Holding plates or evaporator plates

[captden]

Hi all, I thought I was all set with the new refrigeration system to be installed in the galley refit. We were planning to have two sets of holding plates, one plate for the refer box and one or two holding plates for the freezer box depending on the btu usage. These were to be run off of one 12 volt compressor with the option of having one or both boxes cooling at the same time.
The boatyard just sent me an email to dicuss using evaporator plates with two compressiors to run this system. My question is does anybody have any experince with these evaporator plates and how efficient are they? The new boxes are insulated with 6" of foam all around and we will be cruising mostly in tropical area. Somehow I don't think the evaporater plates would be as effecient as the holding plates and the compressors will be running all the time.

Thanks
captden

P.S. You can check out the progress of our rebuild on our blog
yachtrenaissance.blogspot.com

[Richard Kollmann]

Thin evaporator plates are more efficient than holding plates. Holding plates serve only one purpose and that is to store energy the same as a battery for use when energy is not available. First figure out how much daily energy your refrigeration needs then pick a refrigeration system to meet your onboard energy needs. Watch the slide show on my web site for help in selecting a system. At KollmannMarine Boat Refrigeration Specialist.

[senormechanico]

An evaporator plate system will probably run a similar percentage of the time as a cold plate system (I've had both types). An evap system will cycle often. For example if the evap system ran for 20 minutes and was off for 1 hour, the cold plate version would run for 2 hours and be off for 6 hours (or some variant of those numbers). The energy use would be roughly the same. Your choice will depend on whether you will be running an engine for battery charging and you could charge up a cold plate refrigeration system at the same time. Make the system mirror your available power schedule. If you have wind available most of the time as in the Caribbean,
an evaporator system might be fine.

Our cruising boat had a cold plate system and a couple of vacuum insulation panels.
The refrigeration compressor had an "on" temp in the freezer of +6 degrees f. and an "off" temp of -6 f. It had a thermostat, but I added a "start" button so every morning at about 10 AM I'd hit that button. Ten AM was when our 8 solar panels array was really starting to produce. The fridge took 17 amps, but we produced 22 amps all day long until about 5 PM. Alhough the fridge ran for about 3 1/4 hours, our batteries were always nice and fat, and we could keep ice cream!


Steve B.

[captden]

Thanks for the quick replies: Richard I have one question, I went to your site it was very imformative, my question is, if I go with the danfoss bd-50 compressor would you recomend going with air cooled? If I read the info correctly the water cooled unit is prone to failure a lot sooner than the air cooled unit. As I stated in my first post we will be living aboard in the tropics, and will the air cooled unit provide enough cooling without running all day long?
Thanks again
captden

SV Renaissance

[senormechanico]

I would definitely go with water cooling in the tropics.
We installed a cold plate / Danfoss 12volt system and after properly fitting a zinc to the condenser (which the clueless dealer had incorrectly done) we had no problems in 4 years.

Steve B.

[DeepFrz]

About the best thing you can do for an air cooled system is make sure you have good ducting and venting so you get a good cool air flow. You have to get the heat out and away from the heat exchanger and good cool air in. If you do this and you have good box insulation an air cooled unit should work fine.

Your refrigeration power needs should be factored in when you design your electrical system so that you are not depleting your batteries below 50% charge. Unless your refrigeration system and your electrical system are designed properly you will end up being unhappy with each of these systems.

[Maren]

Originally Posted by captden

Hi all, I thought I was all set with the new refrigeration system to be installed in the galley refit. ... Somehow I don't think the evaporater plates would be as effecient as the holding plates and the compressors will be running all the time.

I think you'll find it helps to be clear on not only what section of the world you are in, but if you are going to be anchoring out or at a marina.

This article and the part one (listed at the top of the article) are pretty good. Of note is the variant on the closed water-cooled system, known as a keel cooler.


Hope that helps.

[senormechanico]

Originally Posted by DeepFrz

About the best thing you can do for an air cooled system is make sure you have good ducting and venting so you get a good cool air flow. You have to get the heat out and away from the heat exchanger and good cool air in. If you do this and you have good box insulation an air cooled unit should work fine.

Assuming you have good cool air in...a precious commodity in the tropics.

Ever heard the joke about tropical sex?

Man touches woman finger to finger and says, "It was good for me; was it good for you?"

In Mexico's Sea of Cortez in June, hooboy! is that ever the truth!

In those conditions if another person is any less than 2 feet away from you, you can feel their body heat.

Steve B.

[Richard Kollmann]

Capden, Any refrigeration system on a boat larger than 1/6 HP must be water cooled because the volume of process heat produced is difficult to dissipate in a boat. The BD50 compressor averages less than 300 Btu per hour this is about the same amount of heat per hour generated by an adult person moving around in the cabin. In tropical conditions where seawater is above 78 degrees 24 hours per day there is an energy advantage to air cooling BD compressors. In many systems BD compressors run much longer at lower amperage to gain improved energy efficiency. If water is pump through condensers for longer periods of time the energy to power pump reduces total System Coefficient Of Performance (SCOP)

The BD50 is a new generation of variable speed compressors designed for longevity in air cooled applications. These compressors, Danfoss BD35, BD50 and BD80 achieve energy efficiency by improving power in versus power out. If the correct refrigeration components are selected and they match the refrigerator box’s daily heat load correctly energy consumption could be cut in half.

Capden, If you have watched my slide show, read FAQ #33 and read resent post on water cooling on my forum you will understand why I am against any form of water cooling BD condensing units.

Your original question was about what sounded like a large two box system. On a 40 Ft boat, two boxes normally indicates large energy demand so the first thing you need to determine is the daily electrical load. Is this refrigeration system going to be too large of an amp load to support? I personally prefer engine driven and 12 volt hybrid holding plate system for tropical live aboard boats.

[northerncat]

Originally Posted by Richard Kollmann

Thin evaporator plates are more efficient than holding plates. Holding plates serve only one purpose and that is to store energy the same as a battery for use when energy is not available. First figure out how much daily energy your refrigeration needs then pick a refrigeration system to meet your onboard energy needs. Watch the slide show on my web site for help in selecting a system. At KollmannMarine Boat Refrigeration Specialist.

this is not necessarily true as if you get your holding plates working at the exact temp you want them to you get a little thing called phase change working for you which is where when the solid turns to a liquid it can absorb up to 80 times the amount of heat as the liquid can making holding plates extremely efficient if used right
sean

[Joli]

A number of articles are written about efficiency of both systems. It seems that the holding plate or evaporator decision is made by how you manage energy. If you have wind and solar so you constantly charge the evaporator looks like a better system. If you run a generator daily and cycle fridge and freezer then a holding plate system may be a better choice. Like everything else in sailing, there are trade offs.

[ssullivan]

Richard wrote the book (literally) on this stuff. I have the book. I was even talking shop with an HVAC guy yesterday who thought I was in the business (from reading the book and putting together my last system)

He has sections taking the reader through phase change.

Sadly, I have twin BD50's on this new boat, and they are water cooled (the largest Isotherm system). It's working, but maybe isn't as efficient as if it were air cooled?

Originally Posted by northerncat

this is not necessarily true as if you get your holding plates working at the exact temp you want them to you get a little thing called phase change working for you which is where when the solid turns to a liquid it can absorb up to 80 times the amount of heat as the liquid can making holding plates extremely efficient if used right
sean

[roverhi]

FWIW, talked with a cruiser passing through Kona on his way back to the Mainland. Believe he had a Frigobot water cooled system in his boat. Previously, the he had an aircooled condensor that required constant charging, even though he had solar panels and a windmill. In Tahiti, when he switched to the water cooler for the frigobot, he no longer needed to run the engine to charge the batteries. The solar panels and windmill were suddenly able to keep up with his frig. and electrical needs. If you know Tahiti's waters, it's one of the few places where the water is warm enough to swim.

Aloha
Peter O.

[Richard Kollmann]

Roverhi, It is true that many boaters that have smaller boxes will see a marked improvement in amperage used after installing a new Danfoss BD variable speed compressor system and this has nothing to do with the type of condenser cooling. Variable speed compressors can be set to better match each component in a system and match to a given box’s heat load. If a new style compressor is used in a large heat loaded box and required to run at high speed do not expect much energy efficiency over the old BD fixed speed compressor. It is true that keel cooler condensers can cut 3 to 6 amp-hrs per day in cool seawater temperatures. My openion is for day, night, cool or hot weather the best energy efficiency and realiable system will be on properly installed air cooled unit equipped with one of the automatic speed controller.

[jzk]

Originally Posted by ssullivan

Sadly, I have twin BD50's on this new boat, and they are water cooled (the largest Isotherm system). It's working, but maybe isn't as efficient as if it were air cooled?

Why don't you like the BD50's? From flipping through his site, that guy richard seems to like them.