Air Conditioning Install

[GordMay]

A rough “rule of thumb” recommendation for sizing marine air-conditioning is about ± 14-to- 15 BTU/h per cubic foot of cabin volume [living space].

More glazing, pilot house, etc = more heat gain; so perhaps up to 17 BTU/h per cu. ft.

A professional will size the air conditioner based on the latent cooling load (which considers the relative humidity of the air), as well as the sensible cooling load (which considers the outdoor & indoor design air temperatures) for your boat & location.

A (theoretically) perfectly-sized air conditioner will run continuously during the hottest 2.5% summer design (outdoor) temperatures.

Don't buy an oversized unit. An over-sized unit short-cycles (turns on & off too rapidly), so doesn’t properly de-humidify*, and uses more energy (starting currents).

On the other hand, make sure any ducting is sized large enough to allow low-velocity air distribution.

* The ability of the air conditioner to remove moisture (latent capacity) is lowest at the beginning of the air conditioner cycle. The moisture removed from the indoor air is dependent upon the indoor coil temperature being below the dew-point temperature of the air. The moisture then wets the indoor coil and, should the unit run long enough, will begin to flow off the coil and be removed out of the condensate drain. For short cycles (< 10 min, or so), the coil does not have time to operate at the low temperature, and when the unit stops, the moisture on the coil evaporates back into the indoor air. Thus, in humid climates, a properly sized air conditioner will do a far better job of removing moisture from the air, than oversized units.