CASE STUDY 1: UP­GRAD­ING TO A 12V SYS­TEM

SAIL - - Boat Works -

The en­gine-driven reefer in our Pear­son 39-2 project boat was state-of-the-art in its day, but that day was long past. The boat had sat on the hard for a num­ber of years be­fore we bought it, and the in­di­vid­ual com­po­nents had cor­roded and/or seized up. Given the po­ten­tial cost of re­pairs, it did not take long to de­cide to re­place it with a 12V sys­tem (nor did it make sense to me to have to run the en­gine to keep the fridge cool) and only a lit­tle longer to de­cide to go with a hold­ing plate sys­tem, prefer­ably wa­ter­cooled.

My start­ing point was the Pear­son’s deep and nar­row fridge, which I cal­cu­lated at 5.5ft3 to ar­rive at the size of the evap­o­ra­tor or hold­ing plate that would re­place the ex­ist­ing plate. Look­ing through the ar­ray of tempt­ing op­tions from var­i­ous man­u­fac­tur­ers, I kept com­ing back to Isotherm’s ASU unit with the SP wa­ter cool­ing op­tion. The ASU (Au­to­matic Start Up) con­troller mon­i­tors bat­tery volt­age. When the state of charge is be­low 12.5 volts, the com­pres­sor runs at half power. When it senses more than 12.5 volts, whether from en­gine, so­lar or wind power, it runs at full power. It also shuts down the com­pres­sor if the state of charge drops be­low 11.5 volts. A small con­trol panel gives you the op­tion of au­to­matic or man­ual tem­per­a­ture con­trol.

In­stal­la­tion was easy; ba­si­cally, I just swapped out the old hold­ing plate with the new, slightly smaller 14in x 11in x 2.4in unit, fill­ing in the old mount­ing holes with thick­ened epoxy and in­ject- ing foam into the aper­tures where the smaller coolant lines went through. I in­stalled the Dan­foss BD50 com­pres­sor in an un­der­seat locker ad­ja­cent to the gal­ley; with no re­quire­ment for ven­ti­la­tion, I don’t need to worry about vent­ing hot air.

Lo­ca­tion of the com­pres­sor was lim­ited to the 6ft reach of the coolant lines on the SP unit, which re­placed the gal­ley sink drain sea­cock and through-hull. The ex­ist­ing through-hull was too small, so I ham­mered a wooden bung into it to give the pilot drill some­thing

to bite into and cut it out with a hole­saw sized for the SP fit­ting.

The most dif­fi­cult part of the in­stal­la­tion process was snaking the 12AWG power cable though the boat’s nether re­gions to reach the com­pres­sor. Af­ter that it was a sim­ple mat­ter of con­nect­ing the pre-charged re­frig­er­ant lines to­gether and flick­ing on the breaker. The com­pres­sor hummed into life and al­most im­me­di­ately, frost be­gan to form on the hold­ing plate. Suc­cess!

A year later, I have only one re­gret. The fridge has per­formed pretty much as ad­ver­tised, prov­ing both ef­fi­cient and fru­gal in op­er­a­tion; power draw is 5 amps at startup and once the box has cooled down it varies from 3 to 4 amps when the com­pres­sor is run­ning, which is per­haps 10 to 20 min­utes an hour on the hottest days, and so far a sin­gle 100 watt so­lar panel has eas­ily kept up with its de­mands. The re­gret? No freezer; Isotherm doesn’t rec­om­mend this unit be used as such. When the time comes, I will add some­thing like a small En­gel. — Peter Nielsen

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