Holding Plates vs Evaporators - most efficient in actual use

[magdalena]

Does anyone know if there has been any research done in to which 12V fridge type is most economical - a holding plate system or an evaporator system.

On the one hand, the holding plate can use spare power to freeze a block of something, and thus allow the compressor to be turned off for a while later in the day. Presumably the effectiveness of this depends upon how well insulated your coolbox is.

But on the other hand, when there is no spare power, presumably there is some cost to have a large holding plate to cool as well as the fridge contents. I think I read somewhere that the compressor has to drive the plate down to a lower temperature to extract the same amount of heat? Is this correct?

If one only uses the engine twice a day (in and out of port) do the two "compressor off" periods outweigh the extra compressor working due to having the plate at all?


Anyone know if PBO or YM have done a study on this?

Nosing around the 'net found this:

http://www.frigoboat.com/sysdesign/aluminumevap.html
"Although 2 sizes of holding plates are available for the Frigomatic series (12/24v, Danfoss compressor), their use is not recommended, as they are less efficient than aluminum evaporators on these systems. This is because the capacity of the compressor for heat removal does not change, but the holding plate must be taken down to a lower temperature, increasing the run time. Although the run-time patterns will be different, the holding plate will require more running time overall."

I guess Isotherm's ASU system partly solves this, as it runs the compressor faster when there is power to do so, but I still wonder whether there is a benefit overall in realistic actual use.

I think Nigel Calder has a lot to say on this in his M&E Handbook, but my copy is on the boat at the moment.

Thoughts on whether any of the above is true are most welcome...

Regards,

Robin

 

[damo]

Have you tried the Liveaboard Forum? Thread going on at the moment which may have some relevance

OOPS it's you asking the questions /forums/images/graemlins/blush.gif

 

[Talbot]

This is not a simple answer, because primarily it depends on how you use your boat, and how you maintain battery voltage.

If your system of maintaining battery voltage is primarily by running the engine, you need a system that will rapidly cool using lots of amps and will keep cold for a long time, then you should use a holding plate.

If you have an abundance of power from solar and wind and can maintain power use all day /night for the fridge, i.e. small input but often, then the Evaporator is a better bet.