marinCool Peltier Effect Refrigeration
Just as there’s more than one way to skin a cat, there’s more than one way to chill a beer. Serious cruisers usually opt for expensive holding plate systems, often with engine-driven compressors that make large “refrigerators” and even freezer compartments feasible. For less arduous duty, the less-expensive 12-volt icebox conversion evaporator systems have proven popular, more among coastal cruisers. We tested five models in the December 1, 1996 issue—Adler/Barbour ColdMachine, Grunert Baysider, Norcold Tek II, Nova Kool and the Coolmatic 65, imported by Scan Marine. Of the five, we noted that the ColdMachine had the shortest duty cycle, running 67% of the time. Others ranged up to 82%. Average current draw of the ColdMachine was 3.3 amps, meaning that over a day’s time, you’d consume at least 53 amp-hours. That’s the food bill for 12-volt-powered compressors.
We were therefore intrigued when Origo (the Swedish company noted for its alcohol marine stoves) announced a Peltier Effect ice box system available as a conversion kit or a drop-in module including molded fiberglass icebox.
You’re probably familiar with the concept via portable coolers that plug into the cigarette lighter plug of an automobile. In the same December 1, 1996 issue, we tested four portable chests from Coleman, Koolatron, Power To Go and Igloo. The Peltier Effect is named after Jean Charles Peltier, a wealthy French tinkerer who in 1834 discovered that when an electrical current is passed between two different metals, heat transfers from one metal to the other because electrons pass through different metals at different speeds. In 1838, Russian Emil Lenz advanced the concept by passing a current through a bismuth-antimony joint and froze a drop of water. More recently, astronauts have benefited from the Peltier Effect, which is employed for the cooling and heating of food. Most appealing is the fact that there are no moving parts.
The shortcoming of thermoelectric portable coolers is the amount of current consumed—from 3.4 to 4.5 amps in our tests—and the inability to cool more than about 40°F below ambient temperature. However, one of our contributors, Fred Cornford, an engineer, has experimented with thermoelectric refrigeration and has managed to make ice, but only with huge amounts of electricity. Still, the possibilities are intriguing…if only one could reduce the current draw.
The Origo marinCool
Enter Stefan Larsson, whose company, AutoControl R&D AB of Göteborg, Sweden, developed the marinCool Peltier Effect icebox for boats and sold the rights to Swedish giant Electrolux, whose subsidiary Origo manufactures and distributes the several models.
According to the brochure, “The Origo marinCool is a thermoelectric cooling system based upon the Peltier Principle. A copper braid connects a heat sink inside the cooling box to a copper plate attached as a thru-hull fitting to the outside of the hull below the waterline. Next to the copper plate rests an electronic heat pump. As current is applied to the pump, heat is transferred from the cooling box to the sea by way of the copper braid. All functions are monitored and controlled by the microprocessor within the regulator. The cooling unit is absolutely silent and so efficient that you can maintain desired temperatures within the box regardless of the external sea temperature.”
The marinCool is distinguished from the portable coolers mentioned above in that it uses water to dissipate heat, rather than air, and hence is more efficient. But this requires a very heavy copper braid between the large copper through-hull and the ice box. Retrofitting this braided cable to an existing box could be quite difficult as access to the under-box area is often restricted.
A microprocessor controller has several settings, allowing selection of box temperatures between about 32°F and 43°F. Obviously, the lower temperature consumes more electricity. To protect the ship’s batteries, the controller is supposed to shut off the unit when battery voltage drops to 11.2. In our tests, however, it shut down at about 12.2V.
The marinCool is offered in three forms: the marinCool 85 3-cubic-foot (100 liters) top-loading fiberglass ice box, a smaller marinCool 18 .6-cubic-foot ice box, and a conversion kit for existing boxes of up to 3.5 cubic feet. Prices for the marinCool 85 range from $1,395 to $1,540, depending on length of copper braid (9" or 11") and size of the heat sink (10" x 8" or 13" x 8"). No lids are provided as countertops vary by boat.
Because we were quite curious about claims that the marinCool can maintain a 32°F box temperature, we went to some lengths to test it.
Fred Cornford & Associates performed the tests, setting the marinCool 85 ice box above a 72" x 40" x 10" deep 123-gallon tank. We constructed the large tank because we did not want to risk heating the water on which the system relies for heat dissipation. The copper braid must be well insulated with foam.
A variable power supply enabled us to test the system at different voltages, which has a profound effect on performance. Current consumption was measured with a Cruising Equipment Amp Hour + 2 meter. Fluke 52 K/J dual-channel thermometers recorded temperatures from sensors placed at several locations within the box, both low and high. All tests were conducted with the marinCool’s controller at the coldest setting—0°C or 32°F. A 12-pack of room temperature Pepsi was placed in the box.
The tables show the results. In the low-voltage test (12.2V), with water temperature of about 60°, after 17 hours upper and lower box temperatures were 49.8°F and 39.4°F respectively. This was our first indication that temperatures inside the box are not uniform. These observations were confirmed by Stefan Larsson, who told us that the gradient is designed so that coldest temperatures are lower, warmer temperatures higher. “You don’t need to keep lettuce or milk at 32°F,” he said.
In the high-voltage test (13.7V) with the tank water heated to 80°F, the lower box temperature of 32°F was reached after about 14 hours, suggesting that high voltage is more important than cold seawater temperature. Larsson said we should expect similar results with as low as 12.8V.
We were at first skeptical about the possibility of a Peltier Effect refrigeration system removing enough heat, at reasonable current draw, to keep an ice box close to freezing. From that standpoint, the marinCool was impressive. It is designed to operate continuously (unlike a 12V compressor system that cycles on and off). The marinCool takes much longer to cool, but once it does, current consumption is less than 1 amp. If the boat is kept at a dock and supplied with shorepower, this is no problem. If the boat is kept at a mooring, you’ll either have to have enough battery capacity to handle a 12- to 24-amp-hour per day loss, or, if you don’t visit your boat very often, use solar panels or a wind generator to keep up with the loss. Indeed, the company promotes and offers a solar panel option for the latter scenario. The other controller settings economize on electricity, though temperatures are higher.
The 3.5-cubic-foot capacity of the marinCool 85 is small by U.S. standards, and the marinCool 18 is microscopic. Most 12V compressor systems can handle up to about 8 cubic feet. There was not much insulation in the box supplied; on the positive side, one might obtain even better performance with the marinCool Kit in an existing box with 4" of insulation.
From the data collected, we were unable to determine how much ambient air temperature affects the marinCool’s performance. In our test, air temperature was about 65°F, much cooler than the inside of a boat in the tropics. At the same time, when supplied with 13V and operating with 80°F seawater (about the temperature of water in the subtropics, and much warmer than seawater in northern climates), the marinCool had no problem getting the box down to 32°F.
Perhaps our biggest concern is achieving a good installation in an existing boat. The copper braid does not stretch, so the bottom of the box must be within 11" of the hull. Then, the braid must be insulated. If cabinetry must be pulled apart to access the under-box area, owners will be understandably reluctant.
On the plus side, the marinCool has no moving parts so theoretically should last many years with little or no maintenance. Amperage draw is less than a 12V evaporator system, and though it’s not intended to make ice, 32°F is plenty cold enough to keep food items safe, and in the case of beer, tasty to the American palette.
As the product gets into the field, we’d like to hear from users regarding installation, its performance and reliability.
Contact- Origo, 1121 Lewis Ave., Sarasota, FL 34237; 941/365-3660.