extra cooling on domestic refrigerator

Firstly, I am not a refrigeration engineer but I would like to improve the efficiency of a LEC domestic refrigerator. This is an A rated unit which I have on a Narrowboat and I am trying to cut down on the amount of electricity it uses as it all comes from my battery bank.
I was intending to improve the insulation by adding 25mm of expanded polystyrene to the sides and top of the cabinet. In addition to this I was planning to blow cool air from the boat bilges over the condenser at the back of the unit.
Do you think I would achieve any savings by doing this?

regards Brian on NB Harnser

It won't help because at LEC, a company with a name, they designed it already with the greatest efficiency and blowing wind from the bilges over the condenser will perhaps make that the unit will run outside the design conditions (too low condensing pressure)
By the way, is the air from the bilges not too salty?
Arent' the battery charged while engine is running?

As Peter said , blowing air threw the condenser may cause too low condensing pressure (mostly out of the design) .
Question , is it an absorption or compression cycle ?
If it's an absorption you can manage it to work with propane or butane combustion . . . send the specifications of the system and we will see how we can help

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Originally Posted by Peter_1

It won't help because at LEC, a company with a name, they designed it already with the greatest efficiency and blowing wind from the bilges over the condenser will perhaps make that the unit will run outside the design conditions (too low condensing pressure)
By the way, is the air from the bilges not too salty?
Arent' the battery charged while engine is running?

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Thanks for that, No the boat has dry bilges on fresh water so the air would be clean.
Yes the batteries do charge from the engine but sometimes we are moored up for a couple of days. The fridge uses about 36 ah per day at 24 volts DC via a 240 VAC Inverter. That is about a quater of the battery capacity.
Brian

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Originally Posted by botrous

) .
Question , is it an absorption or compression cycle ?

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Comression

In that case, the only solution, is getting an absorption unit and your problems are over.

In a second thought, why not use one of those mini-bars.
They have a compressor 1/12 HP.
Also less weight on the boat :D

Good luck any way you decide.

Chemi :)

The best way is to get an absorption mini bar , it's more effective and can work with heat source , maybe if you have good techncian they can make you the system work with heat from the yacht engine , and it's silent .... no noise in the yacht room

Ditchcrawler,are you mooring round the good old norfolk broads :)

Im with chemi and botrous invest in a absorption refrigerator,it is better suited for your narrowboat :).

Barely dabbled in marine refrigeration, but thought most employed cold plates. Fridge was chest-type to prevent loss of cold air when opened. Over-insulated was the norm.

Sides had ss plates filled with eutectic salts to change phase at a selected temperature. Chilling system would run with the engine. Plates would maintain temp for a day or two, depending on ambient & usage. Larger plates were used if longer idle time or warmer climates were involved, but that sacrificed fridge space.

More info if needed.

Rog

Like this ones?
Our secret mixture inside the plates? Pure salt added to a fusing point of -10°C for a bin temperature of +/- 0°C (=+/- 14% of the total weight as far as I can remember without looking in my papers)

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Originally Posted by MarkFiddy

Ditchcrawler,are you mooring round the good old norfolk broads :)

Im with chemi and botrous invest in a absorption refrigerator,it is better suited for your narrowboat :).

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I live near the Broads but our Narrowboat is on the South Oxford canal at Napton.

The only acceptable absorption fridge is made by Electrolux and costs about 700ukp In addition to this I would have to have it fitted by their agent, the wont supply for self fitting and I would have to install a gas system on the boat to fuel it.

Act fast.

http://search.ebay.co.uk/absorption-...W0QQsoloctogZ9

Chemi :)

Well I don't know what a NarrowBoat is , but using this eutectic salt system will give more weight to the boat

Oops sorry ,
Giving more weight to the boat=
The energy savings of the fridge will be added as energy consumption to the engine which runs the boat , unless the boat remains in a port , but during trips surely the savings will be consumed by the engine due to the fridge weight that's if we consider that the energy transaction is 100% and with no loss , and you all know that energy transaction has never been 100%

Just for the non UK and non-boaters here...

A narrowboat is anywhere from 25 to 70 feet long and just under 7 feet wide, designed for use on the english canals.

Use of an absorption fridge would, as Brian (ditchcrawler) says, involve a lot of work and expense to install on his boat. The UK models will run on LPG or electric and converting to run off waste engine heat is not practical.

I think the best option for you Brian is to try and increase the insulation around the fridge and ensure that you keep the fridge as fully loaded as possible; cooling air is an expensive waste.

Whether it is worth your while getting a cold plate, as suggested elsewhere, and making your own fridge is perhaps something to look into.

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Originally Posted by botrous

Giving more weight to the boat=
The energy savings of the fridge will be added as energy consumption to the engine which runs the boat , unless the boat remains in a port , but during trips surely the savings will be consumed by the engine due to the fridge weight that's if we consider that the energy transaction is 100% and with no loss , and you all know that energy transaction has never been 100%

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The point is not energy savings. It is never more efficient to employ an intermediate coolant such as a eutectic salt solution than to cool the unit directly because it means operating at a lower suction pressure.

The point is to minimize battery drain by running the cooling only when the engine runs. The extra weight is negligible compared to the weight of the boat, but the size of the plate was always minimized where possible to conserve refrigerated storage space.

Rog

Quote:

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Originally Posted by botrous

Well I don't know what a NarrowBoat is , but using this eutectic salt system will give more weight to the boat

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If you are interested there is a photo on my web site http://www.harnser.info

Thanks for all your help, As an outsider I didn't expect such a good responce

Well ditchtcrawler, now we see it all... we perhaps can find a solution on board itselves. If we all could float somedays on teh English waters with some beers,...we then sometimes have even more brilliant ideas. :p :p :p :D

It look like a really nice boat , good luck with your project ditchcrawler ..........RogGoetsh you've got my point for energy savings , but for the weight , it counts you can't neglect it , the motor will have to run a weight and it is added to it . . . it is more than 100 g no?