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Old 09-02-2012, 10:29   #1
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AC Reefer - Fan on Coils ?

We're using (when power is available) a small AC Haier refrigerator. Next to the compartment is a vent for the boat (and I've run a 2.5" hose into the back of the reefer compartment, down low to funnel air)

The vent is forward facing. I've got a small DC fan to install at the point where the hose comes into the locker. Do I want to suck hot air out or blow outside air on the coils? I can put the fan on a switch and when I checked reversing polarity to see if it would run in reverse it didn't. Power consumption is .3A on the 3" fan. A second fan (4") draws 2.1W.

Which fan would you use an in what direction should it blow?
Eventually I'd like to put in something to suck the heat up and out of the boat but at this point that's out of the question. I'm looking for a fast low-cost solution that will help keep power consumption down.

Heading south so outside temps in the 80's and above would not be unexpected. Thanks for any advice you might be able to offer.
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Old 09-02-2012, 13:42   #2
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Re: AC reefer - fan on coils?

To control the exhaust fan and an added condenser fan I have used a snap action fan control thermostat switch available from www Granger cost $12. Their p/n is 2E245 it closes at 110 degrees F and opens contacts below 90 degrees F. When attached to refrigeration condenser with plastic tie raps fan will run when compressor heats coil above 110 degrees and shuts off fans when condenser cools to 90 degrees. Power wire for this circuit must be fused to correct size. Snap action switch is good for 10 amps 12 or 110 volts See catalog.
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Old 10-02-2012, 06:55   #3
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Re: AC reefer - fan on coils?

Thank you Sir for your reply.
I've explained myself poorly. The two fans available for this problem are both 12 volt. I had an empty 7.5 amp breaker on the panel so will run a wire over to the galley for this fan (either the 2.1W--4" fan or the .30A--3" fan) ... I'll put a switch upstream of the fan to use only when I am running the reefer.

For the past year I have run the refer between 10 and 20% of the time. I'm hoping that if I can keep the coils cooler the energy costs for the refrigerator will decrease and I'll feel comfortable using it more. The 12 volt muffin fans I have -- I can place either (which would you use?) at the hose (exits outside the boat 8" away / no sharp bends) and angle the fan to blow (or suck) directly (12") at the motor and coils.

This makes sense to me but to you?????????
Which fan?
Which direction for the air flow?

I know the ideal now (via Grainger) but would prefer to use what I have available and the direction of air flow has my stumped. The hose that goes from outside the boat (vent) to the reefer cabinet is 2.5" in diameter and that hole (in cabinet) is approximately 3" from the bottom -- at the level of the motor/coils.

Thank you for your attention thus far.

Aside: Basically, the only time I turn on my inverter is to power the refrigerator. Essentially the boat is entirely powered via 12 volts. I've looked at your site (wow!!!) and eventually would like to upgrade to a 12 volt refrigeration system however the budget won't allow that as of yet. Maybe in a couple years.................!
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Old 10-02-2012, 07:06   #4
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Re: AC reefer - fan on coils?

run the air out of the boat, it'll keep heat out of the cabin and also prevent salt air (as much anyway) from attacking the coils.
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Old 10-02-2012, 08:20   #5
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Re: AC reefer - fan on coils?

All of the most efficient systems I've seen with the Danfloss compressors have the fan blowing the air straight across the coils and dissipation fins. Any additional removal of hot air from the space would be a bonus, but air blown across the coils comes first.
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Old 10-02-2012, 19:39   #6
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Re: AC reefer - fan on coils?

The little 12V muffin fans don't have a whole lot of static pressure. A small centrifugal fan might give you more air movement. The other question is where is the makeup air coming from or going too. One hose/duct with a fan on it will not move air if there is no way for additional air to get to / or from it... You need a supply and a return duct. or holes in the cabinet

One other option is to zip tie 1/4" copper tubing to the condenser coils and pump sea water thru it. Sort of a poor girls or guys water cooled condenser. Assuming a rear condenser coil on the typical AC fridge that is.

Gee you could also just put a coil, say ten feet of 1/4" copper wraped up in a circle up high in the space, and pump the water thru it and remove the heat that way. You only need to move 15-20 gallons or so an hour, so any dinky little pump would work. in either case the water is dumped back overboard

There I go thinking outside the box again.
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Old 11-02-2012, 05:27   #7
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Re: AC reefer - fan on coils?

If your plan is to be stingy with the use of your 12VDC, then it's best to keep in mind that moving air requires far less energy than moving water.
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Old 11-02-2012, 09:33   #8
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Re: AC reefer - fan on coils?

Thank you Aythya... that was my thinking as well. I'm putting the fan on a small switch so I can power it when the reefer is on but otherwise will rely on the passive air that comes thru the vent. When the wind's ticking, that's quite a lot.

Eventually we'll put in an updraft and pull all the heat out of the back of that cabinet but for now it's not a priority.

Thanks folks. We appreciate the advice.
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