TOPIC:

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.

………. 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.

Martin Ling wrote:

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.

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.

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 
 

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-decentralised-heat-recovery-unit-single-wall-mounted-d-mvhr-ventilator-smart-wifi-control 

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

Martin Ling wrote:

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

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. 

 

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.

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

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

Martin: Thank you. That is very thought provoking and I can well see that a unit could be designed, perhaps on the tubular basis, that could fit very neatly into for example the back of a wardrobe, perhaps drawing warm but fuggy air from the deckhead in the galley(?) on one side of a bulkhead and delivering warmed input air down at floor level in the next cabin, or elsewhere, which prompts me to mention one of the thoughts that has drifted across my mind occasionally over the years.

In our ship, a typical Luxemotor conversion, we have one sleeping cabin right forward that could get a bit fuggy overnight if all the doors are shut. It has no fixed external ventilation for various practical reasons. We reduced the issue by fitting ventilation through the internal dividing door, and this has helped because one of the facts of life on a long ship with various cabins, a corridor and a raised wheelhouse aft is that a lot of the heat naturally draws through the ship back and up to the wheelhouse, so to a degree air is drawn through the ship. The problem of course is that we lose that air and heat through the traditional and inherently draughty demountable wheelhouse structure. At most times when heating is needed we only use the radiators down at hold sole level in the forward part of the ship, knowing that the heat will draw through the ship from the sleeping cabins and corridor, through the living areas and up to the wheelhouse. Indeed the wheelhouse radiator is almost never turned on, and the one in our mezzanine level saloon is rarely used. So the obvious question is whether we should try and recover the heat from the wheelhouse and send the air back forward again. That would in theory be very simple on a recirculating basis using a fan and say a 4" duct through the ship. That would not of course be specifically venting any stale air overboard, but we only have the slight problem in the one cabin (a guest bedroom) and in most circumstances, particularly in winter when it is often only the two of us on board, we have ample volumes of fresh air in the rest of the ship which could be recirculated forwards. So of course I am talking now about air circulation, not external ventilation and heat recovery. Slightly different but perhaps part of the overall thought process particularly if ventilation is not needed specifically for safety reasons.

If we were to go the external venting / heat recovery route I would want to be drawing the air out of the wheelhouse and inputting the fresh external air at the bow.

It is all a bit academic in my case because (a) we don't have any big problem and (b) it would be just too difficult to retrofit ducting through the ship, but still food for thought perhaps.

Unfortunately (and sorry, negatively!) I would not agree that any heat recovery system as described could be deemed "fail safe". Filtration has not been mentioned so far and I would expect that air to air heat exchangers will very readily clog up, particularly on the outgoing circuit. Look at any bathroom or WC fan. Thin walled multi-tubed plastic heat exchangers or the like will be very hard to keep clean. Any such system should not be expected to override the requirement for efficient free flow passive ventilation in boats where open flued or un-flued fuel burning appliances are in use.

However I do think your friend should be congratulated and I suspect there is a lot of scope for thought and development, particularly for new builds or major refits where the ducting can be designed in.

Balliol..

A friend on land has been experimenting with heat recovered ventilation using 3D printed air-to-air heat exchangers.

The basic ideas are illustrated in this writeup of an earlier effort: www.instructables.com/Heat-Exchangers-and-3D-Printing/

The idea is that you have a 3D printed plastic structure with two ports at each end. Functionally, it consists of two separate ducts running in parallel. Internally however, each of them splits into dozens or hundreds of smaller channels, all interleaved with those of the other duct. Although plastic is not the ideal material for a heat exchanger, it works reasonably well, and the use of 3D printing means that a densely interleaved, thin walled structure can be created. The wall thickness between adjacent channels is only around 0.2-0.3mm: airtight, but quite permeable to heat.

You fit this contraption between inside and outside, with a couple of 12V fans at the inside end, such that one duct brings in fresh air and the other takes out stale air. The warm stale air going out heats the cold fresh air coming in, as they pass through the interleaved channels.

So far the results seem promising. A thermal camera shows a smooth temperature gradient along the heat exchanger, from outside temperature to inside temperature. The two ends of the system are a dozen degrees apart in temperature, but the difference between the "in" and "out" ports at each end seems to be only a degree or so, suggesting very little heat lost.

I think the approach has considerable potential for use on boats. The use of 3D printing means the heat exchanger part can easily be adapted to fit awkward spaces. It should be possible to have a version that fits to a standard mushroom vent, with the heat exchanger and fans hidden in the insulation space between the coachroof and cabin ceiling.

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.

We installed 3 different size 24V computer fans, dependent on the flue size and connected them via a humidity controller.  Works like a charm and we have set the humidity level of each different before they kick in/ turn off

Pondering about making the controller myself with an Arduino, I found ready made ones for less € than just the spare parts.

here is one for under €5
www.aliexpress.us/item/3256804146190754.html?spm=a2g0o.productlist.0.0.2cdc4ac6aeBYxd&algo_pvid=888e0081-2a94-4723-8da7-9a21fee32289&algo_exp_id=888e0081-2a94-4723-8da7-9a21fee32289-4&pdp_ext_f=%7B%22sku_id%22%3A%2212000028791252525%22%7D&pdp_npi=2%40dis%21USD%213.11%212.27%21%21%21%21%21%402101d4a716694761128068182e4a98%2112000028791252525%21sea&curPageLogUid=wJyktSlGLWNx
 

Although my boat was never designed to be lived on over winter, no condensation has ever been experienced. It has hot air heating that I'd never recommend - noisy, dry, ever moving air, no time control, unreliable temperature control, etc. but OK for occasional use.

The saloon roof has 3 non-closable but waterproof vents as described, with the one over the cooker fitted with an extractor fan. GEBO roof / escape hatches are ones that can be locked either fully closed or open a chink and still no water ingress Each is fitted with a combined fly and blackout screen that are well worth considering.

As mentioned, cupboard ventilation is essential for soft materials, clothing storage in particular. If still concerned about damp in these places, a tub of water absorbing crystals will allay any damp worries.

Peter

We went the 50mm spray foam route which also has the added benefit of stiffening the structure, in particular the large areas of superstructure roof.  The reduction in "boing" when walking about after spraying was very noticeable. 

For ventilation we comply with BSS with a permanent roof vent in the galley area. 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. 

Portholes are single glazed with insulation covers and opening bathroom porthole for 10 mins is sufficient after showering.  I had considered a Baxi heat recovery ventilator unit designed for bathrooms, so only 24v DC,  but never got round to getting one.
Gebo roof hatches with removable fly screen or double glazing panel depending on season. 

There are two potentially different situations here.

If your accommodation area(s) house any fuel burning appliances that are not fully room sealed (boiler, most LP gas appliances, solid fuel stoves, oil burning stoves etc.) then you need to comply with at least the minimum recommended fixed (non-closable) ventilation standards as correctly suggested and stressed by Paul and as detailed in his link to BSS standards, which are drawn from EN ISO 10239. These cover minimum ventilation free-flow sizing (calculated in relation to the input rating of all open flue appliances fitted), high and low level provisions for circulation, and through-cabin ventilation. Having complied with these standards you might then wish to look at heat recovery systems, but my experience of these to date suggests that they are cumbersome and space consuming.

If, as for our ship now, you do not have any fuel burning open flue appliances in accommodation areas then the situation is rather easier. Our ship has an oil fired boiler located in an almost completely isolated steel walled engine room. We do not have a wood burner (we would love one on occasions but we didn't want the hassle of sourcing and storing fuel, and the dirt) and we now cook electric. We do still have a few small ventilators in the hold coaming sides from the days when we cooked by gas but these are largely redundant now. The ventilation requirement (with no open flue appliances) is purely for comfort and to disperse damp air. This is amply dealt with by traditional Admiralty pattern skylights (which as always don't seal perfectly so they perform as per trickle vents in houses) and we have opening windows that are small and located under the old coaming rail so they can be opened and remain secure in almost any weather when needed, e.g when showering. We also have hatches effectively at each end of the accommodation which promote a good air flow through the ship in hot weather.

Our insulation is to an older standard, having converted the ship nearly 40 years ago, and is a mix of 75mm Rockwool and 50mm self-extinguishing polystyrene. However this always seems ample (plenty of snow stays on the decks!) and our heating oil bills always seem very moderate, but if I were doing it again it would be 50mm of sprayed urethane foam and a bit more attention to minimising cold bridges. We have no condensation problems other than a bit on the single glazed windows and on exposed areas of the alloy frames. That fairly minimal condensation issue seems to have reduced since we stopped using gas for cooking.

The biggest source of dampness can be lifestyle and of course the number of people on board but a 22 metre barge is quite a large volume for say two people so with a bit of normal care damp can be minimised. Don't dry clothes inside, open the window when showering etc.

The other "comfort" point that many miss is ventilation in cupboards, and wardrobes in particular. Try not to site wardrobes against "outside walls" or fit a double back and ventilate well. Allow good provision for air flow.

So if you are refitting my suggestions would be:

50mm of sprayed urethane foam (the efficiency falls off as you go thicker).
Careful attention to minimising cold bridges.
Consider eliminating any open flue appliances.
Install good hatches for summer air flow.
Install small windows that can be left open in any weather when required.
Ventilate wardrobes and cupboards carefully.

But to repeat Paul's warning, if you are using open flued (non room sealed) appliances then you really should comply with the minimum provisions of EN ISO 10239.

Balliol.

Hi Will

​​​​​​I'm wondering if your subject heading is actually accurate, a sealed boat?

The issue of ventilation in boats is a very important one, deaths have occurred due in part to poor ventilation.

We all want to keep warm, reduce fuel bills etc. But safety has to be first priority.

To my mind the UK Boat Safety Certificate Scheme, which just about all private boats on UK inland waters have to comply with, and are tested against regularly, set the standard that we should be working to.

The ventilation requirements of that standard was determined to ensure safety of life.

Here's a link to information that may be useful.
www.boatsafetyscheme.org/requirements-examinations-certification/non-private-boat-standards/part-8-appliances,-flueing-ventilation/ventilation/

We have ventilation above the minimum requirements. 

Due to having a wood burner, even with single glazed windows, we have little condensation (winter temperatures here have been down to-20⁰ for many days on end), and always have a couple of windows ajar, whilst maintaining a saloon temperature of around 22⁰, with much cooler, around 12⁰ sleeping cabin.

A cooker hood and bathroom extract fans are in my opinion an absolute necessity.

We have been on numerous barges over winters, with radiator heating, ventilators closed over with things from cushions to polythene bags, and the double glazed windows running with condensation.
One instance with stand alone paraffin heaters, it was actually raining inside as condensation dripped from the roof.

Not healthy living conditions. Get ventilation right, be safe and comfortable.

Paul Hayes 

Hi Will, it’s a complex issue.
we have a 25 meter Luxemotor with steel replacing the timber hold cap, it’s important for looks to follow the sheer of the hull.
the main issues are heating and fighting condensation in winter and cooling and ventilation in summer , and the change happens over 6 months.
I have seen some with opening double glazed windows in the hold ceiling. For historic ship look the balance of the steel is canvas covered. We have a ship style gable ended skylight with opening glass panels, and the opening below double glazed with Perspex sheets to stop the draft in winter and removed in summer.
we have some double glazed windows which can open and some metal portholes which get an extra sheet  of Perspex in winter.
There is also a forward opening (escape hatch) in the bow and the stairs up to the wheelhouse which has an insulated captor stain warmth in the main ship when we leave it in winter.
The hull is insulated with 75mm of rock wool plus 50mm of glass insulation, then a sealed moisture barrier of metalised film then 30 mm of a ply timber/ foam pvc / timber ply as the inner skin. Framing Timbers and services run through the glass insulation. Amongst other reasons the rock wool  helps to protect things if there is welding on the hull.
So it’s buttoned up pretty tight. With us just living inside the temp rise from us and simple things like making a cup of tea will raise the internal temp by 7 or 8C.
to get rid of moisture we have some 20cm x5cm plastic ducts in the glass fibre of the roof, under the rock wool.They lead via fans from the range hood, shower and loo to the outside where there is a flush mounted slide opening vent for each. They are a paint brush width under the overhanging lip of the steel hold capping.They are open when we live onboard and closed during winterisation. I don’t want critters setting up camp there.
when we have a fire in the fireplace it is noticeable some air is drawn in via the leaky wheelhouse doors and also a reverse flow is created through these ventilation ducts to supply air to the fire .
so that’s air in and out and moisture out.
in-summer we can remove Perspex panels , open windows, portholes, skylights and the escape door in the bow. Depending which direction the wind is blowing we can put a small fan in an opening to bring fresh air in or out.
Planning is all good fun.

We're renovating our 22M 1936 Stielsteven, and as part of that work we're intending to replace the wooden and very much not airtight wooden hold roof with a steel roof next year at the yard.  This has got me thinking about ventilation and energy efficiency.   There aren't any opening windows in the hold at the moment, and the boat is watertight to the top of the hold walls.   

I'm interested to know how other people have approached ventilation of sealed spaces like this,  I've been looking at heat recovery ventilation.   I'd be interested to know if anyone has ducted ventilation on their boat, where the grills are fitted (at floor or ceiling level for air going in to the boat) and how well it works.   Even if it's not heat recovery ventilation, where are the grills for bringing air into the boat - on cabin sides?  are they ducted inside?