Marine Refrigeration

How does Marine refrigeration work? The major parts of a DC refrigeration system include the refrigerant, a compressor, and a condenser, a cooling system for condenser, and a plate or plates inside the refrigeration box. 

The compressor is part of a closed loop pumping refrigerant through the system and through the evaporator plate in the ice box. The compressor has two sides the High side or discharge side. The discharge side pumps refrigerant under pressure to the condenser. The suction side or low side and sucks refrigerant after it passes through the evaporator plate back to the compressor. The cold plates in the fridge space have either expansion valves or capillary tube that separate the low and high pressure sides of the refrigeration system.

Coolers & Filters

The refrigerant in the compressor starts as a gas. The compressor compresses the refrigerant gas, from low pressure to high pressure between 100-150 psi. When the pressure is increased like this its temperature is raised dramatically. This hot high pressure refrigerant is then fed to a condenser, where it is cooled and turned into a liquid. The condenser is cooled by either air or water. The refrigerant is now a cool high pressure liquid and is fed to an evaporator plate inside the boats refrigerator box.

The evaporator plate takes the refrigerant from the condenser and here it boils rapidly & evaporates back to a gas, at a very low temperature. This change of state absorbs vast amounts of sensible heat from the evaporator which in turn removes heat from the insulated refrigeration box, thereby lowering its temperature. The BTU is the measurement of heat removed. From the evaporator plate the refrigerant is returned to the low side of the compressor, to start the process again.

Evaporator or Holding Plates

Marine refrigeration systems use either an evaporator plate or a holding plate in the boats refrigeration space or freezer space. Each type of plate works differently in drawing heat from the boats refrigerator and ice box space.

Marine Evaporator

Marine Evaporators are just like the ones found in household refrigerators. They can get quite cold (thermostat setting) and many evaporators have the ability to make ice next to the evaporator plate or inside the evaporator box. Evaporators come in several shapes and sizes; they can be horizontal plate's vertical plates and rolled plates. Evaporators are constant cycling, or short cycle. Most use a Danfoss marine compressor with H134 refrigerant.

Thermostat controlled evaporator temperature. Turn to lower ice box temperature. Evaporator plates are less expensive, but need Constant power supply.

Marine Holding plates

Marine Refrigerator Holding Plates act like large blocks of ice and the cold temperature of the holding plate sucks heat out of the boats refrigeration box. Holding plates can keep ice boxes cold for long periods.

The main advantage of a holding plate over an evaporator is that they only need to be recharged 1 or 2 times per day. This charging can coincide with attaching to shore power, running the engine and so the refrigerator does not rely on the battery bank. When incorporated into a properly designed system, holdover plates can significantly reduce average energy consumption. However DC holding plates are also possible.  The holding plate is filled with a solution that has a freezing point below 23 degrees F.  As the compressor runs, the refrigerant passes through the holding Plates coil, freezing the holding plate solution. The compressor turns of and as the holding plate thaws out, heat is removed from the box.

Powering the Compressor

The power supply to the compressor is one of the key elements of the boats refrigeration system. Refrigeration is one of the largest energy consumers onboard, so the power supply is an important element of the system. Power supplies to marine refrigeration systems include AC, DC, Shore Power, Engine power, and hybrid systems. Hybrids are combinations of say 12 volt and engine drive, or engine and shore power. The whole point in looking at power supply to your boats refrigerator is to couple it into onboard power requirements for all your boats marine systems. If you run a generator much of the time then adding on an AC refrigeration unit may make sense, but unless you do, you would be better at looking at 12 V, engine or shore power.

Power can be decided on how you use your boat. Are you tied up at a dock for much of the time and take days trips. Or do you cruise and spend large amounts of time at anchor. Finally are you Powerboating or Sailing will also influence power supply. Sailing means no charging of batteries or power from the engine. Here a solar panel or wind or towed generator can help replenish batteries. If you spend time at the dock, a DC system has plenty of time to recharge on shore power. If you spend time motoring and at the dock and engine drive with shore assist works well.

AC 110 volt marine refrigeration     

These drop in refrigerators are like the one in your home and are commonly seen on larges boats with an abundance of AC power and space. The AC powers the marine compressor, and the condenser is typically air cooled. A reliable AC supply is needed in the form of a generator.

DC marine refrigeration with Evaporator plate

 One of the cheapest marine refrigeration system and easiest to install is the 12 v or DC system. Air cooling is the simplest. The DC system combined with an evaporator plate that is thermostatically controlled gives flexibility over cooling requirements. Many 12 volt systems use the Danfoss compressor. With the increased efficiency of the Danfoss compressor, DC refrigeration onboard is getting more efficient, but is still power hungry.

For most boats with a small box, a single 12V compressor, air cooled condenser, with evaporator type plate will be about the cheapest option. The Adler Barbour Cold Machine has been around for around 25 years and provides great refrigeration for small to medium size ice boxes. 

Shore powered marine refrigeration

Shore powered systems are made to maintain the boat's ice box at set temperature when the boat is at the dock. They offer less power than direct from an engine drive but since you will be at the dock for a while that is not an issue.

If you use a holding plate and shore powered system you can keep the plate cool while away from the dock for 12 hours or so.

 Engine powered marine refrigeration

The idea behind an engine driven compressor system is that the engine gets used anyway for at lest an hour or so. If you are Powerboating this makes sense, if you are sailing calculate how much time you use the engine.

If this is the case an engine drive with a holding plate can draw down the ice box in a short period and after that it can be left for 12 plus hours.

The compressor is run directly off the engine. Belt driven or direct compressor, There are two plates and you can add more, plus ad a separate freezer unit. This creates much power and fast cooling of the holding plate. More power than a 110 volt system. Larger systems and multiple plates are possible. Engine driven systems cost more and also involve a labor higher cost    

Condenser Cooling

The marine refrigeration systems condenser needs cooling. This is how the refrigerant gets cooled and turned into a liquid. There are 3 ways to cool the condenser;

Air Cooled

Air cooling simplifies installation plus it does not rely on water or adding through hulls. It is therefore the cheapest installation. For smaller units air cooling is OK, say 4 cu ft or under 6 cu ft you will get adequate performance. The air cooling unit needs a sufficient supply of re-circulated air for it to work. Ducting and space around the unit will help this.

When you cool by air flow you remove heat from the condenser and ad it to the ambient temperature. The temperature inside of the cabin only has enough capacity to disperse this heat.

Water cooled Condenser

Water cooled compressors will work better in higher ambient temperatures and are more efficient and can be 30% more efficient. Water cooling may be best and is better for larger installs especially if freezer is concerned. Water cooling needs a through hull and a pump to get the water to the condenser. The most efficient way to cool the condenser

Keel cooler Condenser

The keel cooler or keel condenser requires no through hull fitting and will not be subject to clogging. The keel cooler is a 3" x 7" bronze plate that mounts on the outside of the hull and it is the condenser heat exchanger. The bronze plates are connected direct to the compressor which is the only moving part in the system. The Keel Cooler is for a box up to a 15 cu ft refrigerator or 5 cu ft freezer. Since all the heat is passed into the water outside the boat it will does not heat up the interior. Since it works without a water pump there is never a pump or strainer to maintain and best of all it is nearly silent in operation.

Refrigeration Compressor & plate Combination

Before we pick a size of marine refrigerator we need to understand what factors are involved in keeping the refrigeration box cool. They are mainly box size, insulation and cooling water temperature, number of people aboard and the temperature you are setting the plates for.

Refrigerator Box Volume

This is obvious, the larger the box the more heat removal is necessary. A larger box will need more BTUs of heat removal. After this basic size issue we have things like, Front opening or top opening. Front opening lets cold air out quickly but does allow you to get to the bottom of the box. Drains, if you had a drain for you ice box plug it. You will not need to drain water out of the ice box and this will only let cold air out and heat in. Gaskets, these are a must and must be properly sealed. A trick to identify if there are gaps in the gasket is to put a piece of paper in between the lid or door and the cabinet and close it. Pull on the paper and you should feel some drag if the gaskets are sealing properly. It comes out easily there is a gap. Get new or better gasket material.

Insulation  

Typical insulation to a fridge or freezer is foam insulation like Dow Blue board. The recommendation is for 3-4 inches for refrigeration and 4-6 inches for freezer for medium sized boxes. Foam has an R value of 5 per inch thickness, R being a thermal unit. This means in terms of thermal units 3-4 inches represents 15-20R value for the refrigeration unit, and 20-30 for the freezer.

There are manufacturers of vacuum panel thermal insulation. The Glacier bay Barrier Ultra-R super-insulation at R-50 per inch provides lots of insulation without taking up valuable volume. These panels are vacuum panels and are sealed to work. It is very important that you do not drill through or puncture these panels. These panels are custom made, so you would need to provide the manufacturer, exact sizes with locations for copper plate tubes to enter the box. These are built into the panels.

Water temperature

In the tropics water temperature is a lot warmer then northern climates. For every degree water temperature increases a corresponding 2 % increase in required BTU. If you are in the Atlantic portions of the east coast US, you have some cool sea water temps, but of you then cruise down to the Caribbean you may strain your refrigeration system.

Plate Thermostat

The evaporator plate temperature is set by the thermostat. Dial the box temperature down and the system will have to work harder.

Number of people aboard

More people means the box gets opened more and the heat build up from more people adds to the ambient temperature.

How big a Refrigeration System is required?

To calculate how big a refrigeration or marine freezing unit required, you will need to start with an estimation of the BTU requirements of the box. A simple rule of thumb for estimating the BTUs is based on the box volume.

These BTU estimations are based on these assumptions;

- Insulation has an R value of 30 no leaks.
- Water temperatures are tropical in the mid 80s F.
- 2 people aboard, for each extra person add an additional 1,000 daily BTU
- Top opening box, for a front opening door add 15 BTU/inch of door

BTU estimate on refrigeration volume;

Refrigerator daily heat load; 600 Btu per cu. ft.

Freezer daily heat load; 1200 Btu per cu. ft

Lets look at how this works for the 4 cu ft refrigeration system, using the above formula

4 cu. ft. times 600  =   2,400 Btu.

Two additional people on board =   2,000 Btu.

Total required per day   = 4,400 Btu

Choosing 12 volt unit with Evaporator

Match this number to the compressor capabilities, and then calculate amps needed to power the system, and then work on the battery bank capability. Start by using the 4,400 BTU form the above example. The Adler Barbour Cold Machine uses the Danfoss BD50 Compressor is rated at 650BTU / hr based on 25F evaporator temp.

This is well above the 4,400/day we need for the 4 cu ft fridge, using only about 1/3 of the power. We could easily go down the Danfoss DB35.

Amps

To calculate how many amps the system will draw we start by converting BTUs to amps with this formula, using an assumption of 5 BTUs per watt hr of energy used. BTU/5/volts. so say we have 4400 BTUS and 12 volts, 4,400/5/12=74 amp hours/day.

Battery Bank

The Amps needed to power the compressor should be 1/4 of the capacity of the house bank. So for the above 74 amp hours needed multiply by 4 to get recommended house battery capacity = 296 amp hrs

Conclusion

These days being on the water means keeping food and drinks cold. 12 volt refrigeration units are becoming more popular with technological advances. Greater compressor efficiency and evaporator technology brings 12 volt cooling to the smallest of boats.

Marine Refrigeration

Mike Hobson is Editor for MyBoatsGear.com.

For the complete article see http://myboatsgear.com/newsletter/200915.asp

http://bakingtoolsandaccessories.blogspot.com/

Refrigeration Maintenance, Walk-In Coolers and Freezers

Most refrigerators and walk-ins seem virtually indestructible and problem free, but you'll get longer life out of yours by following these safety and maintenance tips. Clean the door gaskets and hinges regularly. The door gaskets, made of rubber, can rot more easily if they are caked with food or grime, which weakens their sealing properties. They can be safely cleaned with a solution of baking soda and warm water. Hinges can be rubbed with a bit of petroleum jelly to keep them working well. Dirty coils force the refrigerator to run hotter, which shortens the life of the compressor motor. They should be cleaned every 90 days, preferably with an industrial-strength vacuum cleaner.

Walk-in floors can be damp-mopped but should never be hosed out. Too much water can get into the seals between the floor panels and damage the insulation. A refrigerator only works as well as the air that's allowed to circulate around its contents. Cramming food containers together so there's not a spare inch of space around them doesn't help. Also try to keep containers (especially cardboard ones) from touching the walls of the cabinet. They may freeze and stick to the walls, damaging both product and wall. Use a good rotation system: First in, first out (FIFO) is preferable. Or put colored dots on food packages, a different color for each day of the week, so everyone in your kitchen knows how long each item has been in the fridge.

Coolers & Filters

WALK-IN COOLERS AND FREEZERS

A walk-in cooler is just what its name implies: a cooler big enough to walk into. It can be as small as a closet or as large as a good-size room, but its primary purpose is to provide refrigerated storage for large quantities of food in a central area. Experts suggest that your operation needs a walk-in when its refrigeration needs exceed 80 cubic feet, or if you serve more than 250 meals per day. Once again, you'll need to determine how much you need to store, what sizes of containers the storage space must accommodate, and the maximum quantity of goods you'll want to have on hand. The only way to use walk-in space wisely is to equip it with shelves, organized in sections. Exactly how much square footage do you need? The easiest formula is to calculate 1 to 1.5 cubic feet of walk-in storage for every meal you serve per day. Another basic calculation: Take the total number of linear feet of shelving you've decided you will need (A), and divide it by the number of shelves (B) you can put in each section.

This will give you the number of linear feet per section (C). To this number (C), add 40 to 50 percent (1.40 or 1.50) to cover "overflow"-volume increases, wasted space, and bulky items or loose product. This will give you an estimate of the total linear footage (D) needed. However, linear footage is not enough. Because shelves are three dimensional, you must calculate square footage. So multiply (D) by the depth of each shelf (E) to obtain the total square footage amount (F). Finally, double the (F) figure, to compensate for aisle space. Roughly half of walk-in cooler space is aisle space. Another popular formula is to calculate that, for every 28 to 30 pounds of food you'll store, you will need 1 cubic foot of space. When you get that figure, multiply it by 2.5. (The factor 2.5 means only 40 percent of your walk-in will be used as storage space; the other 60 percent is aisles and space between products.)

The result is the size of the refrigerated storage area you will need. For a walk-in freezer, simply divide your walk-in refrigerator space by two. Larger kitchens, which serve more than 400 meals a day, may need as many as three walk-in refrigerators for different temperature needs: one for produce (41 degrees Fahrenheit), one for meats and fish (33 to 38 degrees Fahrenheit), and one for dairy products (32 to 41 degrees Fahrenheit). The walk-in is used most often to store bulk foods. Because this often means wheeling carts or dollies in and out, the floor should be level with the kitchen floor.

This leveling is achieved by the use of strips (called screeds) that are applied to the floor. Coolers don't come as a single unit; they are constructed on-site. The walls, ceilings, and floors are made of individual panels. Wall panels should be insulated to a rating of R-30, which means a 4-inch thickness. They come in various lengths and widths, with 12-by-12-inch corner panels at 90-degree angles. They can be as short as 71?2 feet or as tall as 131?2 feet. The most common type of insulation inside the panels is polyurethane, and the outside walls of the panels can be made of stainless steel, vinyl, or aluminum. Stainless steel is the most expensive, and aluminum-because it's the least expensive-is the most popular choice. If the walk-in is an outdoor installation, aluminum is the most weather resistant.

The installer will be sure the unit has interior lighting. The floor panels for walk-ins are similar to the wall panels. Load capacities of 600 pounds per square foot are the norm, but if you plan to store very heavy items (like beer kegs), a reinforced floor can be purchased with a load capacity of up to 1000 pounds per square foot. The refrigeration system of a walk-in is a more complex installation than a standard refrigerator, primarily because it's so much bigger. Matching the system (and its power requirements) with the dimensions of the walk-in and its projected use is best left to professionals, but it's important to note that a walk-in accessed frequently throughout the day will require a compressor with greater horsepower to maintain its interior temperature than one that is accessed seldom.

A 9-foot-square walk-in would need at least a 2-horsepower compressor. The condenser unit is located either on top of the walk-in (directly above the evaporator) or up to 25 feet away, with lines connecting it to the walk-in. The latter, for obvious reasons, is known as a remote system, and is necessary for larger-than-normal condensing units with capacities of up to 7.5 horsepower. In a remote system, the refrigerant must be added at the time of installation. For smaller walk-ins, there's also a plumbing configuration called a quick-couple system, which is shipped from the factory fully charged with refrigerant. This definitely simplifies installation. However, you may need the added power of a remote system if your kitchen has any of these drains on the walk-in's cooling ability: frequent door opening, glass display doors, multiple doors per compartment, or an ambient kitchen temperature that's near 90 degrees Fahrenheit.

Modern walk-ins sometimes offer a frozen-food section in addition to the regular cooler space. There are pros and cons to this concept. It may ease the load on the freezer, because it's already located inside a chilled airspace; but it also can't help but reduce overall usable space, because it requires a separate door. You can also order your walk-in with a separate, reach-in section that has its own door and shelves. Although this may save the cost of purchasing a separate reach-in, some critics claim that a walk-in is not designed to do a reach-in job, such as storing uncovered desserts. Do you really want them in the same environment as cartons of lettuce and other bulk storage items? There may be cleanliness or food quality factors to consider.

The doors should open out, not into the cooler itself. The standard door opening is 34 by 78 inches. Several door features are important for proper walk-in operation. These include: A heavy-duty door closer. Self-closing, cam-lift door hinges. If the door can be opened past a 90-degree angle, the cam will hold it open. A heavy-duty stainless steel threshold. This is installed over the galvanized channel of the door frame. A pull-type door handle, with both a cylinder door lock and room to use a separate padlock if necessary. Pressure-sensitive vents, which prevent vacuum buildup when opening and closing the door. An interior safety release so no one can be (accidentally or otherwise) locked inside the cooler.

Other smart features that can be ordered for walk-ins are: A thermometer (designed for outdoor use, but mounted inside the cooler) with a range of 40 to 60 degrees Fahrenheit. A monitoring and recording system that keeps a printout of refrigeration temperature or downloads to a computer. Glass, full-length door panels (like those in supermarkets and convenience stores), sometimes called merchandising doors, either hinged or sliding. Heavy-duty plastic strip curtains inside the door. (One manufacturer claims a 40 percent energy savings with this feature.)

A foot treadle, which enables you to open the door by pressing on a pedal or lever with your foot when both hands are full. Three-way interior lighting, which can be turned on from outside or inside the cooler, with a light-on indicator light outside. Inside, the light itself should be a vapor-proof bulb with an unbreakable globe and shield. When space is at a premium, think about whether it is practical to install an outdoor walk-in unit. This is an economical way to add space without increasing the size of your kitchen, and you can purchase ready-to-use, stand-alone structures with electricity and refrigeration systems in place. They come in standard sizes from 8 to 12 feet wide and up to 50 feet in length, in 1-foot increments.

They range in height from 7.5 to 9.5 feet. Look for a unit with a slanted, weatherproof roof, a weather hood, and a fully insulated floor. Outdoor walk-ins cost about half of the price of installing an indoor kitchen walk-in, so this is a money-saving idea if it works in your location. If your demands for walk-in space are seasonal, consider leasing a refrigerated trailer, available in most metropolitan areas on a weekly or monthly basis. They can provide an instant 2000 cubic feet of additional storage space, which can be kept at any temperature from 40 to 80 degrees Fahrenheit. They use basic 60-amp, 230-volt, three-phase electricity. Ask if the lease agreement includes hookup at your site and service if anything goes wrong.

Refrigeration Maintenance, Walk-In Coolers and Freezers

Franco Zinzi has been involved with online marketing for nearly 3 years and likes to write on various subjects. Come visit his latest website which discusses of restaurant fridge and restaurant supplies for the owner of his own business.

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