Dual purpose fridge

[Byrnerc]

Hi all, we are new to cruising and thanks to the forum we've solved many problems. Two problems we have not solved, the unavailability of block ice for our icebox and mold. I was thinking that both problems could be solved with one refrigeration unit and a solar panel. The unit would serve as a refrigerator while underway and a dehumidifier while at mooring. I didn't see any threads on this idea.

Are there any HVAC people out there that could tell me the problems with this idea? I know the air flow for dehumidifying would be tricky and cumbersome but how about the unit itself? Will the expansion plates collect water vs ice at a lower setting?

thanks in advance, Rossco

[boatpoker]

What are you doing or where are you cruising that causes such significant humidity that it is a problem ?

[Kettlewell]

I was thinking that both problems could be solved with one refrigeration unit and a solar panel. The unit would serve as a refrigerator while underway and a dehumidifier while at mooring. I didn't see any threads on this idea.

You'll need lots of solar to keep refrigeration and air conditioning running while away from a dock. Both are significant draws on power. I have not seen combo refrigeration/a/c units, but my gut feeling is it would be too complex and use too much power for the average cruising boat.

[Byrnerc]

Thanks for your interest, we live in Connecticut and cruise along the NE coast of the U.S. We get very humid summer air while the water stays cool causing mold to form on the lower cabin surfaces, on clothes and cushions. A solar fan runs continuously but that just brings in more moisture during the hot humid days.

My plan is to use the unit for one purpose at a time, refrigeration while underway and dehumidifier while not using the boat. We are not full time cruisers, just vacation trips. The unit would be installed as any refrigeration unit in the icebox but when I want a dehumidifier, I'd rig a Rube Goldberg contraption to cycle air over the expansion plate drying the air and draining the water to the bilge. There are units that monitor battery voltage and shut down when voltage is low. I'd have a timer to run only long enough to periodically dry the cabin air.

My specific question is, will the expansion plate dry the air or just freeze up with ice?

[George_SD]

Running a 12v fridge from solar is easy and doesn't take much. I run 12v fridge and a separate freezer off a single 100w panel + other electronics (3x100ah FLA batteries, only 2 are used for fridge/freezer use and one for engine)

[donradcliffe]

Originally Posted by George_SD

Running a 12v fridge from solar is easy and doesn't take much. I run 12v fridge and a separate freezer off a single 100w panel + other electronics (3x100ah FLA batteries, only 2 are used for fridge/freezer use and one for engine)

Your fridge may run for a day with that panel, but it won't run 24/7. The freezer is even more of a power hog.

For the mold, get a dehumidifier that can be plugged it at the dock.

[Byrnerc]

Thanks George SD, that is good info.

Thanks donradcliffe, I'm on a mooring, no outlets out there. As a dehumidifier, it should only run for a short time to dry the small volume of air in the cabin perhaps several times per day. Much less time needed to freeze food.

[George_SD]

Originally Posted by donradcliffe

Your fridge may run for a day with that panel, but it won't run 24/7. The freezer is even more of a power hog.

For the mold, get a dehumidifier that can be plugged it at the dock.

It has no problem running two fridges and other electronics. I've had this setup for several years and it has been proven by multiple trips and staying on anchor for 10+ days. We also use it to charge our phones, handheld VHF and son's iPad.

12v built-in Frigoboat unit
12v BougeRV portable fridge/freezer
2x 100ah FLA house bank (charged by solar)
1x 100ah FLA (charged by alternator, not connected to solar)
All LED lights (cabin and navigation)

We run out of space in holding tank first, then run out of fresh water, never of power.

[Bowdrie]

Originally Posted by Byrnerc

We get very humid summer
will the expansion plate dry the air or just freeze up with ice?

The "expansion plate" is an evaporator.
Yes, it will collect moisture which will freeze to its surface.
Household refrigerators/freezers do the same thing and then they use heating devices to heat-up/thaw out the evaporator(s).
They call that "Frost free:.
No free lunch.
You can rig-up all sorts of timers/gizmos/fans, but at the end of the day you've still got a little system with very limited capacity, and all the stuff you add just uses more power.
An earlier post mentioned a dehumidifier.
Hook one of those to a little single purpose inverter, you'll get better results, (hopefully the batteries won't go dead too soon).
Using a miniscule reefer unit as a dehumidifier?
I fear you'll have better luck shoveling sand against the tide.

[Byrnerc]

Thanks Bowdrie, that's what I was afraid of. Maybe a mini dehumidifier if they exist.

[Uncle Bob]

Hi, my boat has three solar fans fitted, two extracting air and one blowing it in and the only areas that have gotten any mold are the couple that don't get good airflow and then only small areas, my first go to would be fit a couple more and drastically improve the airflow. BTW I live in Sydney australia and humidity is a regular companion here.

[smac999]

buy some chemical dyhumidifiers... the white pellets that sit in a bowl.

[GordMay]

Originally Posted by smac999

buy some chemical dyhumidifiers... the white pellets that sit in a bowl.

Dehumidification can be performed by desiccant-based [eg: calcium chloride], or condensation-based processes [compressor cooling].

Disposable desiccant moisture absorbers [eg: DampRid] should only be used in spaces that are NOT perpetually humid, and are also either NOT very humid, or very small in size.
Desiccant type products are also inherently “light duty”, and have a very small capacity for moisture removal.
The average compressor based dehumidifier removes between 30 to 70 pints (approx. 500 to 1000+ ounces) of moisture per day. The average thermo-electric dehumidifier removes between 5 and 25 ounces of moisture per day.
Disposable desiccant moisture absorbers, such as DampRid, remove only a few ounces of moisture over the course of several weeks.

I used them in pill bottles, tool/parts bags, drawers, & SMALL lockers.

[catsketcher]

Originally Posted by George_SD

It has no problem running two fridges and other electronics. I've had this setup for several years and it has been proven by multiple trips and staying on anchor for 10+ days. We also use it to charge our phones, handheld VHF and son's iPad.

12v built-in Frigoboat unit
12v BougeRV portable fridge/freezer
2x 100ah FLA house bank (charged by solar)
1x 100ah FLA (charged by alternator, not connected to solar)
All LED lights (cabin and navigation)

We run out of space in holding tank first, then run out of fresh water, never of power.

George, I have no doubt your set up works, but I think it works because you use the capacity of your batteries on your short term cruises.

A 100 watt panel can only put in say 8 amps max. It can put this in for only a few hours so let's say 12 hours at 6 amps = 72 Amp hours per day. That is optimistic.
A normal fridge takes between 4-6 amps - but you have two so there is probably at least 8 amps going out because of the fridge. With a 40% duty cycle you get 8 x 24 x 0.4= 76.8 amp hours per day.

You will barely scrape by even when you charge nothing else and if you have full sun. Obviously it works for you, but I think your battery will be at a low state of charge after a normal week long cruise. On the mooring the batteries get charged up again. A fine setup for the occasional cruiser.

I think it is better to calculate using numbers from winter - less daylight time and less powerful sun and also assume the fridge will have a duty cycle of 50%. Even then, a couple of days of cloud will get the batteries low. As a liveaboard I have to do the calculations for winter with a bad couple of days.

I found it hard to always keep the batteries at a good state of charge with a fridge and 200 watts of solar. 400 watts is really nice. It is very easy to afford the cost of larger panels, if you can site them somewhere. My advice would always be get the largest panels you can put on easily and start from there. It's great to have the controller click off in the morning and your batteries will love you too.

[Byrnerc]

Thanks again all, very helpful info since my plan is only partially similar. The numbers help since I intend minimul dehumidification time and the refrigeration time can be assisted with the engine alternator.

My wife continues to use desiccant despite my comments about using a spoon to bail the bilge if running the external fan. I'm going to try more fans though, easy to run off solar.

I use several dehumidifiers in my basement and those use evaporators. I assume the temp is set below freezing.

Yes, I know that this all gets more complicated requiring more gadgets, more maintenance, more expense. I entertain the Bernard Moitessier philosophy of ultimate simplicity but my career has been the repair and design of gadgets and Bernard didn't even like sextants, he was crazy.