[PUP] coldplate efficiency

[Jon Boy aka:TrawlerGuy]

Yes, I understand the operation of these units as we have three on our trawler. A fridge, a freezer unit and a 33cu ft chest freezer unit. We, also, run a gen-set once a day to charge the batteries, pull the holding plates down, and make water every other or three days. 

However the comment was regarding "efficiency" and they use far more total energy to freeze the eutectic to much below zero than to hold a constant freezing, or fridge, temp. 
As far as "efficiency" is concerned, less actual energy is consumed with short cycles maintaining a more constant temp... IF, as you point out, you have the battery/inverter system to maintain it during the time between generator runs. 

Our boat is old tech and although we have a battery bank capable of this we don't yet have the inverter system for it and it will take some major remodeling to remove the "built-in" holding plate unit... But we will soon. We will then change out to a more modern fridge/freezer unit, prolly a "Zub-Zero", that gives us beauty, modern internals structure, self defrosting, good lighting and an icemaker while keeping the big chest freezer unit. 

BTW: the holding plate units pull down to a MUCH LOWER temperature, in the plates, (what is doing the actual work) and that--is the primary reason for their lower energy efficiency. Holding that energy in a battery is more efficient with less loss, even with the losses of the DC-AC system. Several keel-cooled highly insulated Danfoss DC units would be even more efficient.
John

-----Original Message-----
>From: John Marshall <johnamar1101 at gmail.com>
>Sent: Dec 4, 2008 8:22 PM
>To: "Jon Boy aka:TrawlerGuy" <jsclipper at earthlink.net>, Passagemaking Under Power List <passagemaking-under-power at lists.samurai.com>
>Subject: Re: [PUP] coldplate efficiency
>
>
>The key difference is that evaporators cycle multiple times per hour  
>for a short period each time... Ok if you have inverter and decent  
>batteries.
>
>In contrast, cold plate can hold cold for many hours, perhaps only  
>cycling once or twice per day when you run generator, but for much  
>longer periods each time.
>
>Which one is best depends on how you generate and store electricity  
>and how consistent a temperature you want in freezer/refrigerator.
>
>On my trawler, I have lots of batteries and a good inverter plus extra  
>chargers, so I only run generator once, occasionally twice, a day at  
>very high amperage into the battery bank, and then use that bank as  
>the storage source through my inverter the rest of the time. This  
>allows me to use more flexible evaporator type refrigeration.
>
>Evaporator freezers also get colder than cold plate... good if you  
>plan on keeping stuff there for a while.
>
>But really, in the end, its all about how you manage electrical energy  
>on your boat. Presumption is that we all want to minimize genset run  
>time.
>
>John Marshall
>
>
>On Dec 4, 2008, at 5:02 PM, Jon Boy aka:TrawlerGuy wrote:
>
>> Coldplate refrigeration IS NOT more efficient... It's much less  
>> efficient. However, if running on gen-set only the "holding plate"  
>> does the job of the "battery bank" in an inverter run system.
>>
>> John
>>
>>
>>
>>> On Tue, Dec 2, 2008 at 7:26 PM,  <johnph at comcast.net> wrote:
>>>> The cold plate is generally a more energy efficient approach to  
>>>> refrigeration but at the sacrifice of food preservation time.  
>>>> Personally I feel the preservation time sacrifice doesn't make the  
>>>> cold plate an attractive option.
>>>>
>>>> John
>> _______________________________________________
>> http://lists.samurai.com/mailman/listinfo/passagemaking-under-power
>>
>> To unsubscribe send email to
>> passagemaking-under-power-request at lists.samurai.com with the word
>> UNSUBSCRIBE and nothing else in the subject or body of the message.
>>
>> Passagemaking Under Power and PUP are trademarks of Water World  
>> Productions, formerly known as Trawler World Productions.