Oh boy, if only that were true! But unfortunately there is no such thing, and so comparing the performance of one marine air conditioning manufacturer's product to another comes down to comparing the manufacturer's published specifications.
Keep the following in mind if you are in the market for air conditioning for your boat.
Q – How can I be sure that a 16,000 Btu air conditioner from Brand X actually produces 16,000 Btu of cooling and heating?
A – To be blunt, you can't! If it were a residential or commercial unit you'd be assured of the capacity rating as there are strict compulsory standards in these industries, but not in the marine business.
A marine air conditioning manufacturer can label his system as whatever takes his fancy, which is usually dictated by marketing strategies. If only we had that "Btu Meter" to assess performance .....
Q – But surely there must be a base-line for a prospective buyer to be able to assess one manufacturer's system against another's.
A – Yes there is, it is the compressor. Every compression system has a compressor, and every compressor manufacturer publishes performance data for their individual models. Most marine air conditioning manufacturers simply use the compressor's Btu rating in determining what to label their products.
That's a simple solution, but
there are many other components in a system besides the compressor that greatly effect the performance of the finished product. The quality and effectiveness of these other parts, plus significant differences in the way it is all put together, all contribute to the end result.
The difference in performance and efficiency between manufacturers' products is not necessarily reflected in the price, but with no "Btu Meter" there is no simple way of telling if one product has more cooling power or is more efficient than another.
Q – So why can't the marine industry come up with a standard like the ones in use in the residential and commercial fields?
A – The easy part would be to come up with the standard. The real challenge would be the testing, compliance, and enforcement. It is a complicated and expensive process to gain performance data for an air conditioner, and the residential/commercial compliance authorities demand that a certain percentage of product be submitted for testing.
It is not as simple as, say, a water pump where any one of us could easily measure how much water is pumped in a certain period. Many marine air conditioning manufacturers don't have the necessary equipment to perform accurate in-house capacity testing at specified conditions, and even if they did have a "Btu meter", they are not required to use those actual results in designating the Btu capacities of their air conditioners.
Q – So what exactly are marine air conditioning manufacturers supposed to use when rating their systems?
A – As stated above, there is no compulsory standard, but if a manufacturer follows the voluntary guidelines set out by the American Boat and Yacht Council (ABYC), then a water-cooled air conditioning unit Btu rating will be: "based on the compressor manufacturer's published performance data at an evaporating temperature of 45°F (7°C) and a condensing temperature of 100°F (38°C)".
Now although that sounds pretty technical, it is actually simply a matter of referring to the compressor manufacturers published performance data and noting the Btu figure at the relevant point. That itself is a five-minute job, but it doesn't end there.
The phrase "based on" at the beginning of the ABYC guidelines leaves lots of wiggle room for manufacturers to add on a few thousand Btu's if they wish, as long as the final figure is "based on" compressor performance at the specified conditions.
The voluntary and advisory ABYC standards are the closest thing to compulsory standards that we have in the marine air conditioning industry, and although they relate solely to the compressor and not the complete system, they are at least a basis for comparison.