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Ventilation - how to get air into a sealed boat effectively.

  • Martin Ling
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01 Dec 2022 14:18 #1 by Martin Ling
As I understood it, one of the reasons ventilation is needed is that we create quite a lot of humidity inside. Humans breathe out damp air. Burning gas also creates water vapour as a byproduct. Hence the common advice that if you're seeing a lot of condensation inside, the ventilation probably needs to be improved.

I think that trying to keep the indoor humidity below that of outdoors is probably a losing battle, unless you have a lot of power to throw at a dehumidifier. Rather, keeping it balanced with outside but not losing the heat in the process is probably the best we can do.
The following user(s) said Thank You: Jan Pieterse

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  • Balliol Fowden
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01 Dec 2022 07:27 #2 by Balliol Fowden
………. and having just taken the bins out on a cold and rather misty morning (on land) what are the counter risks of pumping damp misty air from over the canal into a nice warm dry boat? Is this what Paul is hinting at? Could not any form of heat recovery system actually be counter productive in some conditions and encourage the ingress of damp air into a boat? External humidity sensing?

Balliol.

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  • Balliol Fowden
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01 Dec 2022 07:16 #3 by Balliol Fowden

I've seen heat recovery ventilators online which work by reversing airflow every so often, thus eliminating the need for the ducting required with 4 port systems.  I guess this is similar to the 3d printed system discussed?

No, it's a different principle. The reversing ones have a ceramic element in them that the air passes through. While the fan is pumping outward, the ceramic absorbs heat from the warm outgoing air. Then when the fan reverses to pump inward, the cold incoming air is heated by the ceramic.

The 3D printed designs are 4-port counterflow heat exchangers.

That is my understanding too.

Hypothesising, the difference might be that the discharge and intake take place at the same point, which in a sheltered location or in certain conditions could lead to output foul air being sucked back in. A ducted system with heat recovery outlet and separate inlet trunkings could allow input and output points to be in different locations. Also, and probably a better argument, with a ducted 4 port system output air can be exhausted from a high level in the cabin and input air ducted down to floor or bilge level, such that a better air circulation can be promoted.

Balliol.

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  • Martin Ling
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30 Nov 2022 17:09 #4 by Martin Ling

I've seen heat recovery ventilators online which work by reversing airflow every so often, thus eliminating the need for the ducting required with 4 port systems.  I guess this is similar to the 3d printed system discussed?

No, it's a different principle. The reversing ones have a ceramic element in them that the air passes through. While the fan is pumping outward, the ceramic absorbs heat from the warm outgoing air. Then when the fan reverses to pump inward, the cold incoming air is heated by the ceramic.

The 3D printed designs are 4-port counterflow heat exchangers.

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  • Paul Hayes
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30 Nov 2022 07:37 #5 by Paul Hayes
Hi Will
​​​​​​I don't know where you are mooring, but beware of condensation.  It's not just about heat recovery, relative humidity play a big part in keeping ait above the dew point.

Presumably there will be a condense drain from the heat recovery unit 🤔.

The old rule of thumb for buildings was three complete air changes per hour for healthy conditions.

Paul 
 

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  • Will Lahr
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29 Nov 2022 11:57 #6 by Will Lahr
At the moment the only open flue appliance we have is a gas hob, we're going to replace it with an induction hob when we redo the gallley.   We've got a kabola kb400 but it's the ducted kind with a dedicated air inlet on deck above it.   So the air we need inside is just for breathing. 

I'm quite interested the idea of heat recovery ventilation,  it seems better than warming the air inside the boat with radiatiors etc then just blowing it outside and losing the heat.  Opening doors and windows for ventilation makes sense in the summer, but I still want to breathe in the winter when our watertight (and therefore presumably air tight) portholes are closed.   

I've seen heat recovery ventilators online which work by reversing airflow every so often, thus eliminating the need for the ducting required with 4 port systems.  I guess this is similar to the 3d printed system discussed?

www.blauberg.co.uk/en/blauberg-mini-air-...r-smart-wifi-control  

Has anyone bought one of these? or thought about it?

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  • Tam Murrell
  • www.foodieafloat.com
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28 Nov 2022 12:46 #7 by Tam Murrell

A key feature is that it is "fail safe" - if you're not powering the fans, it still functions as a fixed vent. However since the narrow channels will restrict the airflow, you would need more or larger vents to make up the same amount of ventilation as you would without the heat exchangers.
 
When I converted our ex-trade beurtschipp back in1985 I built in a basic version of this which was quite effective. I used  4 standard deck ventillators with plastic ducting effectively connecting them to the bilges behind the wall lining. Two of them allowed fresh air to the bilges, and the other two were powered by solar fans sucking air, creating a steady slow movement through the bilges. The system worked quite well and the boat always smelt quite fresh when we returned having left it for some time. The main problem was unreliability of the fans.

Tam

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  • Colin Stone
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27 Nov 2022 18:43 #8 by Colin Stone
Yes, Will. No internal ducting, the floor grilles are just open down into the bilges at the space sides.
I should have included that I do also have 4 ducts from bilges, wiggling up the sides, to superstructure roof. 2 are inlets and 2 solar powered fan exhausts.  In hindsight, probably no necessary as internal hatches to bilges are lifted regularly. 
A couple of small PC fans blow cooler bilge air up over the fridge condenser. 

 

Colin Stone
It's not the destination, it's the glory of the ride.
Barge Register KEI

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  • Martin Ling
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27 Nov 2022 14:48 #9 by Martin Ling
Balliol, that's a good point about the exchanger clogging up. It would be good to find a solution though, since obviously the benefits are quite defeated if fixed ventilation has to be kept open in parallel with the heat exchanger.

Perhaps the next step up is a full-diameter bypass path, that can be closed off by a flap which is driven by the airflow through the heat exchanger, whilst being spring loaded to return it to the open bypass position if that airflow stops.

You could have filters at each end of the heat exchanger to prevent internal clogging, which would need to be cleaned/replaced periodically. If the filters clogged up enough that the airflow through the heat exchanger became reduced, the covers to the bypass path would spring open, restoring the fixed ventilation.

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  • Will Lahr
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27 Nov 2022 11:29 #10 by Will Lahr
Hi Colin,  
I wanted to learn a bit more about your low level ventilation.  This sounds like you've linked rooms through the floor and the bilge, is that right?  There's no ducting or anything to get air from outside to low down in the boat?

Low level internal ventilation is by vent grilles in the floors down to the bilges and high level ventilation is by the same vents in the tops of cabin internal doors.  Vents from Screwfix.  Cabin cupboards have louvre doors to encourage air to move

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