[THEFERMANATOR]

Originally Posted by Destroyer

I did specify a small window unit. While I agree with you on a whole house unit using more electricity that's not really the case with small window units.
In many cases the difference between a 4500btu or a 5000btu is the size of the evap coil with the compressor being the same size for both of them. The electric usage is less per btu with the larger unit while achieving the same RH decrease and cooling. And of course, a case could also be made that using several window units to cool a home will cost more than running just one large central unit to do the same thing, because the central unit will be running one compressor on 220v while the window units will be running multiple compressors at 115V. (But that's no longer comparing apples to oranges, so it's really not a good comparison).

Additionally, the compressors duty cycle is a good thing to know while sizing a unit for a particular job.. Some need to have a rest period of a certain percentage of their operating time, to give the compressor time to cool down. You want this to happen to prevent breakdowns and to prolong the life of the compressor in your A/C unit. Usually, the duty cycle is expressed as a percentage of a certain time frame, often a 10 minute segment. So a duty cycle of 50% for a particular brand and model of A/C would mean that this particular unit could run steadily for 10 minutes, and then it must have a 10 minute rest period before it kicks in to cool again. Often it's the home owner that gets caught in the duty cycle trap, not knowing what the duty cycle of their unit is, and burning it out prematurely through too prolonged a usage. The point being that any money you might save in electricity by running a higher duty cycle unit might be negatively impacted if your unit fails in X years instead of Y.

I think the same could be said for a 200hp vs a 150hp. If all you're doing is cruising along at say 30 knots wouldn't the 200 be just loafing along at a lower rpm while the 150 would need to be running at a higher rpm just to maintain the same speed? I'd think that the 200 would be more fuel efficient under those conditions. (And really, when you're out in the ocean, you hardly ever get the nice flat seas that allow you to really let it all hang out. Most times it's 30-35 if you're lucky).

Most compressors get cooled by being properly charged, and having the correct charge in the system. A correctly charged system will have a compressor that is condensating at the suction line, and even on that side of the housing. The idea is to have the system charged to the point so that once the system is stabilized and the home is cooled down, there is just enough liquid making it to the compressor to cool it.

As to the 200 loafing along VS the 150 spinning up, this is only true to a small degree. It takes X amount of HP to push a vessel at Y amount of speed. And for the most part, it takes pretty close to Z amount of fuel to make X amount of HP. Where the biggest differences come in is in the engines efficiency to produce HP. The 2.4L 200HP engine was FAR more efficient than the 2.0L 150 at putting out X amount of HP. Or look at it this way. A mid 80's 150 EVINRUDE will gulp down an EASY 12 GPH cruising along at say 4400 RPM's cruising putting out say 120 HP. A 2.0L MERCURY doing the same exact RPM's puttting out the same exact amount of HP would burn probably 8-9 GPH. Now my old 140 EVINRUDE running along even at 5000 RPM's probably putting out the same 120HP would do this burning around 7-8 GPH, and it's turning more RPM's than the other 2, using less fuel than either one doing it.

Or take a MERCURY 2.5L engine. It could be had anywhere from 150-280HP, but only to 200HP for feeshing engines. Now the same basic engine(I realize they had horizontal and vertical reed engines as well as I believe some had finger ports, and some did not) with a 50HP power spread, and yet they all burned with a few GPH of each other running along at say a 4000 RPM cruise.