000 square foot house that is yet to be designed and built. This would provide a total air change every 1.8 to 2.2 hours.

No the compressor really does not care if air is blown across it. Will it reduce the freon pressure? Not really. It will not stop it from collecting ice if the box gets to cold either.

Fred.

landyacht318

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Posted: 10/08/12 01:19am Link  |  Quote  |  Print  |  Notify Moderator

Thank you very much.

The fan current is limited to .5 amps (1 amp for upto 2 seconds) according to the Danfoss PDF sheet I was just studying. The fan is positioned so it is level with the top of the condenser, so the lowest tube and fins are not directly in the airflow of the fan.

I was not so much interested in putting a much more powerful fan in as one that actually pulls air across the whole of the condenser. For that I would need to build a shroud. The 92mm fan it comes with is, I believe, ~38 cfm and 25db and I can find a same size one at 42 cfm and 15 db. I could also fit in a larger fan that moves even more air for less amps and noise, and would make fabricating the shroud easier too.

I did see in the Danfoss PDF that the compressor can be speeded up from the minimum 2000 rpm by adding a resistor to the thermostat circuit. Perhaps at faster speeds there would be more benefit to a much faster CFM fan and the compressor would run less frequently.



Thank you for confirming that the direction of flow through the condenser is better from left to right, and that the warm air on the compressor is of no benefit.

With the extra insulation I plan on adding and this added airflow, I bet I can achieve a very efficient fridge.


That Grainger fan is ridiculously expensive. You can find similar CFM fans in that size for significantly less, though I cannot vouch for their durability.

Here are some sites to browse for fans:
Frozen CPU

190 cfm dual ball bearing 4.75 inch/ 120mm 12 volt fan.

These fans are super loud when they spin 4000 rpm. You can get larger ones (180/200/220 and 360mm) which move move nearly as much with less noise and amp draw.

I have a 12vdc 92 mm fan (Vantec tornado) which spins 3800 rpm and is rated at 1 amp 118 cfm. The first time I hooked it to 12 volts, it sucked itself right across the table, screaming. Highly recommended!

I have it wired to a voltage controller and to an adjustable arm with a good clamp and run it from 3 to 12 volts in 1.5 increments. With the fixed curved blades in front of the spinning fan concentrating the flow, it sends a dense column of air wherever I point it. Very impressive flow, and at 9 volts, it only pulls .5 amps.

* This post was edited 10/08/12 01:38am by landyacht318 *

ScottG

Bothell Wa.

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Posted: 10/08/12 08:25am Link  |  Quote  |  Print  |  Notify Moderator

I have a wine cooler that uses a very similar setup. I found that it would regurgitate it's own hot air. So I designed and installed a couple of simple baffles that prevented it. I'm thinking that yours could do the same thing by drawing air over the top of the fins. A simple piece of PlexiGlass or some other hard material would block this path off.
On mine it made a huge difference in how hot the compressor gets and how long it runs.


Scott, Grace and Wesly
2003 Dodge 3500 4x4, 6 speed Cummins (lightly bombed),
2018 Silver Fox 32A - many mods to come!
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MEXICOWANDERER

las peñas, michoacan, mexico

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Posted: 10/08/12 02:13pm Link  |  Quote  |  Print  |  Notify Moderator

I would take condenser inlet and outlet differential temperature readings and compare them to ambient temperature before I did anything.

landyacht318

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Posted: 10/08/12 03:37pm Link  |  Quote  |  Print  |  Notify Moderator

I've been scouring the web for all the info I can find, and basically the consensus is that The Danfoss compressors are extremely reliable. Their electronic controllers, much less so.

Adding resistors in the thermostat circuit can change the compressor rpm, and amp draw, but slowest is most efficient.

They say the control modules fail due to excessive heat, because the compartment is not ventilated properly, and the same heated air gets recycled again and through the condenser, reducing it's efficiency with each pass.

The best thing for efficiency is keeping a flow of ambient temp air flowing through the condenser. I am going to ensure this is the case, taking a few extra steps that the bean counters decided were too many beans worth.

I can easily power 2 120 mm 53 cfm fans that draw 0.08 amps each. One drawing air through the whole condenser via a shroud , one keeping a positive flow of ambient temp air flowing into the compressor compartment. More air moved quieter, less amps used and cooler compressor, and control module.

Am also considering putting in a variable resistor to change the compressor rpm, but this is likely overkill.

http://www.kollmann-marine.com/Fans.aspx........g_and_process_heat_disposal_Fan_or_fans.

bdosborn

Colorado

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Posted: 10/08/12 06:29pm Link  |  Quote  |  Print  |  Notify Moderator

I replaced my fridge with a Tundra 12V compressor fridge last year. I was worried about heat build up as well so I tapped into the fridge fan circuit to close a relay, which in turn runs an axillary fan. I then added a snap relay so that the fan only comes on when its over 85F. Solved the heat build up issue.

[image]

I added an inch of polyisocyanate insultion around the box for an extra R7. It might not help much but it won't hurt any. I also added a layer of reflectix insulation on the sides, underneath the fridge and over the back. I figure every little bit will help.

[image]

Mine uses 1 amp-hr on average at 80F.

Tundra Meter Readings

Bruce


2010 6.5'X11' TTT - Boxcar
Custom Frame, Poptop, AC, Espar Diesel Furnace, HW Heater, Sink, Shower, 12V-120V, LED Lights, TV and XM Radio, DVD Player, 300W PV Panels, PD 9140 Charger, Tongue Box, Filon Exterior, 1000W Generator, Patient Wife
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landyacht318

Near a large body of salty water

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Posted: 10/08/12 06:56pm Link  |  Quote  |  Print  |  Notify Moderator

Bdosbourne,

Funny, I was just checking out your site, then checked back over here and saw you posted.

My father has a larger Tundra on his boat. It only had three small passive vents in the rather large compartment behind it. I blocked off one of the uppers and put a 120 mm fan wired to the controller on the other exhausting the hot air and pulling in cold air by the condenser.

Duty cycle was reduced substantially.

MEXICOWANDERER

las peñas, michoacan, mexico

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Posted: 10/08/12 06:57pm Link  |  Quote  |  Print  |  Notify Moderator

I added a 135 ohm RELAY to the fan circuit of a DanFrost on a sailboat and the controller freaked out. A SKYPE call back to the USA to the company had me listening to a tech who claimed exactly perfect line resistance values are *that* critical. Sure surprised me.

landyacht318

Near a large body of salty water

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Posted: 10/08/12 07:08pm Link  |  Quote  |  Print  |  Notify Moderator

I briefly considered the relay option, but since the controllers directions say it can handle upto .5 amps, I don't see the need with the 2 0.08 amp fans I plan on.

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