Calculations on front opening fridges

[mako]

OP you’re spot-on. Focus on high efficiency digital inverter residential fridges. LG, Samsung, etc.

[BobFord]

Good points rslifkin- I'll add to my blog- space was no problem but I would go for a (2) door ,side by side , if I did it again. Yes, I was ,'caught bending', with doors opening in a seaway, Answer was a simple pair of occky straps and hooking them on becomes a normal part of prep for a rough passage.

[Simi 60]

Plenty of VHB affixed child proof catches available on eBayZon

https://www.ebay.com.au/sch/i.html?_...0aAgkxEALw_wcB

[catsketcher]

Originally Posted by Pete7

Well first thing, does it need servicing or even cleaning the cooling fins? How thick is the insulation on it particularly the bottom?

However, clearly you are thinking about changing, therefore could you fit two. One for long term stuff little used and one for the milk making a dozen cups of tea each day. Perhaps even change the existing one to a freezer ?

Pete

It would be a bit of a shame to get rid of the old fridge. It has really good insulation (over 100mm thick polyurethane for the most part done in 2013). It is the dodgy installation (also done by me) that worries me. It does get coldish but the freezer doesn't really freeze. I like the idea of leaving it there, even if I get another one.

[catsketcher]

Originally Posted by Uncle G

Shouldn't the left-hand side of the equation for 'the watery stuff' be divided by 1000?
litres to cu m

I had to divide the specific heat capacity of the air because I found a unit that was for 1 cubic metre. However the 4.2 kJ/L is litres already so I didn't convert it.

cheers

Phil

[MVDarlin]

Some years ago I replaced my "not cold" ac&dc marine refer with an off the floor "acros" (Whirlpool) ac 5' tall upright refer with small internal freezer chest and an added inverter. The refer was purchased at a Wallmart in Mexico. On inspection I found the ac operation of my old Norcold was accomplished with a bridge rectifer running the dc compressor motor. I figured I could reverse this. The Acros has a peak momentary power draw of 500 watts but only 200 watts operating draw when running according to the watt meter on my inverter. I fill the freezer box with ice cube trays and leave the refer closed overnight. It runs on solar during the day for 9 hours. It works great. Morning milk temp is 48' in 90' weather. Caution. Be careful about adding insulation. Modern refers and freezers use the exterior surface as a heat sink. Best to leave uncovered and well ventilated. Cost: $350. Easily replaced. Norcold replacement cost estimate was $1,500 plus shipping and import tax to Mexico. I also have a 5cf chest freezer with its own solar and lithium battery. Price for freezer at Costco $150 some years ago. Now $180.

[kubota]

what am i missing?
my bd5 cools 1cu meter at 4.5 amps 12v at 50%
duty cycle. also a hard freezer compartment with meat for six weeks. been doing that for 22 yrs of cruising in tropics and northern climes.
thats round 237 kw-hr/yr.
those lg inverter fridges with capacity 1cu meter are 685 kw-hr/yr.
sounds like 189% less efficient to me.

thats before you include the inefficiencies of ac
appliances on inverters and all that cool jwsin(theta) bouncy power factor stuff getting burned off in the outputs of your inverter as heat that grid tied home appliances dont worry about. loses efficiency and shortens inverter life.

scoped a variety of home led bulbs on inverter. some
were little better than incandescent in power use due to poor matched pwr supply in base of bulb for inverter use.

short answer is appliances designed for grid dont necessarily behave the same on inverter.
(btw, buy cree, only one chinese brand came in at better than 19% efficient on inverter vs grid. coincidentally it was also cheapest at walmart ).

i agree, upright vs pit is in the noise.

what does make a diff is my bd5 is 10 ft from my box in a locker with lots of free air in touch with cool hull and water cooling only turned on in tropics. a home unit has all its temp sensitive stuff crammed under or behind where it is suffocating.

happy to find out i am wrong. live off grid in mtn when not on boat. tested many fridge. modified compressors, added run caps, parallel caps, anything to get efficiency up.

finally went with full size propane fridge built by amish for home use. no moving parts and the thing rusts faster than it will wear out. (typ life 50yrs). less climate impact and cost than starting the backup gen on rainy days to charge batteries. (we get 80" of rain on our mtn so happens frequently).

if anyone has some data on a home unit that works with equivalent end to end efficiency to a bd5 i will try and get one to test in the lab. trying to get as close to full solar as possible and jettisoning propane would still be a plus as climate police drive my propane prices up.

[PineyWoodsPete]

Originally Posted by Chotu

Got the numbers online:

My upright LG refrigerator uses 62A per day or 2.6A per hour.

Maintenance free and will likely last 20+ years.

AND looks better and cost $400

This European home-sized fridge/freezer - whose maker I can't recall now - made her eyes bug out when we saw the pristine 6 year-old boat we bought back in '19, along with the rest of the 120VAC galley. Hauling ice and propane tanks in Mexico and Central America with past boats not among our favorite memories!

The best I can determine about it's DC consumption in the temperate Monterey climate is that it has a duty cycle of 10 min. continuous close to hourly, for 24 hr total ~4hrs @ 250W draw from the 48V LiPo feeding the 5kW Victron inverter/charger. With decent summer sun on cruises down to S. Cal. the 500W/48V solar on the roof would allow at least three days anchored before the 12kWh Lipo fell below 50%, with liberal use of the elect stovetop, microwave, and boiler feeding four. And the freezer will keep ice-cream frozen at a Med. setting!

[billyehh]

On my Voyage 380 catamaran, it had a front opening refrigerator and a chest type freezer. After the first season of constantly charging my batteries, I converted the freezer which had holding plates to an evaporator type refrigerator. A couple years later I bought a small Engle freezer which I store under the chart table. Now the solar panels cool them both without having to run an engine. Slightly smaller capacity, but a lot more efficiency.

[Jef & Marin, Netherlands]

We have a very energy-economical 230 liter Liebherr front opening fridge for 4 years now. It takes around 100 kWh per year, so less than 300 Wh per day, less than 25Ah. That is around 10W average consumption. Liebherrs have the lowest energy consumption but they are a premium brand so not the cheapest.


It is not necessary for us the lock the door (opening in the bow direction).
We have had no issue of condensation water overflowing the evaporator tray which is over the compressor.


It has vegetable drawers which are between 0 and 1 degree centigrade. Very nice to have fresh salad while crossing oceans.

[Toccata]

Re Post 1.
FWIW, my sister in law (super qualified to do this) ran the calculations using your assumptions and achieved an answer within %10 of your result.
She added: She supports the proposition that cooling a warm item down will use significantly more energy than replacing the lost cold air when the fridge is open (within reason)
All broad statements, but we're not about establishing credentials here nor about peer reviewed papers.
I too have been wrestling with building a "pit fridge" using ozefridge components vs buying an off the shelf RV Style unit.
I did the former on the last boat. It worked really well, basically holds -20C with minimal power use. But very costly to build and a pita to use.
Im currently rebuilding a Stuart 47 on The Gippsland Lakes
My limiting factor choosing a prebuilt front opening unit is the door size (of the boat) to move the fridge into the boat.
In addition to the front opening fridge, I will use a small chest style dedicated freezer. There used to be a eutectic type, small chest fridge called an "Autofridge", available/made in Australia, apparently someone has taken over the company, but not yet producing them again. Sometimes they are available second hand.

[Chotu]

Originally Posted by kubota

what am i missing?
my bd5 cools 1cu meter at 4.5 amps 12v at 50%
duty cycle. also a hard freezer compartment with meat for six weeks. been doing that for 22 yrs of cruising in tropics and northern climes.
thats round 237 kw-hr/yr.
those lg inverter fridges with capacity 1cu meter are 685 kw-hr/yr.
sounds like 189% less efficient to me.

thats before you include the inefficiencies of ac
appliances on inverters and all that cool jwsin(theta) bouncy power factor stuff getting burned off in the outputs of your inverter as heat that grid tied home appliances dont worry about. loses efficiency and shortens inverter life.

scoped a variety of home led bulbs on inverter. some
were little better than incandescent in power use due to poor matched pwr supply in base of bulb for inverter use.

short answer is appliances designed for grid dont necessarily behave the same on inverter.
(btw, buy cree, only one chinese brand came in at better than 19% efficient on inverter vs grid. coincidentally it was also cheapest at walmart ).

i agree, upright vs pit is in the noise.

what does make a diff is my bd5 is 10 ft from my box in a locker with lots of free air in touch with cool hull and water cooling only turned on in tropics. a home unit has all its temp sensitive stuff crammed under or behind where it is suffocating.

happy to find out i am wrong. live off grid in mtn when not on boat. tested many fridge. modified compressors, added run caps, parallel caps, anything to get efficiency up.

finally went with full size propane fridge built by amish for home use. no moving parts and the thing rusts faster than it will wear out. (typ life 50yrs). less climate impact and cost than starting the backup gen on rainy days to charge batteries. (we get 80" of rain on our mtn so happens frequently).

if anyone has some data on a home unit that works with equivalent end to end efficiency to a bd5 i will try and get one to test in the lab. trying to get as close to full solar as possible and jettisoning propane would still be a plus as climate police drive my propane prices up.

you are off in two areas, I think:

first, the efficiency of the refrigerators. My upright regular refrigerator uses 275 kWh per year.

Second, all of the stuff about the inverter. That really only applies if you have a piece of junk square wave. You need to use a pure sine wave inverter for everything on a boat that relies heavily on the inverter.

Now, I definitely enjoy the propane refrigerator. And I would still have one. I started off with one of those and a very small battery bank. However, a series of events while unattended caused my propane refrigerator to break. Through corrosion. When I was looking at buying a new one and shelling out closer to $2000, I thought to myself it might be nice to have a more robust electrical system and a $400 refrigerator that uses 275 kW per year so that’s the route I took.

But wait. The most important thing about your entire post is YOU HAVE A LAB????

very interested. Can you tell us about your lab? Maybe in a different thread or something? This is a dream come true

[mako]

Originally Posted by kubota

those lg inverter fridges with capacity 1cu meter are 685 kw-hr/yr. sounds like 189% less efficient to me.

Numbers are way off. A typical American, low efficiency, non-inverter 25cf refrig uses about 600kW-hr annually. That's about 2.5 cubic meters volume, with a wasteful ice-maker in the door.

My Samsung digital inverter refer from Europe was over 360 liters (12+ cf) and measured about 1 kW-hr daily, or 365 annually. Extrapolated to 1 cubic meter, that would equate to about 300kW/yr, which is not quite as good as your BD5, but getting closer. I bought my Samsung at Carrefour and it was a "typical" unit, but today's super high efficiency units (costing more money of course) would likely be approaching the same as your unit.

Also agree with @Chotu's comment about inverters. PSW units run around 90% efficient, +/- a couple points.

[sailingunity]

Originally Posted by Toccata

I too have been wrestling with building a "pit fridge" using ozefridge components vs buying an off the shelf RV Style unit.

Our boat came with a top opening fridge, which I replaced with a front opening fridge, which I'm now replacing again with a top opening fridge

What we found was that the front opening frosted up A LOT. I have 4 kids constantly opening and closing it, and I would need to defrost it about every 2 weeks.

Second issue - our fridge faces athwartships and items would shift when heeled, opening the fridge on a port tack was sometimes a gamble. Not a problem if your fridge faces bow/stern

Third issue - space - you can stack things in the top opening fridge and use up much more of the space than you can with shelves. Yep, you have to pull stuff out to get to what you need. My new design is shallower but wider and longer, so there will be less digging needed.

Fourth issue - efficiency. I know there are folks here who say there is little difference, but we used way more power IMHO.

[rslifkin]

Originally Posted by sailingunity

Fourth issue - efficiency. I know there are folks here who say there is little difference, but we used way more power IMHO.

Part of that is the fridge itself. If your front loader was an off the shelf 12v fridge, I've found that many of them just aren't well insulated, unfortunately. With equal insulation and the same mechanical components between the 2 designs, it should be fairly close.