Heat recovery ventilation (MHRV / ERV) again

[wakey_wake]

My thinking of how a narrowboat should be is that an MHRV is essential equipment for live-aboard, but it brings one large question (below) for the BSS.

 

What does it do?

 

Mechanical = fans: Suck out the warm, stale, humid air...  from the kitchen / shower. Suck in cold, fresh, dry air from outside, and try to do this in a balanced way so you're not pressurising the place.

Heat Recovery (also Energy Recovery in hot places with aircon) = put a heat exchanger in with these fans: Use the outgoing air to warm up the incoming air. There are filters on both inputs to the heat exchanger, else it will clog up.

Ventilation: send fresh and warm air to the opposite end of the boat.

 

Heat recovery is never 100% efficient but can produce great savings. It also isn't useful as a heat source - you still need a heater somewhere. The heat recovery is also not meaningful or useful if there is no heating. Any MHRV is undermined by draughts, so houses with it fitted tend to be pretty much air-tight - let me know if you want a link to some youtube guys taking that to extremes.

 

This is in the context of a live-aboard boat which will get some heavy-handed refitting after I find it. It will be a huge project, please wish me luck!

 

My question is "Will having active ventilation remove the need for passive ventilation (ie. holes everywhere), which are normally required for BSS?"

Or if it doesn't by itself, what else would need adding?

 

If it has LPG / fuel gas on board I'll be removing that as soon as I have an alternative. I don't like it, it's too boomy for me.

Solid fuel burning will be needed, but I want a balanced flue not a front-feed stove. That's a story for another day, but I also dislike having a potential carbon monoxide source in my box.

I'm relying on the boat having plenty of electricity, which is also a story for another day.

 

MHRVs last popped up in these old posts -

 

Any thoughts appreciated!

[nicknorman]

MHRV is a great system ... in a house! In a narrowboat it will create various problems - it's quite bulky, where will it be fitted? Even ducts take up too much space.

It makes noise. Not noticable in a house because you can tuck it away somewhere eg in the loft, but there is no such space in a boat and you will be living with it at close quarters.

It needs a constant supply of power to run the fans, something that an off-grid live aboard boat has to be very frugal with.

I can't see any allowance against the BSS requirements for fixed ventilation - after all, what happens when the fans stop working? You die.

And so with fixed ventilation, the point of MHRV is rather defeated.

As to balanced solid fuel stoves,  not sure where you will get a boat-sized one of those from.

People new to boating have all these good ideas and whilst I don't want to crush them, boats are the way they are because of decades of experience in what works and what doesn't work. Re-inventing the wheel can be fun as a thought project, but in reality can be an expensive disaster.

 

Edit: I didn't look at your links but I see I am pretty much saying the same as I did 4 years ago. It's good to be consistent!

Edited January 31, 2021 by nicknorman

[David Mack]

Mechanical heat systems rely on having electric power a available to drive the fans. If this is on a permanent mooring with shore power supply, no problem. But if it's a mobile boat, how are you going to generate the electricity?

[Alan de Enfield]

8 hours ago, wakey_wake said:

"Will having active ventilation remove the need for passive ventilation (ie. holes everywhere), which are normally required for BSS?"

 

The BSS listings for ventilation are not a requirement, they are simply an advisory, you cannot fail a BSSC even if you have no ventilation at all.

 

Have a look at section 8 in the BSS, you will note an "A" in the top RH side of the details 'tables', this means 'Advisory only'.

You will note that it applies to every item listed in section 8  "Ventilation" subsection 8:9 and " Appliance Flues & Exhausts" subsection 8:10

 

 

Remember the BSS is not about your safety, or the safety of the boat, it is only concerned with ensuring the boat is safe (will not explode, burst into flames or cause pollution) and will not affect / harm passers by, C&RT employees or other boaters.

 

 

[1st ade]

9 hours ago, nicknorman said:

it's quite bulky, where will it be fitted?

 

I'd wondered if "long and thin" in the roof void - extract air from near the middle of the boat and expel at the front; draw fresh air at the front and distribute internally from the middle. I'm sure with a bit of thought someone can come up with a heat exchanger 6 feet wide, 10 feet long but only two inches high... Of course their will be compromises with air flow which probably need bigger fans - and more power

[Jen-in-Wellies]

In a grid connected house, something consuming a few tens of watts 24 hours a day is trivial. In a boat without a shore connection, it is a major consumer of battery power. Needs a totally different mind set when deciding how to do things. You can generate kW of heat on board easily, by burning stuff, wood, coal, diesel, or LPG. Making kWhrs of electricity and stuffing it in to lead acid batteries is hard and takes a long time to do. Unfortunately, most sorts of electric heat pump on board, a fridge, freezer, or heat recovery gadget uses a significant amount of the electrical power you can get each day. Most people have enough trouble keeping a fridge going.

[cuthound]

In my experience (assuming you have a log/coal/oil drip stove as the primary wintwr heat source) there is more heat on a boat than you need and end up regulating it by opening windows.

 

Even in summer there is too much heat and again it is regulated by opening windows, doors and hatches.

 

Assuming an adequate electrical supply to drive the fans what would you do with the recovered heat?

[Tracy D'arth]

I love these pipe dream boater ideas.

Not wanting to dampen your enthusiasm but its all too far removed from a canal boat to ever work. If you want all these clever features, install them in a bungalow with 24/7 electricity, not in a mobile skip with a few watts available when the engine is running.

Seen boats with weird systems, they are a bitch to sell and the new owners buy them for a song because nobody else wants them. Then they rip out all the smart stuff, install new batteries and go cruising.

[wakey_wake]

Thanks for many great answers! For me these split into difficulties & practicalities, and then separately with regard to the BSS.

 

15 hours ago, nicknorman said:

MHRV is a great system ... in a house! In a narrowboat it will create various problems -

I've lived with MHRV in a recently built property and I've seen the benefits. I've been watching the electricity consumption, had the noise keeping me awake (clear the cooking smell from the kitchen, go to bed... get up again to turn it down). Also I've seen the space it takes up: D670xW450xH1450/mm with four 8 inch air pipes coming out of the top and gobbling up to 200 watts - this one is grossly oversized for the job! But when I consider a whole boat, I want one in.

 

 

15 hours ago, nicknorman said:

it's quite bulky, where will it be fitted? Even ducts take up too much space.

It makes noise. Not noticable in a house because you can tuck it away somewhere eg in the loft, but there is no such space in a boat and you will be living with it at close quarters.

It needs a constant supply of power to run the fans, something that an off-grid live aboard boat has to be very frugal with.

[...]

Edit: I didn't look at your links but I see I am pretty much saying the same as I did 4 years ago. It's good to be consistent!

The COTS ones are bulky, but 1st ade is thinking in my direction. It will have to be long and thin, which might mean I have to make my own. Efficiency will likely be lower than a manufactured one, but that's OK with me.

6 hours ago, 1st ade said:

I'd wondered if "long and thin" in the roof void - extract air from near the middle of the boat and expel at the front; draw fresh air at the front and distribute internally from the middle. I'm sure with a bit of thought someone can come up with a heat exchanger 6 feet wide, 10 feet long but only two inches high... Of course their will be compromises with air flow which probably need bigger fans - and more power

Two parts will make noise: the fans and places where the air goes around sharp corners. So the fans have to be "in the garage" and then the rest needs to be smooth.

The whole boat will need a power budget and it has to include the fridge, the computers (yes I'm one of those ?) and the ventilation. That's a story for another day.

Yes, these are the sensible objections you raised 4y ago and that's why I linked those threads. I didn't want to dig up an ancient thread.

 

 

15 hours ago, nicknorman said:

I can't see any allowance against the BSS requirements for fixed ventilation - after all, what happens when the fans stop working? You die.

And so with fixed ventilation, the point of MHRV is rather defeated.

As to balanced solid fuel stoves,  not sure where you will get a boat-sized one of those from.

People new to boating have all these good ideas and whilst I don't want to crush them, boats are the way they are because of decades of experience in what works and what doesn't work. Re-inventing the wheel can be fun as a thought project, but in reality can be an expensive disaster.

I'm not looking for "should I do it?" but "when I do it, how do I minimise the other problems it will cause". The one thing that could stop me is BSS, because no BSS means no insurance means no moorings. If the BSS required permanently flowing fixed/passive ventilation then I agree, MHRV is not going to be useful.

After that I am aware that I could make an expensive mistake, but I believe it's possible so...  pays yer money, makes yer choice; but without putting anyone else's life or wallet at risk.

 

So when the fans stop working, if the CO2 monitors get high, if the battery is getting low enough that it thinks it can't run the fans another 12 hours... it should sound a mild warning alarm. It's not going to kill me suddenly or sneakily, I would just find the place getting stuffy.

But this is why I absolutely don't want LPG flames or solid fuel sharing my air supply. I would still have a pair of standard CO alarms, and I would go as far as a decorative candle, but IMO all other combustion must have a verifiably independent air supply.

 

(You'll next be asking "how will it sound an alarm when the battery is flat?" and my answer is to have more than one DC supply...  but even running of one domestic lead acid, if the fans cut out at 11 volts the squeaky alarm can run for hours before the battery is trashed at 10 volts)

 

 

15 hours ago, David Mack said:

Mechanical heat systems rely on having electric power a available to drive the fans. If this is on a permanent mooring with shore power supply, no problem. But if it's a mobile boat, how are you going to generate the electricity?

It seems to me that "electric everything" is much more feasible these days. It's also clear that living in a small box with limited grid-connect services means I have greater awareness of my demands on the environment...  but I'm not doing this because I'm an eco warrior.

That said, I expect to have EHU a lot of the time. Yes it is cheating, but I can't build everything at once. I don't have the money budget for that.

 

 

5 hours ago, Jen-in-Wellies said:

In a grid connected house, something consuming a few tens of watts 24 hours a day is trivial. In a boat without a shore connection, it is a major consumer of battery power. Needs a totally different mind set when deciding how to do things.

I agree, but I can do the calculations.

I can't calculate the actual power required for something that is effective because I don't yet know what size I need. But I can (when I get somewhere to put it) build something that looks about right, measure how well it works, tweak it and then measure the power required.

 

5 hours ago, Jen-in-Wellies said:

You can generate kW of heat on board easily, by burning stuff, wood, coal, diesel, or LPG. Making kWhrs of electricity and stuffing it in to lead acid batteries is hard and takes a long time to do. Unfortunately, most sorts of electric heat pump on board, a fridge, freezer, or heat recovery gadget uses a significant amount of the electrical power you can get each day. Most people have enough trouble keeping a fridge going.

I do agree with all of what you've written, but I see the whole collection as challenges which are actually practical to beat with modern tech.

Lead acid batteries, solid fuel stoves sharing the human breathing air and the notion of opening windows in winter when the solid fuel stove is putting out too many kW heat... these all horrify me. ???

[Alan de Enfield]

4 minutes ago, wakey_wake said:

The one thing that could stop me is BSS, because no BSS means no insurance means no moorings. If the BSS required permanently flowing fixed/passive ventilation then I agree,

 

 

I take it you didn't read my post. (Post #4)

[wakey_wake]

52 minutes ago, Tracy D'arth said:

I love these pipe dream boater ideas.

Not wanting to dampen your enthusiasm but its all too far removed from a canal boat to ever work. If you want all these clever features, install them in a bungalow with 24/7 electricity, not in a mobile skip with a few watts available when the engine is running.

Seen boats with weird systems, they are a bitch to sell and the new owners buy them for a song because nobody else wants them. Then they rip out all the smart stuff, install new batteries and go cruising.

If I could afford a bungalow and even wanted one then... I wouldn't be on this forum ?

So that's a fair warning. I'll take it and bear it in mind - if/when I want to sell up, I probably have to be able to turn it back into a boring olde-style boat or take a financial hit.

 

Another thing I like from this thread,

7 hours ago, 1st ade said:

(sig)

The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair.

New house builds have this horrible habit of hiding things behind panels which don't come off. Build it in, cover it over and glue the lid on. How am I going to service that when it breaks?

 

 

So overall, yes this is a fair observation (repeat from above)

15 hours ago, nicknorman said:

People new to boating have all these good ideas and whilst I don't want to crush them, boats are the way they are because of decades of experience in what works and what doesn't work. Re-inventing the wheel can be fun as a thought project, but in reality can be an expensive disaster.

I'm not completely new to boating, but haven't owned one directly before now. Also I'm a confessed idealist.

Thought projects are cheap but there are limited circumstances where they can prove anything either way. It has to be tried to see, and when the available technologies improve it is probably worth trying again.

[wakey_wake]

6 minutes ago, Alan de Enfield said:

I take it you didn't read my post. (Post #4)

 

Oh I did, and I'm delighted - thanks for that. I just can't type fast enough. ?

 

As I said,

13 minutes ago, wakey_wake said:

Thanks for many great answers! For me these split into difficulties & practicalities, and then separately with regard to the BSS.

[...]

I'm not looking for "should I do it?" but "when I do it, how do I minimise the other problems it will cause". The one thing that could stop me is BSS, because no BSS means no insurance means no moorings. If the BSS required permanently flowing fixed/passive ventilation then I agree, MHRV is not going to be useful.

 

What I meant there is: if not for your information (post #4) then I would have to have a serious re-think of the whole project.

During winter, traditional fixed ventilation gives me flashbacks to single glazed houses with inadequate heating that struggles to keep the place warm - while burning £££s.

What I'm imagining is a hygge little place where it's cosy inside and not gobbling my money to do it.

 

So on to the BSS part,

8 hours ago, Alan de Enfield said:

The BSS listings for ventilation are not a requirement, they are simply an advisory, you cannot fail a BSSC even if you have no ventilation at all.

 

Have a look at section 8 in the BSS, you will note an "A" in the top RH side of the details 'tables', this means 'Advisory only'.

You will note that it applies to every item listed in section 8  "Ventilation" subsection 8:9 and " Appliance Flues & Exhausts" subsection 8:10

 

 

Remember the BSS is not about your safety, or the safety of the boat, it is only concerned with ensuring the boat is safe (will not explode, burst into flames or cause pollution) and will not affect / harm passers by, C&RT employees or other boaters.

 

This is hugely reassuring that I'm not going to end up with an immediately uninhabitable boat. I believe I have sufficient education to avoid earning myself a Darwin Award, even though I'm cautious that I don't have practice and skill in boat fitting.

Initially I'm taking this as "it is theoretically OK to have a sealed boat with MHRV", but there is the follow-on question: is the average BSS inspector actually going to understand that and agree, or am I likely to have a fight on my hands to get that recognised?

 

For summer mode and while I'm absent from the boat, I think passive ventilation is also a good thing if it is optional.  I can imagine a BSS inspector freaking out to see ventilation holes that can be sealed airtight.

[Alan de Enfield]

22 minutes ago, wakey_wake said:

but there is the follow-on question: is the average BSS inspector actually going to understand that and agree,

 

Most of the BSS examiner make up their own rules anyway (or at least rather than applying the rules, the interpret the rules) so you will need to print out the BSSC rules (section  8 and if / when he fails your boat you can show him that it is an advisory not a requirement).

 

If you are confident of your position then stand your ground.

 

I have had to 'report' a couple of examiners to the BSS for incorrect interpretation of the rules.

Edited January 31, 2021 by Alan de Enfield

[nicknorman]

1 hour ago, wakey_wake said:

 

Oh I did, and I'm delighted - thanks for that. I just can't type fast enough. ?

 

As I said,

 

What I meant there is: if not for your information (post #4) then I would have to have a serious re-think of the whole project.

During winter, traditional fixed ventilation gives me flashbacks to single glazed houses with inadequate heating that struggles to keep the place warm - while burning £££s.

What I'm imagining is a hygge little place where it's cosy inside and not gobbling my money to do it.

 

So on to the BSS part,

 

This is hugely reassuring that I'm not going to end up with an immediately uninhabitable boat. I believe I have sufficient education to avoid earning myself a Darwin Award, even though I'm cautious that I don't have practice and skill in boat fitting.

Initially I'm taking this as "it is theoretically OK to have a sealed boat with MHRV", but there is the follow-on question: is the average BSS inspector actually going to understand that and agree, or am I likely to have a fight on my hands to get that recognised?

 

For summer mode and while I'm absent from the boat, I think passive ventilation is also a good thing if it is optional.  I can imagine a BSS inspector freaking out to see ventilation holes that can be sealed airtight.

It seems I haven’t dissuaded you! If you do do it, please come back and tell us how it is working out, it will be very interesting.

[Tony Brooks]

3 hours ago, wakey_wake said:

(You'll next be asking "how will it sound an alarm when the battery is flat?" and my answer is to have more than one DC supply...  but even running of one domestic lead acid, if the fans cut out at 11 volts the squeaky alarm can run for hours before the battery is trashed at 10 volts)

 

That shows a certain lack of understanding. for optimum battery life you should not discharge to below about 12.2 volts apart from on the very rarer occasions. To do so eats in the batteries cyclic life and also risks excess sulphation and loss of capacity. Maybe you should start looking at Lithium batteries , plenty on here about them and how to implement them.

 

 

3 hours ago, wakey_wake said:

 

10 hours ago, Jen-in-Wellies said:

In a grid connected house, something consuming a few tens of watts 24 hours a day is trivial. In a boat without a shore connection, it is a major consumer of battery power. Needs a totally different mind set when deciding how to do things.

I agree, but I can do the calculations.

I can't calculate the actual power required for something that is effective because I don't yet know what size I need. But I can (when I get somewhere to put it) build something that looks about right, measure how well it works, tweak it and then measure the power required.

 

Its not the consumption figures you need to worry about. How you are going to replace that consumption every day of the year is the problem. having done the consumption calculations then do the charging calculations. remember with lead acid batteries over the first three to four hours of charging you can only rely upon about 50% of the alternator's rated output and for each hour more it falls more and more until for the last few hours to fully charged you only get 10 amps or less. If you don't fully charge you will sulphate the batteries. Fully charging once a week is often considered a reasonable compromise.  Remember for the winter three moths the solar output may be all but zero for days on end.

 

[wakey_wake]

4 hours ago, cuthound said:

In my experience (assuming you have a log/coal/oil drip stove as the primary wintwr heat source) there is more heat on a boat than you need and end up regulating it by opening windows.

[...]

Assuming an adequate electrical supply to drive the fans what would you do with the recovered heat?

This is universally what I've read, and it makes perfect sense with a wood/coal stove.
What I want to do is avoid burning fuel to make heat which I then throw out the window - for me, that's one of the horrors.

 

So it requires two things: not throwing heat out when I can keep it in (hence MHRV) and having heat source(s) with a total average output that can modulate from "it's getting a little chilly today, maybe I'll put the heating on" all the way down to "I'm not going outside in that without four layers of thermals", ie. temperature differences indoors to outdoors from say 4C to 40C.

 

 

4 hours ago, cuthound said:

Even in summer there is too much heat and again it is regulated by opening windows, doors and hatches.

That's a separate problem. What summer usually requires is a good through draught of nice cool air. This is something I've given much less thought to, so far.

 

I'm hoping that I won't want air conditioning (!!) on my boat, because the power budget is silly and cannot so easily be supplied by burning stuff. But if I did, an MHRV (or ERV in this context) will serve the purpose again. If a place is actively cooled, the heat exchanger will serve to cool the hot, fresh incoming air. There will be condensation where that happens. Then the cool, stale and dried air has to be pushed through the heat exchanger on the way out.

 

Some relevant Youtube vids which affected or illustrate my thinking

• airtightness testing of a passivehaus
• HRV vs. ERV - What's the Difference?  Hmm, it looks like I've misunderstood ERVs a little, but I don't think they're so relevant in our climate.

• This process is a game changer for building an efficient home,

• The vid I mentioned in my OP: This Insulation is BETTER than Spray Foam!!  They also use air-sealing with positive pressure to keep out fine dust from dust storms (see at 6:30).

• Foam Free House - Is this Silly, or should we ALL BE BUILDING LIKE THIS? is about going to great lengths to avoid spray foam and EMFs.

I'm not fanatical about this sealing & filtering lark, and I have some concern about the dangers of bad spray-foam jobs, but I will take the ideas and use the ones I like.

[Tony Brooks]

It seem to me this heat recovery and ventilation system will be most used in winter, just the time solar input is all but zero. It therefore follows that unless you are on a shoreline (and probably even if you are) you will be burning some form of fuel to provide the electricity to run the heat recovery system.   

[Sea Dog]

10 minutes ago, wakey_wake said:

What I want to do is avoid burning fuel to make heat which I then throw out the window - for me, that's one of the horrors.

I would have thought that even the better insulated boats are really quite poor at retaining heat, so the difference recovering some heat from the smaller amount lost through vent exhaust would be tiny in comparison. Maybe I'm wrong, but I'd have thought those calculations would have to be done first and be most favourable to justify the expense and effort.

[wakey_wake]

2 hours ago, nicknorman said:

It seems I haven’t dissuaded you! If you do do it, please come back and tell us how it is working out, it will be very interesting.

I will but don't hold your breath - no boat yet, and I've seen some of the threads about state of the market. ?

 

Also I'm not the fastest project executor, and that's one of my larger worries. Any tips on this would be most helpful!

 

 

1 hour ago, Tony Brooks said:

That shows a certain lack of understanding. for optimum battery life you should not discharge to below about 12.2 volts apart from on the very rarer occasions. To do so eats in the batteries cyclic life and also risks excess sulphation and loss of capacity.

Also a fair comment, but in this case it's more laziness of expression than lack of understanding. What I was trying to do is illustrate how I would protect boat occupants from unplanned battery exhaustion, when the MHRV relies on DC. The lazy datapoint I'm using is inverters, which tend to shut down at 10v input.

I believe that taking a domestic battery down to 10v or 11v for a brief time may do it some damage, but less damage than if it sits like that for a week. I believe a traction battery treated the same way will have more damage...  I've learned the hard way with car batteries that I've been irresponsible for ? and tried to help several others following the same path.

 

For either of them, when they're badly discharged (by any measure) you have to stuff some joules back in ASAP. When they are discharged, and that's your only DC source, it does make perverse sense for a control system to continue running the microcontroller that's monitoring it (even though it's continuing a discharge which is degrading the battery), provided that microcontroller has some way to summon the human and charge the battery.

After all that though I come back to: electricity is essential, so I plan to have several buckets of it. Another story for another day.

 

1 hour ago, Tony Brooks said:

Maybe you should start looking at Lithium batteries , plenty on here about them and how to implement them.

 

Its not the consumption figures you need to worry about. How you are going to replace that consumption every day of the year is the problem. having done the consumption calculations then do the charging calculations. remember with lead acid batteries over the first three to four hours of charging you can only rely upon about 50% of the alternator's rated output and for each hour more it falls more and more until for the last few hours to fully charged you only get 10 amps or less. If you don't fully charge you will sulphate the batteries. Fully charging once a week is often considered a reasonable compromise.  Remember for the winter three moths the solar output may be all but zero for days on end.

 

LTO batteries are what I would buy if I was going out today for them. I do need to learn more about the various types of lithium battery, and I have ongoing discussions with a friend who works for a company that puts some kind of lithium ion battery in trains.

 

This article (paywall / first fetch free) https://www.magzter.com/article/Lifestyle/Canal-Boat/POWER-TO-THE-PEOPLE is a good indication of my kind of direction, but I don't think I would tie it to a lead acid.

 

Another thing that'll make y'all say I'm crazy: that hob which isn't going to run on LPG... I'm planning for an induction hob ? so the MHRV will be in good company.

I need to do more research, but I'm not frightened of electricity shortage.

[David Mack]

Not sure you have understood all the advice on electricity generation. Without shore power you are going to need to run your engine for hours and hours to generate enough power to top up your batteries to run all this electrical equipment. True if you use Lithium batteries it will be fewer hours, but it won't be trivial, if you are not to run out of power or knacker the batteries.

So that means running your main propulsion engine or a generator for long periods, where the noise is going to get to you, and will most certainly p*ss off the neighbours.

[nicknorman]

I’m not a fan of electric cooking. It was a fad for a while (gas free boats) but the problem is that storing electricity in large quantities isn’t easy, and generating it “on the hoof” is noisy and antisocial.

 

As an example, we were kindly allowed to breast up to a boat on a secure mooring whilst we were waiting to go into Liverpool. They didn’t mention that they were all electric, and shortly after the rumbling started as they started cooking their dinner and fired up their inbuilt generator. Not at all loud, but the low frequency vibration / rumble is very pervasive through hulls and water, and I find it rather unsettling. Of course we couldn’t and didn’t complain because they had kindly offered to let us share their mooring, but in other circumstances I would have found it pretty irritating.

 

So I suppose it depends on what sort of person you are - if you are concerned about not disturbing and annoying other people, electric cooking that requires power generation will always cause you stress, “can they hear it?” Etc. Of course if you are not concerned about disturbing other people you will be fine, but hopefully you’re not like that.

[Tony Brooks]

10 hours ago, wakey_wake said:

LTO batteries are what I would buy if I was going out today for them. I do need to learn more about the various types of lithium battery, and I have ongoing discussions with a friend who works for a company that puts some kind of lithium ion battery in trains.

 

Why trains? They are not leisure boats and from what I can see tend to operate for a high number of hours per day so charging is not an issue.

 

People here have a lot of experience of implementing lithium on boats and have written articles on it and frequently carry out long and detailed discussion on this Forum. They all seem to use LiFePo4 batteries. I would go as far as to say three of them should be viewed as the UK experts on the topic for inland boat use.

 

I suggest you use the forum search function. For a start try this one.

 

[IanD]

10 hours ago, nicknorman said:

I’m not a fan of electric cooking. It was a fad for a while (gas free boats) but the problem is that storing electricity in large quantities isn’t easy, and generating it “on the hoof” is noisy and antisocial.

 

As an example, we were kindly allowed to breast up to a boat on a secure mooring whilst we were waiting to go into Liverpool. They didn’t mention that they were all electric, and shortly after the rumbling started as they started cooking their dinner and fired up their inbuilt generator. Not at all loud, but the low frequency vibration / rumble is very pervasive through hulls and water, and I find it rather unsettling. Of course we couldn’t and didn’t complain because they had kindly offered to let us share their mooring, but in other circumstances I would have found it pretty irritating.

 

So I suppose it depends on what sort of person you are - if you are concerned about not disturbing and annoying other people, electric cooking that requires power generation will always cause you stress, “can they hear it?” Etc. Of course if you are not concerned about disturbing other people you will be fine, but hopefully you’re not like that.

I've done a lot of investigation into generators while looking at electric boats, and the problem is that most boat installations simply ignore the precautions that land-based generators take to reduce noise and conducted vibration when this is extremely critical -- for example, when they have to run at night in residential buildings when everything else is silent.

 

Just buying a cocooned generator with standard (or even "hospital") silencer isn't good enough; there's still too much noise from the generator itself, and even with the usual flexible engine mountings inside the cocoon vibration is still coupled into the structure of the boat and from there to the water.

 

To cut the radiated noise a cocooned generator is a good start, but then this needs to be put inside a sealed soundproof box (e.g. bow locker) completely lined with proper sound insulation (e.g. the Quietlife stuff from asap-supplies), with heavy access hatches (e.g. steel) also lined with sound insulation, and with acoustic seals at all the joins. Then this needs ventilation (cold air in/hot air out), and just grilles are not enough, these need to have proper acoustic labyrinths (with lots of bends) lined with acoustic foam behind them, possibly with a quiet fan to extract hot air. If you've ever looked into the design of soundproofed studios (or ultra-silent generator installations) all this is familiar stuff, but few boat designers know anything about this...

 

The "hospital silencers" used on boats are also not good enough, they don't cut low-frequency noise by enough, and they also radiate noise from the metal casing (see blog of NB Perseverance). The best solution is something like a "super-hospital-plus" grade multisection box silencer (see attachment) which has much lower noise, but these are big and heavy (60x60x25cm 60kg) and expensive, and you have to pre-plan space for them.

 

To cut conducted vibration into the hull (and then the water, and then the boat next door...) the standard and widely-used solution on land is an inertia base; the generator (in its cocoon with flexible feet) is mounted onto a heavy mounting frame which is in turn mounted on flexible feet. The generator then moves and vibrates, the force in its own feet goes into the inertia base which hardly moves at all, and this massively cuts the energy fed into the structure. Quite easy to do on a boat, use a slab of baseplate steel with more slabs bolted to it, on four soft mounting feet. Only problem is the weight; the rule-of-thumb is that the base (plus cocoon) should be at least 50% heavier than the generator, which means about 300kg of steel for a typical 10kVA generator, so the whole lot now weighs 600kg...

 

All perfectly possible if you're designing a boat from scratch, will add several grand to the cost but if you're spending 8k-10k on a generator anyway (presumably in a boat costing an arm and several legs) this is a small price to pay. With extreme care it should be possible to install a generator so that it's very difficult to tell if it's running or not, either from inside or outside the boat or in a boat next door.

 

The only reason I suspect this hasn't been done is either that nobody cares, or they think just using a cocooned generator is good enough, or boatbuilders and/or buyers don't know what is possible to reduce noise if you *really* try.

 

That's going to change... ?

 

 

Edited February 1, 2021 by IanD

[cuthound]

1 hour ago, IanD said:

I've done a lot of investigation into generators while looking at electric boats, and the problem is that most boat installations simply ignore the precautions that land-based generators take to reduce noise and conducted vibration when this is extremely critical -- for example, when they have to run at night in residential buildings when everything else is silent.

 

Just buying a cocooned generator with standard (or even "hospital") silencer isn't good enough; there's still too much noise from the generator itself, and even with the usual flexible engine mountings inside the cocoon vibration is still coupled into the structure of the boat and from there to the water.

 

To cut the radiated noise a cocooned generator is a good start, but then this needs to be put inside a sealed soundproof box (e.g. bow locker) completely lined with proper sound insulation (e.g. the Quietlife stuff from asap-supplies), with heavy access hatches (e.g. steel) also lined with sound insulation, and with acoustic seals at all the joins. Then this needs ventilation (cold air in/hot air out), and just grilles are not enough, these need to have proper acoustic labyrinths (with lots of bends) lined with acoustic foam behind them, possibly with a quiet fan to extract hot air. If you've ever looked into the design of soundproofed studios (or ultra-silent generator installations) all this is familiar stuff, but few boat designers know anything about this...

 

The "hospital silencers" used on boats are also not good enough, they don't cut low-frequency noise by enough, and they also radiate noise from the metal casing (see blog of NB Perseverance). The best solution is something like a "super-hospital-plus" grade multisection box silencer (see attachment) which has much lower noise, but these are big and heavy (60x60x25cm 60kg) and expensive, and you have to pre-plan space for them.

 

To cut conducted vibration into the hull (and then the water, and then the boat next door...) the standard and widely-used solution on land is an inertia base; the generator (in its cocoon with flexible feet) is mounted onto a heavy mounting frame which is in turn mounted on flexible feet. The generator then moves and vibrates, the force in its own feet goes into the inertia base which hardly moves at all, and this massively cuts the energy fed into the structure. Quite easy to do on a boat, use a slab of baseplate steel with more slabs bolted to it, on four soft mounting feet. Only problem is the weight; the rule-of-thumb is that the base (plus cocoon) should be at least 50% heavier than the generator, which means about 300kg of steel for a typical 10kVA generator, so the whole lot now weighs 600kg...

 

All perfectly possible if you're designing a boat from scratch, will add several grand to the cost but if you're spending 8k-10k on a generator anyway (presumably in a boat costing an arm and several legs) this is a small price to pay. With extreme care it should be possible to install a generator so that it's very difficult to tell if it's running or not, either from inside or outside the boat or in a boat next door.

 

The only reason I suspect this hasn't been done is either that nobody cares, or they think just using a cocooned generator is good enough, or boatbuilders and/or buyers don't know what is possible to reduce noise if you *really* try.

 

That's going to change... ?

 

 

 

Indeed, I used to design, and implement standby diesel generators for a living for a significant part of my career. Everything Ian says about noise and vibration attenuation is correct.

 

I used to work on 50dBA noise breakout at the site perimiter (which would be the hull of a boat) to avoid annoying nearby residents. This level of attenuation would be almost impossible to engineer in a structure just over 2 metres wide, be very costly and make large inroads into the room intended for the occupants!

 

Also what type of heating do you envisage on your boat?

If you rely on a radiator based system, them you will get much more condensation than if you heat the bost with a stove, simply because the stove ensures a high throughput of fresh air whilst it is lit.

 

[wakey_wake]

2 hours ago, Tony Brooks said:

It seem to me this heat recovery and ventilation system will be most used in winter, just the time solar input is all but zero. It therefore follows that unless you are on a shoreline (and probably even if you are) you will be burning some form of fuel to provide the electricity to run the heat recovery system.   

All true, except probably not running a generator while on EHU unless I'm testing something.

Burning fuel to make electricity will also make heat and I would like to catch more of that if I can. Another of those stories for another day.

 

2 hours ago, Sea Dog said:

I would have thought that even the better insulated boats are really quite poor at retaining heat, so the difference recovering some heat from the smaller amount lost through vent exhaust would be tiny in comparison. Maybe I'm wrong, but I'd have thought those calculations would have to be done first and be most favourable to justify the expense and effort.

Yes, I don't think I want 4 inches of insulation on a 6'10" wide boat so it has limited potential.

I did calculate heat loss from surface area / U-value, it was a few kilowatts but I didn't keep the numbers. Any holes or bridges in the insulation will make a big difference, but I do have access to a thermal camera.

 

I haven't done the equivalent for air(heat capacity / changes per hour) and it's another fair question.

Can anyone give estimates for how many air changes per hour a passively ventilated boat will give, under assorted wind conditions? Presumably it's fair to include air going up the stove chimney.

 

In the interest of science I should do all possible calculations before the experiment!

What I expect not to have easily available is actual heat output from solid fuel stove, but any kind of electric heating would be offer a reliable comparison and I probably will have that. It may be a couple of years...