Part 2: The system I saw was not complicated.By Capt. Bill Pike — January 2003
But a difficulty arose immediately. Kehren simply couldn’t find a small, super-efficient, reasonably priced, production-type air-conditioner anywhere—at least not one he was really satisfied with. So, with characteristic vigor, he decided to take matters into his own hands and design his own unit. This line of thinking took him straight to the Miami International Boat Show and Motro, whose small, versatile company is open to new ideas and manufacturing ventures. Within weeks the two men were working on an air conditioning unit they hoped would run on half the current consumed by most mainstream machines—or maybe even less. They opted for the comparatively small, 6,000-Btu model because the size of their test platform, the 800-cubic-foot interior of Kehren’s boat, was actually quite small and because they were both aware of a critical but generally underutilized truth: Because small, continuously operating A/C units remove more moisture from the air than larger, intermittently running units, they offer higher comfort levels at the same cabin temperature.
Kehren and Motro did several things to boost the efficiency of their new 6,000-Btu machine. First, they added a rotary compressor, which is quieter, smoother, and more efficient than most piston types. Then they installed a high-quality blower motor, again, quieter, smoother, and more efficient than many others. And finally, after adding a top-of-the-line evaporator and precisely matching it to an equally top-of-the-line condenser, they figured out how to conjoin all these components in extra-savvy but proprietary ways. “It’s not just high-end parts that’ll make this thing work,” Motro opined at one point, “it’s how we’ll put them together.”
Reports on the finished product were convincing enough to put me on a plane to Miami and eventually to Kehren’s home, where the Harley awaited on her waterside lift. My plan was to conduct a lengthy but simple experiment. Kehren would turn on his new A/C system early in the afternoon, when the Florida sun is typically at its hottest. After checking everything out thoroughly, I’d proceed to keep tabs on the system through the ensuing evening, and on into the next morning, to see if it indeed did what Kehren and Motro claimed it would do.
The system I saw was not complicated. Kehren had interfaced a 2,000-watt Xantrex PROsine 2.0 inverter with a battery bank consisting of one 12-volt Trojan J185H deep-cycle battery paralleled with a pair of series-connected 6-volt Trojan L16H batteries. Since the series-connected 6-volt batteries simply doubled the voltage but did nothing to change amperage or capacity (measured in amp hours, or AH), the cumulative rated capacity of the entire battery bank, based on Trojan’s specifications, was 610 AH, a figure achieved by simply adding 215 AH for the single 12-volt battery to 395 AH for the two 6-volt batteries.
The inverter, its control panel (with readouts for input and output voltage and amperage), and the battery bank were stacked neatly on Kehren’s dock, and the A/C unit was temporarily set up inside the boat, which remained on the lift. Cooling water entered the evaporator via a ten-foot hose trailing down into the canal and a small, 320-gph CAL A.C. pump that was separate from the system as well as from the experiment. Pump installations vary from application to application, and power draw is negligible anyway. Heavy-duty wires connected the unit and the inverter. Before I flipped the starting switch, I examined all hoses and wires to make sure there was no extraneous power source hidden anywhere.
This article originally appeared in the January 2003 issue of Power & Motoryacht magazine.