Let's Design a Custom HVAC System

Discussion in 'Boatbuilding' started by CatBuilder, Feb 19, 2012.

  1. CatBuilder

    CatBuilder Previous Member

    Is there anyone on the forum who would be interested in helping design a reverse cycle heat pump system based on a marinized Kubota?

    The system would be made up of components like this:

    *Cupro Nickel sea water cooled condenser
    *Twin 3 ton Sanden compressors, spun by small, marinized Kubota
    *4 way reversing valve
    *Pair of evaporators and fans
    *Appropriate expansion valves
    *Filter Dryer
    *Suction line accumulator
    *Ducts to carry the air to cabins

    Does anyone here want to get all down and dirty and help me go through the numbers on this one and talk it out, so the design is going to work as needed?

    Any HVAC pros on here?
     
  2. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

  3. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Cat, HVAC is what earns me most of the money in these times of crisis for the marine industry.
    But tell me, what makes you think that you wouldn't be better off with off-the-shelf air-conditioning systems, tested, certified, safe and with a manufacturer's warranty?
     
  4. CatBuilder

    CatBuilder Previous Member

    It has to do with energy efficiency and keeping weight off a catamaran.

    I am using outboards engines and solar to propel and power the boat. However, when guests are aboard, I need heat, air conditioning, watermaker and possibly a little boost of power to keep up with hair dryers.

    In the interest of fuel efficiency and weight efficiency, a small, 3 cylinder, under 20 HP kubota engine can provide all of this using a small amount of diesel.

    Buying a large (heavy and fuel wasting) ac generator, then converting energy from chemical to kinetic to electrical to kinetic to move heat is a bit much. I'd like to save weight and fuel, just going from chemical to kinetic directly to moving heat via the auto style compressor.

    Also, I need twin 36000 btu systems. Start looking at weight and generator weight on those in an off the shelf marine unit.

    Michael: weight. No pipes full of fluid and multiple evaporators. Air in an insulated duct weighs much less than fluid.

    I've worked on many marine refrigeration units and have a decent general understanding of the cooling cycle, including superheat, expansion valves, etc... So i see how simple it all is and figure it's worth doing.

    I could put together a system easily, except there are tricks to doing reverse cycle I'm not familiar with.

    Lastly, when heating, a heat pump is the most efficient means of heating, so I want to use that.
     
  5. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Hmm...how do you control the enviroment inside the ship when you are plugged into shorepower ?
    Air ducting, the air in.. air out loop , is complex and takes up great slabs of interior space. On a cat ,with two hulls to service, the installation sounds even more complex.
     
  6. CatBuilder

    CatBuilder Previous Member

    Michael, the parameters of the design are clearly laid out. I am not interested in wasting time second guessing the overall requirements of the project.

    I do not use docks or shore power.
     
  7. hoytedow
    Joined: Sep 2009
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    Location: North of Cuba

    hoytedow Wood Butcher

  8. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Gee Cat, youre the one asking about air ducts into cabins.
     
  9. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Cat, I am sorry to question your input but 2x36000 btu/h is a huge amount of heating power for a properly insulated 45' boat (I understand from your previous posts that's the size of your boat, right?). Actually, that's a heating power required for a 300 sq.m apartment in a cold climate! I would have expected around 1/3 of that power for a boat of that size - are you sure about your data?
     
  10. mydauphin
    Joined: Apr 2007
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    Location: Florida

    mydauphin Senior Member

    Your heating and cooling numbers are way out of line. Post a plan of your boat and we can get you a better design. I find keeping heating and cooling separate is best. Heating is easy just use engine to heat water and circulate. To cool use compressor to cool a plate and circulate water to cool. You take care of freezer and ac in one. That with good insulation and covering glass and it can works without having massive units eating electricity and fuel.
     
  11. Boston

    Boston Previous Member

    Not sure if anyone suggested it yet, but a unit off a box truck might do the trick. Self contained and all ready to go. You might be able to strip it down and put it on a carbon frame as well as replace the steel canisters for carbon ones, might lighten it up enough to satisfy the need. Comes with an engine included. Some of them run on electricity but many run on there own propane. So you might have to fiddle with it but the components are all there. As far as duct work its all about the layout and what size plenum chamber you need, which is related to the CFM and the length of the run + number of vents. Which I know very little about other than residential.

    Best of luck
    Cheers
    B
     
  12. CatBuilder

    CatBuilder Previous Member

    Thanks for the participation, everyone. Michael, thanks for getting past the "I am using ducted air" stuff and continuing on. Your input is valued.
    
    Ok, down to the numbers. I apologize for them being in imperial units. I do convert to metric at crucial points in the post.

    The boat consists of 3 basic parts to be climate controlled: port hull, starboard hull and bridgedeck area.

    Here are the areas of livable space inside those hulls. These areas do not account for the engine rooms aft, or watertight bulkheads forward, nor does it include the bilges. This is only living space...

    Port Hull: L=32 W=5 H=6.5 Volume=1040
    Starboard Hull: L=32 W=5 H=6.5 Volume=1040
    Bridgedeck Area: L=13 W=16 H=6.5 Volume=1352

    *TOTAL VOLUME TO BE HEATED AND COOLED: 3432 cubic feet or 97.18 cubic meters

    Looking at several marine air conditioning sites, I found that in order to cool an area during the day, you need 14 BTU per cubic foot. Again, sorry for the imperial units.

    14 BTU per cubic foot with 3432 cubic feet of space is 48,048 BTU or 4 tons required, NOT INCLUDING GALLEY HEAT.

    36,000 BTU Sanden compressors run at 36,000 BTU max. If at lower rpms, they tend put out a little less... say 25K BTU. (remember... 12,000 BTU is a ton of air conditioning). This would put me nicely at 50,000 BTU of cooling power, which allows me to be able to deal with a little extra heat from the professional galley.

    So, a pair of 36,000 BTU compressors would be nice because I could blast both of them during the day, cooling the entire boat, plus galley, but then switch over to just one of them engaged if I want to cool just the hulls in the evening, which require somewhere in the 20K BTU range, combined, to cool at 10 BTU per cubic foot.

    This is where forced air comes in handy because I could switch off one of the evaporators and route the cooling to both hulls at night in a more simple fashion than with liquids being pumped.

    Daquiri: My boat is not "insulated" per se, but it is already constructed out of 25mm (1") Corecell with an R value similar to 25mm insulation from the hardware store - specifically: R4.16 per inch or 25mm. So, it is fairly well insulated by default, but not in addition to the 1" of foam surrounding the entire hull. Also, do not forget that my boat will have a forward cockpit and all windows all around in 360 degrees up on the bridgedeck.

    Mydauphin, using engine waste heat to heat a boat is so inefficient, I'd have to say it's criminal! :) Seriously, it is a huge waste of diesel. I have a fuel budget to keep in mind here. Efficiency is a must. That is Florida talk. ;) I will sometimes need actual heat that is just as powerful as air conditioning needs to be in say... Melbourne, FL, though I do need warmer water to pull it off. Reverse cycle systems don't work in much less than 40F degree water.

    Charters will operate from 43'39" deg N to 23'30" N. Lot of temperature variation to account for, so heating and cooling a must.
     
  13. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    As far as cooling goes, keep it simple. Couple of large fans and some blocks of dry ice ought to do the job. Give them a frozen hot water bag to take to bed with them.
     
  14. CatBuilder

    CatBuilder Previous Member

    Ok, I'm thinking that's a joke. :D

    I just want to reiterate that this is a serious, by the numbers, "let's design and HVAC system" thread. There are no deviations from the requirements, as they are not my requirements. They are the requirements of people paying a lot of money to be comfortable while on vacation. They will get everything they want.

    I'd consider off the shelf, electric based systems, if anyone could come up with a more efficient system than the one I (and WestVanHan) have proposed, but it would also have to have a similar weight. It would also have to somehow fit nicely into the boat. No junk yard looking, half assed, cheapskate stuff here. It has to be the best and look the best. This is how I make my living. Some nasty looking thing would cause my customers to go elsewhere. Think "yacht" not boat.


    Boston: The APU or refer unit on a truck is not marinized. It would cost a fortune to marinize and get that into place, plus, they are not set up for cupro nickel condensers. They are air cooled and attached to the rig's engine cooling systems. I did look at them though. Thought about it for a few moments, but ran into all of those problems.
     

  15. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    Cat
    Builder, It is not a joke just a very simple, cheap solution. But my son comes over here Wednesday night for dinner. He is a heat/air engineer and his firm does million dollar houses. and large commercial. I will see if he has any thoughts for you. Also, have a friend who was on call for 25 years to rush anywhere in the World to fix nuke subs AC.
    I'll call him tomorrow and ask for his ideas. I know those subs had 2 - 500,000 BTU chillers. so I will have to downsize him a bit. Can you estimate for me the average temp of the waters you sail in 20' down.
     
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