Maximising the number of systems on DC while minimising those on AC reduces the cost and complexity of the electrical system.
© 2008 David Shaw,
david.shaw.x23@gmail.com
Design Considerations
A passagemaker should be designed so that, when necessary, it can use shore power almost anywhere in the world. When cruising or anchored, it should provide its own power with the simplest possible redundant system, and a minimum of fuss for you and any neighbours. The major complication in this scenario is the different frequency (Hertz) of the world’s different alternating current (AC) shore-power systems, and the effect that has on AC equipment and the battery charger.
To meet our goals, you could equip your boat with an AC system, just like in your house, whether you are in North America with a dual 120/240 VAC service or in Europe or elsewhere with a single 230-VAC service. This would be very simple in most respects. There are a lot of good AC appliances and fixtures, and wiring is inexpensive relative to direct current (DC). [DC flows in one direction; AC switches (cycles) back and forth. Cycles are measured in Hertz (Hz)].
The problem is you can’t store AC energy in a battery. You would have to run an engine constantly to drive an alternator. If either failed, there would be no fallback source of electrical power. Also, AC is generally less efficient than DC.
What about DC then? You could have a DC battery system, typically 12 or 24 V, with an alternator to recharge it, just like in your car. With a big battery, you wouldn’t have to run the engine all the time.
This is a good idea but it turns out there are few good DC appliances. All the better ones are AC.
Using AC appliances on a DC system requires a DC-AC converter, called an inverter. Unfortunately, large DC-AC inverters are expensive. Many produce quasi-sine wave (square wave) output. Some equipment, like computers, requires true sine wave and won’t run on square waves. Another problem is appliances like refrigerators have a large surge current when the motor kicks in, requiring a larger inverter. Some appliances are just plain energy hungry. For example, microwave ovens readily consume 1500 watts, ovens even more. Also, DC-AC conversion is less efficient overall due to power losses in the inverter.
An alternative to an inverter found on many boats is a separate AC generator (genset). But this would have to run anytime you wanted to use AC, bringing us back to square one.
The only practical solution is a dual system consisting of a DC system with battery storage, and a DC-AC inverter for AC appliances. This system will have an engine-driven alternator to charge the batteries at sea and a battery charger for use with shore power. But because of the aforementioned cost and inefficiency of the inverter, we should try to keep AC requirements to a minimum.
With this in mind, the design objective of
Sharina’s electrical system is to run as much as possible on the DC system and use an inverter for AC while, hopefully, eliminating the need for a separate AC generator. This requires a careful balance in all the electrical systems, and maximum energy efficiency in appliances and fixtures. The rest of this chapter describes the conclusions reached to achieve this objective.
The Solution
Having decided to run as much as possible on DC, we have to figure out how to maximise the number of systems on DC while minimising those on AC. Hopefully, we can design a system that can be sustained by the batteries for most of the day, and not take more than an hour to recharge (least fuss to other people). As it turns out, today’s batteries and charging systems are advanced enough that we should be able to attain this goal. Because this solution resulted from an iterative process, it’s easier to outline it, and then explain it, rather than trying to take you through the iterations.
The oven will be a diesel-fired Dickinson [35], to reduce AC electrical needs, but an electrical stovetop and microwave will provide flexibility. Diesel ovens throw off a lot of excess heat. In summer, it will be more comfortable cooking with the stovetop, microwave or the barbecue in the stern cockpit. (This is a consequence of the one-fuel type decision in Chapter Two. You might want to use propane instead.)
Having eliminated the oven, our point of departure is that the following will be DC:
- All electronics except the TV and computers
- All lighting except in the engine room
- All engine-room systems and motors
- The refrigerator
The following will be AC:
- All appliances except the refrigerator
- The TV
- Computers
- The hot-water heater
- Electrical outlets
Electronics such as engine and navigational instruments, including two-way radios, satellite receivers, sonars and radars, are readily available in DC. Consumer electronics such as stereos and AM/FM/SW radios are also available, many developed for the automobile and recreational vehicle (RV) market. None of these will be considered further in this chapter. The exception is the TV and any computers, which will be AC.
Fig 7-2 – Navigation, radar and sonar are readily available in DC
– Photo with permission © FarSounder, Inc, http://www.farsounder.com/
Lighting is readily available in DC; we will add AC lighting in the engine room as a backup when using shore power. The refrigerator will be DC because we can design a custom DC refrigeration system that is much more energy efficient than a store-bought appliance. Other appliances will be AC. The major AC appliances discussed further below are:
- Dishwasher
- Icemaker
- Kettle
- Microwave
- Refrigerator/Freezer
- Stovetop
- Television
- Towel rails
- Trash compactor
- Vacuum cleaner
- Vapour cleaner
- Washer/Dryer
All electrical appliances must not have a neutral to ground wire. This is standard in residential installations, but very dangerous in a steel hull. Finally; in a crossover between electrical and HVAC, heated towel rails will be a combination of AC and hot water.
Other reasons behind this proposed optimization will be explored in more detail below.
Lighting
To reduce consumption all lighting except in the engine room will be DC, fitted with dimmer switches where appropriate. The engine room will have dual DC and AC fluorescent lighting. The latter will make it easier to work in the engine room when connected to shore power, especially if the DC system must be disconnected. The long tube length of fluorescents will give more even illumination than other types of lighting. However, the DC lighting should give sufficient illumination for work at sea.
All of the light types discussed below are available in low-voltage DC. Dimmer switches can be used with most tungsten and halogen lights but only certain types of fluorescent. Make sure the dimmer switch is compatible with the light and its wattage. In a marine environment, use double-pin ungrounded lamps for all types.
Lighting must satisfy several criteria:
- Illumination (light output)
- Colour (biological and visual comfort)
- Energy efficiency (amount of light output for a given energy input)
- Application (ambient, accent, task and utility)
It’s tempting to start by discussing the application of lights, because this is like not running out of hot water or never having the toilet plug. You don’t want to spend cruising hours pissed off because you can’t read comfortably (or whatever). But to make the best choices for different applications, we have to take the long road through the technology of lighting. Illumination and colour are the main aspects of lighting.
Illumination
Illumination is measured in lumens. The SI measurement of illumination is lux, or one lumen per square metre (about 1/10 foot-candle). A lumen is the amount of light falling on a surface. A foot-candle is one lumen distributed over one square foot.
The illumination required for casual reading is 200-550 lumens/sq metre. The standard for office desks is 500 lumens. Some general guidelines are given in Table 7-1 [1-4]. These are generally in excess of ABYC standards but you should check when you build.
Table 7-1
Recommended Illumination |
|---|
| Area | Lumens/sq metre | Lumens/sq foot
(rounded up) |
| heads/Companionways | 200-500 | 19-47 |
| Berths | 550-1100 | 52-103 |
| Galley & Dinette | 108-1100 | 10-103 |
| Salon | 108-1100 | 10-103 |
| Workshop | 550-1100 | 52-103 |
| Engine Room | 1100-2100 | 103-197 |
Colour
The colour of light falling on an object affects our perception of the colour of the object (a very complex subject in itself). The colour of a light is expressed as the correlated colour temperature (CCT) or the Colour Rendering Index (CRI).
CCT is measured in degrees Kelvin. CRI is measured on a scale of 0-100, where a light source with 100 CRI is best at producing vibrant colour in objects. A higher CRI rating typically denotes a higher quality lamp. A CRI of 84 or better gives very little shift in an object's colour. Incandescents have an index of 95-100, and tri-phosphor fluorescent runs 84-88.
The main colour spectrum of a lamp determines how it makes us feel in an interior space. Colour spectrum is related to a lamp’s temperature. Colour temperature can be soft and comfortable for relaxing or sharp and precise for work environments. The higher the temperature, the cooler the colour of the lamp. For example, a colour temperature of 3000K is warm while 4100K is cool. Indoor lighting is typically 2700K Outdoor lighting is 6500K.
Blue light is important during the day. Essentially we are blue-light detectors when it comes to keeping our internal clock well adjusted. This is especially important in the winter when blue-light levels might not be sharp enough to maintain our 24-hour clock.
Light of around 555 nanometres is accepted as the most efficient level of light for daytime vision. But recent research has shown that we also have biological receptors for non-visual response peaking in the blue wavelength range of 446-477 nanometres, a range abundant in clear daylight. Researchers at Brown University in 2002 discovered that non-visual ganglion cells in the eye detect sky-blue light to set our internal clock.
Daylight has an abundance of wavelengths at 446-477 and in the 555 nanometre range, satisfying both perceptual and biological demands. The challenge is to develop lighting solutions that will perform like daylight.Because our night vision functions differently than our day vision, the objective of night lighting is to preserve night vision. Night vision deteriorates when the eye is subject to intense light. This destroys the essential chemical rhodopsin, which can take 45 minutes for 80% recovery. So night lights should be designed for low intensity, no matter their colour, and you should avoid looking directly at bright lights.
The choice of colour is controversial, in part because many colours we perceive are not interpolated but are ‘invented’ by the brain. The theory is that some colours enhance low-light vision provided by the cones in the eye. The eye also has rods, used for normal intensity light. Originally, it was believed that the cones, occupying a narrow slice in the centre of the retina, were red sensitive, so using red lighting would enhance night vision. But the cones are blue-green (507 nm) sensitive; although the fovea, an even more narrow slice at the centre of the cones is very red sensitive.
Night vision also has constraints: your night eye can't see colours or details, or directly ahead, or differentiate objects that don't move.
For night vision in the pilothouse, switch lighting between daytime white and night-time green or turquoise instead of the traditional red. Turquoise may be better for men with red/green deficiency.
Red (630 nm) is an internationally recognized attention colour traditionally favoured for its excellent ability to preserve night vision. However, red erases red lines that indicate hazards or danger on aeronautical and military maps and charts.
Today most pilots and the military have switched to other colours for night vision protection. Green is now the established colour. It is used in the 2004 Daimler-Chrysler 300C. Green is also great for retaining night vision, and it is easier on the eyes.
However, there appears to be a slow transition to blue. The military is using blue over red increasingly. Blue eliminates many colours on maps and charts, changing everything to shades of a bluish-grey. Blue is also a great reading light. It imposes less eye strain than incandescent, especially for ageing eyes. Turquoise (495 nm) appears slightly brighter than blue. Turquoise is an excellent alternative to red for night vision preservation.
Current literature on night vision recommends:
- Blue-green (507 nm) for the fastest dark adaptation recovery
- Deep red (around 700 nm) at very low intensity for maximum detail
- White at low intensity if you need to see colours
Energy Efficiency
Energy efficiency is the amount of light output generated per watt of input energy consumed. This is important because it directly affects the size of our electrical system. The main choices in types of light in order of efficiency are:
- LEDs post-2007
- Fluorescent
- Halogen
- Incandescent
- LEDs pre-2007
All of these types are available in low-voltage DC. Xenon lights are also available in 24 V marine types but are not considered here because of the danger when they break.
LEDs have had a very high profile in the energy market for some time. But until recently they did very poorly in energy efficiency. Fluorescents were best, producing about 30-100 lumens per watt, while halogens produced 10-18, and incandescents 8-15.
Before 2007, LEDs used less than 10% of the energy of an incandescent lamp, but did not produce as much light output per watt of energy consumed. To disguise this, some vendors rated LED efficiency as the amount of light output generated per watt of total output energy instead of the input energy.
However, ongoing research has dramatically improved the efficiency of LEDs; although this is only starting to appear in production versions. LED efficiency improved dramatically in 2006. Nichia Corporation of Japan demonstrated white LED prototypes with an efficiency of 113 lumens per watt. The industry target is 100 lumens per watt, which is better than fluorescent tubes. The Nichia work was partly funded by the UK Department of Trade & Industry. (White LEDs are actually blue in wavelengths of 450 nm – 470 nm.)In addition, LEDs produce no discernible heat and are more robust than fluorescents and incandescents. They have become the lighting of choice for many marine applications.
LEDs have a long life (100,000 hours) and low heat output. They give off a soft natural light in white, red, green or blue. White or blue are used for reading, e.g., a reading spot lamp. Red, green or blue are used for night vision.
In a low voltage DC system, their driving system is simple and cheap compared to a fluorescent, which requires an oscillating ballast circuit. LEDs use a simple voltage-dropping resistor. They are tough and resistant to shock and vibration. They are safe near explosive gases and liquids. In a marine installation, use a dual-pin ungrounded LED. Until recently LEDs were rated in millicandela (mcd), as measured at the light source, not lumens. This made direct comparisons with other light types fuzzy. (One lumen is approximately 79.5 mcd [7].)
Now that LEDs are more competitive, manufacturers are also rating them in lumens.
Prior to breakthroughs in the efficiency of LEDs, fluorescent lamps were the clear winners in energy efficiency. They last about 34,000 hours and have low heat output.
Fluorescents have electrodes at both ends of a tube coated inside with phosphor. Inside the tube, a gas contains argon and mercury vapour. A stream of electrons flows through the gas from one electrode to another. This excites the mercury atoms, giving off ultraviolet photons. In turn these excite the phosphor, giving off visible light.
Invented by A.E. Becquerel of France in 1857, today’s fluorescents are available in full spectrum types with quiet electronic ballasts replacing noisy magnetic ones [5]. Cycling rates have been increased to reduce flicker. Because of the mercury, be careful not to break fluorescents, and dispose of them in an environmentally safe way. The USA Environmental Protection Agency publishes guidelines on what to do if a bulb breaks [57]. Also, don’t use fluorescents in places where you would be at risk if a tube broke. Use LEDs instead.
Cold cathode fluorescents (CCF) are similar in construction to neon tubes and have up to 25,000 hours of service life. They are readily dimmable. Look for models that are listed for marine, RV UL, CSA and CE (Europe), and meet the Ignition Proof test requirements of the United States Coast Guard, as stated in Title 33 CFR 183.410. CCFs are more efficient than other fluorescents but the tri-phosphor fluorescents have the most pleasing colour.
Compact fluorescent lights (CFL) are more robust than tubes. They use only a small amount of mercury, typically less than 5 mg per bulb.
Halogens are a type of incandescent having higher efficiency. The tungsten filament in all incandescent types is very thin, offering high resistance. When a current passes through the filament it glows, giving off light and (mostly) heat.
Halogens last between 2000-6000 hours and give off enormous heat. They are hot enough to be used in stovetops as burners. They use 20% less energy than incandescent for the same output.
Halogens are enclosed inside a small quartz lamp containing halogen gas, which increases the light output. Halogens, like most incandescents, have a very natural light. The halogen gas allows the filament to be run much hotter, giving off more light per watt. It also combines with the tungsten in the filament, giving it a longer life by re-depositing vaporized tungsten.
Standard incandescents are very inefficient. About 90% of the energy given off is in the form of wasted heat. They yield about 13 lumens/watt and have a life of 750-1000 hours.
Sir Joseph Swann invented them in the 1870s; although most Americans credit Thomas Edison [6]. Watch for improved versions using deposited carbon nanotube filaments by 2009. This may not matter since many governments are banning tungsten bulbs. Australia is targeting 2010, the USA 2012-2014.
Application
Finally, we come to
application, how we use these light types. The main applications are:
- Ambient
- Accent
- Task
- Utility
Ambient Lighting
Ambient lighting provides a soft general level of light in a room. Accent lighting focuses directional light on architecture, artwork or reading. Task lighting illuminates a work area like the galley or a tool bench. Usually it is directed directly on to a work surface. Utility lighting is used to flood an area with light, e.g., in the engine room.
In each type of application, you should not be aware of the lamp, in the same way you are not aware of the stud wall in a house. The purpose is to make you aware of the objects the lamp illuminates. If you must go there, ensure the lamp is designed in its own right as an object d’art.
For general ambient lighting throughout, ceiling mounted, dimmable, low-voltage tri-phosphor or cold-cathode fluorescents will give the best results. Select tri-phosphor or cold-cathode depending on how you feel about natural colour. Put dimmer switches everywhere except in companionways and the engine room.
Accent Lighting
For accent lighting, use small low-voltage LEDs or halogens with dimmers. Don’t use halogens in the berths, galley and dinette where close proximity makes their heat uncomfortable. Because of their very high heat output, ensure halogens are in proper enclosures and at least six inches away from objects.
Task Lighting
In the galley, put fluorescent lighting under the cupboards, hidden behind a valence, to provide task lighting on a separate switch. Don’t use a dimmer here.
In the engine room, have a separate circuit for AC fluorescents for use with shore power. Provide outlets for both DC and AC trouble lights.
In the berths, galley and dinette use low-voltage white or blue LEDs as spot or reading lights. Their cooler temperature will make enclosed spaces more comfortable. For courtesy lighting in corridors and companionways, use blue LEDs.
Utility Lighting
For utility lighting such as external spotlights, use halogen. Dual-head emergency lights, with battery backup, are available in all light types. But on balance use the newer LEDs for emergency lights. Dual-head (dual lamp) provides redundancy.
In the pilothouse, use blue-green (507 nm) or turquoise (495 nm) LEDs for night vision. Eight percent of males are red-green deficient [8], and will be groping blindly with low-level red or green night vision lights. (Women have an extra strong response to red-orange.) Even a higher percentage may have temporary alterations in perception of blue under varying conditions. Most people over 45 suffer from reduced light transmission into the eye.
Electrical Outlets
All electrical outlets are AC except in the engine room, where both AC and DC are provided. There does not seem to be any good reason for providing DC outlets in the accommodation. Guests are unlikely to come on board with DC appliances. This is fortunate, because of the size of wiring required. All AC outlets are equipped with ground fault circuit interrupters (GFCI).
Hot Water
The hot water heater will be covered more in depth in the chapter on water systems. Suffice to say here that it will have a backup AC element for use when connected to shore power, or when alternate energy sources are not available.
Dishwasher
The dishwasher should also be AC. Most dishwashers clean dishes as well as the next; however, higher priced ones are generally quieter. Frigidaire, GE, Maytag, and Whirlpool make most dishwashers in North America. They sell them under their own names, and associated brands like Sears Kenmore. GE offers a wide range of choices in full size, compact and under-the-sink models under the GE brand and also Hotpoint. Maytag makes the high-end Jenn-Air, mid-priced Amana, and low-priced Admiral. Whirlpool makes high-end KitchenAid, Kenmore and low-end Roper. Asko, Bosch [17], and Miele are high-end European brands; Haier is made in China. Fisher & Paykel [18] is made in New Zealand.
Most models fit into a 24-inch-wide space under a kitchen counter top and are attached to a hot-water pipe, drain, and an electrical line. Compact models fit into narrower spaces. Space-saving models like Vesta [19] fit under stovetops, etc. Fisher & Paykel fits into a drawer under the sink. AEG also makes a line of small dishwashers. Hobart makes institutional dishwashers [32]. The Briva KitchenAid [20] is integrated into a sink but takes 48 in of counter space. Julien [21] makes a series of high-end combination stainless steel sinks and dishwashers.
Fig 7-3 – Fisher & Paykel innovative dishwasher in a drawer– Photo with permission © Fisher & Paykel, http://fisherpaykel.com/
When selecting a dishwasher, look for:
- Energy efficiency
- An option for heat-drying and air-drying
- A feature that senses how dirty the dishes are and runs appropriate cleaning cycles
- A multiple-level wash system
- A thermostat and heating capability
Dishwashers are energy rated in kWh/year, typically 700-850. They draw around 9 A when running. Check the water pressure requirements, typically 100-145 psi, and make sure you have enough pressure in the galley.
Icemaker
Compact under-the-counter ice makers are 13-15 in wide and consume about 75 W AC. U•line [22] makes a series of compact marine ice makers. Other makers are Avanti, GE, Marvel, the well regarded Scotsman, and Whirlpool [23-27].
Kettle
Surprisingly Americans tend to use stovetop kettles while Europeans (and Canadians) use more efficient electric kettles, according to Slate [50]. If you elected a propane stove, go with the stovetop kettle in keeping with our goal of minimizing electrical loads. If you chose an electric stovetop, go for an electric kettle for energy efficiency. But pack a stovetop kettle as an emergency back up.
Microwave
There are a few DC microwave ovens, but they are small and not very attractive. Better to go with an AC combination microwave/convection oven with a rotating platter inside. If you’re health conscious, check out the Sharp AX-HC1, a microwave/convection/condensation oven that uses steam heat to reduce the fat in cooked meat.
Refrigerator & Freezer
On weekend cruises, energy efficiency might not be the chief criteria for a cooling box. But for passage making, energy efficiency should be the sole criteria. The most energy efficient refrigeration system is the one requiring the least amount of total energy per day to keep your fridge or freezer at the required temperature.
Obviously insulation is a key factor. The more and better the insulation, the less energy required to keep a unit cold. A good design will have four to six inches of extruded polystyrene, such as the Dow Blueboard (STYROFOAM™) [38] or the Owens Corning [39] InsulPINK® Foam Insulation Board, plus radiant barrier insulation (RBI). Polystyrene is water repellent, meaning it does not absorb water, which gives better performance in a moist environment. For the tropics, Glacier Bay recommends R20 in a refrigerator and R30 in a freezer, which corresponds to four to six inches of foam [34]. RBI has not been tested in a fridge/freezer, but it is inexpensive to add in a custom build so worth the chance as an outermost layer.
Separating the fridge and freezer units is another good idea. You can optimise each unit without compromising or spilling air from both when you only need access to one. Fridges are usually kept at 4.4 degrees C (40 F), while freezers are kept at -6.6 C (20 F). Keep the freezer as small as possible.
Top opening is best for a small chest freezer. Cold air is denser and sinks. You can put larger and less frequently used items in the bottom and use wire baskets on top for smaller stuff. It’s easy to remove a wire basket to get at the food in the bottom.
Front opening is more convenient for a refrigerator. It is easier to reach in and remove day-to-day items from a shelf.
The type of refrigeration system and its power source are the remaining factors. Cooling systems can use everything from acoustics to heat pumps, but constant-cycling and cold-plate systems are best on boats.
Constant-cycling systems are like a home refrigerator. A refrigerant gas is compressed and circulated through the unit. Compression removes heat. The compressed gas expands in the unit, absorbing heat. This works only while the compressor is running, so the unit cycles on and off frequently. This keeps the temperature fairly constant. One unit can be used for both fridge and freezer.
The compressor gives off heat, and must be air- or water-cooled. Air-cooling adds heat inside the boat, either in the accommodation or the engine room. In the accommodation, in the summer it will be working against the air conditioning, causing a double energy load. In the engine room, it will be struggling against other heat sources, and increasing the ventilation requirements. Water-cooling, using a keel cooler, is the best way to go.
A cold-plate system works like an old-fashioned icebox. Small metal tanks, called cold or holding plates, contain a solution that freezes at subzero temperatures. The compressor runs just long enough to freeze the plates. The plates will keep the unit cold for several hours or days, in what is called the holdover cycle. Cold-plates for fridges should run at -3.3 C (26 F) while freezers should run at -15 C (5 F), so separate units are required.
The solution in the plates is either brine, or some other antifreeze, or a eutectic salt. Eutectic solutions don’t thaw out gradually. They maintain a constant frozen temperature until they thaw out instantly in a phase change. A phase change is what happens on the highway when traffic suddenly goes from 120 kph to a crawl for no obvious reason. A system with eutectic salts will have a more constant temperature than one with a brine solution, which increases gradually in temperature as it thaws.
Like heating and air conditioning, you will find no easy answers when trying to calculate refrigeration requirements. Theory and practice based on experience are often apart. As a result, everyone tends to over estimate, which of course increases the energy needed. Conversely, under estimating leads to inadequate performance and frustration. Approaches differ. Some experts use guidelines, and then add a fudge factor; others use heat transfer calculations, and then add a fudge factor. Sigh – maybe we should just use fudge factors.
For fridges, a general guideline is to provide 400-600 Btu of cooling per cubic foot of interior fridge space. For freezers, it is 900-1200 Btu per cubic foot. If you’re buying a commercial unit, hopefully the manufacturer will have right-sized the interior volume, insulation and compressor efficiency.
When you have determined the cooling capacity and compressor size, the next step is to consider the energy requirements and source. A typical constant-cycling system, using a popular Danfoss compressor, will draw around 7 amps when running. If it cycles 30 minutes per hour, it will require 39 Amp Hours (AH) (7/2*24). A typical cold-plate system, drawing 35 Amps, and cycling for two straight hours per day, will require just 3 AH (35*2/24). Overall, a cold-plate system is far more energy efficient, but requires a heftier peak-load energy source (larger DC system or engine) when it is running.
Many production trawlers are fitted with residential Sub-Zero fridge/freezers. These are constant cycling high-end fridges requiring 110 VAC. Their key feature is dual refrigeration. They have separate compressors for the fridge and freezer sections. This maintains ideal conditions in each compartment. Frozen foods need very cold, dry air. Refrigerated foods need warmer and moister air. Because each compartment has a separate door, air does not circulate between fridge and freezer, making it harder for foods to pick up unwanted flavours. Sub-Zero fridges are front opening, which means cold air spills out every time you open a door. They also look great [9]. Many other manufacturers offer models with similar features.
Putting aside all other considerations, these types all require 110 VAC. If you spend most of your time hooked up to shore power, or have a large yacht with an AC generator running constantly, this is not an issue. But for a medium-sized passagemaker, you either must have a large-enough battery bank and inverter, or have an AC generator running constantly. Thus, fridge/freezer
combinations designed for AC are not a good fit.
A better fit is a marine constant-cycle system such as Frigoboat [33] Nova Kool [53] or Tundra [54]; or a cold-plate system such as the Micro HPS™ [34] running on DC or directly off the engine. Because the constant-cycle system cycles every 10 or 15 minutes (go listen to your home fridge), it is not a good candidate for a direct drive off the engine. You would have to keep the engine running 24 hours per day. It is a good fit to power with a smaller DC system, since the maximum current draw of around 7 Amps does not require a large battery bank.
A cold-plate system is a good candidate for a direct drive off the engine, or large DC battery system. Because it will cycle only once a day for a few hours, you can time it to coincide with a daily engine run to charge the batteries. You can also run it directly off the battery bank.
Another advantage of DC over AC refrigeration is that a well designed system, e.g., with trickle-charge backup, can keep your food fresh unattended for periods [10-13]. An AC system would require remote starting an engine.
If you have a propane stove, you might want to consider a propane fridge such as the Norcold [52].
The next generation of fridges to watch for may use magnetic, thermoelectric (used in space shuttles) or thermoacoustic cooling.
Magnetic cooling uses a material such as powdered gadolinium (Gd) that exhibits a phase change when it is put in a magnetic field. Excess heat is transferred to a heat exchanger using a mixture of water and antifreeze. Commercial viability is expected by 2008.
For
Sharina, a high-efficiency DC holding-plate design was chosen for the refrigeration to reduce AC loads, while not imposing a continuous DC load. Excess cooling capacity may be used for air conditioning a zone.
Stovetop
Gas or Electric
If you’re planning on using propane for the oven, you can also have a gas stovetop. Cooking with gas is the preference of most chefs because it offers better control and the heat can be changed rapidly. However, gas delivers only 35-40% of its heat energy to the pan.
In the case of
Sharina, where I decided to have a diesel oven, there were two issues: what to use for a stovetop since diesel or propane burners are a poor energy choice, and what to do if the diesel oven were too hot to use in the summer (which I fully expect).
The solution was twofold: an AC electric stovetop and a large microwave oven. This gave me the best summer/winter combination; spread the risk of total failure over two different energy systems; and decentralised the heating in winter since there would be at least two heating sources.
There are other reasons to consider electric cooking on a trawler:
- Safer.
- Easier to clean than gas.
- Less waste heat and lower air-conditioning costs.
- Superior low heat control.
- Faster cooking with microwave, convection and induction stovetops.
In passing, you can also reduce energy consumption by developing some best practices:
- Use ceramic or glass pans – they cook food 3.8 C (25 F) degrees lower than metal pans.
- Match the pan to the burner size.
- Fill ovens as much as possible.
- Maintain seals.
- Limit pre-heat time.
- Maximise use of microwave – most efficient oven type because it only heats the food, not the pan.
- Use convection where microwave is not possible – convection ovens cook in 10% less time at 3.8 C (25 F) lower. The US Dept Energy estimates convection is 23% more efficient than a standard oven [16].
- Use a pressure cooker on a gas or electric stovetop to use up to 70% less energy (no direct comparisons with microwave available).
- Use a lid on pots. This reduces the time to reach the desired temperature. When temperature is reached, turn the heat down to maintain it.
- Pre-soak grains, dry legumes, pasta to reduce cooking time.
Types of Electric Stovetop
The type of electric stovetop you choose depends on your psychometrics. From an energy perspective, induction types are clearly the best. In decreasing order of energy efficiency, other choices are: ceramic glass with halogen heat sources, other radiant elements under ceramic, standard coils, and solid disks.
Induction elements are around 90% efficient, using less than half the energy standard coil elements use. They transfer electromagnetic energy directly to the pan, leaving the cook-top itself relatively cool. A disadvantage is that you must use ferrous metal cookware like stainless steel, cast iron, and enamelled iron, with a flat bottom. Other types of cookware won't work.
Ceramic glass units with halogen elements are the next most efficient. They deliver instant heat and respond quickly when you change the temperature setting. They are very easy to clean. They work best with flat-bottomed cookware. A disadvantage is that they stay very hot after you turn them off. Other slightly less efficient radiant elements are also available under ceramic glass.
Standard electric coils are among the least efficient, and are difficult to clean. Solid disk elements are the least efficient. They are easy to clean but heat up and cool down slowly and use higher wattage elements.
Pressure Cooker
A pressure cooker (retort) such as the stainless-steel Kuhn Rikon Duromatic [40] or a Fagor [58] is very efficient, cooking food three-four times faster for a given energy input. Pressure cookers keep steam from escaping, thus increasing the air pressure inside. As air pressure is increased, the boiling point of water increases in temperature, too. This means that under pressure, food can be cooked at a higher temperature, i.e., faster, without boiling. You can cook a wide variety of meals this way: whole chicken, roast beef/pork, stew, baked yams, risotto, roasted/boiled potatoes, black beans, fish fillet, gravy/jus, braised oxtail, jam roly poly and more.
A pressure cooker can be used with a gas or electric stovetop. They come in 4-10 quart sizes. Some have more than one basket inside so you can cook two dishes together. Look for a pressure cooker with multiple safety valves and an interlock or a safety bar across the top.
Slow Cooker
Slow cookers (crock-pots) are used to cook food slowly over a period of 6-8 hours. Proponents of pressure cookers argue that they cook the same recipes substantially faster. This may be true, but slow cooking imparts a unique blended flavour to suitable recipes. However, slow cooking neutralizes vitamins and other trace nutrients in vegetables.
Television
Although most electronics are available with satisfactory performance in DC models, televisions are a different matter. Miniature TVs are available in DC but larger ones are all AC. And, of course, current technology is a flat screen. Large flat panel screens are produced with Liquid Crystal Display (LCD) and plasma technologies. Pioneer is considered the best manufacturer of plasma screens while Sharp excels at LCD.
Between the two, picture quality is very similar. Plasma screens are available in larger sizes (60 vs. 46 inches) and have a better refresh rate, which makes them better for action viewing and sports. Larger LCD panels are in development, and LCDs are made in a wider range of sizes than plasma screens. LCDs can show ‘ghosting’ trailing after a fast-moving image. Plasma screens suffer from burn-in caused by static images such as logos down in the corner. The screen resolution of LCDs is higher, e.g., 3840 pixels per inch (nearly 200 dpi); although prices at this resolution are several thousand dollars for a 22-inch screen. LCDs are better for daytime viewing.
The viewing angle of both is similar. Overall, LCDs are up to four times brighter, and have better contrast ratios of 350-450:1 compared to 200:1 for plasma. But LCD colour saturation is not as good. Blacks are not pure black, and stray back light reduces colour saturation. In 2004, Sony announced the Wega series that uses LCDs for back light, which improves colour performance over the more widely used cathode fluorescent lamps (CCFL). The image quality of a plasma TV is good when viewed off to the side; whereas an LCD TV will lose contrast or brightness. This is an important consideration in a salon with fixed furniture.
– Fig 7-4 – Sharp 37-in LCD flat-panel TV
Plasma screens consume more energy, and run hotter, requiring cooling fans. Because plasma televisions were developed before LCDs, they are less expensive for the same size; although the gap should narrow soon. The sweet spot targeted by LCD manufacturers is 42 to 50 inches.
LCD panels will last 50-80 thousand hours, roughly twice as long as plasma screens. LCD is lighter, more durable, and more likely to support HDTV [14, 15]. Make sure LCDs and connecting devices have a DVI (digital visual interface). An LCD panel is a purely digital device.
It is wasteful to use a graphics card to convert the digital signal to analog, send the analog signal to the LCD panel, and then convert it back to digital inside the panel. If you
want ultra-high resolution, use two DVI channels.
Of course you will also need a TV antenna such as the PR-411 [15-1].
Towel Rails
Heated towel rails dry out towels, reduce humidity and contribute to heating in the winter. They are available for hot water heating, AC or in combination. If you use hot water heating, a combination type will give you the best of both worlds. In the summer, you can use AC for local drying while in winter the towel rails can be switched to the hot-water furnace, thus reducing the AC load.
If you use forced-air heating, then you will want only an AC towel rail.
Towel rails come in many shapes and sizes: towel-radiators, clotheshorse towel, wall-, corner- or floor-mounted rails and ladders in traditional, modern and Art Deco styles [44-49]. Combination electric towel rails and room heaters are also available. Consider putting towel rails in the heads and berths.
Trash Compactor
A trash compactor located under the counter or in the engine room will reduce the storage required for refuse. A unit such as the Broan 1052 Stainless Steel Compactor [42] will compress 14 bags of garbage into one compactor bag.
Vacuum Cleaner
Trawlers are becoming more and more like floating homes. Although built-in vacuums are common ashore, on a trawler they represent another set of ductwork passing through watertight bulkheads. Dyson [36] makes a very compact vacuum, the DC11 Full Gear, and Hoover [37] has the somewhat less compact WindTunnel™ model. If you must have a built-in unit, Boat Electric Co., Inc., [55] makes models that have a hose long enough to do a 52-ft boat.
Vapour Cleaner
A vapour (steam) cleaner such as the small Vaporettto 900 makes cleaning easy. It can be used on any surface to clean, degrease, disinfect and deodorize [56].
Washer/Dryer
Clothes washer/dryers use a lot of water and electricity, so they have been a focus of regulators and energy-saving programs. Washers come in full-size and compact, with stand-alone, stackable and combination models.
Washers are top-loading or front-loading. Top-loading has long been the USA standard, but energy considerations are switching the market to the European front-loading standard. These are also called horizontal-axis washers.
There are several ways of making a washer more energy efficient: reduce water consumption, reduce electrical consumption, and increase the spin speed. Reducing water consumption is a big winner, because it also reduces the amount of electricity required to heat water during the hot-water cycle, and reduces the amount of detergent needed. Reducing the detergent reduces the water needed for rinsing. Higher spin speeds eliminate more water and detergent from the clothes, so they require less time in the dryer, and are softer. Front-loading washers win on all of these accounts.
Top-loading machines use an agitator to swish the clothes back and forth in a big bucket of water, at a fairly slow speed. The clothes tend to tangle and clump together, impeding the washing action. After the wash cycle, the clothes are soaked in rinse water.
Front-loading machines use less than 50% of the water for the same size. They tumble the clothes through the air into a small pool of water, at speeds over 1000 rpm. The clothes don’t clump together, which means a better wash. The tumble action also rinses better, and is gentler on clothes. Front-loading machines are also stackable, and easier for the infirm to use.
Compact washer/dryers are available separately or as combination units, in vented and unvented models. Interestingly, the unvented combination models use hot water during the drying cycle. While eliminating hull openings is a big priority, experience has shown that the vented types perform much better and, of course, reduce water consumption.
Fig 7-6 – Horizontal-axis washers tumble clothes through a smaller pool of water
Combination units have a key disadvantage: you have to wait for the entire wash cycle to finish before the drying cycle starts.
Right sizing is the most important decision – washers are most efficient when fully loaded. National (USA) average is eight loads per week for a family of three, or about 60 lb per week per adult, or three loads per week per adult.
Temperature and cycle control are also important for health reasons. A 30-40° C cycle will not kill 93.5% of dust mites, to which many people are allergic. A 60° C cycle kills 100%. Alternatively, two cold-water cycles of three minutes each will also kill mites [51]. Some other things to look for are:
- Stainless steel drum
- Zinc-coated galvanized steel
- Suspension system to reduce vibration
- High-pressure spray for extra rinsing
- Built-in water heater
- Multiple rinse cycles
- Sanitation cycle
Energy efficient models include Splendide [28], Equator [29] and Specialized Appliances LG [41] combinations, and separate units like Asko [43], Bosch Nexxt [17], Equator, Staber [30], Spin-X [31], and Fisher & Paykel [18]. For performance, look for around 10-20 lb loads and water consumption of around 0.7 to 0.9 gal per pound of load. Some commercial units are available for up to 80-lb loads. They have the additional advantage of stainless steel wash baskets, and zinc-coated galvanized steel construction. Plus, because of their large size they have fewer tendencies to shake rattle and roll.
Fig 7-7 – Splendide combination washer/dryer UL/CSA approved for installation in a cabinet
Spin-X is a high-speed centrifugal dryer for removing water and detergents from clothes before they are put into a normal hot air, tumble dryer. Tumble dryers turn around 1200-2800 rpm while Spin-X turns at more than 4000.
Summary
The design of an efficient electrical system maximizes DC services while minimizing AC. Ambient lighting is DC tri-phosphor or cold-cathode fluorescents. Accent lighting is DC LED or halogen, depending on the desired effect, except in the berths, galley and dinette where DC LEDs are used. Utility lights are DC LED or halogen. Courtesy and night-vision lights are DC LED. Emergency lights are DC LED with a backup battery. Electrical outlets are AC. Hot water has AC backup elements. Fridge and freezer are a cold-plate DC design. The AC TV is LCD. The stove is diesel with electrical stovetop and microwave for backup. The AC stovetop has induction elements. An AC microwave/convection oven is used. Dishwasher and icemaker are DC. The AC washer/dryer is vented. Towel rails are combination AC and hot water.
References
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http://www.iesna.org/
2.
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48. [
Deleted]
49. Tadley Bathrooms,
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©2008 David Shaw
