Alternatives to conventional HVAC systems.

Discussion in 'Boat Design' started by chrisyk, Dec 4, 2012.

  1. chrisyk
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    chrisyk Junior Member

    In some large vessel its has been deduced that a large portion of the auxiliary load is consumed by HVAC systems. These systems can also take up a considerable amount of space and in some cases have been the result of bad health due to microbial growth within ducting.

    However, we are now seeing new developments within architecture which permits the use of natural lighting, ventilating & heating, these technologies come under the term of passive design. Passive design has been stimulated by its growing success within Europe, with some buildings operating “without the use of active forms of air conditioning despite high internal heat gain sources” (Thomas, R. & Fordham, M., 2006).

    I have been working on several different platforms to understand the potential of passive design within the marine industry.

    One uses a roof design which enhances the Bernoulli effect and thus creates low pressure regions pulling air from the interior without the use of mechanical systems. The other uses a development of a solar thermal chimney where the mast section is used to enhance the stack effect and induce natural ventilation.

    Clearly these systems require advanced engineering and experimentation but the principles have been exercised successfully in architecture which begs the question: Could passive design be used in the large domestic yachting industry?

    I look forward to hearing your thoughts!

    Regards

    Chris

    p.s Attached a few basic schematics demonstrating the potential use of passive design for ventilation and for lighting.
     

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  2. TANSL
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    TANSL Senior Member

    I do not know if this new system takes into account that the air conditioner, as well as controlling the temperature, and above all, should control the humidity. And this, with a "passive" system, I do not see how you can get.
    Air conditioning systems on ships, usually have a energy recovery system that I do not know if a "passive" system can have.
    Regards
     
  3. Stumble
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    Stumble Senior Member

    Chris,

    Passive cooling and ventilation has a long history on boats. The roof design you proposed is quite similar to standard dorado vents. The problem with these, and your design, is that during bad weather they must be fully sealed. Not just from rain, but from intermittent submersion. It is certainly doable, but that's your challenge. Anything that can't be made to be 100% water tite won't work.

    The second issue is you need some way to vent fresh air into the boat. Unlike buildings, the lower sections of a hull are by definition waterproof. Thus air tight in a way a building can't dream of. I don't know enough about your system to comment on this, but it would need to be taken into account.


    As for using the mast. It might be possible, but most masts have a significant amount of stuff running in them. Think wires, line, cables, ect. How would this effect the heat stack principle.

    Secondly the top of the mast typically has a plate or cap installed over it. This acts as an attachment point for halyards, lights, wind instruments, radio antennas, ect. You would have to find a way to still allow for all of this, since most of it cannot be compromised.

    Third masts are in pretty high compression, and the plate they rest on needs to be extremely strong. It would take a good bit of engineering to cut open the deck into the bottom of a deck step mast, without sacrificing this strength.


    As you mention this would be a very significant undertaking, and require a good amount of engineering work. I wouldn't be opposed to it, but I see some pretty big hurdles to overcome.
     
  4. jonr
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    jonr Senior Member

    I would put your efforts into air sealing and insulation.
     
  5. michael pierzga
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    michael pierzga Senior Member

    Natural cooling is Well worth studying. House loads from AC and lighting are the biggest energy users on board.

    In your study also remember that the summer sea temp..25 to 30 degrees will always be cooler that the air temp. For years I've used low power blowers to pull cool air out of the bilge or off water tanks to reduce cabin temp. Any system that refines this would be worthwhile.

    Natural air flow , fore and aft, inside a boat is always interrupted by cabins , cabin doors and bulkheads..

    Natural airflow into and out of the boat is always retarded by mosquito screens.


    Also study isolating and extracting machinery heat and particularly the battery bank heat.

    The big problem with generator driven air conditioning is that as soon as you shut down the generator and AC the latent heat of the machine room and charged battery banks re warms the entire boat.

    Do investigate LSA paint LOW SOLAR ABSIRBTION paint.
     
  6. daiquiri
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    daiquiri Engineering and Design

    IMO, avoiding to design summer heat-traps and winter heat-dissipators like these:

    [​IMG] :eek:

    [​IMG] :rolleyes:

    is the best first step towards increasing the occupants' thermal comfort and reducing the size and power requirements of air-conditioning systems on board.
     
  7. michael pierzga
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    michael pierzga Senior Member

    Typically the wheelhouse of a yacht is built on top of the engine room.

    When motoring, the engine room heats the floor of the wheelhouse and drives the temperature inside the house to 40 plus degrees.

    Pay particular attention to the engine room ceiling and the wheelhouse floor.

    Seawater ...Watercooling ....the floor might be worthwhile
     

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  8. chrisyk
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    chrisyk Junior Member

    Whole System Design Stratergy

    Thank you for your comments!

    I understand that the premise of my proposal is primitive at the moment. But I do believe that Passive design has a high potential within the marine industry, particularly on large vessels.

    I have also been doing some work on PCMs (Phase Change Materials) as an alternative to preconditioning incoming air.

    The idea being that the natural ventilation strategies will pull the air through (Perhaps supported by low voltage mechanical systems) the PCMs and thus cool the incoming air. Many of the PCMs I have discovered are salt hydrate based and can be engineered to have different phase change temperatures. Making the vessel very site specific but may be of use to medium sized catamaran platforms. (Review the attachment which demonstrates a multi hull platform with a ETFE roof, capturing solar energy to stimulate the stack effect and pull air from the interior via simple convection. - apologies in advanced for the shoddy CAD work)

    Fundamentally I want to design a vessel which reduces the use of HVAC systems. So air infiltration, and insulation are a major concern. However from preliminary research I managed to find that a large portion of the HVAC load is from solar thermal energy coming from the windows. In architecture it is known that 42% of the cooling load is from windows orientated to capture solar energy. e glass helps to combat this effect but careful planning and understanding of solar orientation can reduce this figure furthure. (haha I have just seen the post by daiquiri - thanks for the pics!)

    Internally I have come up with some very basic concepts of channelling exhausts from high heat gain sources to furthure reduce the load on conventional HVAC systems. (Please see my primitive Google sketchup schematic attached). Here I was thinking of using a polymer shield between a large TV and media system (which would otherwise exhaust heat into the room) attached to an exhaust ventilation shaft directly above. The heat from the TV and media systems, could potentially help good ventilation behind the installation and reducing the risk of mould growth etc. Otherwise the basic intention here is to ensure that high heat gain sources are close to exhaust shafts. The polymer shield can also be polarized so as to allow only the TV screen to be seen thus doubling as an interesting design feature.

    I would like to know your thoughts on this and possible other ways of reducing HVAC loads.

    p.s Thanks for the suggestions Michael, Jonr, stumble & TANSL, they are much appreciated! I will keep you posted on my progress.
     

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  9. daiquiri
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    daiquiri Engineering and Design

    The AC load is not only due to heat exchanged through the windows. A lots of power is expended to heat and cool the fresh air moving through the ventilation system.
    High-efficiency (90% and more) heat recuperators, like the ones produced to meet the stringent EU energy efficiency goals, can be used to recover a major part of the power expended for heating and cooling the inlet air.

    An example:
    In mid-winter, at harsh 0°C outside and 20°C inside temperatures, a 90% efficient recuperator will pump in the air at 18°C, thus requiring only a minimal additional power (2°C difference, against 20°C without the recuperator)) for the post-heating of the inlet air to the cabin temperature.
    During the summer, at 35°C outside and 25°C inside temperatures, the same recuperator will give you air at 28°C, again requiring a very small additional power (3°C difference, against 10°C w/o the recuperator) to cool the inlet air down to the cabin temperature.

    Regarding your solution of capturing the hot air above the point where it is created, it is ok for the summer condition. In the winter, however, that same hot air is a free collateral heating for your cabin, so you have to devise a system which will allow you to make use of it before expelling it outside. One way of doing it might be to make it got through the above-mentioned heat recuperator, where it will be used to pre-heat the inlet air.

    Cheers
     
  10. philSweet
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    philSweet Senior Member

    I see several have chimed in while I was typing this. This is a pretty scattered response, but you did ask for ideas and opinions.:)

    You are going to have to come up with a specific case to consider. A cruise ship is different from a 50' cruising sailboat. Passive usually works if there is the ability to control or encourage the usage of certain areas at times that make the most sense. So General Arrangement plays a huge role in passive, and houses and other buildings usually have a lot more freedom in the GA department than do boats.

    You need to calculate some basic engineering quantities as well-

    Cubic space per passenger.
    Thermal mass of controlled space per passenger
    Heat exchange with the environment per passenger.(Conduction and that associated with mass transfer)
    Internal thermal load per passenger.
    Required air quality, air exchange rate, and humidity control.

    These need to be figured hour by hour based of usage, and as a function of outside conditions so seasonal effects and changing routes can be figured in.
    It needs to be done regardless of whether it's passive or conventional and there are charts of this stuff for anywhere in the developed world.

    Another big factor is who has what control. Is there a thermostat in every suite for the guest? do crew have a thermostat? Can the crew adjust the temp in the galley? Passive puts huge restrictions on zoning since it usually requires big zones that influence one another.

    If there's a bar on board (or casino, or other revenue center), emphasis goes there. Places that are loss leaders- not so much.

    I can't overemphasise the importance of GA and daily cycles of usage and occupancy. They are the real drivers of energy efficiency. To get passive to work, you need a fairly good time dependent model of the individual spaces, and this model needs to be incorporated into the control system of the actual space when built. You need a lot of extra sensors to monitor comfort and assess the effect of the passive system from moment to moment.

    On board systems differ from shore systems principally in that the cost is pretty steady on board, where there is a peak rate system of pricing for shore systems. Onboard power costs are generally higher, much so in smaller boats. A/C systems are still getting better and smarter and smaller and cheaper and more efficient, but I doubt the improvements can keep up with the rising cost of fuel. So the crossover point is probably drifting towards better and more sensors, more control over separate zones, better predictive control systems, and occupancy sensors that turn remote control over to central control when a space is unoccupied.

    For passive systems, you are lossening up the temp control and you must do everything you can to retain comfort control. Oiled wood and natural fibers feel comfortable over a wider range of temps and humidities than plastics. Cushion foams need careful selection. You need to design with respect to how the human body regulates it's temp. But these materials require more maintenance, so is there a net gain?

    On something like a cruise ship, the tonnage divided by the passenger count is staggering. Weight reduction is a huge deal with respect to propulsion, and I suspect that using light weight furnishings and tight climate control is better than luxurious, heavy, cozy, high maintenace furnishings and a less intensive climate control. For a five knot owner/operator motor sailor, perhaps a different answer.
     
  11. michael pierzga
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    michael pierzga Senior Member

    Your Cat design looks naturally HOT. Colour, surface area, closed house, no shade ....... inside the boat, forward of the mast ,will be an oven .

    It will need a massive cooling system .

    The boat pictured represents valuable lessons in design .
     

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  12. philSweet
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    philSweet Senior Member

    My tv draws 23 watts. My dvd is 6 watts. Not the first place I would look to save energy. For a boat such as the cat pictured (edit, I just noticed the size of the boat- a bit bigger than the 50'er I sailed on), isolating the engines and tanks from thermal transfer to the aft cabins would be number one. Sleeping on a 100 gallon tank of warm diesel in the tropics is no way to go. (So switch the feed to the other guy's bunk in the afternoon:D). I assume that All of the equiment is aft- gensets, watermakers, engines, hot water heaters, hydraulics, and fuel. some water also, probably. If possible, set a couple ac compressors there as well, but they would normally be in a cabnet in the aft cabins. On an Alliaura I sailed on, it had nine identical little compressors. Six running comfort air and three for fridge, freezer and ice maker. All were water cooled (which sucks if you are on the hard for a week) and seven were in the bilge where the heat helped keep the bilge dry.

    All up, the boat ran at about 80 amps average while under way, so the tv wasn't really the problem. Do you have an energy budget for your boat yet?
    A live heat load? Solar load? What water temps will you be operating in? And what is the expected trip duration or design endurance. That has a big effect on the fuel capacity needed to service hotel loads. The solar panels should only be located over equipment spaces, not insulated spaces. They require large amounts of conductive cooling. Better to use them in a canopy where there is a big airgap for convective cooling.
     
  13. michael pierzga
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    michael pierzga Senior Member

    Mechanical system optimization mean nothing if you cant get the solar energy off the decks.

    If you want to stay cool , concentrate on design details that gets the sun off the boat.

    When a yacht is sailing it is never hot..the sail provide shade , water sucks the heat out of the topsides and wind does the rest.

    As so as you stop..you burn.

    An innovative yacht would have sun awnings that magically roller furl out of the wheel house.the boom ..anything that shades the deck.
     
  14. jonr
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    jonr Senior Member

    While windows with solar reflective coatings work well, I also agree with some type of shades or snap on covers for windows.

    Decks should be white (anodized aluminum is even better, but it's not as practical) and well insulated (as in inches of foam).
     

  15. groper
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    groper Senior Member

    These days, solar assisted air conditioning systems claim upto 80% less energy requirement... they are only just beginning to sell here in australia, i dont know of anyone using them on boats yet... might be worth a look if you have the space for the solar collector gas heater tubes to be mounted?
     
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