Fridge - optimize Heat Exchanger temp by using a Thermostat for Fan Control

[rickst29]

Answering my own question: According to a page in "ehow", the Norcold's Heat Exchanger (the radiator-like thingy at the top of the upper panel) works best if the temperature is held to less than 85-90 F. I presume that figure is meant for the area on the left side of the unit (facing the Fridge backside from completely outside) - and isn't meant to recommend that you "prematurely" cool down the hot pipe which isn't bonded to most of the fins - the pipe along the rear from the right side heater stack.

So, the exhaust fans (the TM-provided exhaust fan which pulls from the top to the bottom, through flex tubing, and/or your own added-in fan blowing straight out from the upper panel) should probably turn on somewhere within this temperature range, and probably turn off when temps at the Heat Exchanger are below 80F. There is probably a cheap 12V thermostat which would be adequate for this, but because I'm already familiar with the JLD-7100 temp controller, I'll waste a little more money and buy another one of those: http://www.lightobject.com/JLD7100-D...oller-P66.aspx. Using Farhenheit settings, I'll try starting from SV=0085 (desired temperature), HY= 0005 (variability for On/Off control around SV), and (of course) rd = 1 (cooling mode, not heating).

The TM exhaust fan sounds like jet engine; I have added an extremely quiet computer fan to the left side of the removable panel (the side opposite the heater stack) - and used "FlexFix" flex duct tape to tape it on the inside surface, and to seal up all the other gaps in the rest of the left side. (That's "UL 181-B", not everyday "Duct Tape"). It has extremely good heat resistance, the glue doesn't smear around, the tape doesn't slip, and it's vibration-proof. Big box hardware stores all have it.
My fan is this one: http://www.newegg.com/Product/Produc...82E16835426016 It moves just 37 CFM, but that's quite adequate for this application - and you can barely hear it when standing outside, leaned over, with your ear right next to the panel.

I'll report on results when the TM is next out of the garage, and I have finished the installation.

I added a 4" computer fan to the top of the fridge compartment. I added a switch next to the switch panel under the sink. I turn it on when the temp gets hot and off when it cools down. I can see immediate results when I turn it on on a hot day. The TM exhaust fan is pretty much useless when the shells are up, but works ok when closed.

[rickst29]

Exactly; but I want to go with "auto-magical" switching, rather than add another manual switch.

But yeah, my way has a bit of a downside- it costs about 12x more money.

I have added Zalman Fan PWM controller

http://www.newegg.com/Product/Produc...82E16835118217

to make a fridge fan silent at night.

I did the same upgrade for standard (not Fantastic) vent. Plus initially I replaced this garbage motor by four 140mm high flow computers fans.

[rickst29]

My Thermocouple is measuring 102 F, continuously, at it's location above the upper left of the heat exchanger (looking in from outside). Ambient is only 91F. The air which is in contact with the heat exchanger (i.e., the air which it must "fight against") must be at least a few degrees hotter than that figure. The original TM fan is blowing out some warm air, and my fan is blowing out more ... but I suspect that that the fridge would cool down faster, and reach a lower temperature, if the surrounding air was being cooled better under these conditions.

What temps are you guys keeping at the top of the heat exchanger compartment, while the fridge is running continuously? BTW, I'm testing 120VAC, and it is 119-120V. (Temp within the Fridge is correct, staying within one degree of 35F.)

I've ordered a pair of slightly more capable fans: 47 CFM, 140 mm (5-1/4"). I might not have a chance to test in 100+ days (this week will be much less hot than usual), but I'm pretty sure sure that doing the replacement would help. I'll replace one fan, and keep the other - adding it if a future high-temp test shows more than 110F in 100-103F conditions.

[rickst29]

A DC fan may help improve refrigerator performance when the refrigerator is not installed in accordance with Norcold's installation requirements or when operating the refrigerator in high ambient temperatures (see "Refrigerator Installation Manual"). A DC fan will assist in providing the necessary amount of airflow. Be sure the fan is controlled by a thermostat and begins to operate when the area behind the refrigerator reaches approximately 95 degrees F. The fan should run until the temperature lowers to about 80 degrees F. Consult with your RV dealer for the correct fan and specifications.

They allow an operating range of 15 degrees between "Fan-ON" and "Fan-OFF" temperatures. Per my #1 post, I guessed perfectly: "Fan-ON" at 90F (85+5), staying on while the temperature is above 80 (85 - 5). And my current fan, allowing as much as 102F on a day which was only 91F ambient, is definitely inadequate.

[rickst29]

Switching from the 120mm, "37 CFM" model to the larger fan (140mm, "47 CFM") has reduced the "excessive" hot air temps around the Heat Exchanger by a great deal. (Remember, anything more than 90F is underirable.) I didn't use the the TM's "OEM" exterior fridge fan in any of these performance tests. Per the previous post, with the smaller fan, temperature inside the Heat Exchanger compartment was reaching 102F (11 degrees above an outside temp of only 91F on that test day). With the larger fan moving more air, I'm getting only 6 degrees above the outdoor value (95F, 6 degrees above today's outdoor temp of 89F).

When running with no fan at all, my thermocouple was reaching 116F - but my upper panel is 50% blocked by the fan, and so I'm not surprised by that bad reading. I didn't try with just the TM's OEM fan, but I know that it is much less effective, and vastly more loud, than my add-on. It's still mandatory for towing, of course.

Next, I moved that 120mm, 37-CFM fan to the inside of the Fridge, taking the place of a "Double-D-Powered mini-fan" I used to use. I have it set horizontal on the upper shelf, blowing directly into the fins on the left side.
After I finished that wiring and cleaned up the bits of trash I'd created, I turned the Norcold to AC power for cool-down, expecting that my traditional "over-night" cool-down would still be appropriate. Before this fan arrangement, the fridge would require 6-7 hours in these afternoon temperatures (88-89) to cool down to 36F. But, with these fans in place, and without packing in any cold food at all, it was completely chilled in just 100 minutes. WOW.

[ThePair]

I've noticed dramatically reduced cool-down times with a similar set-up, yep.

It's cool. ;-)

Originally Posted by rickst29

Switching from the 120mm, "37 CFM" model to the larger fan (140mm, "47 CFM") has reduced the "excessive" hot air temps around the Heat Exchanger by a great deal. (Remember, anything more than 90F is underirable.) I didn't use the the TM's "OEM" exterior fridge fan in any of these performance tests. Per the previous post, with the smaller fan, temperature inside the Heat Exchanger compartment was reaching 102F (11 degrees above an outside temp of only 91F on that test day). With the larger fan moving more air, I'm getting only 6 degrees above the outdoor value (95F, 6 degrees above today's outdoor temp of 89F).
...

Not sure if this applies to the different frig's in the folding Trailmanors, but with the Elkmont, I've found that removing the vent covers (esp. the upper one close to the heat exchanger) on hot days really helps reduce the fan's frequency of operation. The vent covers do a pretty good job of keeping out the rain, but definitely restrict air flow.

So far that's all I've needed to do. Not sure why Trailmanor didn't put in a roof vent on the Elkmont, which should help as well.