Refrigeration unit replacement - Price vs Performance

[Typhoon]

Hi Richard.

I get a total btu into the box with R12 insulation and the fridge at 32 and the freezer at -10 to be 5472 btu when the ambient temperature is 90F all the time , I understand it will be cooler at night but I averaged on the high side just for the extra margin . And of course if the door seals are good and the box remains closed. I would have to add more btu if the kids grabbing drinks all day.

At R24 insulation the same box in the same circumstances would allow 2736 btu into the box from a simple 2.5 inches more insulation 50% more efficient. Thats using XPS at R5 per inch .

I would actually be surprised if he has got R12 insulation in his box. I would not like to find that out when you are down in the tropics and your system cant keep up to the high temperatures and you start loosing food .

R12 is fine in Nova Scotia .

Regards John.

[newhaul]

Originally Posted by Richard Kollmann

John. I tried to come up with a refrigerator design system concept based on information provided by BluJu :
Want a spillover system 3.4 cu ft refrigerator and 2.5 cu ft freezer.
Plan cruising in tropics for 1 to 2 years.
Two adults and two children on board.
Present box insulation a guess maybe R 12
Does not have the time to replace insulation.

Upgrades and projections to meet the owner refrigeration requirements.

Worst case daily Btu 4200, design consideration in summer tropical climate condition.
Thirty to 50% of the additional daily Btu consumed is do to the increased liquid requiring refrigeration in the tropics.

Doubling the insulation R value could increase its performance by fifteen percent.
I have found selecting the right refrigeration and upgrading boat’s power grid is far more effective than redoing the insulation. Unless insulation is full of moisture and only then replacement is necessary.

Cruising below 26 Latitude should always be considered as tropical conditions.

sorry but I don't get your math how can doubling insulation from r12 to r24 only gain a 15% efficiency? ( I need to know if its worth it to change from 2 inches foam to 2 inches aerogel. Its just over 500 USD for change)

[glcalahan]

Now I somewhat confused...if I double 2- 2" Thermax (R-13x2=26), where is this 15 % coming from? BTW...what is best adhesive to use? I plan to line inside box with sheet aluminum.

[Richard Kollmann]

Originally Posted by ColdEh Marine

Hi Richard.

I get a total btu into the box with R12 insulation and the fridge at 32 and the freezer at -10 to be 5472 btu when the ambient temperature is 90F all the time , I understand it will be cooler at night but I averaged on the high side just for the extra margin . And of course if the door seals are good and the box remains closed. I would have to add more btu if the kids grabbing drinks all day.

At R24 insulation the same box in the same circumstances would allow 2736 btu into the box from a simple 2.5 inches more insulation 50% more efficient. Thats using XPS at R5 per inch .

I would actually be surprised if he has got R12 insulation in his box. I would not like to find that out when you are down in the tropics and your system cant keep up to the high temperatures and you start loosing food .

R12 is fine in Nova Scotia .

Regards John.

When designing for compressor run time at fifty percent and an over sized power grid there will still be another fifty percent fudge factor. There is no way to cover all the variables when dealing with mobile live aboard boat refrigeration. Now with the new variable speed Danfoss compressors over or under capacity can be corrected by changing compressor speed. One needs to live in the tropics and designed a hundred boat different refrigeration systems to avoid mistakes. Yes, I have mistakes but I try not to make the same errors again. For the last seventeen years my equipment recommendations pretty much follow the Slide Show on my web site Of What Works and What Does Not.

I know the fall back position for refrigeration designs is is lack of insulation but I try to work with what can be done with existing insulation. If moisture forms on exterior of insulation or the delta T between boat interior air temperature and exterior temperature of insulation exceeds five degrees insulation is not except-able..

[Typhoon]

Originally Posted by glcalahan

Now I somewhat confused...if I double 2- 2" Thermax (R-13x2=26), where is this 15 % coming from? BTW...what is best adhesive to use? I plan to line inside box with sheet aluminum.

Polyiso has an aluminum foil on it , so any good glue designed for aluminum or is compatible with aluminum should work just fine.
Be sure not to get it on the insulation itself , as it may dissolve it .

Regards John.

[glcalahan]

Thank you John!

Gary