An Idea for 12V AC

[RickMorgan]

Tinkering around with a few ideas this winter, and, having installed a new SeaFrost BD refrigeration system on our Leopard 38, I wondered about a way to keep cool in summer when on the hook. Our new Seafrost works really well, holding temps at well below 22F, day and night.

After installing a Hydronic heating system in the Boat, I wonder if I could do the same with a cooling system. Just spitballing at this point, so hear me out.

If I ran a hose through the wall of the refrigeration box, looped it through with a about a meter of hose in the box, and then to a fan coil unit that could turn coolant (glycol) into cold air (pulling some of the 22F from the fridge).

Of course, the closed loop requires a 12V low GPM pump and a reservoir (for expansion and topping up. All parts are off the shelf at this point.

Drawbacks? What am I missing? If I can drop the temps in the staterooms by 5-10 degrees, it’ll be worth it!

Thanks, Rick

[s/v Jedi]

Originally Posted by RickMorgan

Tinkering around with a few ideas this winter, and, having installed a new SeaFrost BD refrigeration system on our Leopard 38, I wondered about a way to keep cool in summer when on the hook. Our new Seafrost works really well, holding temps at well below 22F, day and night.

After installing a Hydronic heating system in the Boat, I wonder if I could do the same with a cooling system. Just spitballing at this point, so hear me out.

If I ran a hose through the wall of the refrigeration box, looped it through with a about a meter of hose in the box, and then to a fan coil unit that could turn coolant (glycol) into cold air (pulling some of the 22F from the fridge).

Of course, the closed loop requires a 12V low GPM pump and a reservoir (for expansion and topping up. All parts are off the shelf at this point.

Drawbacks? What am I missing? If I can drop the temps in the staterooms by 5-10 degrees, it’ll be worth it!

Thanks, Rick

You’re basically building a chiller unit for a cold water system. It’s a regular add-on for hydronic units.

[S/V Illusion]

Keep thinking. Without boring you with the equation, Heat transfer efficiency precludes simply running a water line through the box. You need the effect of pressure and expansion such as what happens in an A/C compressor with a refrigerant gas.

[Bowdrie]

Originally Posted by S/V Illusion

You need the effect of pressure and expansion such as what happens in an A/C compressor with a refrigerant gas.

Well, yeah, kinda.
If one already has a supply of external water that is "chilled" it's possible to achieve at least somewhat reasonable results.
An ingenious fellow I knew hung a submersible pump down a few feet in the water while at the dock.
He plumbed it to an old truck heater box/fan, the discharge water went overboard.
With 50F water on a 100F day he had more relief from the heat than many others did.

[CarlF]

Your problem is BTU. A SeaFrost BD50 compressor can remove 249BTU of heat per hour. That’s enough because the fridge is only about 5 cubic feet in size, is gasketed so outside warm/most air only enters briefly when the door is opened, is heavily insulated and has no clear windows or hatches.

A typical catamaran has 500-1000 cubic feet of interior volume. Is not insulated. And has large windows that let the sun radiently heat the cabin. That’s why cat A/C systems are often 60,000 BTU.

Your hose in the box would require many more BTU’s of cooling from the refrigerator compressor/evaporator to remove the heat. With the SeaFrost you’d just end up with a warm refrigerator and not a noticeably cooler cabin.

[SailingHarmonie]

Everybody is missing the most important point.

A BD50 refrigerator compressor has a cooling capacity of about 650 BTUS. A 38 foot catamaran typically needs on the order of 10,000 BTUs. You are not even close to making a difference.

There is a reason engineers get paid the big bucks!

[RickMorgan]

Thanks everyone for your responses. I agree it is akin to a chilled water system. In fact, I got the idea while installing my hydronic heating system. While I don’t expect miracles, I only want to make summers in the Chesapeake less miserable. If I can cool one stateroom a few degrees without running down the batteries, it’s worth the effort. The cost is only a few bucks for a pump, a fan unit and some hose.

Rick

[S/V Illusion]

Absent some efficient heat transfer equipment, expanded surface area, sufficient hose length to provide a residence time to promote heat transfer, all of which require large surface area and volume, the only result here is to decrease the size of your wallet.

But it seems clear you intend to ignore all the advice you asked for.

[David Mathis]

You want to transfer the heat from your cabin into the refrigerator?

[Madehn]

I think having a radiator type device with a low volume low noise fan and a small pump might work for an aft cabin if you could drop the water intake down close to the bottom. Should be enough temp differential to provide a fair amount of cooling. Be an interesting experiment

[SailingHarmonie]

Originally Posted by Madehn

I think having a radiator type device with a low volume low noise fan and a small pump might work for an aft cabin if you could drop the water intake down close to the bottom. Should be enough temp differential to provide a fair amount of cooling. Be an interesting experiment

I hate to be a spoiler, but numbers don’t lie, no matter what you “feel” about it. It will not work. And if it is an air cooled fridge, guess where all the heat is going? RIGHT BACK INTO THE CABIN!

[Madehn]

Maybe I didn’t explain well. No fridge no compressor involved simply a radiator with relatively cool water being circulated thru it ( sourced from near the bottom of anchorage by a longish suction hose by a low volume pump and discharged overboard ) with a fan pushing cabin air thru the the radiator. If you can get a 15 degree difference between the radiator temp and ambient you should be able to remove significant btu of heat from the air in the cabin. Enough to make a difference? I don’t know but certainly cheap enough to try