Two different holding plate systems?

[berwick]

Hi, the boat I'm buying has an older engine driven Seafrost with holding plate which works really well. Also in the freezer area of the spillover system is another separate holding plate driven by an A/C compressor. I am adding lots of solar and would like to take out the A/C compressor system and that holding plate and put in a Technautics Coolblue and plate in it's place.
My thought is I will have some redundancy but does this have a hope of working ok?
Will it be too easy to overfreeze the icebox unless I am vigilant about keeping the coolblue off when motoring (if I turn on the engine driven part).
Is there a type of thermostat that can do this automatically?
If the engine cold plate defrosts because I am using the Coolblue at anchor does it take extra energy out of the Coolblue holding plate?

Thanks

Richard

[Adelie]

If you are buying the boat how do you know it works well? Do you personally know the current owner?

Not trying to trying to rain on your parade, I’m occupationally suspicious of what people tell me, especially salesmen.

[Bowdrie]

Originally Posted by berwick

Hi, the boat I'm buying has an older engine driven Seafrost with holding plate which works really well. Also in the freezer area of the spillover system is another separate holding plate driven by an A/C compressor. I am adding lots of solar and would like to take out the A/C compressor system and that holding plate and put in a Technautics Coolblue and plate in it's place.
My thought is I will have some redundancy but does this have a hope of working ok?
Will it be too easy to overfreeze the icebox unless I am vigilant about keeping the coolblue off when motoring (if I turn on the engine driven part).
Is there a type of thermostat that can do this automatically?
If the engine cold plate defrosts because I am using the Coolblue at anchor does it take extra energy out of the Coolblue holding plate?
Thanks
Richard

While not a particularly common arrangement, it's certainly not rare.
The only time either system would use/need "extra energy" is if the temp of the un-used holding plate is higher or within the range of the thermostat setting at which the operating system is, (cut in/cut out).
In that scenario, the operating system is working to remove heat from the "off duty" holding plate as well as the "normal" box load.
Basically, the off-duty plate is just some additional heat load in the box.
If the AC system is in good operational condition, what is the gain to replace it with a 12V unit?
The AC system is undoubtedly of much greater power and can take care of the dockside demands with better efficiency and less total run times.
For much less cost than a new 12V unit you can have a small, dedicated inverter for use with battery power when desired.
A typical AC unit is actually quite user friendly and intuitive; service and repairs are easily carried out anywhere in the world with readily available parts, and no special knowledge or proprietary parts needed.
Offhand I know of no "automatic" type thermostats that will operate as you suggest.

[berwick]

Well if the engine one works well (not sure yet) I would like to leave it in place. The A/C is not a good option for me as I don't plug into a dock and feel I am using more power by running it through the invertor to keep the system going when at anchor and really only want to run the engine when needed for motoring and not for charging, but when that happens would like to help freeze things and perhaps reduce using current from the batteries.
Not sure how the 2 plates will get along but I guess just treat the other plate as something that the other unit needs to try and cool when not used. I think it will take a bit of screwing with it to try and make it work.

thanks

Richard

[Bowdrie]

Fair enough, and the 12V will be smaller and quieter.
The "Technautics" system is a good unit.

[Madehn]

Call Charlie at technautics. Very helpful and ver knowledgeable. He can help you sort it out. Won’t be cheap but it can be done. ( I have two of their systems ).

[berwick]

Yes got ahold of Rich at Technautics and think it will work good.

[RaymondR]

There are some fairly high capacity 12/24 volt DC compressors available these days if you just wanted to change the AC eutectics system to DC. With that you would pretty well have a new system.

Whilst pulling down a non working eutectic tank (holding plate) would result in a greater heat load, once it is pulled down it does not and all the heat load will come either from warm things being added to the box or heat bleed into the box from the outside environment. Consequently the extra mass of fluid in the non operating tank will act as a "thermal flywheel" and store "cool" and the condensing unit cycle numbers will reduce.

Ozyfridge ran a number of comparative tests to demonstrate how their eutectic systems exploited the day time availability of power from a boats solar farm could be more efficiently exploited to reduce battery cycles and therefor battery life. One of the surprising outcomes was that the eutectic system resulted in an overall electrical power use reduction of about 40% over the continuously cycling system. This was attributed to the wastage of power every time the compressor cycled on and had to run before the system actually stabilized into cooling mode.

[Bowdrie]

Originally Posted by RaymondR

One of the surprising outcomes was that the eutectic system resulted in an overall electrical power use reduction of about 40% over the continuously cycling system. This was attributed to the wastage of power every time the compressor cycled on and had to run before the system actually stabilized into cooling mode.

Yep, while all other companies were using evaporators with their 12V systems, Technautics immediately went to using eutectic plates with their 12V systems back in the '80s, and that advantage was made apparent.
They still have, (AFAIK/IMHO,) the best "off the shelf' eutectic plate.