Holding plates or evaporator plates

[ssullivan]

Originally Posted by jzk

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

Sorry... could have been hallucinating. Too much bottom paint, zinc, resins, etc...

I thought I just read in this thread that it was bad to water cool the BD50s. I have a pair of them that are water cooled. They are the Isotherm top of the line system, minus the intelligent control unit, which the PO said kept blowing up. My guess is he kept wiring it incorrectly. He said the Link 10 on board "blew up" as well. When I wired it up, it worked... ha ha

Man... I need to get on that PO thread.

[captden]

Originally Posted by 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.

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.

Richard wow is this getting involved; Yes this is a large system, I don't have the measurements here, but the boxes are large. I wanted to go with holding plates but the company the boatyard wants to use said no way.
They want to use evaporator plates. I really frown on using an engine driven unit unless I put it on the generator, but I thought I would be better off with the 12 volt system to give me more options. Right now I have a battery capacity of 1600 amp hours and planning on increasing it. I would like to run this system during the day without running the generator if possible, and when running the generator for battery charging cool the boxes too. I guess I could put the comperssor on the generator but then I would have to run the generator at least twice a day. I plan to be on the hook most of the time. If I'm connected to shore power I could run the system with the 12 volts from the inverter/charger.
Captden

[Richard Kollmann]

Capten, lets start over you want a two box refrigerator freezer on your 47 ft sailboat.
Size of boxes unknown at this time but they are large.
Boat is equipped with Generator.
Battery capacity 1600 amp-hrs.
Plan to be on the hook most of the time.
Cruising in tropics.

Your decision of what refrigeration system will work for you must be based on the following: Size of boxes, The temperature you want to maintain in boxes, Climate conditions where you plan to cruise and where the energy will come from to operate refrigeration.

The following recommendation is based on worst case summer temperatures in tropical climate. North of latitude 30N boxes could be twice as large as listed.

If each box is 6 cu ft or less a BD 50 condensing unit and standard thin plate evaporators in each box is my recommendation. Compressor would run 50% of the time and should be equipped with adjustable speed control

If each box is 8 to 10 cu ft I would recommend holding plates and a ¾ HP belt driven 12 volt compressor. It would run two hours per day.

If each box is larger than 10 cu ft I would recommend engine driven system with holding plates as there is three times the btu capacity available in a one hour engine run.


I would try to stay will the more reliable 12 volt BD compressors as the large 12 volt motor driven require heavy maintenance every two years, and engine driven systems are not as user friendly and maintenance free as the small 12 volt systems.
Solar and wind alternative energy is a good idea for a cruising boat. Redundancy in equipment is also something to consider high output alternator on main engine, inverter/ charger with smart regulator.

If you will send the box sizes and size of all energy sources I will be able to better advise you on equipment selection and daily amp-hrs if there is a 12 volt answer.

[captden]

Hi Richard, first I would like to thank you for your time and information. I'm going down to the boat this weekend and I will measure both boxes. I can tell you that we want to be able to maintain a 34* temp for the refrig and about 21* temp for the freezer. These new boxes are a complete rebuild as the galley was destroyed in the collision last summer. I know there is 6" of foam all around the boxes and they are top loading. I will measure the boxes and openings and get back to you. If I had to guess I think they are in the 8 to 10 cu. ft. range As I posted earlier I have 1600 ah capacity, a 80 amp alternator on the main engine, 5.5kw generator and the inverter/charger 3000 watt/100amp. I have a wind generator but not installed yet but plan to do so before we head south, as for solar I have thought about it but haven't gone any further than that.
I have a picture of the boxes on my blog page if that helps any.
SV Renaissance

Thanks again
captden

[northerncat]

As an example, using a quantity of water as a eutectic solution and knowing that water's phase change occurs at approximately 0°c, this water will absorb and dissipate 80* (Yes eighty!) times as much thermal energy while freezing and thawing as it would for any other rise or fall of a degree centigrade.
(*All eutectic solutions with a lower phase change point than water also have a lower Latent Heat value. Expect low temperature eutectic mixes to absorb and dissipate approximately 65 to 70 watts while phase changing)
With a system refrigerating a solution through its' phase change temperature until frozen solid during each run cycle, then staying off for very long periods while this thermal mass thaws completely before running again, many advantages become obvious including the following..
* Tremendous 'hold-over' off periods due to the thermal mass of the stored eutectic solution and more importantly because of the eutectic's phase change.
* Refrigeration run periods can be at a time that suits individual variations of power supply, or during cooler periods of the day when all refrigeration system are more efficient.
* Much lower overall power consumption due to more efficient refrigerant evaporation in a saturated environment, and far less stop / start operations.
* The eutectic solution can be varied to have a phase change point at much lower temperatures than water to suit refrigerator or freezer cabinets.
* As a eutectic system is virtually 'cooling in advance', use of shore power or other abundant power supplies allows a day or so of refrigeration in storage.
* A day or two or three of sailing without the need of additional cooling is possible if battery power supply is down. (i.e.. solar but no sun!)
* The eutectic system stores energy at a third of weight that would be required in batteries to provide the same refrigeration effect.

just some info on holding plate systems, the important thing is to set them up correctly in the first place
sean

[Maren]

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. ...

That slideshow was really worth the watching, thanks.

The question was initially framed as either a holding plate or evaporator. But I know there are hybrid systems, and apparently there are ones that aren't truly hybrid systems. Could you go into this a bit more? It would seem to be the best of both worlds. But then practice sometimes differs from theory and you are well versed in both.

Thanks,

[Richard Kollmann]

A car that combines a gasoline engine with electric motor to propel it is defined as a Hybrid vehicle. A holding plate with a single energy source to cause it to absorb heat is not a hybrid. Years ago when an engine driven refrigeration system and an electric refrigeration system were connected separately to a holding plate it was defined as engine drive with shore power backup. Today with several sources of alternative energy onboard many cruising boats it makes more sense to define these systems as true Hybrids.
Having designed and built several hundred holding plate I know their true benefit. A holding plate acts the same as ice or a storage battery it stores energy when surplus energy is available. I agree with the previous information on holdover plates but what is often misunderstood is when a holding plate provides an advantage and when it does not. There is a major difference in the thermodynamics of a thick holding plate and a thin plate evaporator. In order for a holding plate to appear to use less energy than a thin plate evaporator the box temperature must have a broad temperature differential ( defined as swing). Thin plate evaporators will maintain box temperature swing to one or two degrees because they conduct heat much faster than holding plates. Holding plates have evaporator coils inside surrounded by a eutectic solution. This solution starts freezing first around plate’s tubing low in plate. As ice builds up it acts as an insulator causing expansion device to lower temperature and Btu output. If a thermostat controlling a holding plate’s temperature were set to a low temperature Off On differential it can match the box temperature of an evaporator system by consuming more daily energy.
With all that is said about evaporators and holding plates my guess is that half the boaters are interested only in refrigeration to have cold drinks. One other advantage to thin plate bin evaporators is fast ice cube production.