Sizing Marine Air Conditioning Systems & Ducts and Grills Selection

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 Air Conditioner Sizing

When an A/C unit works more than 30 minutes per hour is an indication that the unit is undersized. Take into consideration the following factors to size an A/C unit in your boat.
Room Volume and Material 
Source of Power AC or DC
Average people in the room
Unit location
Ducts route
Wire gauge
Seacock, Sea strainer, and Raw water pump location
Thermostat location and Harness length
Air conditioner size is rated using the number of BTU's or British Thermal Units of heat that it can remove per hour. 
1 BTU is the amount of energy to raise the temperature of one pound of water by one degree Fahrenheit.
You may also hear A/C size referred to in "tons" which is the equivalent of 
12,000 BTU’s = 1 Ton.

Conversion for heat and power units.

1 kwh is equivalent to 0.7457 horsepower. 
1 Kwh  is equivalent to   3,413 BTU/hr
1 Hp = 746 Watts
To Calculate Main Breaker Capacity:  
P(Kw) = Volt X I(Amp)
1 ton is equivalent 12,000 BTU/hr 


Square feet method for Air Conditioner Sizing


BTU’s per Area ft2 1 ton  = 500 ft2 of floor area
Heat gain from person 380 BTU per person
Heat gain from cooking 1,200 BTU per kitchen
Increase BTUs by 600 for each additional person (using room) over 2 persons 
Increase BTUs by 10% for sunny areas


Get here the Marine Air Conditioning Systems Book where you can find all the information on this and many other topics.





Example:


We are going to calculate the capacity of an Air conditioning unit for the Saloon + Galley, the master room, two guest rooms, and the flybridge in a boat with the following characteristics :

 - Boat Total Length: 67 ft
 - Saloon Area 16ft X 15ft
- Saloon Material: Fiberglass
- The Saloon is considered a Sunny Area
- Amount of People at the Saloon = 6
- Galley is included in the Saloon

- Master Room Area 12ft X 11ft
- Master Room Material: Fiberglass
- Amount of People at the M.R = 2
- The M.R is considered a Dark Area
- Galley is included in the Saloon
- Guest Room No 1 Area 4ft X 11ft
- G.R  Material: Fiberglass
- Amount of People at the G.R = 2
- The G.R is considered a Dark Area

- Guest Room No 2 Area 4ft X 11ft
- G.R  Material: Fiberglass
- Amount of People at the G.R = 2
- The G.R is considered a Dark Area

- Flybridge Area 10ft X 10ft
- F.B Material: Acrylic (Clear Plastic)
- Amount of People at the F.B = 6
- The F.B is considered a Sunny Area

The AC panel is 240 V AC
You should calculate the breaker capacity at the AC panel and select the appropriate unit or units according to the units available in the market. Good Luck.


Learn more in the following video



Finally, this is the solution.




Schedule a Video Call with Mr. Lopez for remote troubleshooting


Learn more about Marine Technical Training at www.mttedu.org



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