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Old 05-03-2020, 19:57   #181
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Re: The Worst pleasure boat refrigeration.

These ice box converted to refrigerator or freezers rarely have normalized temperatures throughout. Top of box is warmer with bottom colder so if you are lucky enough to have a temperature reading thermometer that has a calibration adjustment it does not matter where its sense probe is as long as it is not touching one of the box's six sides.

To calibrate thermometer I suggest placing a empty cardboard box in box so with an inexpensive thermometer on top of it, then calibrate your remote thermometer to mach test thermometer on cardboard box. Now you have a good idea of average box temperatures knowing it is a little warmer at top and colder at bottom of insulated box.
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Old 05-03-2020, 20:23   #182
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Re: The Worst pleasure boat refrigeration.

Well, I think I can see why that particular installation might have excessive cycling times. Vertical, front-opening boxes are *renowned* for being less efficient for the same volume than a chest-type, top-opening fridge-freezer.

Here's why: every time you open the door, all the cold air falls out (being denser than warmer air outside) and so compressor has to cycle frantically to replace lost cold air.

The more often you open the door, the worse the power consumption.

So a "test" on such a fridge ought to feature several "open / close" events to better replicate *actual* usage.

Where 12V is concerned, chest type fridges are a no brainer. BUt they can be useful in domestic environments as well.

Of course, if you have the acreage for solar, or the space to mount a large batt bank, or don't mind running your engine/generator to recharge said bank, then by all means go with "front-opening convenience".

Anyone who has such a fridge is further advised to keep it full (with bottles of water taking up spaces) so as to A) reduce the volume of air that drops to the floor every time the fridge is opened, and B) provide a heat sink to soak up the warmth of the air that rushes in to replace it.

This is 'Refrigeration 101'.

It's also why domestic fridge makers now utilise plastic boxes on drawer slides for freezer compartments, as this reduces the compressor cycling time and thus enables them to claim a more "green" operation cycle and increase the number of 'stars' on their efficiency labelling (such as we have here in Oz).
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Old 05-03-2020, 21:25   #183
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Re: The Worst pleasure boat refrigeration.

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Originally Posted by ayates View Post
Note sure if you were referring to my measurements or not. But my temperature probes were free air. You can see small boxes in this photo, along with the evaporator fan, and a 4 litres of frozen water in the freezer to provide some mass to be more realistic.


Allan.
Would you consider mounting the fan so as to perform a powered spill over function. I placed a small thermostatically controlled fan in the spill over port. The fridge temp is controlled independently but the source of cooling is the freezer which has it's own thermostat. If I bleed enough energy from the freezer the compressor via the freezer controller takes care of it. You would have to connect your compressor controller up to a capillary style thermostat using conventional mounting location. I use inexpensive PID controllers from AUBER Instruments. I'm not suggesting using a PID algorithm some have simple relay closure for what we need.


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Old 05-03-2020, 21:35   #184
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Re: The Worst pleasure boat refrigeration.

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Would you consider mounting the fan so as to perform a powered spill over function. I placed a small thermostatically controlled fan in the spill over port. The fridge temp is controlled independently but the source of cooling is the freezer which has it's own thermostat. If I bleed enough energy from the freezer the compressor via the freezer controller takes care of it. You would have to connect your compressor controller up to a capillary style thermostat using conventional mounting location. I use inexpensive PID controllers from AUBER Instruments. I'm not suggesting using a PID algorithm some have simple relay closure for what we need.


Phil
Rereading, would you be able to use the existing capillary thermostat for the fan and only having to get a hold of a suitable freezer stat?


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Old 25-03-2020, 20:05   #185
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Re: The Worst pleasure boat refrigeration.

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Ozefridge does a clever air/water cooled condenser which they recommend you pipe from your water tank for fresh water cooling rather than sea water.

My air cooled condensing unit is under the sink and I cruise mostly in the tropics and it's amazing how much hotter it is in the galley on a hot day than in the rest of the boat.
Absolutely!
We have a chest freezer, front opening fridge (with 'ice box'), and a drawer fridge. On a hot day when there is no breeze running through the boat, it gets quite hot down below (and the three units are of course working harder at flattening our battery bank). The secret is air movement - and I'm still working on that

For the Ozefridge idea, that water tank is going to get really hot quite quickly if it's the heatsink for your fridge.
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Old 25-03-2020, 20:14   #186
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Re: The Worst pleasure boat refrigeration.

Might make more sense to plumb the heatsink for the fridge to the HOT water tank, and have it act as a pre-heater.....?????

That's if you ahve the luxury of a hot water tank....

LOOXURY..!! But you tell tha yoong peeple that, an they don' believe yer!
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Old 25-03-2020, 20:16   #187
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Re: The Worst pleasure boat refrigeration.

"For the Ozefridge idea, that water tank is going to get really hot quite quickly if it's the heatsink for your fridge."

I have a water cooled Ozefridge that has been in use in Queensland for many years. The summer sea water temperature gets to 30c. The water is circulating through 200 litres, with no noticeable changes to the water temperature in the tanks.
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Old 25-03-2020, 20:21   #188
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Re: The Worst pleasure boat refrigeration.

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Might make more sense to plumb the heatsink for the fridge to the HOT water tank, and have it act as a pre-heater.....?????

That's if you ahve the luxury of a hot water tank....

LOOXURY..!! But you tell tha yoong peeple that, an they don' believe yer!
Definitely not correct. Ozefridge have been supplying these water tank cooling freezer & fridge systems for years. Many happy customers who have them in the tropics, me included.
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Old 25-03-2020, 22:07   #189
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Re: The Worst pleasure boat refrigeration.

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For the Ozefridge idea, that water tank is going to get really hot quite quickly if it's the heatsink for your fridge.
Nah, we have ours plumbed into a 300 liter tank and the water in the tank is maybe a degree or two above the sea water temp. 300 liters absorbs a lot of heat and that heat is then dissipated through the tank, hull, and hoses pretty quickly. Probably want to keep the tank above 1/3 full, for better efficiency. I've actually run a fairly large freezer unit using only a 5 gallon bucket of water as a heat sink and the water there only got up to about 104 degrees. Not perfect, but still ok.

Definitely don't want to run it plumbed into a hot water supply. The idea is for the heat from the refrigerant to transfer to the cooler water. If its running through hot water tank, you'll never cool the refrigerant and the system won't work.
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Old 25-03-2020, 22:08   #190
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Re: The Worst pleasure boat refrigeration.

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Definitely not correct. Ozefridge have been supplying these water tank cooling freezer & fridge systems for years. Many happy customers who have them in the tropics, me included.


Im pretty sure Buzzman was being ironic.
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Old 25-03-2020, 22:12   #191
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Re: The Worst pleasure boat refrigeration.

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Im pretty sure Buzzman was being ironic.
Or sardonic!!
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Old 25-03-2020, 22:21   #192
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Re: The Worst pleasure boat refrigeration.

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Absolutely!

For the Ozefridge idea, that water tank is going to get really hot quite quickly if it's the heatsink for your fridge.
They recommend using the fresh water tank to minimize corrosion problems. With it's fairly large surface area a water tank used with and a constant cycling unit would probably work well as a heat sink because it would continue to reject heat between compression cycles. Different matter with a system with holding tanks as they may run all day and would be better cooled with a flow of cold sea water.
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Old 26-03-2020, 10:43   #193
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Re: The Worst pleasure boat refrigeration.

Using fresh water tank to dispose of refrigeration process heat is not OK under certain conditions:
1. The box size must be small enough to dispose of heat removed from compressor and box. In 24 hours with a 4 cubic ft box operating in a warm climate 2400 btu a day could need to be deposited of in fresh water tank. Water temperatures above 75 degrees cause insufficient cooling and higher amperage consumed.
2. All hermetically sealed compressors whether 12 volt or AC powered will discharge low voltage current into water cooled systems, so even a fresh water tank can contain damaging corrosive current.
3. Properly designed air cooled condensing units installed correctly do not require water cooling. A visual inspection of 12/24 air cooled condensing units is a good indication you have in selected a more friendly unit. Technautics has a U Tube video on line explaining why manufacturers avoid any form of water cooling small pleasure boat refrigeration.
Larger refrigeration systems for boats do require seawater cooled systems and isolation transformers to reduce system failures.
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Old 26-03-2020, 14:46   #194
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Re: The Worst pleasure boat refrigeration.

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Originally Posted by RaymondR View Post
They recommend using the fresh water tank to minimize corrosion problems. With it's fairly large surface area a water tank used with and a constant cycling unit would probably work well as a heat sink because it would continue to reject heat between compression cycles. Different matter with a system with holding tanks as they may run all day and would be better cooled with a flow of cold sea water.
Its just the opposite. Holding plate system runs only once or twice a day maybe 1 to 2 hours each time then shuts off. Constant cycling system runs on and off much more often. But either way the same amount of heat must be dissipated over time, and any heat sink that maintains its outside temperatue no matter how much heat is dumped into it (seawater), is theoretically better than one that heats up as you use it (water tank) or forbid, cabin air in the tropics.
Actual results of any heat exchanger system depend very much on design and maintenance of course, but from what I see, a large closed loop keel cooler system appears very attractive.
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Old 26-03-2020, 18:49   #195
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Re: The Worst pleasure boat refrigeration.

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Its just the opposite. Holding plate system runs only once or twice a day maybe 1 to 2 hours each time then shuts off. Constant cycling system runs on and off much more often. But either way the same amount of heat must be dissipated over time, and any heat sink that maintains its outside temperatue no matter how much heat is dumped into it (seawater), is theoretically better than one that heats up as you use it (water tank) or forbid, cabin air in the tropics.
Actual results of any heat exchanger system depend very much on design and maintenance of course, but from what I see, a large closed loop keel cooler system appears very attractive.
Beg to differ.

Holding tank systems with small 12V compressors may need to run all day.

My old system with a BD50 compressor was on a timer which allowed it to turn on at 8 am and turned it of at 03.30 pm, it often ran all day. Be mindful that the reason for using a holding tank with a small compressor is so that it does not run at night when there is no solar power. The water in the rank will absorb heat all day and if tank rejection is less than condenser rejection the water is going to heat up all day.
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