"HRV" Air to Air exchanger for ventilation?

Discussion in 'Boat Design' started by ldrumond, Dec 5, 2006.

  1. ldrumond
    Joined: Feb 2005
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    Location: SW Ontario

    ldrumond Ya...I look like him

    Was thinking about the use of a residential type air to air heat exchanger (HRV heat recovery ventilator) to improve onboard ventilation without giving up hard won heat? Been looking at a number of products from numerous manufacturers, some of the smaller units are very low in noise and power consumption at about 100 cfm thru put with 85 to 90% efficiency. I have room for the unit and required ducting. Would have to find a way to cycle unit on and off because based on my caculations for cubic volume, at 100 cfm it would replace the air every half hour or so. In land based residential applications the recommended frequency is 6 times per day. To go a step further, what about using an ERV (Energy Recovery Ventilator) unit to remove excess humidity as well, would naturally have higher power consumption but I'm thinking it would greatly improve onboard comfort in a liveaboard situation in the PNW.
    Been trying to think of a way to homebuild an HRV, one more closely scaled to my requirements, based on a 12v 20 cfm computer fan, but when I look at the guts of the manufactured units, its pretty hard to replicate the efficiency of the aluminum exchange core.
    Comments?
     
  2. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    By nature boats are poorly insulated , have single pane glass and hatches and doors that compromise the heat.

    A simpler concept is a GOOD heating system with lots of extra capacity.

    The results of breathing and cooking are easy to direct vent.

    FAST FRED
     
  3. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    Hi Lou,
    The devices you talk about, essentially little more than specialized crossflow heat exchangers, work great in houses. The same idea could transfer to a boat.
    Where I think you'll run into trouble is if you try to slap a house unit straight into the boat. The marine environment is a lot more corrosive to metal stuff than the furnace room of a house is. I'd be worried about it corroding out really quickly, and losing more money replacing HRVs than would be spent on extra heating.
    As a fellow Ontarian I imagine you're trying to extend the comfortable boating season to outside of June-August. I would look at improving the insulation of your cabin, first. (And by that I mean insulation designed for boats; Roxul or Pink Glass will soak up water and go all mouldy and nasty on you.) Humidity can also be a big problem on boats; here the HRV might be of some use.
    I would suggest taking some good readings of temperature and humidity in various places throughout the boat, in the conditions you want to run in, before you start making changes. Once you know more about the problem, workable solutions become much easier to find.
     
  4. Man Overboard
    Joined: Oct 2006
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    Location: Wisconsin

    Man Overboard Tom Fugate

    Vanee makes exchangers with a polypropylene heat exchanger that may be more conducive to a marine environment. Their HE models are in the 90% efficiency range, They also have a compact model that might be better for a boat. There is not as good a warranty on the smaller unit though, you might want to find out why. I built a timber frame home in which I installed one of their HE models. It runs about 6 months out of the year and has for about 9 years. It is fairly quite. There website is:
    http://www.vanee-ventilation.com/eng/produits.html

    Info off their website for HE models:
    Features 1000 HE 2000 HE 3000 HE
    CFM at low-high speed 65-133 115-197 180-321
    Apparent sensible effectiveness at 0°C 92 % 95 % 94
    Warranty on components years 5 years 5 years
    Warranty on the core Lifetime Lifetime Lifetime
     
  5. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    I presume that those effectiveness ratings of 90% and above are on a first-law basis? (I'd be pretty impressed if those were exergetic ratings.)
    (Point of terminology- heat exchanger effectiveness on a first-law basis is defined as (h_out,1 - h_in,1) / (h_in,2 - h_in,1) where h_out,1 is the enthalpy of the stream returning to the room, h_in,1 is the enthalpy of that stream as it enters the exchanger from outdoors, and h_in,2 is the enthalpy of the stream leaving the room on its way into the exchanger. NEVER refer to heat exchangers by 'efficiency' as that term has no definition in such devices.)
    Polypro shouldn't mind the ocean as much as aluminum exchangers do (they hate it).
    Quebec-made.... usually a sign of high quality. They know how to deal with nutty weather out there.
    The trick will be finding one that can run on boat power instead of 120 VAC.... unless you want to have the inverter going all the time. Which isn't that big a problem, really, if you're running a good one.
     

  6. ldrumond
    Joined: Feb 2005
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    Location: SW Ontario

    ldrumond Ya...I look like him

    Thanks for the input guys.
    I use one in my "so called airtight home" now.
    Seemed like it would work on a boat given that one tries to make a boat as air or watertight as possible.
    I was just thinking that if one could lessen the potential heat loss while gaining the benefits of maximum ventilation, it might be worth trying.
     
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