Fridge cool down expectation

[Mirage35]

Originally Posted by ayates

I should have been more clear. The ship, St. Lawrence II - Brigantine Inc., is a youth sail training vessel, and sails the great lakes throughout the summer. So the ship, and the fridge, are in constant use, I am just not present (I do volunteer maintenance work in the winter).


Allan.

Off topic, but where does this maintenance happen? Thing is, I'm retired and looking for ways to keep busy outside of sailing season.

[OzePete]

[QUOTE=ayates;2489554]Brilliant observation! Attached is another excerpt, this time with a corresponding batter current graph. This confirms the unit cycling on/off during his period. I would guess my duty cycle is around 60%; that is a lot of wasted cooling time. The original temperature graph corresponded to the batteries being charged, so there compressor cycling cannot be seen in the current readings for that period.



Yes Allan, this later chart confirms what I stated earlier, only clearer. While like others said, the cabinet has nothing going in its favour with its minimal insulation, small capacity compressor and being front opening, it is what it is. The 'duty cycle' of 60% quoted confirms a massive inefficiency. This unit is cycling on and off dozens of times BEFORE reaching temperature and as there is considerable ineffective running at the commencement of each cycle, I would estimate that bridging the thermostat to cause constant running would reduce the pull down time to well under half! Rapid short cycling at any time is grossly inefficient power use but doing so prior to reaching temperature not only wastes power but is putting the stored perishables at risk. A manual bypass switch bridging the thermostat (as standard on Ozefridge systems) is you best remedy.

I hope this helps,
Cheers.. OzePete

BTW For folk with fridges that do cycle too often there is a simple trick... Locate the end of the thermostat's sensor probe where it is clamped to the cold plate. Un-clamp and wrap this clamped sensor end (like skinny tubing!) with a few turns of insulation tape then re fit under clamp. This will slow the cooling and warming of the sensor thus increasing run and off periods. Reset the thermostat warmer after doing this.

[Panacea2183]

I installed two Novacool units on my last boat.
Pretty good unit.
Did have to install a cooling fan though.
Mine were the type that used convection to cool the condenser (no fan). Even with the recommended vent size area, the space it was in got quite warm.
There is a built in relay function to attach an external cooling fan that runs with the compressor.
I used an electronics cooling fan (about 4in square) fan only draws about .25 amps to vent the enclosure
Kept the enclosed space much cooler and increased performance quite a bit.
They cost about $10 online.

[ayates]

Originally Posted by kenbo

with only 1.5" of foam insulation! Man those BD35's are good. Imagine how good that would look if it was top loaded with 30R insulation.

Actually, I did laminate more insulation to the outside of the fridge before installation. See attached photo. I added 3 1/2", for a total of 5", or ~R25. I would have like to have added more, but it had to be balanced with the space available.


Allan.

[ayates]

Originally Posted by AnglaisInHull

Off topic, but where does this maintenance happen? Thing is, I'm retired and looking for ways to keep busy outside of sailing season.

The ship winters in Kingston, Ontario, its home port. Most of the work is done there, but in my case, living in Merrickville, I will do repairs and replacement cabinetry/etc work at home and then take down the finished product (its only a 1 hr 15m drive for me).


Allan.

[ayates]

Originally Posted by Zep

You are obviously on shore power which is good so it's not taxing your batteries.

Actually, the fridge runs off a 740 AH house battery bank (4 x Trojan L16E-AC). The bank is typically recharged on a daily basis by a generator or shore power. According to the data logging, 10,146 AH were drawn off the batteries over the course of the summer (about three months).


Allan.

[ayates]

Originally Posted by Panacea2183

I installed two Novacool units on my last boat. <snip> Did have to install a cooling fan though. Mine were the type that used convection to cool the condenser (no fan). Even with the recommended vent size area, the space it was in got quite warm.

This NovaKool unit does come with a condenser cooling fan. But your comment does make me think that logging the temperature in the condenser area would have been interesting.


Allan.

[Rorzech]

That logger appears to log the Air temperature. To get a more accurate temperature of your food ,you'd need to have a temperature probe immersed in a cup or bottle of water. The door openings won't be as pronounced either.

[Rorzech]

That is called a "Fast Freeze" switch on freezers.Just makes for continuos running.

[Rorzech]

That is really a tiny cold plate. A fridge that size should have a cold plate with at least 4 times the surface area as that one. Being that small , it frost's up 4 times faster and frost on the evaporator acts as an insulation so the heat from the food has a harder time getting into the evaporator to be pumped out of the box. You must have a real tiny compressor that is matched to that evaporator. That system may be sufficient for a chest fridge but it's going to always be playing catch up, and you'll be defrosting it a lot.

[Rorzech]

When I sail Lake Superior I use my cabinets that are below the water line as my fridge to keep beer wine an other cold drinks. If you fall overboard in July you'll stiffen up in a few minutes and your hands will stop working,when water is that cold.

[ayates]

I have been doing a little more data analysis, looking at the overall power consumption for the fridge. From the graphs below I get:

Compressor Current Draw: 5.6 Amperes
Duty Cycle: 30%

and thus:

Average Daily Power Consumption: 40 Ampere-Hours


Allan.

[john61ct]

Excellent logging capabilities there!

Have you done any improvements yet to try to improve that efficiency, or do you plan to just live with it?

[ayates]

Originally Posted by john61ct

Have you done any improvements yet to try to improve that efficiency, or do you plan to just live with it?

Not done anything yet, but it is in the plan for this winter. The plan is to pull the fridge from the ship so I can work on it in comfort. I'll get the Stainless Lobster controller working first and see if that "solves" the "short-cycling" due to the temperature sensor on the evaporator. I'll look at the other options after that if need be.

I am also looking at adding 2 1/2" of Styrofoam SM to the outside of the door (like I did to the other sides of the cabinet). However, I am not convinced I'll be happy with the looks/ergonomics, so I am still on the fence on that one.


Allan.

[Typhoon]

Originally Posted by ayates

Not done anything yet, but it is in the plan for this winter. The plan is to pull the fridge from the ship so I can work on it in comfort. I'll get the Stainless Lobster controller working first and see if that "solves" the "short-cycling" due to the temperature sensor on the evaporator. I'll look at the other options after that if need be.

I am also looking at adding 2 1/2" of Styrofoam SM to the outside of the door (like I did to the other sides of the cabinet). However, I am not convinced I'll be happy with the looks/ergonomics, so I am still on the fence on that one.


Allan.

It is the nature of a cap tube system to cycle many times to bring down the box temperature . This is why the temperature sensing bulb is attached to the evaporator plate . These systems are controlled by evaporator temperature. Defeating this may allow the system to run out of its design perimeters causing it to run unbalanced and inefficiently or even possibly damaging your compressor .

I would leave the control system as is and concentrate on the insulation.

Regards John.