The Chest style definitely have an advantage, because there is no seal at the bottom where it is coldest like a front loading fridge. <br /><br /> But in terms of air spilling out when the door is open, I think the act of opening the top lid or the front door purges nearly the same percentage of cold air anyway. If all the items within are already cold, then the difference is negligible I bet.<br /><br />How efficiently the condenser's heat is removed directly effects the battery consumption. Most Danfoss powered fridges use forced air through the condenser with a 92 or 120mm computer fan, but some are passive and use no computer fan. NovaKool uses the passive approach with Danfoss compressor. Norcold and Engle use the passive condenser with the Sawafuji compressors. I believe all of the chest coolers have forced air on the condenser. Some use condensers that look passive and have a fan moving air around them. Some use condensers that look like car radiators that are designed for use with a fan.<br />Here you see the latter type:<br />
<br /><br /> Where you plan to store the fridge should sufficient ventilation so the fan does not recycle heat generated by the condenser and compressor, but pulls in cooler air and exhausts it. Fridges don't force things cold, they remove heat from things, and the condenser itself is where this heat is released to the atmosphere, so the more efficient this is accomplished, the less energy ultimately used.<br /><br />I found the fan noise was louder than the running of the Danfoss compressor itself.<br /><br />The 120mm fan which came with my fridge was rated at 72 CFM and was mounted to pull air through the condenser, and blow it onto the compressor and the then the electronic controller. Many other Danfoss powered fridges, even larger ones, come with 92 mm condenser fans rated at only 40 CFM and covering less of the condenser.<br /><br />I replaced the original 120mm 72 CFM fan with a 120mm 54 cfm fan(Noctua NF F-12), which has a very high static pressure rating, and pulls 1/2 the current of the original. I mounted it to push air through the condenser, and found it is significantly quieter in this orientation, and if anything, this location and this fan improved performance in terms of overall duty cycle.<br /><br />Danfoss compressor speeds can be increased for even faster cool downs. Mine came with a resistor in the thermostat circuit to run it at 2500 rpm as opposed to 2000 if removed. I removed it. Speeds upto 3500 are possible but most likely very overkill. It would probably overpower the evaporator(coldplate) of a smaller fridge.<br /><br />The slower the compressor runs to maintain sub 40 degrees and less than a 50% duty cycle the better the efficiency. I removed the resistor in mine and rarely exceed a 33% duty cycle to maintain sub 39 internal temps in upto 85 ambients.<br /><br />All these fridges with Danfoss compressors have slightly different coldplates, and condensers, and their own compressor speeds. Thus the different consumption ratings listed for similar size fridges with the same compressors. No doubt some sweet spot of compressor speed vs condenser size and fans speed exists, but many are optimised for certain functions, like faster compressor speeds for cool down time vs overall efficiency of a slower compressor speed. I think my fridge was running the compressor faster than needed. A faster compressor pulls more current, but runs for shorter periods.<br /><br />
http://www.veco-na.com/images/Compr..._Guardian_and_Merlin_v2_with_pics_7.25.11.pdf<br /><br />
http://coastalclimatecontrol.com/Me...;Product_Code=E51045&Category_Code=access<br /><br />
http://www.equipt1.com/Company Prod...l B Travel Box Test and Comparison Report.pdf<br /><br />
http://www.rvworldstore.co.nz/blog/waecoengel/<br /><br />
http://www.ra.danfoss.com/Technical...f_electronic_unit_ac-dc_04-2009_ei100g402.pdf<br /><br />Keep in mind how ambient temps in an enclosed Van will significantly increase duty cycle. Keeping the Van interior cooler means using less battery power, even considering the electricity used to move a fan.<br /><br />The air which cools my condenser is brought from the floor under the fridge by the condenser fan is pushed out a louvered vent behind the fridge with no chance to recycle preheated air. <br /><br />I've got an additional 3/4" to 1.5" of Foam board insulation all around the fridge, and made a Stainless steel cap/tunnel to protect the cooling unit from installation/removal stresses and funnel the air past the compressor and electronic controller with the help of a soft, heat resistant fan shroud.<br />
<br /><br />I've also installed a 40 mm interior fan rated at 0.03amps and 6.3 cfm. This allows faster cool downs of items placed within, more even temps throughout the box, and a lower setting on the dial. While this Fan won't necessarily reduce overall duty cycle or current pulled from battery.<br /><br /> It Does allow me to faster cool down the fridge contents when I have a solar surplus, or am driving.<br />I can crank up the dial to 4 from 2(out of 7) and pull all the contents down to near freezing, then at night return the dial to 2, and use significantly less electricity overnight while the contents slowly rise back up to 38f. <br /><br />Isotherm fridges have an optional($$$) extra feature, an additional coldplate for storing extra energy when charging voltages are present. These units speed p the compressor to freeze the holding plate when charging voltages are present. I basically do the same thing manually but only with the thermostat, and store the energy in the colder Fridge contents, and the interior fan increases how effective this strategy is. I do think increasing the compressor speed during such times would be better. I got some ideas in the works for varying compressor speeds with the turn of a dial.<br /><br />I do have enough solar and battery power to not really concern myself about how efficient the fridge is, but insuring it is not working harder than it needs to is just in my blood.<br /><br />While the chest style fridges are probably slightly more efficient, I think their biggest advantage is portability.<br /><br />If portability is of no concern to you, your needs might be better met with a front loading fridge and efficiency can be likely matched and perhaps bettered with an insulated cabinet designed to evacuate condenser fan air.<br /><br />The Danfoss compressors are significantly less annoying than the buzz of a Sawafuji, but in a Van, in a quiet atmosphere, the noise can be bothersome. Design it so the compressor is not right next to where you plan to put your head when sleeping<br /><br /><br /><br /><br /><br /><br /><br />