AC radiant power extraction

[docmirror]

Whelp, I'm gonna replace the AC in my Sea Ray. It's working, but it's 20 years old, runs on R-22, making a buzzing noise, and it just doesn't push much cold air anymore. I knew it was kinda weak when we got the boat, and it's been on my 'to do' list since buying. Here's the rub:

While I had the unit running today, I did some tinkering around down in the cabinet where the unit resides. The door in front, and the light bulkhead above the unit was pretty warm, and I quickly realized I'm not getting the full measure of the cooling capacity due to the unit itself being inside the contained vessel(literally a vessel) where the cooling unit has to overcome the radiant heating value of the AC system itself. So, I grabbed up the maths and wondered if I'm just shiffing in the wind, or if it's -- serious. Bottom line, it's serious.

Running 10.3A with 110V give 1133 watts. Going to the hand BTU/hr to watts online conversion gives me a BTU rating of 3866, add in the small watts of the water exchange pump and round it up to 3900. Since the AC is rated at 16,500, a simple percent calc says that the running of the AC unit is taking up 23.6% of the output of the AC! This is why home units have the condensing outside, and the evap in the ceiling, or a separate cabinet within the home(not quite as efficient).

The condense side is where the big current draw is of course, to get the pump going. I watched a video comparing various AC setups and most of them showed the pump running at 150F and the condensing coil over 100F. I want to get that out of the vessel so I'm not sucking up so much of my AC utility cooling the cooling unit.

Which means, going to a split system, with the evap in the cabinet 2 pressure lines through the deck, and the condensing unit outside - somewhere. Problem is, there's nowhere on the boat that is a 'good' place to put the split condenser part of the AC sys. Right now, I'm leaning to setting it up on a pedestal on the swim step. I have a lot of swim step area, and trying to do some planning so it won't look absolutely horrible. Add to this, none of the split units I've seen so far have any kind of shell, or cover, or boxed enclosure, so that would leave me to making something up from StarBoard or similar. Hmmm.

Anyone have ideas, done this before, other options for condensing units? I don't want an air to liquid condenser as I'm in a very hot climate, so I want a water to liquid condenser as I have the pumping already avail.

 

[alldodge]

Haven't done or heard it being done on anything but a house boat

Those units work pretty well but do need cleaning even in fresh water due to build up inside the coils

 

[dingbat]

Whelp, I'm gonna replace the AC in my Sea Ray. It's working, but it's 20 years old, runs on R-22, making a buzzing noise, and it just doesn't push much cold air anymore. I knew it was kinda weak when we got the boat, and it's been on my 'to do' list since buying. Here's the rub:

While I had the unit running today, I did some tinkering around down in the cabinet where the unit resides. The door in front, and the light bulkhead above the unit was pretty warm, and I quickly realized I'm not getting the full measure of the cooling capacity due to the unit itself being inside the contained vessel(literally a vessel) where the cooling unit has to overcome the radiant heating value of the AC system itself. So, I grabbed up the maths and wondered if I'm just shiffing in the wind, or if it's -- serious. Bottom line, it's serious.

Running 10.3A with 110V give 1133 watts. Going to the hand BTU/hr to watts online conversion gives me a BTU rating of 3866, add in the small watts of the water exchange pump and round it up to 3900. Since the AC is rated at 16,500, a simple percent calc says that the running of the AC unit is taking up 23.6% of the output of the AC! This is why home units have the condensing outside, and the evap in the ceiling, or a separate cabinet within the home(not quite as efficient).

The input power to the unit has nothing to do with refrigeration tonnage.

Seriously doubt you’re using 10A while running either. While you have a high inrush current to charge the starting capacitors, you need very little current to run the compressor and fan.

Split systems are a pain. I advise my customers not to use them if at all possible.

Would consider Air to water exchangers if your water temps support it

 

[docmirror]

The input power to the unit has nothing to do with refrigeration tonnage.

Seriously doubt you’re using 10A while running either. While you have a high inrush current to charge the starting capacitors, you need very little current to run the compressor and fan.

Split systems are a pain. I advise my customers not to use them if at all possible.

Would consider Air to water exchangers if your water temps support it

Well, You might want to review the physics of radiant energy transfer, and also view this video which shows exactly the power consumed by the top three combined units:

The LRA is over 60amps(which is pretty meaningless), the inrush current is around 27amps, and the continuous duty amps is between 10.3 and 11. So, I was actually being rather conservative in my power consumption curve.

And, if you don't like the wattage to BTU/hr calcs I did you can do them yourself here; https://www.convertunits.com/from/watt/to/btu/hr or choose one of your liking. I'm not making up stuff from thin air(no pun intended). 117V x 10.3A = 1205W(twelve 100 watt light bulbs heating value). Conversion to BTU/hr = 4111.6. The ACs are rated at 16,000BTU/hr. 4111.6 div 16,000 = 0.2569. Times 100 for percentage and the thermodynamic 'cost' of developing 16,000BTU/hr is 25.69% of that production. So, I'm paying for 16,000BTU/hr to be produced, and it's costing me 4111.6 BTU/hr to do it, I'm getting a less than 12,000 net cooling value.

 

[docmirror]

I spoke to a marine AC guy down near the marina. His advice was to get either a 16,000 or 12,000 split system, and put the condensing unit in the back of the engine compartment. We can then use a small blower fan(like the bilge vent) over the top of the condenser to duct hot air out the hull side vent. That way, the only radiant energy in the cabinet in the salon is the evap blower at 1.6 amps. Seems reasonable to me. But, I have to run the freon lines(yes I know it's not really 'Freon') from the condenser to the evap and evacuate then insulate them. Seems like a reasonable cost to me to gain ~25% improvement in efficiency. Cost is somewhat higher, but so is the return on investment. Plus, no more condenser humming in the salon. yea!