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Old 27-03-2019, 11:42   #1
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Join Date: Aug 2015
Location: Marina del Rey
Boat: Hunter 31
Posts: 747
Air Conditioning Calculations

I came across a tiny compressor dehumidifier, from perfect aire, that I modified to serve as a small air conditioner (basically splitting the airflow, so that I can have one fan going over the evaporator and one fan going over the condenser. It works but I am having trouble with adjusting the airflow to maximize the performance, so I am looking for some advice on air conditioning calculations.

The original specs are 11 pints/day dehumidifying capacity, 1.9A @ 115V = 220W compressor power, the motor is specified up to 5.7A when the rotor is locked (max instantaneous power, not sure if it is relevant). The original fan that was driving air over both coils is 0.2A @ 12V, 200mm fan which I think gives about 100 cfm. It also says 171 psi low, 342 psi high.

Currently, I run it with the original fan, driving 100 cfm through the condenser and a variable speed fan, up to 200 cfm through the evaporator. If I reduce the airflow through the evaporator, it starts frosting up, similarly with the condenser, lower airflow causes the evaporator to frost up. I understand that for cooling, you want higher airflow and higher coil temperature, while for dehumidification you want as low coil temperature as possible with respectively the lowest possible airflow.

What would be the appropriate airflows for an air conditioner of this size? Based on the compressor size, I estimate it can produce around 2,500 BTUs @ 15A @ 12.5V which is what it runs at right now. Based on a common industry metric of 400 cfm / ton, I estimate that 100 cfm should be sufficient, although I may be getting lower cfm because of the curved airflow. Basically, I am looking for guidance on what size computer fans to use. I plan to use these three speed fans on the intake and out take, so that I can adjust the speed for cooling vs. dehumidification.

Overall, I am happy with the project, the unit is small, consumes 15A and provides enough cooling for a v-berth or rear cabin on a small boat.

Thank you,
SV Pizzazz
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